Gripping structure for membrane removal

Abstract

A surgical instrument includes a flexible outer gripping member and a flexible inner gripping member for peeling a membrane from the retina of a patient's eye. The surgical instrument includes a handle and at least one actuator. An outer tube has a proximal end attached to the handle. The outer gripping member and the inner gripping member extend outward from the distal end of the outer tube or are configured to extend outward from the distal end of the outer tube. The at least one actuator can be used to move at least one of the outer gripping member and the inner gripping member relative to the other such that the inner and outer gripping members are brought together to grip the epiretinal membrane.

Description

[Background technology]

[0001] The internal limiting membrane (ILM) is a thin, transparent membrane located between the vitreous and retina of the eye. The ILM plays a role during eye development and is not necessary for proper functioning of the mature eye. The ILM pulls on the retina, potentially causing conditions such as macular hole, macular pucker, vitreomacular traction syndrome, diabetic macular edema, and cystoid macular edema secondary to inflammation, venous occlusion, or other conditions. An epiretinal membrane (ERM) is a membrane that can form on the retina in response to retinal damage, such as that caused by posterior vitreous detachment.

[0002] The ILM or ERM may need to be peeled away from the retina to prevent retinal damage. Peeling of the ILM or ERM may also be necessary in preparation for a surgical procedure to be performed on the retina. To peel away the ILM or ERM, a surgical instrument is inserted into the patient's eye through a cannula. Typically, forceps or a specialized scraper is used to extend from the instrument and raise a flap in the ILM or ERM. The flap is then grasped with the forceps, and the ILM or ERM is peeled away from the retina using a circular motion. However, applying excessive force to the forceps can result in perforating the retina.

[0003] Therefore, reducing the risk of retinal damage resulting from ILM or ERM detachment would be an advancement in the art. Summary of the Invention [Problem to be solved by the invention]

[0004] FIELD OF THE DISCLOSURE The present disclosure relates generally to film stripping tools. [Means for solving the problem]

[0005] In certain aspects, the membrane peeling tool comprises flexible concentric loops. For example, certain aspects provide a surgical instrument comprising a handle and an actuator attached to the handle. An outer tube has a proximal end attached to the handle. An outer loop extends outward from the distal end of the outer tube. An inner loop extends outward from the distal end of the outer tube and is disposed within the outer loop. The inner loop is coupled to the actuator and configured to move relative to the outer loop in response to movement of the actuator.

[0006] In certain embodiments, the membrane peeling tool includes independently controlled scrapers. For example, certain embodiments provide an ophthalmic surgical instrument for peeling epiretinal membranes, the instrument including a handle. A first actuator and a second actuator are attached to the handle. An outer tube has a proximal end attached to the handle. An outer arm has an outer scraper fixed thereto, and an inner arm has an inner scraper fixed thereto. The first actuator is configured to control extension of the outer arm from the outer tube, and the second actuator is configured to control movement of the inner arm relative to the outer arm.

[0007] The following description and the annexed drawings set forth in detail certain illustrative features of the one or more embodiments.

[0008] The accompanying drawings depict certain aspects of one or more embodiments and therefore should not be considered as limiting the scope of the disclosure. [Brief explanation of the drawings]

[0009] [Figure 1A] FIG. 1 illustrates an isometric view of a surgical instrument having a grasping structure with concentric loops, in accordance with certain embodiments. [Figure 1B] 1B illustrates a cutaway view of the concentric loops of FIG. 1A, in accordance with certain embodiments. [Figure 2] 1C is an isometric view of an alternative embodiment of an actuator for controlling the gripping structure of FIGS. 1A and 1B, in accordance with certain embodiments. FIG. [Figure 3] 1C is a cross-sectional view illustrating a mechanism for actuating the concentric loops of the gripping structure of FIGS. 1A and 1B, according to certain embodiments. FIG. [Figure 4A] 1C is an isometric view of the concentric loops of the gripping structure of FIGS. 1A and 1B in an open configuration, according to certain embodiments. FIG. [Figure 4B] 1A and 1B in an open configuration with the alignment structure of the inner loop engaged with the outer loop, according to certain embodiments. FIG. [Figure 5A] 1C is an isometric view showing the concentric loops of the gripping structure of FIGS. 1A and 1B in a closed configuration, according to certain embodiments. FIG. [Figure 5B] FIG. 1C is an isometric view showing an outer tube extending partially over the concentric loops of the gripping structure of FIGS. 1A and 1B, in accordance with certain embodiments. [Figure 6A] 1C is a cross-sectional view illustrating peeling of an ILM using the gripping structures of FIGS. 1A and 1B, in accordance with certain embodiments. [Figure 6B] 1C is a cross-sectional view illustrating peeling of an ILM using the gripping structures of FIGS. 1A and 1B, in accordance with certain embodiments. [Figure 6C] 1C is a cross-sectional view illustrating peeling of an ILM using the gripping structures of FIGS. 1A and 1B, in accordance with certain embodiments. [Figure 7] 1C is an isometric view illustrating an ILM being peeled using the gripping structure of FIGS. 1A and 1B, according to certain embodiments. FIG. [Figure 8A] FIG. 10 is an isometric view of a surgical instrument having an alternative gripping structure with independently actuated arcuate scrapers, in accordance with certain embodiments. [Figure 8B] FIG. 8B is an isometric view of the arcuate scraper of FIG. 8A having barbs on its bottom edge, in accordance with certain embodiments. [Figure 9] 8C is an isometric view of an alternative embodiment of an actuator for controlling the gripping structure of FIGS. 8A and 8B, in accordance with certain embodiments. FIG. [Figure 10] 8C is a cross-sectional view illustrating a mechanism for actuating the arcuate scraper of the gripping structure of FIGS. 8A and 8B, according to certain embodiments. FIG. [Figure 11A] FIG. 8C is an isometric view of the single arcuate scraper of FIGS. 8A and 8B in an extended position, in accordance with certain embodiments. [Figure 11B] FIG. 8C is an isometric view showing both the arcuate scrapers of FIGS. 8A and 8B in an extended position but offset from one another, in accordance with certain embodiments. [Figure 11C] FIG. 8C is an isometric view of the arcuate scraper of FIGS. 8A and 8B drawn together to grip a flap of a membrane, according to certain embodiments. [Figure 12] 8C is an isometric view illustrating an ILM being peeled using the gripping structure of FIGS. 8A and 8B, according to certain embodiments. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] For ease of understanding, the same reference numerals have been used, whenever possible, to designate identical elements common to the figures, and it is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.

