Pupil Expander

Abstract

A pupil expander 101 for expanding and maintaining a pupil 3 in a dilated state during ophthalmic surgery, comprising a body comprising an iris engaging portion 6 comprising a plurality of iris engagi

Description

Field of Invention The present disclosure relates to a pupil expander for use in dilating and / or maintaining a pupil of an eye in a dilated state during ophthalmic surgery, e.g., cataract surgery and lens replacement surgery. Introduction Cataract, (clouding of the crystalline lens of an eye), resulting in visual impairment, is one of the most common diseases of the eye particularly amongst the elderly and those with certain medical conditions, such as diabetes. When the cataract has progressed to the extent that the vision becomes impaired the only remedy is surgery. Cataract surgery involves replacing the natural lens that has become cloudy with a prosthetic intraocular lens. This involves making an incision at the limbus of the cornea, making a circular incision through the anterior capsule of the lens and physically removing the lens from its enclosing capsule. Before surgery can start the pupil must be sufficiently dilated to allow the surgeon to have a clear view of the anterior capsule. Removal of the lens involves breaking up the lens, using an ultrasonic phacoemulsification instrument, so that it can be aspirated. The process of breaking up the lens and removing the pieces of broken lens is known as phacoemulsification. To perform phacoemulsification of the lens using the ultrasonic instrument, it is paramount that the pupil is sufficiently dilated and maintained in a dilated state during surgery. Contraction of the pupil during ophthalmic surgery creates substantial difficulty for a surgeon because it inhibits visibility and access to the lens. Moreover, there is the risk that the tip of the phacoemulsification probe may touch the inner edge of the iris resulting in damage to the iris and subsequent inflammation; if the pupil is insufficiently dilated. Thus, it is advantageous for the pupil to be dilated sufficiently to enable the surgeon to have good visibility and access to the lens. Generally, the size of the pupil is controlled by the iris, which is a ring-shaped structure positioned behind the cornea and in front of the lens, and comprises both dilator and spincter muscles for respectively expanding and contracting the pupil. In a bright environment the iris sphincter muscle contracts and the dilator muscle relaxes to reduce the size of the pupil, i.e., contracts the pupil, so that the amount of light entering the eye is reduced. In a comparatively darker environment, the iris sphincter muscle relaxes and the dilator muscle contracts, increasing the size of the pupil so as to increase the amount of light entering the eye. Whilst topical drugs can be used to dilate the pupil, their effects can be inadequate in certain cases. Alternative mechanical means are then required to dilate the pupil for ophthalmic surgery. This involves the use of a tool to physically expand the inner circumferential edge of the iris radially outward in order to enlarge the pupil. The process begins with injecting a “visco-elastic” material into the anterior chamber of the eye, between the back of the cornea and the front of the iris, to keep the anterior chamber fully inflated during insertion of the physical tool for dilating the pupil. Various tools can be used to physically pull the iris edge radially outward sufficiently to gain access to the natural lens. One such method involves making four small incisions at roughly 90° intervals around the periphery of the cornea and inserting a small hook (iris hook) through each incision to engage with the inner circumferential edge of the iris. The iris hooks are retracted to exert a pulling force on the inner peripheral edge of the iris so as to cause the iris to be pulled outwardly, so enlarging the pupil. Because of the position of the hooks at 90° intervals, the pupil is expanded to form a substantially square shaped opening. Such surgical methods to mechanically enlarge the pupil are invasive, time consuming and can result in permanent damage to the iris sphincter resulting in an irregular shaped pupil that no longer reacts properly to light. More recent devices for expanding the pupil include the Malyugin Ring, the OASIS Iris Expander and Morcher Pupil Dilator. Such pupil expanders are made from a resilient polymeric material and formed into a square or ring shape structure when in a relaxed or expanded state. Such a pupil expander is contractible so as to be stored in a dedicated injector or inserter so that it can be inserted into the anterior chamber of the eye via a small incision in the cornea. Once inserted into the anterior chamber, the pupil expander is allowed to return to its original shape inside the eye due to the shape memory properties of the material of the pupil expander. Depending on the type of pupil expander, this could be a square or ring shape having a diameter in the range 5mm to 7mm. Expansion of the pupil expander causes its iris engaging portions to engage with the inner circumferential edge of the iris which in turn results in physical dilation of the pupil. Typically, the iris engaging portions comprises anterior and posterior flanges providing a C-shaped channel within the body of the pupil expander for receiving the inner circumferential edge of the iris. To help engage the pupil expander with the inner circumferential edge of the iris, more particularly the iris engagement portions of the pupil expander, a tool, commonly a Sinskey hook, is used to hook the iris engaging portions of the pupil expander onto the iris. The process involves progressively engaging adjacent or opposite sides of the inner circumferential edge of the iris with the iris engaging portions of the pupil expander. In order to prevent the pupil expander rapidly returning to its expanded state when inserted into the eye, the pupil expander can be injected little by little allowing the surgeon to sequentially engage the iris engagement portions with the inner circumferential edge of the iris while the pupil expander is inserted into the anterior chamber of the eye. This removes the need to manipulate the pupil expander to the pupil edge once injected into the anterior chamber of the eye. However, engaging the pupil expander to the inner circumferential edge of the