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Current Concepts in Ophthalmic Surgery
Symposium on Ophthalmology
Current Concepts in Ophthalmic Surgery Robert L. Peiffer, Jr., D.V.M.*
The past decade has seen the development of a new technology and the refinement of conventional methods, both of which have enhanced the veterinary ophthalmic surgeon's capabilities to manage intraocular disease. Included within the technological advances are the development of instruments for phakoemulsification, irrigation and aspiration techniques for cataract surgery, suction-cutter instrumentation for vitrectomy, and the intraocular insertion of plastic lenses to improve vision following cataract surgery. These advances have found universal acceptance in human ophthalmology, but their application to veterinary ophthalmic surgery is somewhat limited because of practicality and species differences in physioanatomy and pathology. The comparative potential of these techniques, however, has not been fully explored. The refinement of conventional surgical methods includes the consistent application of microsurgical principles including microscopes, instruments, and sutures. While I have never been accused of conservative surgical philosophies and have explored the realm of gadget-oriented ophthalmic surgery, I find the refinement of conventional ophthalmic procedures more rewarding than the dramatic changes involved in gadget-oriented surgery. Most intraocular surgical procedures performed by the veterinary ophthalmic surgeon involve the management of glaucoma and the removal of a cataractous and/or dislocated lens. This article reviews current concepts of these procedures, and statistics from my personal experiences over the past five years have been included where they help illustrate these concepts. Because only a small number of practitioners are interested in performing these techniques, the concepts rather than the specific manipulations will receive greater attention. *Assistant Professor and Director of Laboratories, Department of Ophthalmology, University of North Carolina School of Medicine, Chapel Hill, North Carolina, Diplomate, American College of Veterinary Ophthalmologists Veterinary Clinics of North America: Small Animal Prar:tice- Vol. 10, No. 2, May 1980
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MICROSURGERY Ophthalmic surgery performed under microscopic magnification of four to forty times means that all surgical procedures can be performed with more precision and that threatening complications, such as vitreous presentation into the anterior chamber, can be recognized earlier and more effectively prevented or managed. The variety of operating microscopes available is extensive and ranges from portable table-top models that may be purchased for several hundred dollars to elaborate floor or ceiling mounted, completely automated microscope systems that cost many thousands. A good microscope system will include coaxial illumination and an oblique slit-lamp illuminator. I find that most of my surgery is done at a magnification of 8 to 10 times. In conjunction with the microscope, microsurgical ophthalmic instruments and fine suture material must be used. The use of standard ophthalmic instruments and suture precludes the advantages of using the microscope. Microsurgical techniques are not difficult to learn but require practice. When techniques are properly utilized by an experienced microsurgeon, they will result in minimal surgically-induced trauma to tissue and precise apposition of wound edges with no increase in operating time. If the surgeon has not mastered basic techniques with many hours of practice, however, results will be discouraging and the procedure prolonged. While microsurgery will make a good surgeon better, it will not make capable surgeons out of those with minimal natural talent. In essence, microsurgery enables the surgeon to do the same manipulations he would otherwise perform with more respect for the tissues, meticulous technique, and improved results.
GLAUCOMA Almost without exception, primary and secondary glaucoma in the dog and cat must be treated surgically if vision is to be maintained on a long-term basis. Topical and systemic ocular hypotensive medications are costly and have undesirable side effects. Most importantly, they are not effective in controlling intraocular pressure in the dog and cat over extended periods of time, either as a result of disease mechanisms and sensitivity and/or owner compliance. These drugs are helpful in controlling acute episodes prior to surgery and may be useful at low therapeutic levels as an adjunct to surgical procedures for long-term control of intraocular pressure and maintenance of functional vision. An occasional Poodle with open angle glaucoma and intraocular pressure of 40 to 50 mm Hg or a Cocker Spaniel with slight narrowing of the iridocorneal angel and mild elevation of intraocular pressure may be controlled with
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topical drops and/or oral carbonic anhydrase inhibitors, but these animals are the exception rather than the rule. I believe that effective pharmacologic control of glaucoma in the dog and cat has long been overemphasized and that a large number of blind or euthanatized pets attest to this fact. This is not to say that surgical procedures always provide acceptable results. Glaucoma, at best, is a challenging disease to manage and, not infrequently, intense and dedicated efforts yield discouragement and frustration. Surgical procedures will not always provide acceptable results, but I believe that if you operate early in the course of the disease you will have many more sighted patients and contented clients.
Surgical Judgment Selection of patients for glaucoma surgery is not difficult. Any patient with acute elevation of intraocular pressure greater than 50 mm Hg or chronic non-responsive deviated intraocular pressure from 30 to 50 mm Hg is a surgical candidate. Prognosis for restoration of vision is difficult to predict accurately, but impressions can be made from duration and extent of increased intraocular pressure, whether or not the globe is noticeably enlarged, and ophthalmoscopic examination. Elevation of intraocular pressure greater than 50 mm Hg over a course of three to seven days will result in irreversible damage to the retina and optic nerve. A noticeably enlarged globe and advanced fundic disease (vascular attenuation, optic atrophy and cupping, peripapillary pigmentation, and tapetal hyper-reflectivity) are unfavorable signs. Early diagnosis, then, is critical in proper management. This responsibility generally lies in the hands of the primary practitioner rather than the specialist and requires an awareness of which breeds are predisposed, a knowledge of the clinical signs of glaucoma, and a method to quantitate intraocular pressure. To practice small animal medicine and surgery without a tonometer borders on the unethical and will almost assuredly cost the practitioner the sight of several patients over a professional career. Surely this justifies the $125.00 cost of a Schi0tz tonometer and the minimal practice effort it takes to learn to use it well. Once acute glaucoma is diagnosed, intraocular pressure must be reduced as expediently as possible. In general, I administer mannitol and acetazolamide intravenously and compounds of pilocarpineepinephrine topically at hourly intervals. If intraocular pressure is reduced to less than 30 mm Hg in four hours, maintenance with oral glycerine and carbonic anhydrase inhibitors and topical drugs may be attempted. Further diagnostic tests such as tonography and gonioscopy are performed and surgery becomes a semi-elective procedure. This course of events occurs in approximately 75 per cent of patients with primary glaucoma and 50 per cent of patients with secondary glaucoma. If intraocular pressure is not reduced to less than 30 mm Hg in four hours, immediate surgical intervention is necessary.