[0011] Aspects of the present disclosure provide a surgical instrument for peeling a membrane from a patient's retina. In certain aspects, the surgical instrument comprises a gripping structure comprising a flexible loop. In other particular aspects, the surgical instrument comprises a gripping structure comprising an independently actuated arcuate scraper. It should be noted that, as used herein, the distal end of a component refers to the end closer to the patient's body, and the proximal end of a component refers to the end away from the patient's body, or, for example, the end closer to the handle of a surgical instrument.

[0012] FIG. 1A illustrates a surgical instrument 100 according to certain embodiments described herein, comprising a handle 102 sized and contoured to be grasped by the hand of a surgeon performing ophthalmic surgery, such as peeling a membrane from the retina of a patient's eye, including an ILM or ERM. A gripping structure 104 can extend from a distal end of an outer tube 106, which further comprises a proximal end connected to the handle 102. The handle 102 can have one or more manual control structures (e.g., actuation mechanisms) disposed thereon. In the embodiment of FIG. 1A, the manual control structure includes a slider 108 and clamshell arms 110a, 110b. The illustrated manual control structure is merely exemplary; other manual control structures, such as a deformable basket or a second slider as shown in FIG. 2, may also be used.

[0013] 1A , the gripping structure 104 is embodied as an outer loop 112 and an inner loop 114. The outer loop 112 may also be referred to as the outer gripping member of the gripping structure 104, and the inner loop 114 may also be referred to as the inner gripping member of the gripping structure 104. In some embodiments, the outer tube 106 and / or the inner loop 114 are translatable relative to the outer loop 112. For example, one of the slider 108 and the clamshell arms 110 a, 110 b is coupled to the outer tube 106, and the other of the slider 108 and the clamshell arms 110 a, 110 b is coupled to the inner loop 114. In use, the outer tube 106 may be extended over the outer loop 112 and the inner loop 114, such as when the outer tube 106 is inserted into or withdrawn from a cannula (e.g., called a trocar cannula) inserted into a patient's eye. The outer tube 106 can then be withdrawn or retracted, thereby extending the outer loop 112 and the inner loop 114 relative to the outer tube 106. As discussed in more detail below, the inner loop 114 can then be translated towards the outer loop 112 to grasp the membrane between the outer loop 112 and the inner loop 114.

[0014] The outer loop 112 and the inner loop 114 may be made of a highly flexible material such as Nitinol (a nickel-titanium alloy), spring steel, or other material. The flexibility allows the outer loop 112 and the inner loop 114 to elastically deform to fit within the outer tube 106 and, when extended from the outer tube 106, to expand to a size much larger than the outer diameter of the outer tube 106, for example, at least 2, 4, 8, or at least 16 times the outer diameter of the outer tube 106.

[0015] In the illustrated embodiment, outer loop 112 has ends 112a, 112b fastened to an inner tube 116 that is slidably disposed within outer tube 106. Inner tube 114 has ends 114a, 114b fastened to an inner rod 118 that is slidably disposed within inner tube 116. Outer tube 106, inner tube 116, and inner rod 118 may be made of nitinol, stainless steel, spring steel, a rigid polymer, or other materials.

[0016] The outer tube 106 defines a longitudinal direction 120a that is parallel to and collinear with the axis of symmetry of the outer tube 106. The axes of symmetry of the inner tube 116 and inner rod 118 are substantially collinear with the longitudinal direction 120a (e.g., within 0.5 mm (millimeters)) and substantially parallel to the longitudinal direction 120a (e.g., within 5 degrees). A transverse direction 120b may also be defined as being perpendicular to the longitudinal direction 120a such that the ends 112a, 112b of the outer loop 112 are offset from one another along the transverse direction 120b and the ends 114a, 114b of the inner loop 114 are offset from one another along the transverse direction 120b. A vertical direction 120c may also be defined as being perpendicular to the longitudinal direction 120a and the transverse direction 120b.

[0017] The outer loop 112 may include straight portions 112c, 112d extending from the ends 112a, 112b, respectively. The straight portions 112c, 112d may intersect a plane containing the longitudinal direction 120a and the transverse direction 120b (the "longitudinal cross-section"). The straight portions 112c, 112d may extend in different directions from each other in the longitudinal cross-section, i.e., may diverge outward from each other as they move away from the distal end of the outer tube 106. As used herein, a "straight line" should be understood as having a radius of curvature in the longitudinal cross-section that is greater than 1 cm (centimeter). As used herein, a longitudinal cross-section includes a plane containing both the longitudinal direction 120a and the transverse direction 120b.

[0018] Straight portions 112c, 112d may be connected to one another by rounded end portion 112e. Rounded end portion 112e may either (a) be formed to retain a rounded shape without an external force, or (b) be the result of bending outer loop 112 and securing ends 112a, 112b to inner tube 116. The rounded shape may be circular, oval, or any rounded shape.

[0019] Rounded end portion 112e can be secured to straight portions 112c, 112d by flexible portions 112f, 112g. Flexible portions 112f, 112g have a reduced height (e.g., perpendicular to the longitudinal cross-section) and / or thickness (e.g., parallel to the longitudinal cross-section) relative to one or both of rounded end portion 112e and straight portions 112c, 112d. For example, in the illustrated embodiment, the thickness of flexible portions 112f, 112g is substantially the same as (e.g., within 10 percent of) the thickness of straight portions 112c, 112d and rounded end portion 112e, while the height of flexible portions 112f, 112g is 0.25 to 0.75 times or 0.4 to 0.6 times the height of straight portions 112c, 112d and rounded end portion 112e. As is evident from FIG. 1A, there may be a smooth transition between the reduced cross-section of the flexible portions 112f, 112g and the cross-section of the rounded end portion 112e and straight portions 112c, 112d.

[0020] Flexible portions 112f, 112g can function as live hinges that facilitate rotation of rounded end portion 112e relative to straight portions 112c, 112d. In other embodiments, there are no separate flexible portions. In such embodiments, some or all of the extension between rounded end portion 112e and ends 112a, 112b provides the flexibility.