iris is not easy task and the Sinskey hook may have to be used via one or more additional incisions in the cornea in order to manipulate the pupil expander so as to correctly position its iris engaging portions against the inner circumferential edge of the iris. However, repeated manipulation of the pupil expander within the anterior chamber of the eye increases the risk of damaging the tissue of the iris by contact with the Sinskey hook or at the very least results in the excessive stretching of the iris tissue and subsequent inflammation of the iris. Moreover, manipulation of the pupil expander by the Sinskey hook to correctly position its iris engaging portion against the inner circumferential edge of the iris requires a high level of dexterity and experience of the eye surgeon to avoid damaging the back surface of the cornea. However, given the rigid nature of the pupil expander constituted by plastic having shape memory properties that has a tendency to return its original expanded state once contracted, there is little control in the expansion of the pupil expander once inserted into the anterior chamber of the eye. US 5,267,553 (John M. Greather) tries to address this problem by providing a pupil expander which has an elongated plastic resilient hollow ring that is C-shaped in crosssection and formed into a partial circle. The ends of the ring member have perforated tabs thereon, and are connected together by a strap. By virtue of the partial circle, the pupil expander can be compressed into an elongated shape. Forceps tips are inserted into the ends of the ring member to hold the ring member in a contracted state during insertion of the pupil expander into the anterior chamber of the eye through an incision in the eye outside the location of the iris. The ring member is allowed to gradually expand and engage the inner periphery of the iris as the forceps are gradually withdrawn. However, expansion of the pupil expander in the eye is very much limited by the rate by which the forceps can be gradually withdrawn from the ring member and since this cannot be controlled accurately, this is reflected in the sudden expansion of the pupil expander in the eye. As a result, an elongated tool has to be frequently inserted into the eye to facilitate engagement of the ring member with the iris. Moreover, the rigid nature of the pupil expander makes manipulation of the pupil expander within the anterior chamber of the eye difficult and in an extreme case excessive manipulation with the elongated tool such as the Sinskey hook is required to correctly position the pupil expander into engagement with the iris. Additional tooling is also required to remove the pupil expander from the anterior chamber of the eye by cutting a strap adjacent one of the tabs, grasping the tab adjacent the cut, and longitudinally pulling the expander through the incision in the cornea. All this makes manipulation and engagement with the inner circumferential edge of the iris laborious and prone to causing injury to the iris. To help position the pupil expander when inserted into the anterior chamber of the eye, US 6,620,098 (John Milverton) teaches a pupil dilating device for dilating a pupil and / or maintaining a pupil in a dilated station. The device being generally hook shaped in plan view so to define an open ended arcuate iris engaging body portion having distal free end and at or adjacent the other of said end an integral positioning arm extending outwardly in a generally radial direction therefrom. The positioning arm is sized to extend in use beyond the outer periphery of the iris. The integral arm provides remote means for assisting in the “dialling” into the anterior chamber of the eye and subsequent positioning and removal of the device from the pupil. The arm also provides means for securing the device in the preferred location and, if necessary, means for rotating the dilator to a preferred orientation. Like the pupil expander discussed above, the body portion of the device is formed from a rigid, resilient material and therefore, suffers from the problem of a lack of control in the expansion of the device once inserted into the anterior chamber of the eye. As a result, a tool such as a Sinskey hook, is additionally required to ensure proper engagement of the iris engaging formations of the device, which is generally C-shaped in cross-section, with the inner circumferential or peripheral edge of the iris. The problem of proper engagement of the iris engaging formation of the pupil expander with the inner circumferential edge of the iris is exacerbated when the patient suffers from Intraoperative Floppy Iris Syndrome (IFIS) which is syndrome known to cause intraoperative complications during cataract surgery. This is a syndrome that causes billowing of the iris during surgery. In the worst case scenario, the iris prolapses towards any incisions made through the cornea as irrigating fluid used during surgery has a tendency to flow behind the iris. Traditionally, hooks discussed above can be used to maintain pupil dilation during phacoemulsification in patients with severe 1FIS. As a result, the damaging effects of engaging the hooks with the inner circumferential edge of the iris is more pronounced in patients with IFIS. A pupil expander requiring little dexterity to be easily manipulated into engagement with the iris is thus required. Summary of the Invention Although the root of the iris is attached to the ciliary body of the eye, the rest of the iris is unsupported. In certain circumstances the iris may prolapse through the corneal incision. This is particularly the case where the iris has lost its structural integrity resulting in a floppy iris. Intraoperative Floppy Iris Syndrom (IFIS) is a side effect of certain drugs, e.g. tamsulosin. Multiple corneal incisions are required to complete cataract surgery and it is through these that iris prolapse occurs. The present invention has mitigated the above problem by providing a pupil expander comprising an overlay portion and an iris engaging portion comprising a plurality of iris engaging formations, the overlay portion being configured to radially extend across a substantial portion of the iris and remain on the anterior (front) surface of the iris when one or more of the plurality of iris engaging formations engage with the inner circumferential edge of the iris or sphincter. By radially extending across the