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Surgical Techniques Many surgical procedures are utilized to manage glaucoma in human and veterinary ophthalmology, and they are divided into two general types based on their mechanisms of action. Filtering procedures, which include iridectomy, iridencleisis, cyclodialysis, goniotomy, sinusotomy, trabeculotomy, trabeculectomy, sclerotomy and sclerectomy, open primary drainage channels or provide alternate pathways for the outflow of aqueous humor. Cyclocryothermy, cryogoniotomy, and cyclodiathermy utilize thermal destruction of the ciliary body and epithelium to decrease production of aqueous humor and possibly to open outflow channels. Techniques employed in veterinary ophthalmology have generally been adaptations and modifications of procedures described for humans. Significant species differences in ocular anatomy, physiology, response to the disease process and corrective surgery, and the nature of both the disease and the patient make glaucoma more difficult to control surgically in the dog than in humans. Filtering procedures are approximately 80 per cent effective in humans. 8 • 10 In the dog, success rates of satisfactory, long-term control of intraocular pressure ranges from 30 to 50 per cent, primarily due to fibrosis and closure of surgically-produced outflow pathways.L 2 • 6, 9, u, 13 Posterior sclerotomy was one of the earliest techniques utilized in the surgical management of glaucoma in humans, and its results on a limited number of cases of canine glaucoma have been described in the veterinary literature. 2 This technique involves establishing direct communication between the subcortiunctival space and the vitreous cavity. Its potential complications and unphysiologic basis made it less desirable than those filtering procedures that allow direct drainage of aqueous humor. Iridencleisis is technically not difficult, but success rates are low owing to fibrosis and closure of the filtering area. Silastic implants have been used to maintain drainage of aqueous humor with inconsistent results. 13 Removal of scleral tissue with or without cautery to prevent closure of trans-scleral drainage pathways has been described. 8 • 10 Bedford reported his results with cyclodialysis (which provides a supraciliary communication through the sclera between the anterior chamber and the suprachoroidal and subconjunctival spaces); iridencleisis; thermal sclerectomy and iridectomy; cyclodiathermy; and corneoscleral trephination with a peripheral iridectomy. The latter technique provided the most consistent results. 1 Vainisi described a technique developed by Wyman that combined posterior sclerectomy, cyclodialysis, or iridocyclectomy.1 1 Our experience with this procedure was unsatisfactory because of intraocular hemorrhage and inflammation associated with the iridocyclectomy. The procedure was modified to include a transscleral iridencleisis through the excised sclera and has provided more consistent, positive results than iridencleisis, cyclodialysis, and trabe-
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culectomy in the dog (Fig. 1). The results of the technique on nine eyes were reported in 1977, and since that time the operation has been performed on an additional 24 eyes. 11 Success based on maintenance of a normotensive eye without hypotensive medication for a minimum of six months was observed in 22 of 33 eyes, or 67 per cent (Fig. 2). Reoperation was required on two of these 22 eyes four weeks after the primary procedure. Of the 11 failures, three were cases of glaucoma secondary to inflammation.
Chronic Glaucoma Cosmetic surgery may be performed on blind enlarged globes. Enucleation is an effective but not always acceptable alternative to an owner. Vigorous cyclocryotherapy will reduce intraocular pressure in approximately 7 5 per cent of cases, but the globe may remian enlarged in spite of lowered intraocular pressure. Filtering procedures have the same disadvantage. The insertion of an intraocular prosthesis provides excellent results, the only disadvantage being the 4 to 12 week postoperative course of therapy necessary to control the inflammatory response.12
CATARACTS Cataracts are among the most common ocular diseases seen in my practice, with one out of five referrals presented with cataracts or suspicion of cataracts. While not all of these patients are candidates for surgery, cataract extraction is among the most successful and most rewarding procedures the veterinary ophthalmologist can perform. Aphakic dogs and cats function quite well without correction and compensate adequately for the surgically-induced hyperopia.
Selection of Patients The objective of cataract surgery is to restore functional vtston. Because of the ability of the dog and cat to adjust and compensate for incomplete lens opacity and/or monocular blindness, functional vision is not significantly impaired until bilateral cataracts approach maturity. The owner of the pet is the best judge of when surgery should be contemplated. When the animal is bumping into objects constantly and is unable to maintain its normal lifestyle and personality, cataract extraction should be considered. Of prime importance is to establish the integrity of the retina and the central visual pathways. It is discouraging to both client and surgeon to have a technically successful procedure fail to restore vision because of concurrent disease of the retina or optic nerve, or both. To evaluate the neural visual components history, ophthalmoscopy, visual function tests, and electrophysiology should be used in combination.
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B
Figure 1. A, Following routine preparation for intraocular surgery (the dog is shown undraped for maximum orientation), a lid speculum is placed and a lateral canthotomy performed. B, A wide, limbal-based conjunctival flap is prepared by incising through the conjunctiva and Tenon's capsule about I em from the limbus and C, combining blunt and sharp dissection to separate these tissues from the sclera to mobilize the flap. D, A rectangular block of sclera, approximately 5 by 2 mm is outlined, the posterior border of which is approxilnately 5 mm from the limbus.
