Capsular tension ring

Abstract

An open capsular tension ring (10) for implanting in a capsular bag of an eye comprising a posterior surface (12) and an anterior surface (14) extending between a first end and a second end of the rin

Description

Field of the Invention The present invention relates to an open capsular tension ring for implanting in the lenticular capsular bag of an eye, use of the ring in ophthalmic surgery, such as cataract surgery or refractive lens exchange, and for the prophylaxis of posterior capsule opacification (PCO). The present invention also relates to an injector for injecting an open capsular tension ring and a kit comprising the open capsular tension ring and the injector. Background Capsular tension rings are used in cataract surgery, where the natural lens of a patient is replaced with an artificial intraocular lens (IOL). During surgery, the natural capsular membrane is opened by an incision on the anterior surface and the natural lens substance removed. A capsular tension ring can be added into the capsular bag through the anterior incision to support the structure of the capsular bag or to relieve tension on the lens zonules (the ligaments that connects the lens to the ciliary body). In some circumstances the ring can be sutured to ocular structures for further support of the capsular bag. The capsular tension ring may be implanted by manual insertion or using an injector system either clockwise or counter clockwise into the capsular bag. An IOL is then inserted into and positioned within the capsular bag. However, there are a number of problems with known capsular tension rings. A common complication arising from cataract surgery is posterior capsule opacification (PCO), where the internal posterior surface of the capsular bag becomes cloudy and opaque following surgery. PCO occurs in about 20 % of patients within two years of surgery. PCO is caused by the migration and growth of residual lens epithelial cells from the equator of the capsular bag or anterior capsule across the posterior surface of the capsule adjacent the IOL. The growth of these cells gradually opacifies the posterior surface of the capsule reducing the subject’s quality of vision. PCO is particularly problematic in younger patients, due to remnant cells in such patients having a higher proliferative and migratory potential, and with particular types of IOL, such as hydrophilic lOLs and multifocal lOLs, because a relatively small area of PCO can have a dramatic effect on vision quality. Hydrophilic lOLs are also more susceptible to PCO, as the hydrophilic surface is more compatible with cell growth. Although PCO is commonly treated by laser capsulotomy, this requires expensive sophisticated equipment, increases the risk of complications, and adds to the cumulative costs of cataract treatment. In many parts of the world medical lasers are not readily available for this treatment. Moreover, as PCO develops gradually, some patients (e.g. elderly patients) may not realise they have PCO, a treatable condition, and so do not seek treatment. Accordingly, there is a need for improved capsular tension rings which supress PCO. Summary of the Invention At its most general, the present invention provides an open capsular tension ring, the ring comprising a posterior surface, an anterior surface and an external surface for contacting the capsular bag, the internal surface comprising a recess, wherein the ratio of the radial width of the posterior surface to the axial depth of the external surface is from 0.3 to 1. In a first aspect of the invention there is provided an open capsular tension ring for implanting in a capsular bag of an eye, the ring comprising: a posterior surface and an anterior surface extending between a first end and a second end of the ring, wherein the posterior surface and anterior surface are for contacting a posterior and anterior part of the capsular bag respectively, an internal surface and an external surface extending between the first end and the second end of the ring, wherein the internal surface comprises a recess for receiving a haptic of an intraocular lens and the external surface is for contacting an equatorial part of the capsular bag, wherein the ratio of the radial width of the posterior surface to the axial depth of the external surface is from 0.3 to 1, and wherein the open capsular tension ring comprises radial fenestrations. In some embodiments, the ratio of the radial width of the anterior surface to the axial depth of the external surface is from 0.3 to 1. Open capsular tension rings are widely used in cataract surgery, however the structure of these rings is not optimised to prevent PCO, as the rings do not separate the anterior and posterior capsule from sealing together, and thus do not prevent closing of the capsular bag after implantation. Known open capsular tension rings are typically circular in cross section with a diameter of approximately 0.2mm, and have a very low ratio of radial width to axial depth. This also means the rings do not effectively prevent PCO and are poorly effective at preventing toric lOLs from rotating after surgery and do not expand the equatorial capsule to prevent variation in the IOL effective lens position. On the other hand, closed rings which are intended to supress PCO cannot fit capsular bags of varying diameters, either being too small or too large to fit the capsular bag and therefore cannot be used for all patients. The open capsular tension ring of the present invention has a ratio of radial width of the posterior surface to the axial depth of the external surface from 0.3 to 1, meaning the radial width of the ring is relatively high compared to the axial depth of the ring. The axial depth of the ring results in an open ring which separates the anterior and posterior surfaces of the capsular bag to resist closure of the capsular bag and thus supress PCO. The ring also has an external surface which in use contacts the equatorial part of the capsular bag. The axial depth of the external surface serves to expand the equatorial capsule. As a result, the capsular bag remains open post-surgery which prevents a seal between the anterior and posterior capsule. Keeping the bag open is thought to allow for a higher flow of aqueous fluid through the capsular bag. The flow of fluid washes away growth factors and cytokines, preventing growth factor and cytokine accumulation, which in turn discourages growth of lens epithelial cells across the posterior capsule and reduces the occurrence of PCO. The open shape of the ring and the defined posterior, anterior and external surfaces also allow for easier injection of the ring during surgery, meaning the ring can be easily injected in a ‘linear’ configuration, with the first end entering the capsular bag first followed by the second end. As a result, the ring can be inserted through a small corneal incision. The first and second ends (optionally including a dialling hole) also allow for easier manipulation of the ring in the capsular bag. In some embodiments, the first and second ends are rounded to prevent trauma to the capsule during injection. The absence of sharp edges or protrusions on the outside of the ring and the easier insertion procedure increases safety and reduces the risk of tearing of the capsular bag. The ring is particularly suited for use with toric lOLs. Toric lOLs are used to correct corneal astigmatism as part of the normal cataract or refractive lens exchange surgical procedure. The efficacy of this depends on preventing rotation of the toric IOL after surgery. The rotation may be caused by the IOL lying loosely in the bag, wound healing or eye rubbing by the patient. A 30 degree rotation of the toric IOL totally negates the efficacy of the astigmatic correction. The configuration of the ring allows for the IOL to be positioned accurately and stably within the ring and capsular bag. The recess on the internal surface is adapted to receive haptics of an IOL. This provides increased surface area and friction between the ring material and IOL haptic to prevent rotation of the IOL after surgery. In some embodiments, the recess may comprise a high friction surface. The high friction surface further increases the friction between the recess and IOL haptic, to prevent rotation. The prevention of rotation of a toric intraocular lens results in a more effective correction of corneal astigmatism and a better visual outcome for the patient. The targeting of the postoperative refraction of the eye is an essential aspect of the success of the operation and patient satisfaction. This is of especial importance with the use of toric lOLs to correct astigmatism, enhanced monofocal or multifocal lOLs designed to provide greater spectacle independence after surgery. A major and uncontrollable problem at present is the effective lens position - in other words, where the IOL comes to rest within the capsule bag in relationship to the other ocular structures. This ring, by expanding the equatorial capsular bag and with an internal grove to receive the IOL haptics, provides less variation in effective lens position and a more predictable post operative refraction. In another aspect of the invention, there is provided a capsular tension ring of the first aspect for use in a method of treatment. In another aspect of the invention, there is provided a capsular tension ring of the first aspect for use in a method of treatment of cataracts or refractive lens exchange. In another aspect of the invention, there is provided a capsular tension ring of the first aspect for use in a method of prophylaxis of posterior capsule opacification. In another aspect of the invention, there is provided an injector for injecting an open capsular tension ring into a capsular bag, the injector comprising the open capsular tension ring of the first aspect. In some embodiments, the injector also comprises a carrier fluid. In another aspect of the invention, there is provided a kit comprising the open capsular tension ring of the first aspect and an injector for injecting the open capsular tension ring into a capsular bag. These and others aspects and embodiments of the invention are described in further detail below. Summary of the Figures The present invention is described with reference to the figures listed below. Figure 1 shows a cross-section of an IOL placed in the capsular bag of an eye, and how the capsular bag gradually closes after surgery. Figure 1a shows the open capsular bag shortly after implantation. Figure 1b shows the anterior capsule sealing to the anterior surface of the IOL. Figure 1 c shows the sealing together of the anterior and posterior capsule, at the equator of the capsule. Figure 1d shows how the posterior capsule forms a tight seal to the posterior surface of the IOL, as the equatorial capsule closes. Figure 2 shows a circumferential cross sectional view through an example of the open capsular tension ring (10) of the invention. The radial width of the ring is shown by arrow A. The axial depth of the ring is shown by arrow B. Figure 3 shows a plan view of an example of the open capsular tension ring (10a) of the invention. Figure 4 shows a radial view of the internal surface of a reference example of an open capsular tension ring (10b). The length of the ring between the ends is reduced for the illustration. Figure 4a shows a radial view of the internal surface of an example of the open capsular tension ring (10c) of the invention with fenestrations in the recess. The length of the ring and number of fenestrations are reduced for the illustration. Figure 5 shows an axial cross section view of an example of the open capsular tension ring (10) of the invention when implanted in a