Background
Presbyopia is an ophthalmic disease associated with poor mechanical accommodation of the eye due to aging. Mechanical accommodation is driven primarily by parasympathetic innervation of the ciliary smooth muscle. In non-presbyopic eyes, this actuation causes the muscles to slide forward in a uniform manner, moving the muscles inward. The result is a decrease in the diameter of the ciliary muscle ring (collar), which produces a series of events that enable the eye to see clearly close objects.
Although it is clear that the elasticity of the lens capsule in the eye, i.e. the ability of the lens capsule to remodel the lens, diminishes with age, the precise cause of presbyopia remains the subject of debate.
The most common treatment for presbyopia is with presbyopic glasses, bifocal and modified multifocal contact lenses. However, spectacles and contact lenses are inconvenient to use, and so research and improvement on surgical techniques that help correct presbyopia is immediately undertaken.
One such method is Anterior Ciliary Sclerotomy (ACS). ACS is based on the theory that accommodation results are primarily due to ciliary body contraction, which results in forward lens movement. The underlying theoretical basis for this theory is based on the observation that the lens grows constantly throughout life, gradually filling the posterior chamber, and eventually interfering with the overall function of the ciliary body/zonal complex. The "crowded" condition reduces the ability of the lens to attempt to change during accommodation. ACS employs a series of symmetric, radial, scleral incisions of some depth in an attempt to make more room for the ciliary body and thus provide more room for the lens by expanding the ball in the region of the ciliary body. However, there are several side effects of this procedure, including perforation due to infection and hemorrhage, which may result in retinal detachment, iris damage or prolapse.
Another proposed surgical reversal method for presbyopia is based on the theory that presbyopia occurs as a result of the decreasing distance between the ciliary body and the equator of the lens and its capsule as the lens grows normally with age. Thus, based on this theory, treatment of presbyopia is performed by increasing the effective working distance of the ciliary muscles. The treatment is carried out by implanting a series of scleral expansion bands just below the scleral surface, outside the cornea. The expansion band stretches the sclera so that the diameter of the circle representing the intersection of the ciliary body plane with the sclera increases slightly (see U.S. patents US5354331 and US5489299 to Schachar). However, at least one study has suggested that the theory underlying scleral expansion surgery is problematic (see Mathews, "the sclera expansion surgery does not restore the accommodative ability of the presbyopia of the human body", ophthalmology, Vol. 106, No. 5, month 5 1999, p. 873-. This study shows that if scleral expansion surgery does alleviate presbyopia, then an explanation other than restoration of accommodation needs to be found. Schachar also believes that his scleral expansion band can treat early open angle glaucoma by restoring the level of force of the ciliary muscles acting on the trabecular meshwork, thereby opening the drainage pores and releasing intraocular pressure (IOP).
Despite the theory behind this, there is a need for a relatively safe, simple, easily reversible procedure for correcting presbyopia, rather than using eyeglasses or contact lenses. There is also a need for a safe, effective, simple method for treating glaucoma.
The theory of the method of the present invention is based on the reason for the development of presbyopia, which is different from what has been described above. In particular, presbyopia occurs because the ciliary body is unable to adjust the diameter of the crystalline lens in order to focus close objects onto the retina. The ciliary muscle changes the diameter of the lens by using the sclera as a supporting or anchoring structure. As the sclera of the eye weakens with age, the ciliary muscles lack the support required to change the diameter of the lens to focus on nearby objects. Thus, in order for the ciliary muscle to be able to change the diameter of the lens to see close objects, the sclera must be supported or reinforced. Thus, the method provided by the present invention uses a novel clip to reinforce the sclera, thereby providing a stronger and more stable support for the ciliary muscle. In practice, the sclera is strengthened and the ciliary muscles are thus able to function normally to obtain near vision.
It is believed that the method also has corresponding advantages for treating open angle glaucoma. Glaucoma, like presbyopia, is an age-related disease that results from the buildup of fluid pressure in the eye that damages the optic nerve. After a period of time, glaucoma causes loss of peripheral vision, which narrows the visual field. In a healthy eye, fluid produced by the ciliary tissue surrounding the lens is drained out of the eye by drainage tubes surrounding the outer edge of the iris. With age, due to the lack of support of the ciliary muscles, they are unable to keep their drainage tubes open in order to freely drain fluid. After stretching the sclera according to the method of the present invention, the support for the ciliary body is provided and the ocular tissue for drainage is stretched, thus reducing blockage of fluid drainage tubes and facilitating drainage of fluid out of the eye.