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Figure l. Continued. E, The sclera is incised through its entire thickness. The heavily pigmented tissue of the uvea serves as a guide to the proper depth. Hemorrhage is controlled with low-temperature cautery and irrigation. The sclera is easily separated from the uveal tissue and removed en bloc. A cyclodialysis spatula is passed through the supraciliary space into the anterior chamber. Resistance to passage of the spatula is minimal and aqueous humor will flow through the filtration pathway when the anterior chamber is entered. F, A broad cyclodialysis is performed. G, A blunt iris hook is passed through the dialysis into the anterior chamber and the pupillary margin of the iris is hooked. H, The iris is gently exteriorized. I, The iris is grasped with two pairs of iris forceps at the pupillary margin and, using gentle traction, torn to its base. Hemorrhage is minimal.], The iris pillars are then sutured to the episclera with simple interrupted sutures of 7-0 polyglactin 910 with a swaged-on spatula needle. K, The anterior chamber is reformed with an air bubble and the conjunctiva closed with a simple interrupted pattern of the same material. Note the keyhole pupil. The canthotomy is sutured with a routine two-layer closure. (From Peiffer, R. L., et al.: Combined posterior sclerotomy, cyclodialysis and trans-scleral iridencleisis in the management of primary glaucoma. Canine Pract., 4:54-61, 1977, with permission.)
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Figure 2. A, Acute open-angle glaucoma in the right eye of a four year old rnale St. Bernard. The pupil was dilated and nonresponsive to light, the episcleral and conjunct.ival blood vessels were congested, a nd the cornea was edematous. Intraocular pressure was 70 mm Tlg (Mackay-Marg), and tonographic facility of o utflow was 0 .06 JLI per min per nun Hg. B, Six months after posterior sclerotomy, cyclodialysis, and trans-scleral ir idcnclcisis, the eye was visual. !\me the keyhole pupil. Intraocular pressure was 24 mm Hg. and tonographic facility of outflow was O.'lG JLI per min per nun Hg.
The inherited retinal dege nerations, primarily progressive retinal atroph y and central progressive retinal atrophy, are increasing in incidence and are the primary reason for failure in technically successful cataract surgery. Owing to mechanisms that are poorly understood. animals with inherited or inflammatory retinal degeneration are likely to develop associated cataracts. The problem is complicated by the fact that breeds with a large incidence of inherited retinal degene ration, such as the miniature and toy Poodle and the Irish Setter, also have priman genetic cataracts unassociated with retinal disease. Pupillary responses are unreliable as the sole m ethod of assessing peripheral and central visual potential. The majority of cataract patients should demonstrate full, crisp, direct and consensual responses to a bright focal light source in a darkened room in the presence of even th e densest catar act. With some variability, th ese responses will persist in the presence of well-advanced retinal degeneration. The ganglion cell nerve fibers that mediate this reflex are distinct from the usual fibers that extend to the lateral geniculate body, a nd thus provide no information as to the status of the optic radiation and visual cortex . Iris atrophy, occasionally observed in miniature Poodles, and lesions invoh·ing the third cranial nerve may result in absence of pupillary reflexes in the presence of intact visual components. Thus, while it is always reassuring to observe normal pupillary reflexes, they provide minimal definitive information.
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History is helpful in proportion to the owner's ability to be aware of changes in the animal's appearance or behavior. Without exception, visual and ophthalmoscopic changes in progressive retinal atrophy and central progressive retinal atrophy always precede associated cataract development. Thus, a reliable history that visual impairment accompanied or followed rather than preceded noticeable cataract development speaks in favor of an intact visual system. If progressive retinal atrophy is present, a history of initial nyctalopia (night blindness) may be elicited. Critical ophthalmoscopy performed while the cataracts are still immature, rather than waiting until the fundus cannot be critically examined, is of benefit to all involved. Ophthalmoscopy prior to maturity of the cataract approaches 100 per cent reliability. The rare dog with genetic tendencies to develop both progressive retinal atrophy and primary cataracts will provide an occasional disappointment if the retinal atrophy develops subsequent to the primary cataract. Ability to negotiate an obstacle course under photopic and scotopic conditions may be of value in those cases in which fundus reflex can be obtained but lens changes prohibit critical fundic examination. As a general rule of thumb, if a fundic reflex can be obtained, some vision should be present and should change minimally with alterations in ambient light if the retina is healthy. Electrophysiology provides the most reliable criteria for critical evaluation. An electroretinogram should ideally be performed in all patients with cataracts; in those breeds with predisposition to progressive retinal atrophy, electoretinography is a prerequisite to cataract surgery. In a retrospective study of 54 miniature Poodles presented with cataracts, 42 (78 per cent) had associated progressive retinal atrophy as determined by ophthalmoscopy (23 dogs) or electroretinography (19). The surgeon who attempts cataract surgery without an electroretinogram will have fewer successes than will a surgeon who utilizes the test. If history, pupillary responses, and/or neurologic findings suggest the possibility of a defect in the central visual system, evaluation of visually evoked response may be considered in addition to electroretinography. Ultrasonography may be of value in the detection of retinal detachments. A large percentage of young dogs (between one and three years) with inherited developmental cataracts (seen most frequently in the Afghan Hound, American Cocker Spaniel, Irish Setter, and miniature and toy Poodle) will undergo spontaneous resorption of their cataracts. Active resorption, indicated by mild lens-induced uveitis and an irregular lens capsule, is an indication for temporization. While these liquified cataracts may be aspirated, approximately 60 per cent will resorb to the extent that cataract surgery is unnecessary. I prefer to manage these animals with topical application of 1 per cent atropine sulfate to enhance peripheral vision and corticosteroids to temper the uveitis. They should