capsular bag of an eye, and with an IOL haptic located in the recess. Figure 6 shows a plan view of an example of the open capsular tension ring (10) of the invention when implanted in a capsular bag of an eye with an IOL haptic located in the recess. Figure 7 shows a radial view of the internal surface of an alternative example of the open capsular tension ring (10e) of the invention. The length of the ring between the ends is reduced for the illustration. The alternative ring includes breaks at different relative positions in the anterior and posterior surfaces of the ring. The ring also includes fenestrations in the recess. Figure 8 shows a radial view of the internal surface of an alternative example of the open capsular tension ring (10f) of the invention. The length of the ring between the ends is reduced for the illustration. The ring includes fenestrations in the recess. The alternative ring includes a chamfered first end and second end. Figure 9 shows a radial view of the internal surface of an alternative example of the open capsular tension ring (10g) of the invention. The length of the ring between the ends is reduced for the illustration. The ring includes breaks at the same relative positions in the anterior and posterior surfaces of the ring. The breaks in the anterior and posterior surface are axially offset from the fenestrations. The ring includes fenestrations in the recess. Figure 10 shows a plan view of an example of the open capsular tension ring (10g) of the invention. The ring includes symmetrical breaks in the anterior and posterior surface of the ring and that the breaks extend from the inner surface radially to the extent of the base of the recess. Figure 11 shows an axial view of a further example of the open capsular tension ring of the invention, having a spheroidal exterior surface. The external surface of the ring has a curved external profile with parallel anterior and posterior surfaces. Figure 12 shows a radial view of an open capsular tension ring of the invention. The length of the ring between the ends is reduced for the illustration. The ring includes fenestrations within the recess. The ring includes breaks at the same relative positions in the anterior and posterior surfaces of the ring that extend radially from the inner surface of the ring to the extent of the depth of the recess. The breaks in the anterior and posterior surface are axially offset from the fenestrations. The first end and second end of the ring are chamfered, and the chamfer includes the part of the ends including the dialling hole. Detailed Description of the Invention The present invention provides an open capsular tension ring (10) for implanting in a capsular bag (01) of an eye, the ring (10) comprising: a posterior surface (12) and an anterior surface (14) extending between a first end (22) and a second end (24) of the ring (10), an internal surface (18) and an external surface (16) extending between the first end (22) and the second end (24) of the ring (10), wherein the internal surface (18) comprises a recess (20) for receiving a haptic (101) of an intraocular lens (100), wherein the ratio of the radial width of the posterior surface (12) to the axial depth of the external surface (16) is from 0.3 to 1, and wherein the open capsular tension ring comprises radial fenestrations. As explained herein, the ring may reduce the occurrence of PCO, provide secure retention of toric lOLs, expand the equatorial capsular bag to stabilise the effective IOL position and ease surgical implantation. Previous attempts have been made to reduce the occurrence of PCO. Generally, it is understood that a capsular bag changes shape in the healing process postsurgery. This is illustrated in Figure 1. Immediately after surgery the capsular bag 01 is open (Figure 1a), the anterior capsular bag (04) then seals to the IOL anterior surface and the IOL comes into contact with the posterior capsule (Figure 1 b). Over time the equator (06) of the capsular bag also starts to close and the anterior capsule (04) and posterior capsule (02) seal together (Figure 1c). Ultimately this results in a closed bag where the anterior capsule (04) and posterior capsule (02) are tightly sealed enclosing the IOL (Figure 1d). This equatorial closing of the bag and consequential tight seal between the posterior capsule (02), anterior capsule (04) and IOL (100) is thought to be caused by the accumulation of growth factors and cytokines encouraging the re-growth and transformation of residual lens epithelial cells across the capsule surfaces. Migration of these cells on to the posterior capsule causes the clinical picture of PCO. Early capsular tension rings were designed with the aim of supporting the capsule and the anatomical position of the lens. Some capsular tension rings have been designed with the aim of preventing PCO. For example, Pallikaris et al. (WO 2018 / 160800) describe a closed circular capsular tension ring system intended to contact the posterior and anterior surfaces of the capsule after cataract surgery, to reconstruct the shape of the capsule. This ring includes a rigid inner ring (an IOL carrier) and a flexible outer ring intended to expand into the equator of the bag thereby fitting bags of various diameters. Variants with flexible members which contact and expand the equator of the capsular bag are also discussed. The ring was intended to prevent sealing of the anterior capsule and posterior capsule at the equator of the capsular bag and provide a carrier for the IOL. Such a ring is complex and expensive to manufacture. Alon et al. also describe the use of a closed circular capsular tension ring with a sharp-edged tip at the posterior edge of the ring. The sharp tip is intended to prevent migration of the residual lens epithelial cells on to the posterior capsular bag from the equatorial bag, with the width of the ring separating the anterior and posterior capsules. The sharp tip increases the risk of tearing the capsule on insertion. Both known rings have a closed circular configuration, which makes them difficult to implant during surgery. Typically, a larger incision is required in the cornea to insert closed rings, and the rings are challenging to manipulate due to their continuous circumference and lack of manipulation points (e.g., dialling holes). The rings are a one size fits all and the fixed diameter makes the fit of them in bags of varying diameter imprecise, risking being either too tight or too loose. In addition, the sharp protrusions extending from the ring described in Alon et al. would be prone to tear the capsular bags during implantation, making surgery more risky. The complex shape and multiple materials used in these closed rings also makes the rings more expensive to manufacture and assemble. Accordingly, the present invention provides an open capsular tension ring which facilitates easier surgical implantation and manipulation while also providing the ring shape needed to prevent sealing of the posterior capsule to the IOL and therefore suppress PCO, act as a stable carrier for the IOL and expand to the equator of the capsular bag to stabilise the effective lens position. The open capsular tension ring of the invention is easy to insert, expands to fill capsular bags of all diameters, and separates the anterior and posterior capsules from fusing creating an open capsular bag, which allows circulation of aqueous fluid to remove growth factors and cytokines therefore supressing PCO. In addition, by expanding the volume of the equator of the capsular bag, the ring may provide a more consistent haptic and lens position thereby stabilising the effective IOL position and stabilising toric IOL rotation, a major variable in predicting the post operative refraction of the eye. Moreover, the ring can be implanted using a technique already familiar to cataract surgeons. The tension ring also includes a recess for receiving a haptic of an intraocular lens. The recess allows implantation of the IOL haptic within the ring thereby providing greater contact and friction between the two surfaces and reducing the risk of IOL rotation. Open Capsular Tension Ring The invention relates to an open capsular tension ring (10) for implanting in a capsular bag (01) of an eye, the ring (10) comprising: a posterior surface (12) and an anterior surface (14) extending between a first end (22) and a second end (24) of the ring (10), an internal surface (18) and an external surface (16) extending between the first end (22) and the second end (24) of the ring (10), wherein the internal surface (18) comprises a recess (20) for receiving a haptic (101) of an intraocular lens (100), wherein the ratio of the radial width of the posterior surface (12) to the axial depth of the external surface (16) is from 0.3 to 1, and wherein the open capsular tension ring comprises radial fenestrations. An “open” ring typically refers to a ring where the first end and second end are not integrally connected. That is, the ring has a separable first end and second end. This contrasts to a closed ring, which is a continuous ring with no first or second end. The ring includes a posterior surface (12) and an anterior surface (14) extending between a first end (22) and a second end (24) of the ring (10). The posterior surface is the surface of the ring which, in use, is adjacent to the posterior capsule. The anterior surface is the surface of the ring which, in use, is adjacent to the anterior capsule. In some embodiments, the posterior surface (12) is for contacting a posterior portion of the capsular bag (02). In some embodiments, the anterior surface (14) is for contacting an anterior portion of the capsular bag (04). In some embodiments, the posterior surface (12) and / or the anterior surface (14) are a planar surface. Preferably, the posterior surface (12) and / or the anterior surface (14) are planar in a radial direction. In other words, the posterior surface (12) and / or the anterior surface (14) are parallel with the radial direction of the ring. Preferably the posterior surface (12) and anterior surface (14) are parallel. In such embodiments, the posterior surface (12) and the anterior surface (14) may be planar in a radial direction. The ring may be defined in terms of its radial width. The radial width of the ring is typically the distance between the internal surface and the external surface. This is typically the maximum radial distance between the internal surface and the external surface. The ‘radial distance’ refers to a distance measured in a direction in line with the radius of the ring. In some embodiments, the radial width of the ring is 0.6 mm or more, preferably 0.7 mm or more, preferably 0.8 mm or more, more preferably 0.9 mm or more, yet more preferably 1.0 mm or more. In some embodiments, the radial width of the ring is 2.0 mm or less, preferably 1.8 mm or less, preferably 1.6 mm or less, more preferably 1.4 mm or less, yet more preferably 1.2 mm or less. In some embodiments, the radial width of the ring is 0.6 to 2.0 mm, preferably 0.7 to 1.8 mm, preferably 0.8 to 1.6 mm, more preferably 0.9 to 1.4 mm, yet more preferably 1.0 to 1.2 mm. The radial width of the ring may be about 1.0 mm. The posterior surface and the anterior surface may be defined by their radial width. The radial width is typically the distance between the internal surface and the external surface, as measured along the posterior surface or the anterior surface. This is illustrated in Figure 2 by arrow ‘A’. The radial width of the posterior surface is the distance between the internal surface and the external surface as measured at the posterior surface. The radial width of the anterior surface is the distance between the internal surface