anterior surface of the iris, the overlay portion stabilises the iris when one or more of the iris engaging formations are brought into engagement with the inner circumferential edge of the iris. To provide an overlay that is configured to stabilise the iris whilst the pupil is being expanded, the present invention provides a pupil expander for expanding and maintaining a pupil in a dilated state during ophthalmic surgery, the pupil expander comprising: a body comprising an iris engaging portion comprising a plurality of iris engaging formations; an overlay portion extending radially outwardly of the iris engaging portion that is configured to extend across the iris, the overlay is divided into a plurality of supportstructures, the plurality of support structures being arranged such that each of the plurality of iris engaging formations is disposed or positioned between a pair of the plurality of support-structures, wherein the body is resiliently deformable such that, in use, each of the plurality of support structures remain on or extend over the iris when one or more of the plurality of iris engaging formations is pulled inwardly towards the pupil edge. In comparison to known pupil expanders, the pupil expander according to the present invention comprises an overlay portion that remains on the iris when the iris engaging portion is manipulated into engagement with the inner circumferential edge of the iris. The overlay portion stabilises the iris, particularly patients suffering from Intraoperative Floppy Iris Syndrome, during cataract surgery and helps to mitigate iris prolapse during engagement of the iris engaging portions with the inner circumferential edge of the iris. As the pupil expander is a delicate structure having a dimension in the order of 3mm to 6mm in diameter, the overlay portion not only supports the iris when the iris engaging formations are engaged with the inner circumferential edge, but also stabilises the pupil expander during pupil expansion. Other benefits of the overlay portion include assisting the eye surgeon to correctly guide the tool or instrument used to engage the iris engaging formations into engagement with the inner circumferential edge of the iris mitigating the risk of damage to the tissues of the iris. Ideally, to mitigate damage to the iris or surrounding tissues, the tool used to pull the iris engaging formations with the inner circumferential edge of the iris should follow a path along the plane or surface of the iris. Diverging from this path may result in the tool touching the more delicate areas of the eye. The overlay portion of the pupil expander according to the present invention helps the eye surgeon to better follow this path when engaging the iris engaging formations with the inner circumferential edge of the iris. In prior art solutions, the pupil expander offers little support when the iris engaging formations are pulled into engagement with the inner circumferential edge of the iris which results in the tendency of the tool or instrument used to engage the iris engaging formations not to follow this path along the plane or surface of the iris . Optionally, the plurality of iris engaging formations comprises a plurality of hooks. The overlay portion helps the eye surgeon to guide a Sinskey hook used to engage the plurality of hooks into engagement within the inner circumferential edge of the iris and thereby, mitigate one or more of the hooks inadvertently damaging the delicate tissues of the iris or surrounding tissues. Optionally, the plurality of hooks extends downwardly from the overlay portion. Preferably, the overlay portion is configured to constrain the movement of the iris engaging portion. Optionally, the iris engaging portion and the overlay portion lie in a common plane. Alternatively, the iris engaging portion and the overlay portion are deformable to conform to the shape of at least a portion of the eye when in use. Having the overlay portion and the iris engaging portion lie in a common plane, and as the overlay portion rests on the surface of the iris, the overlay portion constrains the movement of the iris engaging portion along the plane in which the overlay portion lies. This reduces the level of dexterity required by the eye surgeon to engage the iris engaging formations with the inner circumferential edge of the iris and thereby, reduces the risk of complications during surgery, particularly in patients with severe IFIS. To enable the overlay portion remain on the iris when one or more of the iris engaging formations are manipulated into engagement with the inner circumferential edge of the iris, the overlay portion is divided into a plurality of support-structures. The plurality of support structures are arranged such that each of the plurality of iris engaging formations is disposed between a pair of the plurality of support-structures. To enable the body of the pupil expander to resiliently deform such that the overlay portion remains on the surface of the iris when one or more of the iris engaging formations are manipulated into engagement with the inner circumferential edge of the iris, optionally, the body of the pupil expander comprises a plurality of preformed folds. Optionally, the plurality of performed folds are arranged such that the body adopts a zig-zag or undulating pattern when being deformed. Optionally, the plurality of preformed folds is arranged such that the body of the pupil expander comprises a plurality of concertina folds. Optionally, the plurality of preformed folds comprises a first fold line and a second fold line, and wherein at least one of the plurality of iris engaging formations is intermediate the first and second fold lines. Having the iris engaging formation intermediate the first and second fold lines allows the body of the pupil expander to be adaptable to having the iris engaging formation between a pair of the support structures, creating an overlay portion. The first and second fold lines either side of the iris engaging formation generates sufficient force as it tries to return the pupil expander to its original shape so as to cause the pupil to expand. The benefit of the preformed folds allows the body of the pupil expander to be resiliently deformable into an overlay portion and an iris engaging portion. Deformation of the body of the pupil expander results in the body of the pupil expander engaged with the inner circumference