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be examined monthly, and cataract surgery should be recommended only when active resorption has subsided without restoration of visual function. Cataract surgery is an elective procedure; thorough multisystem evaluation should be performed prior to surgery. Concurrent related disease (such as diabetes mellitus) or unrelated diseases (such as renal decompensation or heartworm disease) should be identified and adequately controlled. In older patients with systemic disease who have adjusted reasonably well to their visual impairment, the complications of anesthesia should be weighed against the benefits of vision. Philosophies of Cataract Surgery With rare exceptions, I perform cataract surgery on one eye only, because of the ability of a pet to function well with monocular vision, lower cost to the owner, and the reduced insult to the patient in terms of anesthesia time and postoperative discomfort. It also is reassuring to know that, in case of failure, one has an alternative to offer the client in terms of operation on the fellow eye. Of course, both cataracts may be removed at one or two sittings at the owner's insistence or if acute visual function is necessary, as in retrievers or obedience dogs. The procedure for cataract removal, when performed with appropriate preoperative treatment and instrumentation, is not difficult. However, the incidence of intraoperative or postoperative complications is high compared to those for other procedures, and these complications frequently have disastrous effects on the visual outcome. With experience and greater understanding of ocular anatomy, physiology, and pathology, the recognition and management of complications are facilitated with resultant improved success. The results of my series of cataract extractions reflects a progressive increase in success rate commensurate with experience and refinement of technique (Table I). These data support the concept that results are most likely to be rewarding in the hands of an experienced cataract surgeon. Routine Procedures and Techniques Adequate preoperative preparation will mrmmize intraoperative and postoperative complications. The canine eye responds to even meticulous surgery with intraoperative constriction of the pupil, which necessitates increased intraocular manipulation which hampers exposure and intensifies postoperative inflammation. I have found that treatment with oral corticosteroids and aspirin and topical antibiotic-corticosteroid solutions for two days prior to surgery will minimize these problems. Prostaglandins play a role in both of these phenomena, and aspirin, which inhibits synthesis of prostaglandin, provides results superior to the use of corticosteroids alone. Planned extracapsular extraction is the rule. The posterior capsule and the hyaloid membrane of the anterior vitreous are intimately
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Table 1. Outcome of Surgical Procedures for Cataracts Performed by the Author YEAR
NUMBER OF EYES OPERATED
1974 1975 1976 1977 1978 1979 Total
6 24 29 31 46 83 219
NUMBER OF EYES SUCCESSFUL*(%)
3 17 23 26 39 76 184
(50) (71) (79) (84) (85) (92) (84)
*Success was defined as adequate visual function (as determined by owner), the ability to negotiate an obstacle course, and a normal fundus four weeks after surgery.
associated, and intracapsular extraction or tearing of the posterior capsule is invariably associated with vitreous presentation. While not always disastrous, vitreous presentation adds an undesirable challenge that frequently precipitates other complications. In addition, enzymatic dissolution of the zonules is unreliable in the dog, and intracapsular extraction results in excessive traction on the ciliary processes. Stable, deep anesthesia is important. Under light anesthesia, the animal may move when the iris is touched and intraocular pressure may increase owing to extraocular muscle contraction. The stability of anesthesia induced with methoxyflurane is preferred over that induced with fluothane, but the usually quieter recovery from fluothane anesthesia reduces the likelihood of trauma inflicted by thrashing about during recovery. The positioning of the patient is crucial to the success of the procedure. The muzzle should be elevated to enable the surgeon to visualize the iris and lens surface in a horizontal plane. A traction suture of 4-0 silk placed through the conjunctiva under the insertion of the superior uveitis muscle may be necessary to achieve this end. The incision, which also is crucial, should be a minimum of 180°. It is difficult to accurately predict lens size prior to surgery, and attempting to deliver an intumescent lens through a small incision will result in undue trauma and residual lens material in the anterior chamber. I prefer to utilize a limbal-based flap because ( 1) the incision heals more rapidly than a clear corneal incision, (2) corneal scarring at the incision site is minimized, (3) accurate apposition of the surgical wound margin is facilitated, (4) if corneal dehiscence occurs, the intraocular contents are not exposed to the environment, and (5) adsorbable suture knots may be covered by the flap so that postoperative irritation does not occur. These advantages more than offset the additional three to five minutes it takes to dissect the flap and control the minimal hemorrhage associated with the corneoscleral incision. Preplaced sutures hinder exposure and manage-
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ability, and I prefer to have unobstructed access to the anterior segment should complications arise. Capsulectomy is performed with a cryoprobe or a capsule forceps. While it is easier to obtain a good equatorial capsular tear with t he former, the incidence of posterior capsule disruption increases. I prefer to grasp the capsule as superficially and as widely as the dilated pupil will allow without compromising visu alization of the forceps teeth. The forceps are closed and elevated minutely but sha rply. The lens cortex and nucleus a re removed in toto; liquified or residual cortex m ay be gently irrigated or aspirated with a blunt needle. If a pupil of less than 3 mm has resulted, sphincter iridectomy is performed. This is the exceptional circumstance, h owever. Closure is achieved with 7-0 polyglactin 910 in a simple interrupted or with 9-0 nylon in a continuous "boot lace" pattern. Postoperative care is critical and is titered to temper inflammation and to maintain pupil size. Triamcinolone acetonide (0.5 ml) is administered subconjunctivally in the inferior quadrants. Oral corticosteroids are continued for three to five days . Topical I per cent atropine sulfate, 10 per ce nt phenylephrine, and antibiotic-corticosteroid solutions are applied every two hours daily for the first three days, which is the critical period for control of pupillary size. Bandages are not utilized as the surgery is tolerated remarkably well. Atropine a nd topical corticosteroids are continued until the inflammation has subsided, usually at four weeks. The patient is re-examined at 2, 4, 12, and 24 weeks and 1 year after surgery.
Figure 3. Pupilla ry mem brane with a small , occluded, u p d rawn pupil six months after extracapsula r extraction in a fi ve year old miniature Poodle.
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Figure 4. Eight weeks after extracapsular extraction with vitreous Joss and anterior vitrectomy in a two year old miniature Poodle. A, \'\Thile the ant.erior segme nt appears satisfactory (note the corneal scar at the incision site), a traction detachment of the retina with a large nasal periphera l dialysis has occurred (B).