and the external surface as measured at the anterior surface. The radial width is typically measured under ambient conditions when the ring is in a relaxed state, such as a circular configuration. The relaxed state refers to the ring when not implanted into the capsular bag of an eye. Where the radial width varies around the circumference of the ring, the radial width refers to a mean average radial width. The mean average radial width may be calculated using any suitable method, such as measuring the radial width at a number of points around the circumference of the ring and calculating the mean value. The radial width of the anterior surface may be substantially constant between the first end (22) and the second end (24). The radial width of the posterior surface may be constant between the first end (22) and the second end (24). Preferably, the radial width of the anterior surface and the posterior surface is constant between the first end (22) and the second end (24). In some embodiments, the radial width of the posterior surface (12) is 0.6 mm or more, preferably 0.7 mm or more, preferably 0.8 mm or more, more preferably 0.9 mm or more, yet more preferably 1.0 mm or more. In some embodiments, the radial width of the posterior surface (12) is 2.0 mm or less, preferably 1.8 mm or less, preferably 1.6 mm or less, more preferably 1.4 mm or less, yet more preferably 1.2 mm or less. In some embodiments, the radial width of the posterior surface (12) is 0.6 to 2.0 mm, preferably 0.7 to 1.8 mm, preferably 0.8 to 1.6 mm, more preferably 0.9 to 1.4 mm, yet more preferably 1.0 to 1.2 mm. The radial width of the posterior surface may be about 1.0 mm. In some embodiments, the radial width of the anterior surface (12) is 0.6 mm or more, preferably 0.7 mm or more, preferably 0.8 mm or more, more preferably 0.9 mm or more, yet more preferably 1.0 mm or more. In some embodiments, the radial width of the anterior surface (12) is 2.0 mm or less, preferably 1.8 mm or less, preferably 1.6 mm or less, more preferably 1.4 mm or less, yet more preferably 1.2 mm or less. In some embodiments, the radial width of the anterior surface (14) is 0.6 to 2.0 mm, preferably 0.7 to 1.8 mm, preferably 0.8 to 1.7 mm, more preferably 0.9 to 1.4 mm, yet more preferably 1.0 to 1.2 mm. The radial width of the anterior surface may be about 1.0 mm. In some embodiments, the radial width of the anterior surface (12) and anterior surface (14) is 0.6 mm or more, preferably 0.7 mm or more, preferably 0.8 mm or more, more preferably 0.9 mm or more, yet more preferably 1.0 mm or more. In some embodiments, the radial width of the anterior surface (12) and anterior surface (14) is 2.0 mm or less, preferably 1.8 mm or less, preferably 1.6 mm or less, more preferably 1.4 mm or less, yet more preferably 1.2 mm or less. In some embodiments, the radial width of the posterior surface (12) and anterior surface (14) is 0.6 to 2.0 mm, preferably 0.7 to 1.8 mm preferably 0.8 to 1.7 mm, more preferably 0.9 to 1.4 mm, yet more preferably 1.0 to 1.2 mm. The radial width of the posterior surface (12) and anterior surface (14) may be about 1.0 mm. The radial width of the posterior surface (12) and anterior surface (14) may be the same or different. Preferably, the radial width of the posterior surface (12) is equal to the radial width of the anterior surface (14). In some embodiments, the radial width of the posterior surface (12) and / or the anterior surface (14) is constant between the first end (22) and the second end (24). In some embodiments, the posterior surface and anterior surface are identical. As such, the ring can be used with either top or bottom surface acting as the posterior surface or anterior surface. In some embodiments, the anterior surface and / or posterior surface comprise flexible regions. The flexible regions may be present in the anterior surface or the posterior surface. Preferably, the flexible regions are present in the anterior surface and the posterior surface. The flexible regions increase the flexibility of the ring in the radial direction and therefore assist in surgical insertion. The increased flexibility typically allows the ring to expand and contract, to increase or decrease the radius of the ring. The flexible regions may also allow the ring to be more easily deformed, for example, for during injection into the capsular bag and allow for the ring to be manipulated more easily. The flexible regions may take the form from of a break in the anterior surface or posterior surface. The break may act as a relief cut, such as a slice, such adjacent parts of the anterior surface or posterior surface are still in contact but are not integrally connected. Alternatively, the break may be a gap, where the gap is formed from the removal of a section of material from the anterior surface or posterior surface. The breaks may extend from the external surface to the internal surface or may only extend partway between the internal surface and the external surface. Preferably the break extends from the internal surface in a radial direction. Preferably the breaks only extend to the same depth as the recess in the internal surface (the recess being adapted to receive the IOL haptic). In this way, the junction of the external surface and the posterior / anterior surface is unbroken to retain the structural rigidity of the ring. The flexible regions (e.g., breaks) may be present in both the anterior surface and posterior surface. The flexible regions may be provided at different relative positions on the anterior surface and posterior surface, or may be provided at the same relevant positions on the anterior surface and posterior surfaces. Preferably the flexible regions are provided at the same relative positions on the anterior and posterior surfaces. The breaks increase radial flexibility. In addition, the external surface may have fenestrations of varying shape or size to increase circulation of fluid and remove growth factors and cytokines. The breaks may also serve to increase circulation of fluid and remove growth factors and cytokines. Each of the anterior surface and / or posterior surface may comprise two or more flexible regions, such as three or more, four or more, five or more, six or more, seven or more, eight or more, nine or more, or ten or more flexible regions. Each of the anterior surface and / or posterior surface may comprise two or more breaks, such as three or more, four or more, five or more, six or more, seven or more, eight or more, nine or more, or ten or more recesses. Each of the flexible regions (e.g., breaks in the anterior and / or posterior surface) may be the same or different. The ring may include breaks at uniform circumferential intervals, such as every 1.0 to 5.0 mm, preferably every 1.5 to 4.0 mm, more preferably every 2.0 to 3.0 mm. The ring may include breaks of uniform circumferential widths, such as 1.0 to 5.0 mm, preferably 1.5 to 4.0 mm, more preferably 2.0 to 3.0 mm. Typically, the anterior surface and the posterior surface comprise flexible regions, such as breaks, as described above. The ring includes an internal surface (18) and an external surface (16) extending between the first end (22) and the second end (24) of the ring (10). The internal surface (18) is the surface of the ring which, in use, is facing towards the IOL. The external surface is the surface of the ring which, in use, is facing towards the equatorial capsular bag. In some embodiments, the external surface (16) is for contacting an equatorial portion of the capsular bag (06). The external surface may include breaks, gaps, recesses, or holes. The external surface typically refers to the part of the continuous surface at the largest radial extent of the ring. In some embodiments, the external surface (16) is a tubular surface. A tubular surface is a surface having a curve in a single dimension, such as in a circumferential dimension. Such a tubular surface is substantially flat in the axial direction. In some embodiments, the external surface (16) is a spheroidal (e.g., curved) surface. A spheroidal surface is a surface having a curve in two dimensions, such as in a circumferential dimension and an axial direction. In some embodiments, the internal surface (18) is for contacting a haptic of an IOL. The internal surface may include breaks, gaps, recesses, or holes. The breaks, gaps, recesses, or holes may communicate with the external surface. The internal surface typically refers to the part of the surface at the smallest radial extent of the ring. The internal surface may be divided into two portions by a groove. These portions may be referred to as the anterior internal surface and the posterior internal surface. In some embodiments, the internal surface (18) is a tubular surface. A tubular surface is a surface having a curve in a single dimension, such as in a circumferential dimension. In other words, the tubular surface curves with the curvature of the ring. Such a tubular surface is substantially flat in the axial direction. In some embodiments the internal surface (18) and external surface (16) are coaxial. Preferably, the internal surface and external surface are both tubular and coaxial. In some embodiments the external surface and the internal surface are both tubular surfaces. In alternative embodiments the external surface is a spheroidal surface and the internal surface is a tubular surface. A tubular surface may also be known as a cylindrical surface. That is, a surface which defines the outside surface of a cylinder. The ring may be defined in terms of its axial depth. The axial depth of the ring is typically the distance between the anterior surface and the posterior surface. This is typically the maximum axial distance between anterior surface and the posterior surface. The ‘axial distance’ refers to a distance measured in a direction parallel with the central axis of the ring. In some embodiments, the axial depth of the ring is 1.2 mm or more, preferably 1.5 mm or more, more preferably 1.7 mm or more, yet more preferably 1.9 mm or more. In some embodiments, the axial depth of the ring is 2.8 mm or less, preferably 2.5 mm or less, more preferably 2.2 mm or less, yet more preferably 2.1 mm or less. In some embodiments, the axial depth of the ring is 1.2 to 2.8 mm, preferably 1.5 to 2.5 mm, more preferably 1.7 to 2.2 mm, yet more preferably 1.9 to 2.1 mm. Preferably the axial depth of the ring is about 2.0 mm. The external surface and internal surface may be defined by their axial depth. The axial depth is typically the distance between the posterior surface and the anterior surface, as measured along the external surface or the internal surface. This is illustrated in Figure 2 by arrow ‘B’. The axial depth of the external surface is the distance between the posterior surface and the anterior surface, measured along the external surface. The axial depth of the internal surface is the distance between the posterior surface and the anterior surface, measured along the internal surface. Where the internal surface is divided into two portions, the axial depth is the distance between the posterior surface and the anterior surface when measured between the anterior internal surface and the posterior internal surface. The axial depth is typically measured under ambient conditions, when the ring is in a relaxed state, such as a substantially circular configuration. Where the axial depth varies around the circumference of the ring, the axial depth refers to a mean average axial depth. The mean average axial depth may be calculated using any suitable method, such as measuring the axial depth at a number of points around the circumference of the ring and calculating the mean value. The axial depth of the internal