of the iris applying a restoring force in a radial direction causing dilation of the pupil. Other benefits of the preformed folds includes the ability of the pupil expander to be collapsible for insertion into the anterior chamber of the eye. For example, the plurality of preformed folds enable the pupil expander of the present invention to be contained within a pupil inserter tool. In one optional aspect of the present invention, the body of the pupil expander adopts a substantially cross shaped configuration when engaged with the iris. Other examples of the shape of the body comprising performed folds include but is not limited to star shaped. Optionally, the body of the pupil expander is substantially ring shaped. The ring shaped body can be configured as a square shaped or star shaped body. When deformed, the ring shaped body applies a restoring force in a radial direction on the sphincter causing dilation of the pupil. To manipulate the iris engaging formations into engagement with the inner circumferential edge of the pupil, optionally, the body of the pupil expander comprises one or more instrument engaging formations. Optionally, each of the one or more instrument engaging formations comprises an opening for receiving a hook, e.g. Sinskey hook. To apply a force radially inward or radially outward of the iris engaging formations, each of the one or more instrument engaging formations is disposed between a pair of the support structures. To insert or remove the pupil expander from the anterior chamber of the eye, the present invention provides a pupil expander insertion tool comprising an elongated cannula having a forward and rearward longitudinal ends, said elongated cannula housing at least a portion of a pupil expander of the present invention; a retractable blade housed within the elongated cannula, the retractable blade being slideable along the longitudinal axis of the elongated cannula between a forward position and rearward position; said forward end having an opening such that the retractable blade ejects at least a portion of the pupil expander through the opening when in the forward position and retracts the blade through the opening when in the rearward position. 19 06 23 Description of Drawings Further features and aspects of the present invention will be apparent from the following detailed description of an illustrative embodiment made with reference to the drawings, in which: Figure 1 is a perspective plan view of a pupil expander in an open state on the surface of the iris according to a first embodiment of the present invention. Figures 2A to 2C are plan views showing the stages of dilation of the pupil by the pupil expander of Figure 1. Figure 3 is a perspective plan view of a pupil expander in an open state on the surface of the iris according to a second embodiment of the present invention. Figure 4 is a perspective plan view showing the dilation of the pupil by the pupil expander shown in Figure 3. Figure 5 is a perspective side view of the pupil expander shown in Figure 4 showing the iris engaging portion secured to the inner circumferential edge of the iris and the overlay proportion stabilising iris. Figure 6 is a cross sectional view showing the iris engaging portion of the pupil expander comprising a plurality of hooks engaging with the inner circumferential edge of the iris showing. Figure 7 is a cross sectional view showing the iris engaging portion of the pupil expander comprising upper and lower flanges engaging with the inner circumferential edge of the iris. Figure 8 is a perspective view showing the initial step of inserting the pupil expander into the anterior chamber of the eye. Detailed Description To attain the aforementioned object, the present invention is characterised by a pupil expander used to maintain the pupil 3 in an expanded or dilated state during ophthalmic surgery, such as cataract surgery. The pupil expander 1 according to an embodiment of the present invention shown in Figure 1 comprises a body 2 having an overlay portion 4 and an iris engaging portion 6, the body 2 being deformable when the iris engaging portion is engaged with the inner circumferencial edge of the iris to define the overlay portion 4 (see Figure 6). The overlay portion 4 extends across the iris 10 when the iris engaging portion 6 is in engagement with the inner circumferential edge 8 of the iris 10. The overlay portion 4 stabilises the iris when the iris engaging portion 6 is manipulated into engagement with the inner circumferential edge 8 of the iris. This is particularly important when the patient undergoing ophthalmic surgery suffers from Intraoperative Floppy Iris Syndrome due to loss of muscle tone in the iris affecting the structural integrity of the iris. As a result there is a marked tendency for the iris to prolapse through one or more of the incisions made through the cornea 12 resulting in pupil enlargement becoming more troublesome than a patient not suffering from Intraoperative Floppy Iris Syndrome. In the open state of the pupil expander, the iris engaging portion 6 and the overlay portion 4 is sized to lie on the anterior surface of the iris 10. The iris engaging portion 4 comprises a plurality of iris engaging formations 14 that are configured to engage with the inner circumferential edge 8 of the iris 10. Various types of iris engaging formations 14 can be used to engage within the inner circumferential edge 8 of the iris 10. For example, each of the plurality of iris engaging formations 14 can comprise a hook 16 that can be brought into engagement with the inner circumferential edge 8 of the iris 10 as shown in the schematic cross-sectional view of the iris shown in Figure 6. For a less invasive engagement with the inner circumferential edge 8 of the iris 10, each of the plurality of iris engaging formations 14 can comprise an anterior flange 18 and a posterior flange 20 that are connected by an intermediate central wall 22 so as to define a body portion that is generally “U” shaped in crosssection as demonstrated in Figure 7. The benefit of having anterior and posterior flanges 18, 20 to engage with the inner circumferential edge 8 of the iris 10 is that the posterior flange 20 can be made more soft and supple than the anterior flange 18. The use of a relatively soft posterior flange 20 provides significant benefits during non-cataract surgery in order to preserve the existing lens 24 as