Referring to fig. 1, a simple cross-section of a human eye 10 having a lens 12 contained within a lens capsule 14 is shown. The ciliary body and ciliary muscle 16 are connected to the lens capsule 14 and are also connected to the choroid 18. The sclera 20 wraps outside the choroid 18 and outside the ciliary muscle 16 in front of the eye and terminates in a scleral spur 22 at the cornea 24 of the eye. The conjunctiva 26 surrounds the cornea 24 and is wrapped around the bulbous sheath (or sacculus) 28, which is wrapped around the sclera 20 in front of the eye 10. As best seen in FIG. 2, arteries in the superior rectus muscle 30, inferior rectus muscle 32, medial rectus muscle 34, and lateral rectus muscle 36, respectively, supply blood to the sclera.
In the method of the present invention, the eye is treated by first making a series of substantially linear incisions (such as incisions 38 in FIG. 2) in the conjunctiva 26 to gain access to the sclera 20. Preferably, a standard general preparation procedure is performed prior to incision, including marking the edge and cornea with bluish purple at 10, 2, 5 and 8 o' clock positions to indicate the location of the incision.
The incision is made radially outward from the cornea, substantially bisecting the area between adjacent rectus muscles (e.g., the area between the superior rectus muscle 30 and the medial rectus muscle 34 bisected by incision 38 in fig. 2). For each incision 38, the initial incision is cut to open the conjunctiva around the tenon's capsule. The incision is then deepened, and the incision is made deep into the episclera, where an incision of 3 to 7mm in length is made. The incision is opened and the tenon's capsule is then moved laterally, if necessary, to expose the sclera 20.
Either mechanically, such as with forceps, or by applying a vacuum to extend sclera 20 outwardly. A clip 40 is applied to the outwardly extending sclera 20 to cause the sclera 20 to move under tension. The tenon's capsule is then replaced on the clip and the conjunctiva is closed. Because the conjunctiva is self-closing, no suturing is required. The procedure is then repeated for each marked quadrant, thus applying four clips to the eye that are equidistant from the cornea 24 between adjacent rectus muscles.
Fig. 3 is a simple schematic diagram showing two clips 40 attached to the eye 10. The clip 40 grasps the sclera outside the ciliary body 16 adjacent the iris 39. The clip 40 is applied with a generally thin profile (low profile) to adhere to the curved portion of the eye to reinforce the sclera.
Referring to fig. 4-9, the clips used in the above-described process can take many different forms. In general, it is desirable that the clip 40 have overall dimensions of a height (h) of about 1.5-2.5mm, a thickness (t) of about 0.4-0.6mm, and a length (l) of no more than 5.0-6.0 mm. The size of the clip is limited by the distance between adjacent rectus muscles. In particular, it is desirable that the clip fit between the rectus muscles so as not to interfere with the flow of blood from the rectus middle artery to the eye. Thus, instead of using a single clip of about 5.0-6.0mm in length, a series of clips may be used, the overall length of which fits between adjacent rectus muscles. Of course, it will be appreciated that the use of a single clamp of appropriate length will make the overall process easier and faster to perform.
It will be readily appreciated that the above procedure may simply be reversed by merely making a further incision in the conjunctiva over the clip to obtain an incision to the sclera, moving the tenon's capsule to expose the clip, and removing the clip. This is done without cutting an incision into the sclera.
In each of fig. 4-9, the clip 40 includes two arms 42, 44 that are connected to one another so as to be movable relative to one another. On one side of the clip are teeth, serrations, spurs, barbs, fingers, tips 46 or other structures or projections that enable the arms of the clip to engage, or securely hold or grasp, the sclera when the clip is attached to the sclera. The teeth 46 are sized to engage the sclera, but are not sized and configured to penetrate the sclera (which may cause erosion of the sclera). Thus, the teeth 46 may be as small as 20-80 μm. The clip is initially "open" and then "closed" on the sclera with a forceps or other applicator. The clip will maintain its closed state without the application of an external force to separate the two arms of the clip. It is expected that the arms of the clip will close at about 10 to 15 degrees. This would cause the vascular membrane to sag and the sclera to move outward by about 0.5mm, with a total movement of 2mm if four clips were applied. The result will be an increase in the range of accommodation, thereby reversing the effects of presbyopia. This outward movement of the sclera will also increase the angle of schlemm's canal, thereby increasing the flow of fluid and lowering the intraocular pressure to ameliorate the effects of glaucoma. The clip may be made of any biocompatible material, including tantalum, Polymethylmethacrylate (PMMA), and preferably titanium, which has sufficient deformability and elastic properties to allow the clip to "open" and then remain closed when applied to the sclera. Referring to fig. 4, a first embodiment of the scleral clip 40 is shown in which each leg 42, 44 is bent inward to provide some flexibility to the clip 40. Each leg 42, 44 also includes a series of teeth 44 for grasping into the sclera. The scleral clip of fig. 5 is similar to that shown in fig. 4, except that the resiliency of clip 40 is achieved by the outward flexing of legs 42, 44.