surface (18) may be substantially constant between the first end (22) and the second end (24). The axial depth of the external surface (16) may be constant between the first end (22) and the second end (24). Preferably, the axial depth of the internal surface (18) and the external surface is constant between the first end (22) and the second end (24). In some embodiments, the axial depth of the internal surface (18) is 1.2 mm or more, preferably 1.5 mm or more, more preferably 1.7 mm or more, yet more preferably 1.9 mm or more. In some embodiments, the axial depth of the internal surface (18) is 2.8 mm or less, preferably 2.5 mm or less, more preferably 2.2 mm or less, yet more preferably 2.1 mm or less. In some embodiments, the axial depth of the internal surface (18) is 1.2 to 2.8 mm, preferably 1.5 to 2.5 mm, more preferably 1.7 to 2.2 mm, yet more preferably 1.9 to 2.1 mm. Preferably the axial depth of the external surface (18) is about 2.0 mm. In some embodiments, the axial depth of the external surface (16) is 1.2 mm or more, preferably 1.5 mm or more, more preferably 1.7 mm or more, yet more preferably 1.9 mm or more. In some embodiments, the axial depth of the external surface (16) is 2.8 mm or less, preferably 2.5 mm or less, more preferably 2.2 mm or less, yet more preferably 2.1 mm or less. In some embodiments, the axial depth of the external surface (16) is 1.2 to 2.8 mm, preferably 1.5 to 2.5 mm, more preferably 1.7 to 2.2 mm, yet more preferably 1.9 to 2.1 mm. Preferably the axial depth of the internal surface (18) is about 2.0 mm. In some embodiments, the axial depth of the internal surface (18) and external surface (16) is 1.2 mm or more, preferably 1.5 mm or more, more preferably 1.7 mm or more, yet more preferably 1.9 mm or more. In some embodiments, the axial depth of the internal surface (18) and external surface (16) is 2.8 mm or less, preferably 2.5 mm or less, more preferably 2.2 mm or less, yet more preferably 2.1 mm or less. In some embodiments, the axial depth of the internal surface (18) and the external surface (16) is 1.2 to 2.8 mm, preferably 1.5 to 2.5 mm, more preferably 1.7 to 2.2 mm, yet more preferably 1.9 to 2.1 mm. The axial depth of the internal surface and external surface may be the same or different. Preferably, the axial depth of the internal surface (18) is equal to the axial depth of the external surface (16). Preferably the axial depth of the internal surface (18) and the external surface (16) is about 2.0 mm. In some embodiments, the axial depth of the internal surface and / or external surface is constant between the first end (22) and the second end (24). The ratio between the radial width and the axial depth is from 0.3 to 1. Preferably, the ratio of the radial width of the ring to the axial depth of the ring is from 0.3 to 1. In some embodiments, the ratio of the radial width of the posterior surface (12) to the axial depth of the external surface (16) is from 0.3 to 1. The ratio is calculated by dividing the radial width by the axial depth, according to the following equation: Ratio = radial width I axial depth For example, where the axial depth is 1.7 mm and the radial width is 1.0 mm, the ratio is 1 / 1.7, which equals about 0.6. Alternatively, where the axial depth is 2.0 mm and the radial width is 1.6 mm, the ratio is 1.6 / 2.0, which equals 0.8. In addition, or alternatively, the ratio of the radial width of the anterior surface (14) to the axial depth of the external surface (16) is from 0.3 to 1. Preferably, the ratio of both the radial width of the anterior surface (14) to the axial depth of the external surface (16) and the radial width of the posterior surface (12) to the axial depth of the external surface (16) is from 0.3 to 1. ln some embodiments, the ratio of the radial width of the posterior surface (12) to the axial depth of the internal surface (18) is from 0.3 to 1. In addition, or alternatively, the ratio of the radial width of the anterior surface (14) to the axial depth of the internal surface (18) is from 0.3 to 1. Preferably, the ratio of both the radial width of the anterior surface (14) to the axial depth of the internal surface (18) and the radial width of the posterior surface (12) to the axial depth of the internal surface (18) is from 0.3 to 1. In some embodiments, the ratio of the radial width to the axial depth is 0.4 or more, preferably 0.5 or more, preferably 0.6 or more. In some embodiments, the ratio of the radial width to the axial depth is 1.0 or less, preferably 0.9 or less, more preferably 0.8 or less. In preferred embodiments, the ratio of the radial width to the axial depth is from 0.4 to 1.0, more preferably from 0.5 to 0.9, yet more preferably from 0.6 to 0.8. In some embodiments, the internal surface (18) and / or external surface (16) are perpendicular to the posterior surface (12) and anterior surface (14). Typically, the posterior surface (12) connects to the internal surface (18) and the external surface (16) at an internal posterior edge and an external posterior edge respectively. The surfaces meeting at the internal posterior edge and / or the external posterior edge are preferably perpendicular. In such embodiments, the internal surface and / or external surface are also perpendicular to the posterior surface (12). Typically, the anterior surface (14) connects to the internal surface (18) and the external surface (16) at an internal anterior edge and an external anterior edge respectively. The surfaces meeting at the internal posterior edge and / or the external posterior edge are preferably perpendicular. In such embodiments, the internal surface and / or external surface are also perpendicular to the anterior surface (14). The internal posterior edge and / or the external posterior edge are typically not a sharp edge. For example, the internal posterior edge and / or the external posterior edge may have a radius of curvature of from 0.1 to 0.3 mm. Where the internal posterior edge and / or the external posterior are perpendicular edges, the edges may have a radius of curvature of from 0.1 to 0.3 mm. The internal posterior edge and / or the external posterior may form an angle of from 70 to 110°, such as from 80 to 100°, from 85 to 95°, from 88 to 92°, such as about 90°. Preferably, the internal posterior edge and / or the external posterior may form an angle which is substantially perpendicular. The internal anterior edge and / or the external anterior are typically not a sharp edge. For example, the internal anterior edge and / or the external anterior may have a radius of curvature of from 0.1 to 0.3 mm. Where the internal anterior edge and / or the external anterior are perpendicular edges, the edges may have a radius of curvature of from 0.1 to 0.3 mm. The internal anterior edge and / or the external anterior may form an angle of from 70 to 110°, such as from 80 to 100°, from 85 to 95°, from 88 to 92°, such as about 90°. Preferably, the internal anterior edge and / or the external anterior may form an angle which is substantially perpendicular. Typically, one or more of the anterior surface, posterior surface and / or external axial surface are smooth. Preferably, the anterior surface, posterior surface and external surface are smooth. A smooth surface is a surface substantially free of protrusions or other surface features. A smooth surface is typically flat or smoothly curved. The smooth surface enables the ring to be guided atraumatically into the capsular bag during insertion. The open capsular ring includes a first end (22) and a second end (24). The posterior surface (12) and the anterior surface (14) extend between the first end (22) and the second end (24) of the ring (10). The distance between the first end and the second end may be defined by a circumferential length measured along the interior surface of the ring. The circumferential length from the first end (22) to the second end (24) may be from 25 to 35 mm, preferably 29 to 33 mm, more preferably 30 to 32 mm, yet more preferably about 30 mm. The internal diameter of the ring in a relaxed state may be from 7.5 to 12 mm, such as from 8.5 to 11.5 mm, from 9 to 11 mm, from 9.5 to 10.8 mm, from 9.8 to 10.5 mm. The relaxed internal diameter refers to the diameter between opposing internal surfaces of the ring, when the ring is in a relaxed state. The internal diameter of the ring when in the capsular bag may be from 6 to 12 mm, such as from 7 to 11 mm, from 8 to 10 mm. The functional internal diameter refers to the diameter between opposing internal surfaces of the ring, when the ring is in the capsular bag. When in use and implanted in the capsular bag of an eye, the first end and second ends may be separated, the first and second ends may abut or the first and second ends may overlap. The configuration of the first and second ends depends on the size of the capsular bag compared to the size of the ring. In some embodiments, the first and second ends may be complimentary. In other words, the first and second ends may tessellate. For example, the first end may include a concave shape and the second end may include a convex shape (see the example embodiment in Figure 7). Alternatively, the first end may include an angled face extending at an acute angle between the posterior surface and anterior surface, while the second end includes an angled face extending at an acute angle between the anterior surface and posterior surface (see the example embodiment in Figure 8). The open capsular tension ring may comprise one or more manipulation means at the first end (22) and / or the second end (24). Preferably, the ring comprises one manipulation means at the first end and one manipulation means at the second end. The manipulation means may be a hole formed through the anterior or posterior surface. These may conventionally be known as dialling holes. The hole formed through the anterior or posterior surface may have an internal diameter of 0.3 to 0.5 mm, such as about 0.4 mm. The hole extends all the way through the ring. The manipulation means may be integrally formed into the ring body. For example, the manipulation means may be integrally formed through the anterior surface or posterior surface. Preferably, a manipulation means at the first end (e.g., a dialling hole) may be integrally formed through the anterior surface and a manipulation means at the second end (e.g., a dialling hole) may be integrally formed through the posterior surface. In some embodiments, a first manipulation means is appended to the first end (22) adjacent to the posterior surface (12), and a second manipulation means is appended to the second end (24) adjacent to the anterior surface (14). The internal surface of the capsular tension ring comprises a recess. The recess is suitable for receiving a haptic of an intraocular lens. In other words, the recess is adapted to receive haptics of an IOL. In some embodiments, the ring has a continuous recess (e.g., groove) to contain the IOL haptics. In some embodiments, the ring comprises a plurality of recesses and these may be the same in number or more than the number of IOL haptics. Each IOL haptic is then received in a particular recess. Typically, lOLs include two or more haptics, such as two haptics. The two haptics are generally opposite sides of the IOL Accordingly, the ring may comprise two or more recesses, such as two recesses to receive the IOL haptics. The two recesses may be positioned circumferentially opposite on the ring. The recess may take any suitable form which is able to receive an IOL haptic. The recess is typically not a hole. That is, the recess does not extend all the way through the ring. The recess may have a circular, elliptical, triangular or quadrilateral radial cross-section. That