they may be clear and inappropriate for removal. The body 2 of the pupil expander 1 may be made from a material which is resiliently deformable, e.g. a shape memory material. For example, the body 2 of the pupil expander may be made entirely by injection moulding from materials such as nylon, prolene, polyurethane, polymethylacrylate, silastic, silicone polymode, polyamide or a combination of thereof or any other material having the requisite physical properties of resilience, flexibility, and suitability for use in surgical procedures. Considering that the iris diameter ranges from 11mm to 13mm, the pupil expander 1 is envisaged to be made in different size categories having a diameter of 6mm, 7mm, 8mm and 9mm. For the overlay portion 4 to stabilise the iris during ophthalmic surgery, it is envisaged that the overlay portion 4 extends a length R across the surface of the iris to the sphincter of the iris, where R can be in the range 1mm to 5mm, preferably in the range 1mm to 2mm. To enable the pupil expander of the present invention to be deformable into having an overlay portion 4 and an iris engaging portion 6, the body 2 of the pupil expander comprises a plurality of preformed folds 26, 28, 30 to encourage or promote deformation of the body 2. The preformed folds 26, 28, 30 divides the overlay portion 4 into a plurality of discrete support structures 32 separated by the iris engaging formations 14. The discrete support structures 32 are configured to overlay the iris 10 when the iris engaging formations 6 are manipulated into engagement with the inner circumferential edge 8 of the iris 10 by virtue of the one or more preformed folds 26, 28, 30. As shown in Figure 2C, the discrete support structures 32 extend a distance R across the surface of the iris 10 when the iris engaging formations 14 are engaged with the inner circumferential edge 8 of the iris 10. The body 2 of the pupil expander 1 can adopt various shapes when being deformed. Examples of the different shapes that the body the pupil expander can adopt when manipulated into engagement with the inner circumferential edge of the iris are shown in Figures 1, Figures 2(A to C) and Figure 3 to 4. However, the present invention is not limited to the shapes shown in the aforementioned examples and other shapes are permissible in the present invention so as to provide an overlay portion to stabilise the iris and an iris engaging portion, e.g. circular. In all cases, one or more of the iris engaging formations is disposed between a pair of support structures 32 overlaying the iris 10 when the body 2 of the pupil expander is deformed into engagement with the iris. In the first example of the pupil expander shown in Figure 1, the ring shaped body 2 adopts a substantially square shaped configuration comprising four corner portions 34 when in an open ‘unengaged’ state. Each of the corner portions 34 comprise a plurality of preformed fold lines 26, 28, 30 allowing the ring shaped body 2 to be deformable along their respective preformed fold lines 26, 28, 30. In the particular example shown in Figure 2A, each of the comer portions 34 comprises at least three performed fold lines 26, 28, 30. The iris engaging formation 14 shown as a black spot is positioned nearest one of the three preformed fold lines 30. As shown in Figure 2A, the iris engaging formation at the preformed fold line 30 is disposed between a pair of fold lines 26, 28 either side of the iris engaging formation 14 such that when the iris engaging formation is pulled into engagement with the inner circumferential edge 8 of the iris 10, the comer portions 34 is able to fold along their respective preformed fold lines 26, 28, 30. This is clearly demonstrated in Figure 2B and is repeated for the other corner portions as shown in Figures 2B to 2C. Each time the iris engagement formation 14 is pulled into engagement with the inner circumferential edge 8 of the iris 10 of the eye at an engagement point on the iris, the body 2 of the pupil expander adopts an overlay portion 4 and an iris engaging portion 6. The plurality of fold lines 26, 28, 30 at the corner portions 34 of the body of the pupil expander enables the overlay portion 4 to remain nested on the surface of the iris when the discrete iris engaging formations 14 are pulled into engagement with the inner circumferential edge 8 of the iris 10. In the particular example shown in Figure 2C, the body 2 of the pupil expander 1 adopts a substantially square shaped body comprising outwardly extending portions forming the overlay portion 4 of the pupil expander. It should be noted that in the examples given, the fold lines 26, 28, 30 are shown to produce right angle turns in the body 2. This is done for ease of illustration only and in practice the turns may be more gradual. To enable the body of the pupil expander to be manipulated into engagement with the inner circumferential edge of the iris, the pupil expander comprises one or more instrument engaging formations 36 adjacent respective iris engaging formations to receive and incorporate suitable positioning instruments or tools 38 such as “Sinskey” hook or the like (see Figure 2A). For example, the one or more instrument engaging formations comprise one or more openings (not shown) in the body 2 of the pupil expander to receive the Sinskey hook. A corneal incision 40 approximately 2.4 mm long is made at the edge of the cornea (limbus) for insertion of the tool 38 into the anterior chamber 42 of the eye. Once the tool 38 is engaged with the instrument engaging formation 36 (i.e. the hook of the tool being received in the opening adjacent to the iris engaging formation), a pulling force is applied to the tool inwardly in a radial direction towards the pupil edge to cause the iris engaging formation to engage with the inner circumferential edge of the iris. In the case where the iris engaging formations comprises a plurality of hooks 16, each of the plurality of hooks 16 extend downwardly of the overlay portion 4 as shown in Figure 6 so making it easy for the eye surgeon to manipulate the iris engaging portion into engagement with the inner circumferential edge 8 of the iris. As discussed above, the body of the pupil expander is resiliently deformable by virtue of the plurality of preformed folds lines 26, 28, 30 such that when the iris engaging formations 14 are engaged with the inner circumferential edge of the iris at the engagement