Complications
Intraoperative complications include miosis, which can be largely prevented by adequate premedication and minimal intraocular manipulations; h e morrhage from the ciliary process while performing the capsulectomy or from the sphincterotomy incision if one is necessary; vitreous presentation; and posterior capsular opacity. A small pupil is managed by sphincterotomy and postoperative medication. Ciliary process hemorrhage occurs in only 2 per cent of the cases, iris h emorrhage will occur in approximately 20 per cent of animals su~jected to three or four quadrant sphincterotomy. In both cases, bleeding is minimal and self-limited. T he vessels are encouraged to clot on their own by delaying manipulations for three to five minutes. The blood can be irrigated or gently teased from the a nterior chamber. A small amount of residual hyphema, while not desirable, is resorbed over two to three wee ks without adverse consequences. Vitreous presentation occurred in 15 per cent (33 of 219) of planned extracapsular extractions and in all a nimals with incomplete cataract resorption (6 dogs). Vitreous presentation is managed by a n anterior chamber air bubble if the h yaloid me mbrane is intact. Unfortunately, the h yaloid m embra ne usually ruptures a nd the vitreous must be removed from the anterior chamber to reduce the likelihood of disastrous sequelae. I perform radical anterior vitrectomy with cellulose sponges, excising the gel vitreous as close to the plane of th e iris as possible, or with a disposable vitreophage (Kaufman Vitrector II, Concept, Clearwater, Florida) .5 The vitreophage is preferred because it minimizes in-
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traocular manipulation and traction in the retina. Vitrectomy is performed until the anterior chamber is completely free of vitreous and the iris plane assumes a concave appearance. Administration of preoperative mannitol does not appear to influence the incidence of vitreous presentation in the normotensive dog, with one of 12 dogs in each group developing this complication in a prospective study comparing treated and nontreated patients. In approximately 2 per cent of patients with cataracts, the posterior capsule will be translucent or opaque at the time of surgery. If the fundus cannot be visualized on the table, the capsule should be incised and/or removed. Except for a 3 mm superior opening, the incision is closed and the anterior chamber reformed with an air bubble; the posterior capsule is then incised with a hooked 23 gauge needle. The linear incision will usually widen to prevent unimpaired observation of the posterior pole. If it does not, the incised margins are grasped and the capsule teased away from the hyaloid membrane Postoperative complications in the author's series included pupillary membrane without (22 of 35) or with (7) pupillary occlusion and secondary glaucoma, and retinal detachment (6). Of the 35 failures, 20 were associated with vitreous presentation. Those not associated with vitreous presentation demonstrated intense postoperative inflammation related to residual lens material and/or excessive intraocualr manipulation. While focal opacification of the posterior capsule is not uncommon, and, if a pupil is maintained, good functional vision will persist around the secondary cataract. Coreoplasty may be performed as a salvage procedure in dogs with pupillary membranes with or without iris bombe. Vision was restored in two of seven eyes operated by the author. Presently available suctioncutting machines manipulated through the pars plana offer promise in the management of this common complication. My experiences are similar to those of Startup 5 and Magrane; 4 increased success rates may be the result of improved technology and the relatively short-term follow-up for the described series. For example, retinal detachment, may occur several months to years following surgery. Phakoemulsification
Because of the tendency of the canine ms to constrict during surgery and the density of the majority of canine cataracts, especially the nucleus, the sonication and aspiration of cataractous lenses with the instruments currently available is, in my opinion, less rewarding than the extracapsular technique described above. Intraocular Lenses
The use of intraocular plastic lenses is gaining popularity in human ophthalmology. These lenses may be clipped or sutured to the iris or
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inserted into the anterior chamber or lens capsule bag. Because of the marked inflammatory response of the canine eye, significant differences in anterior chamber and pupil size, and the ability of our patients to function well as aphakes, their routine use is not recommended.
LENS DISLOCATION Dislocation of the lens in the dog is almost invariably associated with secondary glaucoma. The mechanisms of the glaucoma are poorly defined and may involve narrowing of the iridocorneal angle related to anterior movement of the vitreous, pupillary block by the vitreous and/or the dislocated lens or both. Regardless of the cause, prevention or effective management of the glaucoma demands removal of the lens, ideally prior to the onset of glaucoma. Intracapsular cryoextraction is the procedure of choice. To enhance exposure, I prefer a broad (up to 240° with posterior luxation) corneoscleral incision initiated with a keratome and extended with corneoscleral scissors. All vitreous that is encountered sh
ACKNOWLEDGMENT
The author gratefully acknowledges the talents of Michael Schenk, the veterinary medical illustrator of the University of Minnesota College of Veterinary Medicine, for providing the line drawings.