is, when looking at the recess from the centre of the ring, the cross-section may be an open rectangle, circular, elliptical, triangular or quadrilateral. The recess may take the form of a slot or channel. The channel may have a rectangular, triagonal, or trapezoidal circumferential cross section. That is, when looking at the recess in line with the internal surface, the cross-section may be rectangular, triagonal, or trapezoidal. The recess may taper. Preferably, the channel has a rectangular circumferential cross section. The recess may take the form of a slot or channel. The depth of the recess may be consistent across its length / width, or the depth may change across its length / width. The recess, such as the channel, may have an axial depth of from 0.4 to 0.8 mm, preferably 0.5 to 0.7 mm, more preferably about 0.6 mm. The recess, such as the channel, may have a radial width of from 0.3 to 1.5 mm, preferably 0.5 to 1.2 mm, more preferably about 1.0 mm. The recess, such as the channel, may have an axial depth which is from 15 to 50% the axial depth of the internal surface, preferably from 20 to 40%, more preferably from 25 to 35%. Preferably the recess, such as the channel, has an axial depth which is from about 30% the axial depth of the internal surface. The recess, such as the channel, may have an axial depth which is from 15 to 50% the axial depth of the external surface, preferably from 20 to 40%, more preferably from 25 to 35%. Preferably the recess, such as the channel, has an axial depth which is from about 30% the axial depth of the external surface. The recess, such as the channel, may be centred in the interior surface. Thus, the centre of the recess may be equidistant from the posterior surface and the anterior surface, preferably the centre of the recess is equidistant from the internal posterior edge and the interior anterior edge. In preferred embodiments, the recess is a channel. The ring may include one or more channels. For example, the ring may include a first channel to receive a first IOL haptic and a second channel to receive a second IOL haptic. The two channels may be positioned circumferentially opposite on the ring. Preferably, the recess is a single channel. Preferably, the channel extends continuously between the first end and the second end of the ring. Where a single channel is present, the channel is adapted to receive a first IOL haptic and a second IOL haptic in different parts of the channel. The recess (e.g., channel) increases the surface contact between the IOL haptic and the ring. The recess may also limit, such as prevent, rotation of the IOL relative to the ring. To further increase the friction between the haptic and the IOL, the recess may comprise a high friction surface. The high friction surface is any surface that has a higher coefficient of friction compared to other surfaces of the ring (e.g., the external surface). The high friction surface may be present in the recess and / or the internal surface. Preferably, the high friction surface is present in the recess only. The recess may comprise a high friction surface on the walls of the recess (or channel) and / or the base of the channel. Preferably, the recess may comprise a high friction surface on the base of the channel. The high friction surface may be provided by any suitable means, such as by increasing the surface area of the surface compared to other surfaces of the ring, by surface treating or surface modifying the surface, or by adding a different surface layer of material. Preferably, the high friction surface is frosted (i.e., roughened), which increases the surface area of the surface to increase the coefficient of friction. Preferably, the recess, such as the channel, is frosted. The ring further comprises radial fenestrations. The radial fenestration typically provides fluidic communication between the internal surface (and / or recess) of the ring and the external surface of the ring. The fenestrations are different from the recess described above. The fenestrations pass through the ring, from internal to external surface whereas typically the recess does not pass through the ring. The fenestrations provide fluidic communication between the internal surface of the ring, adjacent the IOL, and the external surface of the ring, adjacent the capsular bag. Thus, the fenestrations increase the permeability and rate of flow of aqueous humour to the equatorial capsule. The fluid washes away growth factors and cytokines, preventing growth factor and cytokine accumulation, which in turn discourages growth of lens epithelial cells across the posterior capsule and reduces the occurrence of PCO. In some embodiments, the radial fenestration intersects the internal surface and the external surface of the ring. Preferably, the radial fenestration intersects the internal surface, recess (e.g., channel) and the external surface of the ring. Preferably the fenestrations radially intersect the recess (e.g., channel) and the external surface. The fenestrations may have any suitable form which allows for fluidic communication between the internal surface of the ring and the external surface of the ring. The fenestrations may have a circular, elliptical, triangular or quadrilateral radial cross-section. That is, when looking at the fenestrations from the centre of the ring, the cross-section is circular, elliptical, triangular or quadrilateral. Preferably, the fenestrations have a rounded or quadrilateral radial cross-section, such as a circular or rectangular radial cross-section. The ring may comprise 2 or more fenestrations, such as 3 or more, 4 or more, 6 or more, 8 or more, 10 or more, 12 or more. The ring may comprise 30 or less fenestrations, such as 20 or less, 15 or less, 10 or less fenestrations. The ring may comprise from 3 to 30 fenestrations, such as from 4 to 20, from 6 to 15, or from 8 to 10 fenestrations. The fenestrations may be spaced equidistant around the circumference of the ring. That is, the gap between the geometric centre of each adjacent fenestration may be the same. For example, the gap between the geometric centre of each adjacent fenestration may be from 0.5 to 6 mm, such as from 0.7 to 5 mm, from 1 to 4 mm, from 1.5 to 3 mm. Preferably the gap between the geometric centre of each adjacent fenestration is about 2.5 mm. In a specific embodiment, the circumferential length of the ring is about 30 mm, and the ring comprises 10 fenestrations with a gap of 2.5 mm between the geometric centre of each adjacent fenestration. The fenestrations may have an internal diameter in an axial direction of from 0.2 to 0.9 mm, preferably of from 0.4 to 0.8 mm, more preferably of from 0.5 to 0.7 mm. The fenestration may have an internal diameter in an axial direction of about 0.6 mm. Where the fenestrations are located in the recess (e.g., channel) and connect the recess and the external surface, the fenestrations preferably have an internal diameter in an axial direction which is less than the axial depth of the recess. The fenestrations may have an internal diameter in a circumferential direction from 0.2 to 3 mm, preferably from 0.4 to 2 mm, more preferably from 0.6 to 1.6 mm, yet more preferably from 0.8 to 1.2 mm. The fenestration may have an internal diameter in a circumferential direction of about 1 mm. In some embodiments the internal diameter in an axial direction is equal to the internal diameter in a circumferential direction. In such cases, the fenestrations are typically circular or square. In other embodiments the internal diameter in an axial direction is less than the internal diameter in a circumferential direction. In such cases, the fenestrations are typically elliptical or rectangular. If the anterior and / or posterior surfaces comprise flexible regions (e.g., breaks), the flexible regions (e.g., breaks) are typically axially offset from the fenestrations. This allows the ring to have increased flexibility from the flexible regions without materially reducing the strength of the ring, which might risk fracturing on insertion. The radial extent of the fenestration is typically from 0.2 to 0.9 mm, preferably of from 0.4 to 0.8 mm, more preferably of from 0.5 to 0.7 mm. The radial extent of the fenestration is typically the distance between the internal and external surface, or the distance between the base of the recess and the external surface. In some embodiments, the ring has a C-shaped circumferential cross section. The C-shaped cross-section is formed by the recess (e.g., channel) in the internal surface of the ring. Preferably, the ring is symmetrical about a plane perpendicular to the axial direction. In other words, the ring is symmetrical about a plane between the anterior surface and the posterior surface. Preferably, the anterior surface and the posterior surface are substantially identical. In this context, the ring may refer to the parts of the ring between the first end and the second end (i.e., excluding any appendages to the first end and second end). The open capsular tension ring may be formed of one or more layers of material, such as one or two layers. The two layers may be the same or different. Preferably, the open capsular tension ring is formed of a single layer. The two layers may be an internal radial layer and an external radial layer. In other words, the external surface may be part of an outer layer and the internal surface may be part of an inner layer, wherein the internal layers and external layers are concentric. The external layer may be connected to the inside layer using any suitable means, such as by friction fit or with an adhesive. Alternatively, the ring may be formed of an inside layer and an outside layer, where the outside layer is a coating which covers at least a part, such as all, of the layer. The outside layer may be connected to the inside layer using any suitable means, such as by interference fit or with an adhesive. In some embodiments the ring or its surface may be used as a drug delivery system, for example to deliver antibiotics, glaucoma medication or anti-inflammatory drugs to the internal eye. A drug may be provided within a surface coating, incorporation into the ring material or as a localised attachment to the ring with controlled release. In some embodiments the ring may contain a pressure sensing device to measure intra ocular pressure with telemetry transmission. Preferably, the open capsular tension ring is formed of a single layer. Preferably, the open capsular tension ring is formed of a single radial layer. That is, the ring essentially consists, such as consists, of one layer. The one layer is preferably integrally formed of one material. In some embodiments, the ring does not include two layers. The ring may be formed of any suitable material, which will be known to the skilled person in the art. The ring is typically formed from an ocular biocompatible material. The ring is typically formed from a flexible material, such as a resiliently deformable material. The ring is preferably formed from a polymeric material, such as an acrylate polymer, a siloxane polymer or a hydrogel. The polymeric material may be hydrophilic or hydrophobic. The polymeric material is preferably poly(methyl methacrylate), poly(2-hydroxyethyl methacrylate), poly(acrylamide), poly(methacrylic acid) or poly(siloxane), more preferably poly(2-hydroxyethyl methacrylate) or poly(siloxane), or a co-polymer formed from a combination of the constituent monomers thereof. Method of Production In a further aspect of the invention there is provided a method of preparing the open capsular tension ring of the first aspect, the method comprising providing a polymeric composition and shaping the polymeric composition to provide the open capsular