point, the body applies an outwardly extending restoring force to cause the pupil to dilate or expand as demonstrated in Figure 2A to 2C. At each step of engagement of the pupil expander, the iris engaging formation is pulled radially inwardly into engagement with the iris, the body of the pupil expander attempts to return to its original shape and applies a radial force to pull the inner circumferential edge of the iris outwardly. The different stages in the dilation of the pupil 3 as different portions of the body of the pupil expander resiliently expands to its original shape is shown in Figures 2A to 2C. In the particular example shown in Figures 1 and 2A to 2C, four iris engaging formations 14 are shown pulled inwardly into engagement with the inner circumferential edge of the iris resulting in the pupil 3 being dilated or expanded in a substantially square shaped configuration. The force applied to expand or dilate the pupil can be controlled by controlling the bending force of the body of the pupil expander along the preformed fold lines. Where the body of the pupil expander is entirely formed as a single unitary body, the fold lines can be incorporated into the body of the pupil expander as a living hinge, i.e. the overlay portion 4 is connected to the iris engaging portion 6 by one or more living hinges. The thickness and / or type of the flexible web material forming the living hinge controls the applied force to the inner circumferential edge of the iris to expand the pupil 3. For example, more rigid materials such as nylon are less resiliently deformable and therefore, offer a greater degree of force than less rigid materials such as silicone. Equally, the thickness of the flexible web material can also contribute to the applied force to expand the pupil, whereas a thick web material offers a greater applied force than a thinner material. A combination of the thickness and material type of the living hinge can be used to control the applied force to expand the pupil. In order to provide the necessary pulling force to expand the pupil but yet be able to be manipulated into engagement with the inner circumferential edge of the iris, different types of the living hinge offering different degrees of pulling force can be formed at the corner portions 34 of the body 2 of the pupil expander. For example, the living hinge either side 26, 28 of the iris engaging formation 14 at each of the corner portions 34 can be configured to apply a stronger pulling force than the living hinge 30 in between and connected to the iris engaging formation 14 (see figure 2A). This allows the iris engaging formation to be pulled into engagement with the inner circumferential edge of the iris and the living hinges 26, 28 either side of the iris engaging formation 14 providing the necessary pulling force in a radial direction to expand the iris. Once fully engaged with the inner circumferential edge of the iris, the flexibility of the body of the pupil expander allows the overlay portion 4 to adapt to the surface curvature of the iris. By virtue of the being deformable along the preformed fold lines 26, 28, 30 to form an overlap portion 4 and an iris engaging portion 6, the overlay portion 4 also helps to constrain the movement of the instrument engaging tool 38 along a plane in which the iris lies and thereby, mitigating any movement of the instrument engaging tool away from the iris that would inadvertently cause damage to the iris and any surrounding tissue. Moreover, by constraining or guiding the movement of the iris engaging instrument 38 limits or reduces the need for the eye surgeon to possess a high level of dexterity to engage the pupil expander 1 of the present invention with the pupil reducing the possibility of injury to the eye. The ring shaped body of the pupil expander of the present invention is not limited to a substantially square shape and other shapes that are able to provide the benefits of the present invention, namely an overlay portion and an iris engaging portion is permissible in the present invention. In another example of the present invention shown in Figures 3 to 5, the body 102 of the pupil expander 101 adopts a substantially star-shaped configuration when engaged with the pupil. As with the first example shown in Figures 1, 2A to 2C, the iris engaging formations 114 are disposed between a pair of the support structures 132 that extend outwardly on the surface of the iris to form the overlay portion 104. As with the first example, the body of the pupil expander in the second example is deformable by incorporating a plurality of preformed fold lines within the body of the pupil expander. Having a star-shaped configuration allows more engagement points with the pupil edge 8 and thereby, allowing a more uniform expansion or dilation of the pupil 3 than a substantially square shaped body as described in the first example above. The greater the number of engagement points of the iris engaging formation with the inner circumferential edge of the iris, the less trauma to the iris tissue when enlarging the pupil 3 since the pulling force is distributed amongst a greater number of engagement points rather than the fewer engagement points discussed above. The greater the number of engagement points, the more the pupil 3 approaches a substantially circular configuration when fully dilated. Also shown in Figures 4 and 5 is the body of the pupil expander being deformed into a greater number of discrete support structures 132 overlying the surface of the iris 10. In Figure 5, for example, the discrete support structures 132 are shown dispersed across the surface of the iris 10 and extending outwardly from the pupil edge a distance R to stabilise the surface of the iris during ophthalmic surgery. To stabilise the iris 10 sufficiently during ophthalmic surgery such as cataract surgery, preferably R is in the range 1mm to 3mm, preferably in the range 1mm to 2mm. Moreover, the number of engagement points with the inner circumferential edge of the iris 8 has an influence on the flexibility of the pupil expander to fit different sizes and / or shapes of the eye, i.e. manufactured to one size to fit different shapes and / or sizes of the eye. This is because the increased number of deformable regions of the body of the pupil expander as a result of the plurality of preformed fold lines 126,128,130, increases ability of the body of the pupil expander