[0021] To reduce the risk of puncture, it is desirable for the lower surface 132 of the rounded end portion 112e to be relatively parallel to the retina. In response to pressure exerted on the rounded end portion 112e by the membrane during use, the rounded end portion 112e rotates until the lower surface 132 of the rounded end portion 112e rests on the membrane, thereby increasing the surface area in contact with the membrane and reducing the risk of puncture. The cross-sectional shape of the rounded end portion 112e may have a height (e.g., perpendicular to the longitudinal cross-section) that is much greater than the thickness (e.g., parallel to the longitudinal cross-section), such as a height that is at least two, four, eight, or more times the thickness, such that the rounded end portion 112e does not substantially flex in a plane parallel to the longitudinal direction 120a and the vertical direction 120c (the "longitudinal vertical plane"). This may facilitate the lower surface 132 of the rounded end portion 112e to provide a broad surface that resists penetrating the retina.

[0022] In some embodiments, flexible portions 112f, 112g may further define a bend in the absence of a deformation force such that rounded end portion 112e is at an angle 112h with respect to the longitudinal cross-plane and is higher than the longitudinal cross-plane. Angle 112h may further encourage rounded end portion 112e to rotate when pressed against the membrane rather than puncturing the membrane and possibly the retina.

[0023] Inner loop 114 may include straight portions 114c, 114d extending from ends 114a, 114b, respectively. Straight portions 114c, 114d may intersect the longitudinal cross-section. Straight portions 114c, 114d may extend in different directions from each other in the longitudinal cross-section, i.e., may diverge outward from each other as they move away from the distal end of outer tube 106.

[0024] Straight portions 114c, 114d may be connected to one another by rounded end portion 114e. Rounded end portion 114e may either (a) be formed to retain a rounded shape in the absence of an external force, or (b) be the result of bending inner loop 114 and securing ends 114a, 114b to inner tube 116. Rounded end portion 114e may be angled at the same angle 112h or at different angles relative to the longitudinal cross-plane. In the absence of a deforming force, rounded end portion 114e may have an outer surface having a size in the plane of curvature (e.g., in the longitudinal cross-plane or in a plane oriented at angle 112h relative to the longitudinal cross-plane) that is substantially equal to the size of the outer surface of rounded end portion 112e, substantially equal to the size of the inner surface of rounded end portion 112e, or smaller than the inner diameter of rounded end portion 112e. The flexibility of the outer loop 112 and inner loop 114 allows the outer loop 112 and inner loop 114 to nest regardless of their undeformed size.

[0025] In the illustrated embodiment, the straight portions 114c, 114d may be reduced in height and / or thickness relative to the straight portions 112c, 112d and the rounded end portion 114e so that the inner loop 114 is more flexible than the outer loop 112 and so that a separate flexible portion similar to flexible portions 112f, 112g is not formed between the straight portions 114c, 114d and the rounded end portion 114e. However, in other embodiments, flexible portions are used in a similar manner. As discussed in more detail below, the outer loop 112 may be used to raise a flap in the membrane, which may require applying some pressure to the membrane. In contrast, the inner loop 114 only needs to press the flap against the outer loop 112. Thus, the inner loop 114 may be made more flexible to reduce the risk of puncture while still being stiff enough to press the flap against the outer loop 112.

[0026] 1B , one or both of the undersides 132 and 134 of the rounded end portion 112e and the rounded end portion 114e, respectively, may have structure formed thereon to facilitate gripping of the membrane. For example, the undersides 132 and 134 may have barbs 122 formed thereon. In the case of the rounded end portion 112e, the barbs 122 may point toward the rounded end portion 114e, as indicated by arrow 136. In other words, the barbs 122 on the rounded end portion 114e are oriented such that movement of the rounded end portion 112e relative to the membrane is resisted more toward the rounded end portion 114e than away from the rounded end portion 114e. In this manner, the barb 122 enhances the ability of the rounded end portion 112e to tension the membrane and raise the flap between the rounded end portions 112e, 114e. The barb 122 may be tapered so that the membrane's resistance to penetration by the barb 122 increases with depth. This reduces the risk of the barb 122 completely penetrating the membrane. In some applications, the tapered shape of the barb 122 prevents the underside 132 of the rounded end portion 112e from actually contacting the membrane during use.

[0027] 1B, rounded end portion 114e does not have barbs on lower surface 134. In other embodiments, barbs 122 are included on lower surface 134 of rounded end portion 114e. In such embodiments, barbs 122 may face in an opposite direction from barbs 122 on rounded end portion 112e such that barbs 122 improve the ability of rounded end portion 114e to press the membrane toward rounded end portion 112e. Again, in other embodiments, no barbs are formed on lower surface 134 of rounded end portion 114e such that rounded end portion 114e is primarily or exclusively responsible for gripping the flap.

[0028] In some embodiments, the inner surface 142 of the rounded end portion 112e (the surface facing the rounded end portion 114e) and the outer surface 144 of the rounded end portion 114e (the surface facing the rounded end portion 112e) are textured, barbed, or coated with a gripping material (e.g., silicone) to resist slippage of the flap when gripped between the rounded end portion 112e and the rounded end portion 114e.

[0029] 2, various actuation mechanisms can be used to manually control the translation of the outer tube 106 and inner rod 118. In some embodiments, the clamshell arms 110a, 110b can be replaced with a second slider 200 slidably attached to the handle 102. In the illustrated embodiment, both sliders 108, 200 slide within a common slot 202 defined by the handle 102. Thus, one slider 108 can control actuation of the outer tube 106 and the other slider 200 can control actuation of the inner loop 114, or vice versa.

[0030] FIG. 3 illustrates an exemplary mechanism for coupling the slider 108 and clamshell arms 110a, 110b to the outer tube 106 and inner rod 118, or for coupling the slider 108 and slider 200 to the outer tube 106 and inner rod 118. The illustrated mechanism is merely exemplary and illustrates an exemplary relative movement of the components. However, the actual size and relative positions of the components may vary. For purposes of FIG. 3, the terms "first actuator" and "second actuator" refer to the slider 108 and clamshell arms 110a, 110b. The terms "first actuator" and "second actuator" may also refer to the slider 108 and slider 200, or vice versa.

[0031] In the illustrated embodiment, the inner tube 116 is fixed relative to the handle 102. The outer tube 106 is slidable relative to the handle 102 and has a mounting structure 300 fastened to the outer tube 106. The mounting structure 300 is also slidable relative to the handle 102 and is coupled to a first actuator. The outer tube 106 defines a slot 302 and the inner tube 116 defines a slot 304. The mounting structure 306 is fastened to the inner rod 118 and is slidable within the slots 302, 304. The mounting structure 306 is coupled to a second actuator.