tension ring. The polymeric composition may comprise a polymer, such as an acrylate polymer, a siloxane polymer or a hydrogel. In such embodiments, the polymeric composition may be shaped into the ring (e.g., by moulding or 3D printing). Alternatively, the polymeric composition may have material removed to be shaped into the ring (e.g., by machining or 3D printing). Alternatively, the polymeric composition may comprise constituent monomers or prepolymers, such as acrylate or siloxane monomers or pre-polymers. In such embodiments, the method of preparing the open capsular tension ring may further comprise curing the polymeric composition. The constituent monomers or pre-polymers may be cured to form a polymer product in the shape of the ring. The curing typically results in polymerisation of the monomers or pre-polymers to form a polymer material. Curing is typically achieved by heating, optionally with addition of a polymerization initiator. The method of preparing the open capsular tension ring may further comprise annealing the ring. Annealing is typically achieved by heating. The ring may be shaped using any suitable technique, known to the skilled person in the art. For example, the ring may be moulded, machined, 3D printed or a combination thereof. In some embodiments the ring is moulded. The ring may be manufactured by any suitable type of moulding, such as extrusion moulding, compression moulding, injection moulding or rotational moulding. Preferably the ring is manufactured by extrusion moulding or injection moulding. The ring may be moulded as an integrally formed ring. In some embodiments the ring is machined. The ring may be manufactured by any suitable type of machining, such as turning (e.g., lathing), die cutting (e.g., stamping), milling (e.g., CNC milling), laser cutting, drilling or a combination thereof. The ring may be machined from a dehydrated polymer and then rehydrated. Preferably the ring is manufactured by turning and / or milling. The ring is machined from a bulk material. The bulk material may be machined directly to the ring. Alternatively, the bulk material may be machined to a ring blank, and then machined further to form the ring. In one embodiment a block of material is lathed to form ring blank, and the resulting ring blank is milled to shape the ring blank into the ring of the invention. For example, the ring blank may be machined, such as milled, to provide recesses (e.g., channels) and / or fenestrations. The ring may also be machined to include dialling loops. The ring may be milled from a straight rod and conformed to a ring. The ring may be attached to a substrate during machining, such as a rigid substrate. The ring is preferably made of a flexible material which is prone to moving during machining. Thus, a rigid substrate may be used as a scaffold to support the ring and prevent excessive movement during machining. In some embodiments the ring is 3D printed. The ring may be manufactured by any suitable type of 3D printing, such as stereolithography, selective laser sintering, fused deposition modelling, digital light process, multi jet fusion, PolyJet, electron beam melting or a combination thereof. In a preferred embodiment, the ring may be manufactured by moulding or 3D printing, followed by machining. Preferably, the ring is manufactured by moulding, followed by machining. For example, the ring may first be moulded or 3D printed to provide a ring blank. The ring blank is a ring having the rough dimensions and shape of the desired ring. The ring blank then may be further machined to provide the final ring. For example, the ring blank may be machined, such as milled, to provide recesses (e.g., channels) and / or fenestrations. The ring may also be machined to include dialling loops. The method of preparing the open capsular tension ring may further comprise treating the surface of the ring. In some embodiments, the whole of the ring is surface treated. In some embodiments, a portion of the ring is surface treated. Preferably, only the recess, such as the channel is surface treated. The surface treatment may preferably increase friction and prevent IOL rotation. For example, the ring may be treated with a hydrophilic coating, or may be surface modified with a hydrophilic group. Alternatively, the ring may be treated with a hydrophobic coating, or may be surface modified with a hydrophobic group. The ring may also be surface treated to provide a high friction surface. The surface may be treated to increase the surface area of the surface, such as increasing the roughness of the surface, in order to provide the high friction surface. In addition or alternatively, the surface may be coated with a high friction coating, in order to provide the high friction surface. The method of preparing the open capsular tension ring may further comprise a step of adding dialling loops. The dialling loops may be added after ring is shaped. The dialling loops may be adhered to the first end and the second end of the ring using an adhesive. The method of preparing the open capsular tension ring may further comprise any further steps typically used for an ophthalmic device, such as an intraocular device. Such steps may include sterilising (e.g., ethylene oxide gas or steam sterilising), autoclaving, polishing or a combination thereof. Uses and Methods Generally, the capsular tension ring of the first aspect may be used in a method of treatment. The capsular tension ring may be used in a method of cataract surgery or in a method of refractive lens exchange surgery. The capsular tension ring improves visual outcome, improves recovery times, and suppresses PCO. The capsular tension ring supports the capsular bag in the presence of weak or absent lens zonules. In an aspect of the invention, there is provided a method of treating cataracts using a capsular tension ring of the first aspect. In a related aspect, there is provided a capsular tension ring of the first aspect for use in a method of treating cataracts. In another aspect of the invention, there is provided a method of treatment or prophylaxis of posterior capsule opacification using a capsular tension ring of the first aspect. In a related aspect, there is provided a capsular tension ring of the first aspect for use in a method of treatment or prophylaxis of posterior capsule opacification. In some embodiments, the method of treatment is a method of treating cataracts. In some embodiments, the method of treatment is a method of treatment or prophylaxis of posterior capsule opacification. Cataracts may comprise cataracts caused by aging, trauma, radiation exposure, eye surgery, genetics, diabetes, drugs or inflammation. There is also provided a use of the capsular tension ring of the first aspect to prevent rotation of an intraocular lens. Also described is a method of implanting the capsular ring of the invention in cataract surgery or refractive lens exchange surgery. Typically, the capsular tension ring of the invention is inserted using a standard surgical procedure which is familiar to those skilled in the art. Following aspiration of the natural lens material, the capsular bag is opened with viscoelastic material injected through a standard injector, the ring is inserted and the IOL inserted into the ring by locating the haptics in the ring. The natural capsular membrane is opened by an incision on the anterior surface and the natural lens substance removed. A capsular tension ring is added into the capsular bag through the anterior incision. An intraocular lens is inserted into the capsular bag through the anterior incision, and located in the capsular tension ring. The haptics of the IOL are located into the respective recess or recesses of the ring. The capsular tension ring may be inserted into the eye manually or using a suitable injector. The capsular tension ring may be inserted both in a clockwise and counterclockwise direction. The capsular tension ring may comprise a biologically active material. The capsular tension ring may be configured to deliver a biologically active material. The biologically active material may be a pharmaceutical compound, such as a pharmaceutical composition. The pharmaceutical compound may be an antibiotic compound, glaucoma medication or an anti-inflammatory compound. The biologically active material may be coated on the surface of the ring, such as in a carrier composition or matrix. The biologically active material may be attached to the ring, such as in a carrier plug. Alternatively, the biologically active material may be impregnated into the ring material itself. The biologically active material may be provided in a controlled release formulation, such as a coated particle (e.g., nanoparticle). Injectors and Kits In an aspect of the invention, there is provided an injector for injecting an open capsular tension ring into a capsular bag, the injector comprising the open capsular tension ring of the first aspect. In some embodiments, the injector also comprises a carrier fluid. In another aspect of the invention, there is provided a kit comprising the open capsular tension ring of the first aspect and, separately, an injector for injecting the open capsular tension ring into a capsular bag. The injector may be any injector which is suitable for injecting an open capsular tension ring into the capsular bag of the eye, and such injectors would be well known to the skilled person. The injector or the kit may further comprise a carrier fluid. The carrier fluid is typically a viscoelastic fluid. Any suitable carrier fluid may be used, and such carrier fluids would be well known to the skilled person. An injector or a kit may optionally be provided together with instructions for use of the injector or kit. Example Embodiments The following example embodiments are provided to further illustrate the present invention and are not intended to limit the scope of the invention. Figure 2 shows a circumferential cross-sectional view through an example of the open capsular tension ring (10) of the invention. The ring has a U-shaped cross-section. The ring is a broken ring - so the ends (22, 24) are not connected. The ring (10) has a posterior surface (12) and an anterior surface (14) on opposite sides of the ring, which are connected by an internal surface (18) and an external surface (16). The internal surface (18) and external surface (16) are also opposing surfaces. The posterior surface (12) and anterior surface (14) are parallel and annular. The internal surface (18) and external surface (16) are parallel and coaxial. The posterior surface (12) and anterior surface (14) are perpendicular to the internal surface (18) and external surface and parallel to each other (16). The axial depth of the ring is shown by arrow B, and is equal to the distance between the posterior surface (12) and anterior surface (14) as measured along the external surface (16). The axial depth of the external surface is about 2.0 mm. The radial width of the ring is shown by arrow A, and is equal to the distance between the external surface and internal surface, as measured along the posterior surface. The radial width of the posterior surface is about 1.6 mm. The internal surface includes a channel (20) extending continuously between the first end (22) and the second end (24). The channel has a rectangular cross-section, open internally. The channel has a radial width of about 0.6 mm and an axial depth of about 0.6mm, so that the anterior and posterior rims of the channel have a thickness of about 0.7 mm. The bottom of the channel (20) is about 0.6 mm below the internal surface (18). The channel has an axial width of about 0.6 mm. The channel is equidistant between the posterior surface (12) and the anterior