to be adapted to different sizes and / or shapes of the curvature of the eye. Use of the pupil expander according to the present invention is relatively straightforward and will now be described with reference to Figures 6, 7 and 8. Firstly, an incision 40 is made through the cornea for the insertion of the pupil expander into the anterior chamber of the eye. The existing incision created to complete phacoemulsification can also be used. Depending on the entry of the iris engaging instrument 38, the incision can be made in the cornea 12 or the sclera. The incision is usually restricted to a width of approximately 1.8 to 2.4mm and is angled through the cornea into the anterior chamber 42 so as to define an external entry into the anterior chamber of the eye. The anterior chamber of the eye is usually filled with a visco elastic fluid to prevent the anterior chamber collapsing. The viscoelastic fluid is also used to provide lubrication for insertion of the pupil expander and relevant instruments. The deformability of the body of the pupil expander via a plurality of preformed folds enables the pupil expander to be folded into a collapsed state for insertion into the anterior chamber of the eye. An insertion tool 44 comprising an elongated cannula having forward and rearward longitudinal ends is sized to accommodate the pupil expander 1 in a collapsed state as shown in Figure 8. For example and as shown in Figure 8, the plurality of preformed folds in the body of the pupil expander provides a plurality of concertina folds enabling the body of the pupil expander to be folded in a concertina fashion for storage in the insertion tool 44 prior to being inserted into the eye. To extract the pupil expander from the elongated cannula once inserted into the anterior chamber of the eye, a push rod or blade (not shown) within the cannula is slideable along the longitudinal length of the cannula towards the forward end of the cannula. Movement of the blade towards the forward end of the cannula pushes the pupil expander out through an opening in the forward end of the cannula. As the body of the pupil expander emerges from the cannula, the material properties of the pupil expander are such that the body of the pupil expander recovers back to its original open shape and expands. Various shape memory materials discussed above can be used in the fabrication of the body of the pupil expander such that when deformed the material returns back to its original shape. Once fully withdrawn from the insertion tool, an iris engaging tool or instrument 38 having a hook shaped tip such as Sinskey hook via the same incision used to insert the pupil expander into the anterior chamber of the eye or a separate incision made through the cornea can be used to reposition the body of the pupil expander over the surface of the iris. Depending on the shape of the body of the pupil expander and the number of iris engaging formations, one or more additional incisions may be made in the cornea into the anterior chamber of the eye to receive one or more instruments for manipulating the pupil expander into engagement with the tool (see Figure 6 and 7). For example, four incisions may be made in the cornea for manipulating the square shaped pupil expander shown in Figure 2A into engagement with the inner circumferential edge of the iris. Alternatively, relatively few incisions can be made than the number of iris engaging formations and the same incision can be used to manipulate one or more of the iris engaging formations with the inner circumferential edge of the iris. Engagement with the inner circumferential edge of the iris involves applying a pulling force in a radial direction to pull the iris engaging formation into engagement with the inner circumferential edge of the iris. The pulling force causes the body of the pupil expander to deform via one or more of its preformed folds causing the pupil expander to try to return to its original shape. When the iris engaging formations are engaged with the inner circumferential edge of the iris, the returning force of the body of the pupil expander causes the pupil 3 to expand resulting in dilation of the pupil. There are various ways by which a force can be applied to the body of the pupil expander to cause the body to deform. In one example, the body of the pupil expander is positioned on the surface of the iris such that all of the iris engaging formations 14 rests on the iris and the iris engaging formations are individually pulled into engagement with the inner circumferential edge of the iris. The pupil gradually expands in incremental steps at each engagement of the iris engaging formations 14 with the inner circumferential edge of the iris. In another example, the pupil expander is positioned such that one or more of the iris engaging formations are brought or offered up into engagement with the inner circumferential edge of the iris and the ‘free’ or unengaged iris engaging formations are subsequently pulled into engagement with the inner circumferential edge of the iris causing the body of the pupil expander to expand and dilate the pupil. In the particular example of the present invention, the body of the pupil expander is ring shaped that can be adopted into a cross shape or a star shape when in a collapsed state as shown in Figures 2C and 4 respectively. Expansion of the body of the pupil expander results in dilation of the pupil sufficiently for an ultrasonic fractionator instrument (also known as a phaco-emulsifier) to be inserted into the anterior chamber of the eye via an incision made in the peripheral cornea at the limbus to emulsify the lens. Once the new lens is introduced into the eye and unfolded into place, removal of the pupil expander involves retracting the pupil expander back into the insertion device. The pupil expander of the present invention provides a means of quickly enlarging the pupil and maintaining the pupil in a dilated state, e.g. 7mm, with minimal trauma to the iris and the sphincter muscle whilst providing protection to the iris during surgical manoeuvres. The pupil expander does not interfere with surgical manoeuvres within the eye including phacoemulsification of the cataract and implantation of an intraocular lens. The pupil expander may be used during surgery on the vitreous and retina. Furthermore, the pupil expander can be easily and safely removed at the end of the surgical procedure.