[0032] Various alternatives to the illustrated configuration are possible. For example, the inner rod 118 may be fixed relative to the handle 102, and the mounting structure 306 may be fastened to the inner tube 116, which may be slidable relative to the handle 102.

[0033] In use, the first actuator may be moved in a first direction to move the outer tube 106 outward from the handle 102 and over the outer loop 112 and the inner loop 114. The first actuator may be moved in a second direction opposite the first direction to move the outer tube 106 inward, thereby extending the outer loop 112 and the inner loop 114 from the distal end of the outer tube 106.

[0034] A first direction for the slider 108 or slider 200 may be defined as movement 360 toward the distal end of the outer tube 106, and a second direction may be movement 370 of the slider 108 or slider 200 away from the distal end of the outer tube 106. For the basket 110, the first direction may be defined as the spreading of the clamshell arms 110 a, 110 b, i.e., the release of pressure biasing the clamshell arms 110 a, 110 b, and the second direction may be defined as pushing the clamshell arms 110 a, 110 b toward each other. A second actuator may be moved in the first direction to move the inner loop 114 toward the outer loop 112 to grasp the membrane flap. A second actuator may be moved in the second direction to move the inner loop 114 away from the outer loop 112. When the outer loop 112 and inner tube 116 are actuated by a second actuator, the second actuator can be moved in a first direction to move the outer loop 112 away from the inner loop and in a second direction to move the outer loop 112 toward the inner loop 114 to grasp the flap of the membrane.

[0035] 4A, in preparation for raising the flap, outer loop 112 and inner loop 114 may be arranged in the open configuration shown with a gap 400 between rounded end portion 112e and rounded end portion 114e that is many times the thickness of the membrane, e.g., at least 10, 100, or 1000 times the thickness of the membrane. Referring to FIG. 4B, in some embodiments, straight portions 112c, 112d define a slot 402, and straight portions 114c, 114d define a protrusion 404 that may be inserted into slot 402. Protrusion 404 is slidable within slot 402 through at least a portion of the range of motion of inner loop 114, e.g., some range of motion initiated by rounded end portion 114e being pressed against rounded end portion 112e. The protrusions 404 may be freely insertable into the slots 402 or may resist removal (e.g., a slightly enlarged distal end). The positions of the slots 402 and protrusions 404 may be reversed, i.e., the slots 402 may be formed on the straight portions 114c, 114d, and the protrusions 404 may be formed on the straight portions 112c, 112c.

[0036] The engagement of slot 402 with protrusion 404 may function to keep the loops aligned with one another during use. For example, this may prevent inner loop 114 from being positioned above outer loop 112 and failing to engage a flap on the membrane. However, the flexibility of outer loop 112 and inner loop 114 may be used to press both loops against the membrane to ensure engagement with the flap when inner loop 114 is moved toward outer loop 112. Thus, slot 402 and protrusion 404 may be omitted in some embodiments.

[0037] 5A, to achieve the illustrated closed configuration, the surgeon can translate the second actuator (e.g., compress the clamshell arms 110a, 110b or translate the slider 200) toward the distal end of the handle 102 (toward the outer tube 106) to bias the inner loop 114 toward the outer loop 112. As can be seen, the rounded end portion 114e nests within the rounded end portion 112e, thereby firmly gripping the raised flap by the rounded end portion 112e. When in the closed configuration, the spacing between the rounded end portion 114e and the rounded end portion 112e can be no more than four, three, or two times the thickness of the membrane.

[0038] 5B, the outer tube 106 may be extended partially or completely over the outer loops 112 and inner loops 114 at any point during use of the surgical instrument 100. The stiffness of the outer loops 112 and inner loops 114 may be increased by extending the outer tube 106 and reducing the portion of the outer loops 112 and inner loops 114 disposed outwardly from the outer tube 106. Similarly, if greater flexibility is desired, the outer tube 106 may be withdrawn to the extent that more, potentially the entirety, of the outer loops 112 and inner loops 114 are exposed.

[0039] As described above, in preparation for inserting the outer tube 106 through the cannula, the outer tube 106 may be stretched until (a) the outer loop 112 and the inner loop 114 are completely disposed within the outer tube 106, or (b) the portions of the outer loop 112 and the inner loop 114 extending outward from the outer tube 106 are small enough to fit through the cannula (e.g., equal to or less than the outer diameter of the outer tube 106).

[0040] Referring now to FIG. 6A, during use, the lower surfaces 132, 134 of the rounded end portions 112e, 114e press against a membrane 600 (e.g., an ILM or ERM) overlying the retina 602. As shown, the barbs 122 can at least partially penetrate the ILM. The size of the barbs 122 below the lower surfaces of the rounded end portions 112e, 114e can be less than the thickness of the ILM, such as less than 2 microns to less than 10 microns. For example, the barbs 122 can have a length extending outward from the lower surfaces of 0.8 microns to 8 microns. Referring to FIG. 6B, the flap 604 can be raised by pulling the rounded end portion 112e across the membrane 600, and the rounded end portion 114e can be biased toward the rounded end portion 112e to firmly grip the flap 604. 6C, the surgeon may then lift the surgical instrument 100 to peel away the membrane 600. Referring to FIG. 7, the surgeon may move the grasping structure 104 in a circular motion to peel a portion of the membrane 600 from the retina 602.

[0041] Various alternatives to the illustrated method of use of surgical instrument 100 are possible. For example, inner loop 114 may be fixed relative to handle 102 as described above, and outer loop 112 may be actuated. Thus, outer loop 112 may be actuated to move rounded end portion 112e toward rounded end portion 114e, thereby both elevating flap 604 and grasping flap 604 between rounded end portion 112e and rounded end portion 114e, in a single motion. In another method of use, rounded end portion 112e is pulled across membrane 600 in the direction of rounded end portion 114e to elevate flap 604 without decreasing the distance between rounded end portion 112e and rounded end portion 114e. Rounded end portion 112e is then pulled towards rounded end portion 114e using a second actuator, which causes flap 604 to rise further and grip flap 604 between rounded end portion 112e and rounded end portion 114e.