Fig. 6 shows another embodiment of a clip 40 comprising a rectangular central portion folded along an oblique line, with a tooth 46 at each lower corner. A pair of staple-like members, also having teeth 46, rest against opposite ends of the rectangular portion, forming yet another mechanism for grasping the sclera.
Fig. 7 shows a clip similar to that shown in fig. 3 and 4, except that the clip 40 includes an elastic band 48 that connects the two legs together. The elastic band 48 is used to maintain the legs 42, 44 of the clip in tension when the teeth are engaged with the sclera.
The clip 40 shown in fig. 8 has a spider-like configuration with a plurality of legs (4 shown) resting on the central body, each leg terminating in a tooth 46.
The clip 40 shown in fig. 9 is similar to that shown in fig. 3, 4 and 6, except that a central portion of the clip 40 has been removed to give it a fork-like appearance.
Fig. 10 is a further embodiment of a scleral clip 40 of the present invention that is similar to the clip shown in fig. 7 except that it does not include an elastic tension band. The clip 40 includes a notch 50 in the center of each arm 42, 44 to mate with the tensioning instrument on which the clip is placed. Also, the teeth 46 are 200 μm in length and are rounded, beveled or obtuse so as not to present sharp edges that may penetrate the sclera. The outer or upper surface of the clip may be coated with a preferably white latex-free silicone polymer or acrylic coating so as to be less noticeable when the clip is attached to the sclera.
Fig. 11a and 11b are perspective and end views, respectively, of another embodiment of a clip 40. This embodiment is similar to that shown in fig. 4, except that the arms 42, 44 are not curved, but are substantially flat. The clip 40 is configured such that the angle between the two arms is about 175 degrees, such that when the arms are closed at 10 to 15 degrees when applied to the sclera, the angle between the arms is between 160 and 165 degrees. This angle allows the clip to more closely approximate the curvature of the eyeball after application to the sclera. This may be more comfortable for the user and may also reduce tissue erosion outside of the applied clip. The teeth 46 are angled at about 90 degrees from their arms 42, 44.
Fig. 12 is a perspective view of a clip 40 similar to that shown in fig. 11a, 11b, except that the ends of the arms 42, 44 have been reduced in part inwardly at 52. This reduces the portion of the clip that extends beyond the radius of curvature of the eye when attached to the eye, thereby providing the benefit of comfort and reducing the potential for tissue erosion as previously described.
Fig. 13 shows another embodiment of a clip 54 of the present invention. The clip 54 has exactly the same dimensions as the previously described clip, i.e. about 3 to 5mm by 5 to 6mm, so as to fit between adjacent rectus muscles. However, the clip is oval or circular and has a central opening 56 closed by a continuous peripheral portion, so that the clip has a ring-like appearance. Such clips are applied to the sclera by mechanical means, such as a twist hook or forceps, or by applying a vacuum, which droops through the opening in the bone in the clip. Both the central opening 56 and the peripheral edge 58 may be provided with teeth as previously described, or only one may be provided with teeth to secure the clip to the sclera. In addition, the teeth may be curved out of the plane substantially defined by the clip so that they can more securely grip the sclera. Referring to fig. 14, the teeth on the outer peripheral edge or perimeter 58 may be bent downwardly at an angle a from about 90 degrees to about 135 degrees, while the teeth on the central opening or inner perimeter 56 may be bent downwardly at an angle β from about 20 degrees to about 45 degrees.
The clip 54 is substantially flat with little or no angle between the two arms or sides 62, 64 as defined by a centerline through the clip, and thus has a very low profile. Preferably, the clip 54 is thin enough to conform to the natural shape or curvature of the eye.
Thus, there is provided a method and a clip for use in the method that fully achieves the objects of the present invention. While the preferred method and clip have been described above, they are not intended to limit the invention. The scope of the invention is defined by the following claims.