Claims

1. A pupil expander for expanding and maintaining a pupil in a dilated state during ophthalmic surgery, the pupil expander comprising:a body comprisingan iris engaging portion comprising a plurality of iris engaging formations;an overlay portion extending radially outwardly of the iris engaging portion that is configured to extend across the iris, the overlay portion is divided into a plurality of support-structures, the plurality of support structures being arranged such that one or more of the plurality of iris engaging formations is disposed between a pair of the plurality of support-structures,wherein the body comprises a plurality of preformed fold lines, said body is resiliently deformable at the plurality of preformed fold lines such that the body adopts a zig-zag or undulating pattern when engaged with the iris such that, in use, each of the plurality of support structures remain on the iris when one or more of the plurality of iris engaging formations is pulled inwardly towards the pupil edge.

2. The pupil expander of claim 1, wherein the body adopts a substantially cross-shaped configuration when engaged with the iris.

3. The pupil expander of claim 1, wherein the body adopts a substantially star shaped configuration when engaged with the iris.

4. The pupil expander of any of the preceding claims, wherein the plurality of preformed fold lines is arranged such that the body comprises a plurality of concertina folds.

5. The pupil expander of the preceding claims, wherein the apex of each of the plurality of preformed fold lines has an acute fold angle.

6. The pupil expander of any of the preceding claims, wherein the plurality of preformed fold lines comprises a first fold line and a second fold line, and wherein at least one of the plurality of iris engaging formations is intermediate the first and second fold line.19 02 247. The pupil expander of any of the preceding claims, wherein the plurality of iris engaging formations comprises a plurality of hooks.

8. The pupil expander of claim 7, wherein the plurality of hooks extends downwardly from the overlay portion.

9. The pupil expander of any of the preceding claims, wherein the one or more preformed fold lines comprises a living hinge.

10. The pupil expander of any of the preceding claims, wherein the overlay portion is configured to constrain the movement of the iris engaging portion.

11. The pupil expander of claim 10, wherein the iris engaging portion and overlay portion lie in a common plane.

12. The pupil expander of any of the preceding claims, wherein the body of the pupil expander comprises one or more instrument engaging formations.

13. The pupil expander of claim 12, wherein each of the one or more instrument engaging formations comprises an opening for receiving a hook.

14. The pupil expander of claim 12 or 13, wherein each of the one or more instrument engaging formations is disposed between a pair of the support structures.

15. The pupil expander of any of the preceding claims, wherein the body of the pupil expander is substantially ring shaped.

16. A pupil expander insertion tool comprising an elongated cannula having a forward and rearward longitudinal ends, said elongated cannula housing at least a portion of a pupil expander as defined in any of the claims 1 to 15;a retractable hook housed within the elongated cannula, the retractable blade being slideable along the longitudinal axis of the elongated cannula between a forward position and rearward position;said forward end having an opening such that the retractable blade ejects the at least portion of the pupil expander through the opening when in the forward position and retracts the blade through the opening when in the rearward position.