[0042] FIG. 8A illustrates another ophthalmic surgical instrument 800 according to certain embodiments, comprising a handle 802 sized and contoured to be grasped by the hand of a surgeon performing an ophthalmic surgical procedure, such as peeling a membrane, such as an ILM or ERM, from the retina of a patient's eye. A grasping structure 804 can extend from a distal end of an outer tube 806 connected to the handle 802. The proximal end of the outer tube 806 is connected to the handle 802. The handle 802 can have one or more manual control structures attached to the handle 802 for manually actuating the grasping structure 804. In the embodiment of FIG. 8A , the manual control structures include a slider 808 and a deformable basket 810. The illustrated manual control structures are merely exemplary, and other manual control structures and / or combinations of manual control structures may be used (see, e.g., FIG. 9 ).

[0043] The gripping structure 804 in FIG. 8A is embodied as an outer arm 812 and an inner arm 814. The outer arm 812 may be referred to as the outer gripping member of the gripping structure 804, and the inner arm 814 may be referred to as the inner gripping member of the gripping structure 804. The outer tube 806 may define a longitudinal direction 816a parallel to an axis of symmetry of the outer tube 806. The outer arm 812 and the inner arm 814 may include straight portions 812a, 814a extending substantially parallel to the longitudinal direction 816a (e.g., within a range of 5-15 degrees). The outer arm 812 and the inner arm 814 are offset from one another substantially parallel (e.g., within 5 degrees) along a transverse direction 816b, which is defined as being perpendicular to the longitudinal direction 816a. A vertical direction 816c may be defined as being perpendicular to the longitudinal direction 816a and the transverse direction 816b. The straight sections 812a, 814a may be implemented as hollow cylindrical tubes, solid cylindrical rods, or may have some other solid or hollow cross-sectional shape in a plane perpendicular to the longitudinal direction 816a.

[0044] The straight portions 812a, 814a have scrapers 812b, 814b fixed to their distal ends. The scrapers 812b, 814b extend generally perpendicular (e.g., within 15 degrees) to the longitudinal direction 816a and outward from the straight portions 812a, 814a. The scrapers 812b, 814b may each have an arcuate shape, such as an elongated spoon shape. The scrapers 812b, 814b may have an arcuate shape in a plane substantially perpendicular (e.g., within 15 degrees) to the longitudinal direction 816a and the transverse direction 816b. The scrapers 812b, 814b may have an arcuate shape in a plane substantially perpendicular (e.g., within 15 degrees) to the longitudinal direction 816a and the vertical direction 816c. The scrapers 812b, 814b may have an ellipsoidal or any other three-dimensional curved shape. Scrapers 812b, 814b may have arcuate shapes on both their inner surface (facing outer tube 806) and outer surface (facing away from outer tube 806). Scrapers 812b, 814b may be at least partially nested, i.e., a portion of the convex outer surface of scraper 814b may be disposed within a cavity defined by the concave inner surface of scraper 812b. Scrapers 812b, 814b may be identical within manufacturing tolerances, or scraper 812b may be made larger to better accommodate scraper 814b when nested.

[0045] 8B, one or both of scrapers 812b, 814b may include barbs 818. The barbs 818 of scraper 812b may be oriented such that the barbs 818 more effectively capture the membrane when scraper 812b moves in the direction facing the concave surface of scraper 812b than when moving across the membrane in the opposite direction. The barbs 818 of scraper 814b may face in the opposite direction. The barbs 818 of scraper 814b may be oriented such that the barbs 818 more effectively capture the membrane when scraper 812b moves across the membrane in the opposite direction than when scraper 814b moves across the membrane in the direction facing the concave surface of scraper 814b.

[0046] The barbs 818 extend outward from the lower edges of the scrapers 812b, 814b a length that is less than the thickness of the film being peeled. For example, the film may have a thickness of 4 microns. The barbs 818 may have a length extending outward from the lower edges of the scrapers 812b, 814b that is between 1 micron and 3 microns.

[0047] The inner arm 814 and the outer arm 812 may be made of a highly flexible material such as Nitinol (nickel-titanium alloy), spring steel, a polymeric material, or other material. The flexibility allows the scrapers 812b, 814b to resiliently deform to fit within the outer tube 806 and, when extended from the outer tube 806, to recoil outward in the transverse direction 816b farther than the outer diameter of the outer tube 806. For example, the scrapers 812b, 814b may extend outward from the longitudinal direction 816a in the transverse direction 816b at least 1, 2, 4, 8, or some other multiple of the diameter of the outer tube. As shown in FIG. 8A , in some embodiments, both scrapers 812b, 814b extend outward from the outer tube 806 on only one side of a plane defined by the longitudinal direction 816a and the vertical direction 816c.

[0048] 8B further illustrates the shapes of scrapers 812b, 814b. As shown by cross-sectional shape 822, scrapers 812b, 814b have a concave inner surface 834 and a convex outer surface 826. Cross-sectional shape 822 may be defined with respect to a cross-sectional plane parallel to longitudinal direction 816a and vertical direction 816c. The concave inner surface 834 of scraper 812b and the convex outer surface 826 of scraper 814b may be textured to facilitate gripping. The texturing may be any treatment or pattern that improves grip of the film, such as increased roughness resulting from a process such as sanding or grinding, the formation of a regular pattern of peaks and valleys, an array of barbs, or other texturing.

[0049] Line 824 can be defined as tangent to scrapers 812b, 814b at two points above and below concave inner surface 834. Line 824 can be used to understand the orientation of scrapers 812b, 814b. Line 824 forms an angle 828 with respect to a plane 830 parallel to longitudinal direction 816a and transverse direction 816b. The outer tube 806 can be inserted into a trocar cannula offset from the pupil of the patient's eye, while the membrane to be peeled can be located just behind the pupil. Thus, longitudinal direction 816a can be at a non-parallel angle to the membrane normal vector at the point of contact with each scraper 812b, 814b. Angle 828 can be selected so that, in use, line 824 is substantially parallel (e.g., within 15 degrees) to the membrane normal vector at the point of contact between scrapers 812b, 814b and the membrane in cross-sectional plane 822. For example, angle 828 may be between 75 and 105 degrees. This relationship between line 824, normal vector, and tangent point may exist along a major portion, such as at least 80 percent, of the extent of scrapers 812b, 814b in transverse direction 816b.