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REFERENCES 1. Bedford, P. G.: The surgical treatment of canine glaucoma. ]. Small Anim. Pract., 18:713-730, 1977. 2. Brightman, A. H., Magrane, W. F., Huff, R. W., eta!.: Intraocular prosthesis in the dog.]. A. A. H. A., 13:481, 1977. 3. Kolker, A. E., and Hetherington, J.: Becker-Shaffers' Diagnosis and Therapy of the Glaucomas. St. Louis, C. V. Mosby Co., 1970. 4. Magrane, W. G.: Canine Ophthalmology. Edition 3. Philadelphia, Lea and Febiger, 1977. 5. Magrane, W. G.: Cataract extraction: A follow-up study (439 cases).]. Small Anim. Pract., 10:545-553, 1969. 6. Peiffer, R. L., Jr., Gwin, R. M., Gelatt, K. N., eta!.: Combined posterior sclerectomy, Lyclodialysis and trans-scleral iridencleisis in the management of primary glaucoma. Canine Pract., 4:54-61, 1977. 7. Peiffer, R. L., and Weintraub, B. A.: Clinical and histopathologic effects oflensectomy and anterior vitrectomy in the canine eye.]. A. A. H. A., 15:421--432, 1979. 8. Scheie, H. G.: Peripheral iridectomy with scleral cautery for glaucoma. Am. J. Ophthalmol., 45:220-229, 1958. 9. Stack, W. R.: Treatment of glaucoma: Posterior sclerotomy. J.A. V.M.A., 136:453--455, 1960. 10. Startup, F. G.: Cataract surgery in the dog. ]. Small Anim. Pract., 10:457--460, 1969. 11. Vainisi, S. J.: The diagnosis and therapy of glaucoma. VET. CLIN. NoRTH AM., 3:453--465, 1973. 12. Vierheller, R. C.: Surgery for glaucoma: An analysis of technics. Mod. Vet. Pract., 49:46-68, 1968. 13. Vierheller, R. C.: Surgical treatment of glaucoma: Reappraisal of recommended operative techniques in veterinary practice. Proceedings Am. Soc. Vet. Ophthal., pp. 20-27, 1967. Department of Ophthalmology School of Medicine University of North Carolina Chapel Hill, North Carolina 27514
Current Concepts in Ophthalmic Surgery Robert L. Peiffer, Jr., D.V.M.*
The past decade has seen the development of a new technology and the refinement of conventional methods, both of which have enhanced the veterinary ophthalmic surgeon's capabilities to manage intraocular disease. Included within the technological advances are the development of instruments for phakoemulsification, irrigation and aspiration techniques for cataract surgery, suction-cutter instrumentation for vitrectomy, and the intraocular insertion of plastic lenses to improve vision following cataract surgery. These advances have found universal acceptance in human ophthalmology, but their application to veterinary ophthalmic surgery is somewhat limited because of practicality and species differences in physioanatomy and pathology. The comparative potential of these techniques, however, has not been fully explored. The refinement of conventional surgical methods includes the consistent application of microsurgical principles including microscopes, instruments, and sutures. While I have never been accused of conservative surgical philosophies and have explored the realm of gadget-oriented ophthalmic surgery, I find the refinement of conventional ophthalmic procedures more rewarding than the dramatic changes involved in gadget-oriented surgery. Most intraocular surgical procedures performed by the veterinary ophthalmic surgeon involve the management of glaucoma and the removal of a cataractous and/or dislocated lens. This article reviews current concepts of these procedures, and statistics from my personal experiences over the past five years have been included where they help illustrate these concepts. Because only a small number of practitioners are interested in performing these techniques, the concepts rather than the specific manipulations will receive greater attention. *Assistant Professor and Director of Laboratories, Department of Ophthalmology, University of North Carolina School of Medicine, Chapel Hill, North Carolina, Diplomate, American College of Veterinary Ophthalmologists Veterinary Clinics of North America: Small Animal Prar:tice- Vol. 10, No. 2, May 1980
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MICROSURGERY Ophthalmic surgery performed under microscopic magnification of four to forty times means that all surgical procedures can be performed with more precision and that threatening complications, such as vitreous presentation into the anterior chamber, can be recognized earlier and more effectively prevented or managed. The variety of operating microscopes available is extensive and ranges from portable table-top models that may be purchased for several hundred dollars to elaborate floor or ceiling mounted, completely automated microscope systems that cost many thousands. A good microscope system will include coaxial illumination and an oblique slit-lamp illuminator. I find that most of my surgery is done at a magnification of 8 to 10 times. In conjunction with the microscope, microsurgical ophthalmic instruments and fine suture material must be used. The use of standard ophthalmic instruments and suture precludes the advantages of using the microscope. Microsurgical techniques are not difficult to learn but require practice. When techniques are properly utilized by an experienced microsurgeon, they will result in minimal surgically-induced trauma to tissue and precise apposition of wound edges with no increase in operating time. If the surgeon has not mastered basic techniques with many hours of practice, however, results will be discouraging and the procedure prolonged. While microsurgery will make a good surgeon better, it will not make capable surgeons out of those with minimal natural talent. In essence, microsurgery enables the surgeon to do the same manipulations he would otherwise perform with more respect for the tissues, meticulous technique, and improved results.
GLAUCOMA Almost without exception, primary and secondary glaucoma in the dog and cat must be treated surgically if vision is to be maintained on a long-term basis. Topical and systemic ocular hypotensive medications are costly and have undesirable side effects. Most importantly, they are not effective in controlling intraocular pressure in the dog and cat over extended periods of time, either as a result of disease mechanisms and sensitivity and/or owner compliance. These drugs are helpful in controlling acute episodes prior to surgery and may be useful at low therapeutic levels as an adjunct to surgical procedures for long-term control of intraocular pressure and maintenance of functional vision. An occasional Poodle with open angle glaucoma and intraocular pressure of 40 to 50 mm Hg or a Cocker Spaniel with slight narrowing of the iridocorneal angel and mild elevation of intraocular pressure may be controlled with
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topical drops and/or oral carbonic anhydrase inhibitors, but these animals are the exception rather than the rule. I believe that effective pharmacologic control of glaucoma in the dog and cat has long been overemphasized and that a large number of blind or euthanatized pets attest to this fact. This is not to say that surgical procedures always provide acceptable results. Glaucoma, at best, is a challenging disease to manage and, not infrequently, intense and dedicated efforts yield discouragement and frustration. Surgical procedures will not always provide acceptable results, but I believe that if you operate early in the course of the disease you will have many more sighted patients and contented clients.
Surgical Judgment Selection of patients for glaucoma surgery is not difficult. Any patient with acute elevation of intraocular pressure greater than 50 mm Hg or chronic non-responsive deviated intraocular pressure from 30 to 50 mm Hg is a surgical candidate. Prognosis for restoration of vision is difficult to predict accurately, but impressions can be made from duration and extent of increased intraocular pressure, whether or not the globe is noticeably enlarged, and ophthalmoscopic examination. Elevation of intraocular pressure greater than 50 mm Hg over a course of three to seven days will result in irreversible damage to the retina and optic nerve. A noticeably enlarged globe and advanced fundic disease (vascular attenuation, optic atrophy and cupping, peripapillary pigmentation, and tapetal hyper-reflectivity) are unfavorable signs. Early diagnosis, then, is critical in proper management. This responsibility generally lies in the hands of the primary practitioner rather than the specialist and requires an awareness of which breeds are predisposed, a knowledge of the clinical signs of glaucoma, and a method to quantitate intraocular pressure. To practice small animal medicine and surgery without a tonometer borders on the unethical and will almost assuredly cost the practitioner the sight of several patients over a professional career. Surely this justifies the $125.00 cost of a Schi0tz tonometer and the minimal practice effort it takes to learn to use it well. Once acute glaucoma is diagnosed, intraocular pressure must be reduced as expediently as possible. In general, I administer mannitol and acetazolamide intravenously and compounds of pilocarpineepinephrine topically at hourly intervals. If intraocular pressure is reduced to less than 30 mm Hg in four hours, maintenance with oral glycerine and carbonic anhydrase inhibitors and topical drugs may be attempted. Further diagnostic tests such as tonography and gonioscopy are performed and surgery becomes a semi-elective procedure. This course of events occurs in approximately 75 per cent of patients with primary glaucoma and 50 per cent of patients with secondary glaucoma. If intraocular pressure is not reduced to less than 30 mm Hg in four hours, immediate surgical intervention is necessary.