surface (14). The internal surface (18) includes a surface with an axial depth of about 0.7 mm on the anterior side of the channel (20), and a surface with an axial depth of about 0.7 mm on the posterior side of the channel (20). Figure 3 shows a plan view of the example of the open capsular tension ring (10a). The internal surface (18) is shown on the inside face of the ring, and the outside surface (16) is shown on the outside face of the ring. The planar anterior surface (14) is also shown in plane. Figure 3 also shows the first end (22) and second end (24) separated by a gap to form the open ring. The first end (22) and second end (24) include dialling loops (23 and 25) integrally formed with the ring. The circumferential length between the first end and second end is about 30 mm including the terminal dialling holes (when measured along the length of the interior surface). The gap between ends when the ring is implanted in the capsular bag will depend on the bag diameter. The gap between the first end and second end when the ring is in a relaxed state is about 4.5 mm. In other respects, the dimensions of the embodiment are substantially identical to that of the embodiment in Figure 2. Figure 4 shows a radial view of the internal surface (18) of a reference example of an open capsular tension ring (10b). Figure 4 is a schematic drawing, and the length of the ring between the ends is reduced for the illustration. The first end (22) and second end (24) include dialling loops integrally formed with the ring, where the first end (22) includes a dialling hole (23) formed through the anterior surface (14) and the second end (24) includes a dialling hole (25) formed through the posterior surface (12). The total circumferential length of the ring, including the dialling holes, is about 30 mm. The dialling holes extend beyond the external and internal surfaces. The dialling holes have a diameter of about 0.4 mm. Figure 4a shows an example embodiment of the type shown in figure 4, but with the addition of round fenestrations (26) passing through the side wall of the channel (20) through to the external surface (16) of the ring. The example ring (10c) includes 20 fenestrations (26) equally spaced between the first and second ends. The fenestrations (26) are located equidistant from the anterior surface (14) and the posterior surface (12). The fenestrations (26) allow for fluid flow between the channel and the external surface. The fenestrations (26) have an internal diameter of about 0.6 mm. Figure 5 shows an axial cross section view of an example of the open capsular tension ring (10) when implanted in a capsular bag (01) of an eye, and with an IOL haptic (101) located in the channel (20). The anterior surface (14) is contacting the anterior capsule (04). The posterior surface (12) is contacting the posterior capsule (02). The external surface (16) is contacting the equator of the capsule (06). As such, the example ring (10d) prevents closing of the capsular bag, as illustrated in Figure 1. The external surfaces of the capsular tension ring (10) (i.e., those in contact with the capsular bag) are smooth to allow atraumatic insertion into the capsular bag. Figure 6 shows a plan view of an example of the open capsular tension ring (10) when implanted in a capsular bag of an eye. The IOL (100) is located centrally in the ring. The IOL haptics (101) are located in the channel (20). Figure 7 shows a radial view of the internal surface (18) of an alternative example of the open capsular tension ring (10e). The length of the ring between the ends is reduced for the illustration. The alternative ring is substantially identical to the ring discussed above, but further includes breaks (28) in the anterior surface (14) and posterior surface (12) of the ring. The breaks are equidistant and spaced along the length of the ring (10e) between the first end (22) and the second end (24). The breaks (28) extend through the radial rim as far as the external surface (16). The breaks have a width of about 0.5 mm and are spaced evenly apart on the anterior and posterior surfaces about 1 mm apart. The breaks improve the flexibility of the ring. Figure 8 shows a radial view of the internal surface (18) of an alternative example of the open capsular tension ring (1 Of). The length of the ring between the ends is reduced for the illustration. This embodiment is substantially identical to that described in figure 4a. The ring includes a chamfered first end and second end. The chamfer extends between the posterior and anterior surface. The part of the anterior / posterior surface including the dialling hole is not chamfered in this example. The chamfer is complimentary between the first end and second end, allowing the first end and second end to partially tessellate when brought together. The chamfer is at an angle relative to the anterior / posterior surface of about 45°. Figure 9 shows a radial view of the internal surface (18) of an example of the open capsular tension ring (10g) with breaks in the anterior and posterior surfaces. Figure 10 shows a plan view of the anterior surface (14) of the ring (10g). Only a central section of the ring is shown, for illustration. The ring includes breaks (28) at the same relative positions in the anterior surface (14) and posterior surface (12) of the ring. The breaks extend radially from the interior surface (18) towards the exterior surface (16) of the ring (10g), but terminate at the base of the recess (20). The figure shows the fenestrations (26) in the recess (20). The fenestrations are to allow aqueous humour to percolate through the ring. The breaks (28) in the anterior surface (14) and posterior surface (12) are axially offset from the fenestrations (26) to not materially reduce the strength of the ring. In this example, the breaks have a width of 2 mm and are spaced evenly apart on the anterior and posterior surfaces about 2 mm apart. The breaks improve the flexibility of the rings. The fenestrations (26) have an internal diameter of about 0.6 mm. Figure 11 a circumferential cross-sectional view through an example of the open capsular tension ring of the invention. The external surface of the ring has a spheroidal shape with an axial depth of about 2.0 mm. The external surface has a continuous curve between the anterior (14) and posterior (12) surfaces. An IOL haptic (101) is shown located in the recess (20). Figure 12 shows a radial view of an internal surface of an example of the open capsular tension ring. The length of the ring between the ends is reduced for the illustration. The ring includes fenestrations (26) in the recess (20), which allow aqueous humour to percolate through the ring. The ring includes breaks at the same relative positions in the anterior surface (14) and posterior surface (12) of the ring that extend radially from the inner surface (18) of the ring (10) and terminate at the depth of the recess (20). The breaks have a width of 2 mm and are spaced evenly apart on the anterior and posterior surfaces about 2 mm apart. The breaks improve the flexibility of the rings. The breaks (28) in the anterior surface (14) and posterior surface (12) are axially offset from the fenestrations (26), so as not to materially reduce the strength of the ring. The ring includes a chamfered first end and second end. The chamfer extends between the posterior and anterior surface. The part of the anterior / posterior surface including the dialling hole is chamfered in this example. The part of the anterior / posterior surface on the opposite side to the dialling hole is not chamfered in this example. The chamfer extends approximately half way across the axial depth of the ring. The non-chamfered part of the first end and second end are perpendicular to the anterior / posterior surface. The chamfer is complimentary between the first end and second end, allowing the first end and second end to partially tessellate when brought together. The chamfer is at an angle relative to the anterior / posterior surface of about 45°. The ring is formed from a single, integrally formed polymeric material. The ring is formed of poly(2-hydroxyethyl methacrylate). In alternative embodiments, the ring is formed from poly(acrylamide), poly(methacrylic acid) or poly(siloxane), more preferably poly(2-hydroxyethyl methacrylate) or poly(siloxane). The ring is manufactured by injection moulding a ring blank. The ring blank is cured. The ring blank is then machined using CNC milling to machine the channel, fenestrations, dialling holes and breaks (where present). In alternative embodiments, the ring is manufactured by 3D printing. The ring is printed using fused deposition 3D printing, to build up layers of the ring. The ring is then quality checked, sterilized and packaged in a kit optionally together with and injector and / or instructions for use. Definitions The following common definitions are used herein, as determined by the relevant context. The “capsular bag” as used herein typically refers to the natural capsular membrane of the eye enclosing the lens material. Clinically this consists of the anterior and posterior capsule meeting at the equator. The “anterior capsule” generally refers to the side of the capsule facing the corneal side of the eye. The “posterior capsule” generally refers to the side of the capsule facing the retinal side of the eye. The “equator of the capsular bag” typically refers to the join between the anterior and posterior capsule. The axial direction typically refers to a direction parallel with the axis of rotation of the ring. In use, the axial length refers to a length measured in the sagittal plane, i.e., the axial length of the eye. The radial direction typically refers to a direction parallel with the radius of the ring (i.e., a line connecting the centre of the ring and the external surface of the ring). In use, the radial direction refers to a direction in the coronal plane i.e., at right angle or perpendicular to the axial plane. This may also be known as in the plane of the iris. The circumferential direction typically refers to a direction parallel with the circumference of the ring. Where 2D shapes are referred to, such as polygons (e.g., square, rectangle, triangle, trapezoid), the shapes also cover the equivalent shapes with rounded corners. For example, a square also typically covers a squircle. Other Preferences Each and every compatible combination of the embodiments described above is explicitly disclosed herein, as if each and every combination was individually and explicitly recited. Various further aspects and embodiments of the present invention will be apparent to those skilled in the art in view of the present disclosure. “and / or” where used herein is to be taken as specific disclosure of each of the two specified features or components with or without the other. For example, “A and / or B” is to be taken as specific disclosure of each of (i) A, (ii) B and (iii) A and B, just as if each is set out individually herein. Unless context dictates otherwise, the descriptions and definitions of the features set out above are not limited to any particular aspect or embodiment of the invention and apply equally to all aspects and embodiments which are described. Certain aspects and embodiments of the invention will now be illustrated by way of example and with reference to the figures described above. References Publications are cited above in order to more fully describe and disclose the invention and the state of the art to which the invention pertains. Full citations for these references are provided below. The entirety of each of these references is incorporated herein. WO 2018 / 160800 Alon etal., Invest Ophthalmol Vis Sci. 2014; 55:4005-4013