[0050] 9 , various manual actuation mechanisms and / or control structures may be used to control the translation of one or both of the arms 812, 814. In some embodiments, the deformable basket 810 may be replaced by a second slider 900 slidably attached to the handle 802. In the illustrated embodiment, both sliders 808, 900 slide within a common slot 902 defined by the handle 802. The slider 808, the deformable basket 810, and the slider 900 are merely exemplary. Any actuation mechanism or structure known in the art, such as a button, may be used to control the movement of one or both of the arms 812, 814.

[0051] FIG. 10 illustrates an exemplary mechanism for coupling slider 808 and deformable basket 810 to arms 812, 814, or for coupling slider 808 and slider 900 to arms 812, 814. The illustrated mechanism is merely exemplary and illustrates an exemplary relative movement of the components. Furthermore, the actual size and relative positions of the components may vary. For purposes of FIG. 10 , the “first actuator” and “second actuator” may refer to slider 808 and deformable basket 810, or vice versa. The “first actuator” and “second actuator” may also refer to slider 808 and slider 900, or vice versa.

[0052] In the illustrated embodiment, there are two slidable components 1000, 1002. The slidable components may be concentric tubes, i.e., the slidable component 1002 may be disposed within the slidable component 1000. However, other arrangements are possible, such as the slidable components simply being disposed adjacent to each other within the outer tube 806 or within a cavity in the handle 802. The slidable component 1000 may be coupled to the outer arm 812, while the slidable component 1002 is coupled to the inner arm 814. However, the opposite configuration is also possible.

[0053] The slidable component 1002 is coupled to a mounting structure 1004 that is coupled to a first actuator. When the slidable component 1002 is disposed within a slidable component 1000 embodied as a tube, the slidable component 1000 may define a slot 1006 through which the mounting structure 1004 protrudes and within which the mounting structure 1004 may slide along a range of motion along the longitudinal direction 816 a. When the slidable component 1002 is disposed within an outer tube 806, the outer tube 806 may define a slot 1008 through which the mounting structure 1004 protrudes and along which the mounting structure 1004 may have a range of motion along the longitudinal direction 816 a.

[0054] The slidable component 1000 is coupled to a mounting structure 1010 that is coupled to a second actuator. When the slidable component 1000 is disposed within the outer tube 806, the mounting structure 1010 may also protrude through the slot 1008 and have a range of motion along the longitudinal direction 816a within the slot 1008. Alternatively, the mounting structure 1010 may protrude through a different slot.

[0055] The first direction may be defined as outward movement from the distal end of the outer tube 806, and the second direction may be defined as inward movement toward the distal end of the outer tube 806. Moving the first actuator in the first direction (e.g., by sliding a slider or compressing a deformable basket) extends the outer arm 812 from the outer tube 806. When the slidable component 1002 is mounted within the slidable component 1000, there may be some friction or interference with the end of the slot 1006 (the right end in the illustrated orientation), which causes the inner arm 814 to extend outward simultaneously with the outer arm 812. A second actuator may be used to bias the slidable component in the second direction prior to moving the first actuator in the first direction such that a gap exists between the scrapers 812b, 814b along the longitudinal direction 816a when the outer and inner arms 812, 814 are extended simultaneously ( FIG. 11B , discussed below). The length of the slot 1006 can be selected to control the size of the gap. The second actuator can be moved in a first direction after the outer arm 812 is extended to extend the inner arm 814 to the point where the scrapers 812b, 814b are pressed together. The first actuator, or both the first and second actuators, can then be moved in a second direction to retract the arms 812, 814 into the outer tube 806. In some embodiments, the engagement of the scraper 812b with the scraper 814b and the friction between the slidable components 1000, 1002 can be sufficient to push the inner arm 814 into the outer tube 806 when only the first actuator is used. In other embodiments, a user can engage both the first and second actuators simultaneously when extending the inner and outer arms 814, 812.

[0056] 10 is an embodiment in which the outer arm 812 is fixed relative to the handle 802 and the outer tube 806 is slidable relative to the handle 802 and coupled to a first actuator. In use, a user retracts the outer tube 806 by moving the first actuator in a second direction so that the scrapers 812b, 814b extend from the distal end of the outer tube 806. After using the scraper 812b to raise the flap, the second actuator may be moved in the first direction to press the scraper 814b against the scraper 812b. The first actuator may then be moved in the first direction to extend the outer tube 806 over the scrapers 812b, 814b.

[0057] 11A , after the outer tube 806 is inserted through the trocar cannula, the scraper 812b of the outer arm 812 can extend from the outer tube 806 and press against the membrane 1100. The straight portion 812a and the scraper 812b itself can be sufficiently flexible so that pressure on the membrane 1100 causes the bottom edge of the scraper 812b to make substantially full (e.g., at least 80 percent) contact with the membrane 1100. The scraper 812b can then be scraped across the membrane 1100 to lift the flap 1102. Pulling the scraper 812b across the membrane 1100 can simply lift the flap 1102, or it can lift the flap and peel the membrane 1100 away.

[0058] 11B, the scraper 814b of the inner arm 814 can then be extended from the outer tube 806. Note that both scrapers 812b, 814b can be extended simultaneously before the scraping step shown in FIG. 11A, provided that the gap between the scrapers 812b, 814b along the longitudinal direction 816a is sufficient for only the scraper 812b to contact the membrane 1100 during the scraping step.

[0059] 11C, the inner arm 814 can continue to extend from the outer tube 806 until the scraper 814b presses against the flap 1102, capturing the flap 1102 between the scrapers 812b, 814b. As the scraper 814b extends from the outer tube 806, the barbs 818 on the lower edge of the scraper 814b press against the membrane 1100 and can help further lift the flap 1102 until the scraper 814b presses the flap 1102 against the scraper 812b. Alternatively, the barbs 818 can be omitted from the scraper 814b.

[0060] 12, once the flap 1102 is grasped between the scrapers 812b, 814b, the grasping structure 804 may be moved in a circular motion to peel a portion of the membrane 1100 from the patient's retina 1200. The scrapers 812b, 814b may then be withdrawn into the outer tube 806, which may be withdrawn from the trocar cannula.

[0061] Illustrative Embodiments Embodiment 1: A method for peeling a membrane from a retina of a patient's eye, the method comprising: inserting a distal end of an outer tube through a cannula into the patient's eye; extending an outer loop and an inner loop from the outer tube; engaging the membrane with the outer loop to form a flap; and pulling the inner loop and outer loop together such that the flap is grasped between the inner loop and the outer loop.