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Surgical Techniques Many surgical procedures are utilized to manage glaucoma in human and veterinary ophthalmology, and they are divided into two general types based on their mechanisms of action. Filtering procedures, which include iridectomy, iridencleisis, cyclodialysis, goniotomy, sinusotomy, trabeculotomy, trabeculectomy, sclerotomy and sclerectomy, open primary drainage channels or provide alternate pathways for the outflow of aqueous humor. Cyclocryothermy, cryogoniotomy, and cyclodiathermy utilize thermal destruction of the ciliary body and epithelium to decrease production of aqueous humor and possibly to open outflow channels. Techniques employed in veterinary ophthalmology have generally been adaptations and modifications of procedures described for humans. Significant species differences in ocular anatomy, physiology, response to the disease process and corrective surgery, and the nature of both the disease and the patient make glaucoma more difficult to control surgically in the dog than in humans. Filtering procedures are approximately 80 per cent effective in humans. 8 • 10 In the dog, success rates of satisfactory, long-term control of intraocular pressure ranges from 30 to 50 per cent, primarily due to fibrosis and closure of surgically-produced outflow pathways.L 2 • 6, 9, u, 13 Posterior sclerotomy was one of the earliest techniques utilized in the surgical management of glaucoma in humans, and its results on a limited number of cases of canine glaucoma have been described in the veterinary literature. 2 This technique involves establishing direct communication between the subcortiunctival space and the vitreous cavity. Its potential complications and unphysiologic basis made it less desirable than those filtering procedures that allow direct drainage of aqueous humor. Iridencleisis is technically not difficult, but success rates are low owing to fibrosis and closure of the filtering area. Silastic implants have been used to maintain drainage of aqueous humor with inconsistent results. 13 Removal of scleral tissue with or without cautery to prevent closure of trans-scleral drainage pathways has been described. 8 • 10 Bedford reported his results with cyclodialysis (which provides a supraciliary communication through the sclera between the anterior chamber and the suprachoroidal and subconjunctival spaces); iridencleisis; thermal sclerectomy and iridectomy; cyclodiathermy; and corneoscleral trephination with a peripheral iridectomy. The latter technique provided the most consistent results. 1 Vainisi described a technique developed by Wyman that combined posterior sclerectomy, cyclodialysis, or iridocyclectomy.1 1 Our experience with this procedure was unsatisfactory because of intraocular hemorrhage and inflammation associated with the iridocyclectomy. The procedure was modified to include a transscleral iridencleisis through the excised sclera and has provided more consistent, positive results than iridencleisis, cyclodialysis, and trabe-
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culectomy in the dog (Fig. 1). The results of the technique on nine eyes were reported in 1977, and since that time the operation has been performed on an additional 24 eyes. 11 Success based on maintenance of a normotensive eye without hypotensive medication for a minimum of six months was observed in 22 of 33 eyes, or 67 per cent (Fig. 2). Reoperation was required on two of these 22 eyes four weeks after the primary procedure. Of the 11 failures, three were cases of glaucoma secondary to inflammation.
Chronic Glaucoma Cosmetic surgery may be performed on blind enlarged globes. Enucleation is an effective but not always acceptable alternative to an owner. Vigorous cyclocryotherapy will reduce intraocular pressure in approximately 7 5 per cent of cases, but the globe may remian enlarged in spite of lowered intraocular pressure. Filtering procedures have the same disadvantage. The insertion of an intraocular prosthesis provides excellent results, the only disadvantage being the 4 to 12 week postoperative course of therapy necessary to control the inflammatory response.12
CATARACTS Cataracts are among the most common ocular diseases seen in my practice, with one out of five referrals presented with cataracts or suspicion of cataracts. While not all of these patients are candidates for surgery, cataract extraction is among the most successful and most rewarding procedures the veterinary ophthalmologist can perform. Aphakic dogs and cats function quite well without correction and compensate adequately for the surgically-induced hyperopia.
Selection of Patients The objective of cataract surgery is to restore functional vtston. Because of the ability of the dog and cat to adjust and compensate for incomplete lens opacity and/or monocular blindness, functional vision is not significantly impaired until bilateral cataracts approach maturity. The owner of the pet is the best judge of when surgery should be contemplated. When the animal is bumping into objects constantly and is unable to maintain its normal lifestyle and personality, cataract extraction should be considered. Of prime importance is to establish the integrity of the retina and the central visual pathways. It is discouraging to both client and surgeon to have a technically successful procedure fail to restore vision because of concurrent disease of the retina or optic nerve, or both. To evaluate the neural visual components history, ophthalmoscopy, visual function tests, and electrophysiology should be used in combination.
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B
Figure 1. A, Following routine preparation for intraocular surgery (the dog is shown undraped for maximum orientation), a lid speculum is placed and a lateral canthotomy performed. B, A wide, limbal-based conjunctival flap is prepared by incising through the conjunctiva and Tenon's capsule about I em from the limbus and C, combining blunt and sharp dissection to separate these tissues from the sclera to mobilize the flap. D, A rectangular block of sclera, approximately 5 by 2 mm is outlined, the posterior border of which is approxilnately 5 mm from the limbus.