Claims

1. An open capsular tension ring (10) for implanting in a capsular bag (01) of an eye, the ring (10) comprising:a posterior surface (12) and an anterior surface (14) extending between a first end (22) and a second end (24) of the ring (10),an internal surface (18) and an external surface (16) extending between the first end (22) and the second end (24) of the ring (10), wherein the internal surface (18) comprises a recess (20) for receiving a haptic (101) of an intraocular lens (100),wherein the ratio of the radial width of the posterior surface (12) to the axial depth of the external surface (16) is from 0.3 to 1, andwherein the open capsular tension ring comprises radial fenestrations.

2. The open capsular tension ring (10) of claim 1, wherein the ratio of the radial width of the posterior surface (12) to the axial depth of the external surface (16) is from 0.4 to 0.9, preferably from 0.5 to 0.9, more preferably from 0.6 to 0.8.

3. The open capsular tension ring (10) of claim 1 or claim 2, wherein the posterior surface (12) and anterior surface (14) are parallel.

4. The open capsular tension ring (10) of any one of claims 1 to 3, wherein the radial width of the posterior surface (12) and / or the anterior surface (14) is constant between the first end (22) and the second end (24).

5. The open capsular tension ring (10) of any one of claims 1 to 4, wherein the radial width of the posterior surface (12) and / or the anterior surface (14) 0.6 to 2.0 mm, preferably 0.7 to 1.8 mm, preferably 0.8 to 1.6 mm, more preferably 0.9 to 1.4 mm, yet more preferably 1.0 to 1.2 mm.

6. The open capsular tension ring (10) of any one of claims 1 to 5, wherein the anterior surface (14) and / or posterior surface (12) comprise flexible regions, preferably wherein the flexible regions comprise breaks (28) in the anterior and / or posterior surface.

7. The open capsular tension ring (10) of any one of claims 1 to 6, wherein the external surface (16) is a coaxial around the central axis of rotation of the ring (10).

8. The open capsular tension ring (10) of any one of claims 1 to 7, wherein the internal surface (18) and external surface (16) are coaxial.

9. The open capsular tension ring (10) of any one of claims 1 to 8, wherein the internal surface (18) and / or external surface (16) are perpendicular to the posterior surface (12) and anterior surface (14).

10. The open capsular tension ring (10) of any one of claims 1 to 9, wherein the axial depth of the external surface (16) is 1.2 to 2.8 mm, preferably 1.5 to 2.5 mm, more preferably 1.7 to 2.2 mm, yet more preferably 1.9 to 2.1 mm11. The open capsular tension ring (10) of any one of claims 1 to 10, wherein the axial depth of the internal surface (18) is equal to the axial depth of the external surface (16).

12. The open capsular tension ring (10) of any one of claims 1 to 8, wherein the external surface is a spheroidal surface and the internal surface is a cylindrical surface.

13. The open capsular tension ring (10) of any one of claims 1 to 12, wherein the ring has a circumferential length from the first end (22) to the second end (24) of from 25 to 35 mm, preferably 29 to 33 mm, more preferably 30 to 32 mm, yet more preferably about 30 mm.

14. The open capsular tension ring (10) of any one of claims 1 to 13, wherein the recess (20) is centred in the interior surface.

15. The open capsular tension ring (10) of any one of claims 1 to 14, wherein the recess (20) is a channel, preferably wherein the channel extends continuously between the first end (22) and the second end (24).

16. The open capsular tension ring (10) of any one of claims 1 to 15, further comprising one or more manipulation means at the first end (22) and / or the second end (24), preferably wherein the manipulation means comprise a loop of material defining a dialling hole.

17. The open capsular tension ring (10) of any one of claim 16, wherein the manipulation means are integrally formed in the ring (10).

18. The open capsular tension ring (10) of any one of claims 1 to 17, wherein the fenestrations radially connect the recess (20) and the external surface (16).

19. The open capsular tension ring (10) of any one of claims 1 to 18, wherein the capsular tension ring (10) consists of a single radial layer.

20. The open capsular tension ring (10) of any one of claims 1 to 19, wherein the capsular tension ring (10) is unitary, and preferably formed of one material.

21. The open capsular tension ring (10) of any one of claims 20, wherein the ring is formed from an acrylate polymer or a siloxane polymer, preferably poly(methyl methacrylate), poly(2-hydroxyethyl methacrylate) or poly(siloxane), more preferably poly(2-hydroxyethyl methacrylate) or poly(siloxane).

22. An injector for injecting an open capsular tension ring (10) into a capsular bag (02), the injector comprising the open capsular tension ring (10) of any one of claims 1 to 21 optionally together with a carrier fluid.

23. A kit comprising the open capsular tension ring (10) of any one of claims 1 to 21 and an injector for injecting the open capsular tension ring (10) into a capsular bag (01).

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