[0062] Embodiment 2: The method of embodiment 1, further comprising pulling the flap to detach a portion of the membrane from the retina.

[0063] Embodiment 3: The method of embodiment 1, wherein the outer tube is attached to a handle that has an actuator attached and is coupled to the inner loop, and the method comprises moving the actuator to move the inner loop toward the outer loop.

[0064] Embodiment 4: The method of embodiment 3, wherein the actuator is a first actuator, a second actuator is attached to the handle, an outer tube is slidably attached to the handle and coupled to the second actuator, and extending the outer loop and the inner loop comprises moving the second actuator to withdraw the outer tube.

[0065] Embodiment 5: The method of embodiment 1, wherein the outer loop and inner loop, when extended from the outer tube, are at least four times wider than the outer diameter of the outer tube.

[0066] Embodiment 6: The method of embodiment 5, further comprising retracting the outer and inner loops into the outer tube by only elastically deforming the outer and inner loops.

[0067] Embodiment 7: The method of embodiment 6, wherein the outer loop and the inner loop each comprise nitinol.

[0068] Embodiment 8: An ophthalmic surgical instrument for peeling off an epiretinal membrane, comprising a handle, an actuator attached to the handle, an outer tube having a proximal end attached to the handle, an outer loop extending outward from the distal end of the outer tube, and an inner loop extending outward from the distal end of the outer tube and disposed within the outer loop, wherein the actuator is configured to move one of the inner loop and the outer loop so that the inner loop and the outer loop are pulled together to grasp the epiretinal membrane.

[0069] Embodiment 9: The ophthalmic surgical instrument of embodiment 8, wherein the actuator is configured to move the inner loop toward the outer loop in response to moving the actuator in a first direction.

[0070] Embodiment 10: An ophthalmic surgical instrument as described in embodiment 9, wherein the actuator is configured to move the inner loop away from the outer loop in response to moving the actuator in a second direction opposite the first direction.

[0071] Embodiment 11: An ophthalmic surgical instrument as described in embodiment 8, wherein the outer loop and inner loop are at least two times wider than the outer diameter of the outer tube.

[0072] Embodiment 12: An ophthalmic surgical instrument as described in embodiment 11, wherein the outer loop and inner loop are at least four times wider than the outer diameter of the outer tube.

[0073] Embodiment 13: An ophthalmic surgical instrument as described in embodiment 12, wherein the outer loop and the inner loop are configured to deform elastically sufficiently to fit within the outer tube.

[0074] Embodiment 14: An ophthalmic surgical instrument as described in embodiment 12, wherein the outer loop and the inner loop each comprise nitinol.

[0075] Embodiment 15: An ophthalmic surgical instrument as described in embodiment 8, wherein the first surface of the outer loop is configured to grasp a membrane on the retina of a patient's eye and comprises a first tapered barb having a length outward from the first surface that is less than the thickness of the membrane.

[0076] Embodiment 16: An ophthalmic surgical instrument according to embodiment 15, having a length of 0.8 to 8 microns.

[0077] Embodiment 17: An ophthalmic surgical instrument as described in embodiment 16, wherein the second surface of the inner loop, which is positioned to engage with the membrane when the first surface is pressed against the retina, is not barbed.

[0078] Embodiment 18: An ophthalmic surgical instrument as described in embodiment 8, wherein either the outer loop defines one or more slots and the inner loop defines one or more protrusions disposed within the one or more slots, or the inner loop defines one or more slots and the outer loop defines one or more protrusions disposed within the one or more slots.

[0079] Embodiment 19: An ophthalmic surgical instrument as described in embodiment 8, wherein the outer loop defines an end portion, the end portion being connected to the distal end of the outer tube by a flexible portion having greater flexibility than the end portion.

[0080] Embodiment 20: An ophthalmic surgical instrument as described in embodiment 8, wherein the actuator is a first actuator and the ophthalmic surgical instrument further comprises a second actuator coupled to the outer tube, the outer tube being slidable relative to the handle, the outer loop, and the inner loop.

[0081] Embodiment 21: An ophthalmic surgical instrument as described in embodiment 20, further comprising an inner tube disposed within the outer tube, the inner tube being fixed relative to the handle and the outer loop being fastened to the inner tube.

[0082] Embodiment 22: An ophthalmic surgical instrument as described in embodiment 21, further comprising an inner rod disposed within the inner tube, the inner rod being coupled to the first actuator and the inner loop being fastened to the inner rod.

[0083] Embodiment 23: A method for peeling a membrane from a retina of a patient's eye, the method comprising: inserting a distal end of an outer tube through a cannula into the patient's eye, the outer tube being attached to a handle; extending an outer arm from the outer tube having an outer scraper secured thereto; engaging the membrane with the outer scraper to form a flap; extending an inner arm from the outer tube, the inner arm having the inner scraper secured thereto; and pushing the inner scraper toward the outer scraper so that the flap is gripped between the inner and outer scrapers.

[0084] Embodiment 24: The method of embodiment 23, wherein the inner arm, outer arm, inner scraper, and outer scraper each comprise nitinol.

[0085] Embodiment 25: The method of embodiment 23, wherein the outer scraper defines a concave surface and the inner scraper defines a convex surface, and the method further comprises gripping the flap between the concave and convex surfaces.

[0086] Embodiment 26: The method of embodiment 23, wherein engaging the membrane with the outer scraper to form the flap comprises engaging the membrane with barbs formed on the edge of the outer scraper.

[0087] Embodiment 27: The method of embodiment 26, wherein the barbs are oriented to pull the membrane toward the inner scraper.

[0088] Embodiment 28: The method of embodiment 26, wherein the barbs have a length extending outward from the edge that is less than the thickness of the membrane.

[0089] Embodiment 29: An ophthalmic surgical instrument for peeling off an epiretinal membrane, comprising a handle, a first actuator attached to the handle, a second actuator attached to the handle, an outer tube having a proximal end attached to the handle, an outer arm to which an outer scraper is fixed, and an inner arm to which an inner scraper is fixed, wherein the first actuator is configured to control the extension of the outer arm from the outer tube and the second actuator is configured to control the movement of the inner arm relative to the outer arm.

[0090] Embodiment 30: An ophthalmic surgical instrument as described in embodiment 29, wherein a first actuator is coupled to the outer arm and a second actuator is coupled to the inner arm.

[0091] Embodiment 31: An ophthalmic surgical instrument as described in embodiment 29, wherein the outer scraper defines a concave surface and the inner scraper defines a convex surface arranged to press against the concave surface.

[0092] Embodiment 32: An ophthalmic surgical instrument as described in embodiment 31, wherein at least one of the concave and convex surfaces is textured.

[0093] Embodiment 33: An ophthalmic surgical instrument as described in embodiment 29, wherein the outer scraper is formed with barbs on its edge.

[0094] Embodiment 34: An ophthalmic surgical instrument as described in embodiment 33, wherein the barbs are oriented to pull the membrane towards the inner scraper.

[0095] Embodiment 35: An ophthalmic surgical instrument as described in embodiment 33, wherein the barbs have a length extending outward from the edge that is less than the thickness of the epiretinal membrane.

[0096] Embodiment 36: An ophthalmic surgical instrument according to embodiment 35, having a length of 1 to 3 microns.

[0097] Embodiment 37: An ophthalmic surgical instrument as described in embodiment 29, wherein the outer tube 106 defines a longitudinal direction parallel to the axis of symmetry of the outer tube 106, and the outer scraper extends outward in a transverse direction beyond the outer diameter of the outer tube, the transverse direction being perpendicular to the longitudinal direction.

[0098] Embodiment 38: An ophthalmic surgical instrument as described in embodiment 37, wherein the outer scraper and the inner scraper extend outward transversely by at least twice the outer diameter of the outer tube.

[0099] Embodiment 39: An ophthalmic surgical instrument as described in embodiment 29, wherein the outer arm, inner arm, outer scraper, and inner scraper are made of nitinol.

[0100] Embodiment 40: A method for peeling a membrane from a retina of a patient's eye, the method comprising: inserting a distal end of an outer tube through a cannula into the patient's eye, the outer tube being attached to a handle; extending an outer arm from the outer tube having an outer scraper secured thereto; engaging the membrane with the outer scraper to form a flap; extending an inner arm from the outer tube, the inner arm having the inner scraper secured thereto; and pushing the inner scraper toward the outer scraper so that the flap is gripped between the inner and outer scrapers.

[0101] Embodiment 41: The method of embodiment 40, further comprising pulling the flap to detach a portion of the membrane from the retina.

[0102] Embodiment 42: The method of embodiment 40, wherein a first actuator and a second actuator are attached to the handle, the first actuator is coupled to the outer arm, the second actuator is coupled to the inner arm, and extending the outer arm from the outer tube comprises moving the first actuator, and extending the inner arm from the outer tube comprises moving the second actuator.

[0103] Embodiment 43: The method of embodiment 40, wherein the outer scraper and the inner scraper extend outward from the axis of symmetry of the outer tube by at least two times the diameter of the outer tube.

[0104] The foregoing description is provided to enable those skilled in the art to practice the various embodiments described herein. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments. Accordingly, the claims are not intended to be limited to the embodiments shown herein, but are to be accorded the full scope consistent with the language of the claims.

Claims

1. 1. An ophthalmic surgical instrument for peeling an epiretinal membrane, comprising: The handle and at least one actuator attached to the handle; an outer tube having a proximal end attached to the handle; a flexible outer gripping member extending outward from a distal end of the outer tube or configured to extend outward from the distal end of the outer tube; a flexible inner gripping member extending outward from the distal end of the outer tube, or configured to extend outward from the distal end of the outer tube, wherein the at least one actuator is configured to move at least one of the outer gripping member or the inner gripping member relative to the other such that the inner gripping member and the outer gripping member are brought together to grip the epiretinal membrane; An ophthalmic surgical instrument comprising:

2. the flexible outer gripping member comprises an outer loop extending outwardly from the distal end of the outer tube; The ophthalmic surgical instrument of claim 1 , wherein the flexible inner gripping member extends outwardly from the distal end of the outer tube and comprises an inner loop disposed within the outer loop.

3. 3. The ophthalmic surgical instrument of claim 2, wherein the at least one actuator is configured to move the inner loop toward the outer loop in response to movement of the at least one actuator in a first direction, and the at least one actuator is further configured to move the inner loop away from the outer loop in response to movement of the at least one actuator in a second direction opposite the first direction.

4. The ophthalmic surgical instrument of claim 2 , wherein the outer loop and the inner loop are at least two times wider than the outer diameter of the outer tube.

5. The ophthalmic surgical instrument of claim 4 , wherein the outer loop and the inner loop are configured to resiliently deform sufficiently to fit within the outer tube.

6. The ophthalmic surgical instrument of claim 4 , wherein the outer loop and the inner loop each comprise nitinol.

7. 3. The ophthalmic surgical instrument of claim 2, wherein the first surface of the outer loop comprises a first tapered barb configured to grasp a membrane on a retina of a patient's eye, the first tapered barb having a length outward from the first surface that is less than a thickness of the membrane.

8. 8. The ophthalmic surgical instrument of claim 7, wherein a second surface of the inner loop positioned to engage the membrane when the first surface is pressed against the retina is not barbed.

9. the flexible outer gripping member comprises an outer arm having an outer scraper fixed thereto; the flexible inner gripping member includes an inner arm having an inner scraper secured thereto; 2. The ophthalmic surgical instrument of claim 1, wherein the at least one actuator comprises a first actuator and a second actuator attached to the handle, the first actuator configured to control extension of the outer arm from the outer tube and the second actuator configured to control movement of the inner arm relative to the outer arm.

10. The ophthalmic surgical instrument of claim 9 , wherein the outer scraper defines a concave surface and the inner scraper defines a convex surface positioned to press against the concave surface.

11. The ophthalmic surgical instrument of claim 10 , wherein at least one of the concave surface and the convex surface is textured.

12. The ophthalmic surgical instrument of claim 9 , wherein the outer scraper is formed with barbs on its edge.

13. The ophthalmic surgical instrument of claim 12 , wherein the barbs are oriented to pull the epiretinal membrane toward the inner scraper.

14. The ophthalmic surgical instrument of claim 12 , wherein the barbs have a length outward from the edge that is less than a thickness of the epiretinal membrane.

15. the outer tube defines a longitudinal direction parallel to an axis of symmetry of the outer tube; 10. The ophthalmic surgical instrument of claim 9, wherein the outer scraper and the inner scraper extend transversely outwardly beyond an outer diameter of the outer tube, the transverse direction being perpendicular to the longitudinal direction.

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