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Figure l. Continued. E, The sclera is incised through its entire thickness. The heavily pigmented tissue of the uvea serves as a guide to the proper depth. Hemorrhage is controlled with low-temperature cautery and irrigation. The sclera is easily separated from the uveal tissue and removed en bloc. A cyclodialysis spatula is passed through the supraciliary space into the anterior chamber. Resistance to passage of the spatula is minimal and aqueous humor will flow through the filtration pathway when the anterior chamber is entered. F, A broad cyclodialysis is performed. G, A blunt iris hook is passed through the dialysis into the anterior chamber and the pupillary margin of the iris is hooked. H, The iris is gently exteriorized. I, The iris is grasped with two pairs of iris forceps at the pupillary margin and, using gentle traction, torn to its base. Hemorrhage is minimal.], The iris pillars are then sutured to the episclera with simple interrupted sutures of 7-0 polyglactin 910 with a swaged-on spatula needle. K, The anterior chamber is reformed with an air bubble and the conjunctiva closed with a simple interrupted pattern of the same material. Note the keyhole pupil. The canthotomy is sutured with a routine two-layer closure. (From Peiffer, R. L., et al.: Combined posterior sclerotomy, cyclodialysis and trans-scleral iridencleisis in the management of primary glaucoma. Canine Pract., 4:54-61, 1977, with permission.)
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Figure 2. A, Acute open-angle glaucoma in the right eye of a four year old rnale St. Bernard. The pupil was dilated and nonresponsive to light, the episcleral and conjunct.ival blood vessels were congested, a nd the cornea was edematous. Intraocular pressure was 70 mm Tlg (Mackay-Marg), and tonographic facility of o utflow was 0 .06 JLI per min per nun Hg. B, Six months after posterior sclerotomy, cyclodialysis, and trans-scleral ir idcnclcisis, the eye was visual. !\me the keyhole pupil. Intraocular pressure was 24 mm Hg. and tonographic facility of outflow was O.'lG JLI per min per nun Hg.
The inherited retinal dege nerations, primarily progressive retinal atroph y and central progressive retinal atrophy, are increasing in incidence and are the primary reason for failure in technically successful cataract surgery. Owing to mechanisms that are poorly understood. animals with inherited or inflammatory retinal degeneration are likely to develop associated cataracts. The problem is complicated by the fact that breeds with a large incidence of inherited retinal degene ration, such as the miniature and toy Poodle and the Irish Setter, also have priman genetic cataracts unassociated with retinal disease. Pupillary responses are unreliable as the sole m ethod of assessing peripheral and central visual potential. The majority of cataract patients should demonstrate full, crisp, direct and consensual responses to a bright focal light source in a darkened room in the presence of even th e densest catar act. With some variability, th ese responses will persist in the presence of well-advanced retinal degeneration. The ganglion cell nerve fibers that mediate this reflex are distinct from the usual fibers that extend to the lateral geniculate body, a nd thus provide no information as to the status of the optic radiation and visual cortex . Iris atrophy, occasionally observed in miniature Poodles, and lesions invoh·ing the third cranial nerve may result in absence of pupillary reflexes in the presence of intact visual components. Thus, while it is always reassuring to observe normal pupillary reflexes, they provide minimal definitive information.
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History is helpful in proportion to the owner's ability to be aware of changes in the animal's appearance or behavior. Without exception, visual and ophthalmoscopic changes in progressive retinal atrophy and central progressive retinal atrophy always precede associated cataract development. Thus, a reliable history that visual impairment accompanied or followed rather than preceded noticeable cataract development speaks in favor of an intact visual system. If progressive retinal atrophy is present, a history of initial nyctalopia (night blindness) may be elicited. Critical ophthalmoscopy performed while the cataracts are still immature, rather than waiting until the fundus cannot be critically examined, is of benefit to all involved. Ophthalmoscopy prior to maturity of the cataract approaches 100 per cent reliability. The rare dog with genetic tendencies to develop both progressive retinal atrophy and primary cataracts will provide an occasional disappointment if the retinal atrophy develops subsequent to the primary cataract. Ability to negotiate an obstacle course under photopic and scotopic conditions may be of value in those cases in which fundus reflex can be obtained but lens changes prohibit critical fundic examination. As a general rule of thumb, if a fundic reflex can be obtained, some vision should be present and should change minimally with alterations in ambient light if the retina is healthy. Electrophysiology provides the most reliable criteria for critical evaluation. An electroretinogram should ideally be performed in all patients with cataracts; in those breeds with predisposition to progressive retinal atrophy, electoretinography is a prerequisite to cataract surgery. In a retrospective study of 54 miniature Poodles presented with cataracts, 42 (78 per cent) had associated progressive retinal atrophy as determined by ophthalmoscopy (23 dogs) or electroretinography (19). The surgeon who attempts cataract surgery without an electroretinogram will have fewer successes than will a surgeon who utilizes the test. If history, pupillary responses, and/or neurologic findings suggest the possibility of a defect in the central visual system, evaluation of visually evoked response may be considered in addition to electroretinography. Ultrasonography may be of value in the detection of retinal detachments. A large percentage of young dogs (between one and three years) with inherited developmental cataracts (seen most frequently in the Afghan Hound, American Cocker Spaniel, Irish Setter, and miniature and toy Poodle) will undergo spontaneous resorption of their cataracts. Active resorption, indicated by mild lens-induced uveitis and an irregular lens capsule, is an indication for temporization. While these liquified cataracts may be aspirated, approximately 60 per cent will resorb to the extent that cataract surgery is unnecessary. I prefer to manage these animals with topical application of 1 per cent atropine sulfate to enhance peripheral vision and corticosteroids to temper the uveitis. They should
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be examined monthly, and cataract surgery should be recommended only when active resorption has subsided without restoration of visual function. Cataract surgery is an elective procedure; thorough multisystem evaluation should be performed prior to surgery. Concurrent related disease (such as diabetes mellitus) or unrelated diseases (such as renal decompensation or heartworm disease) should be identified and adequately controlled. In older patients with systemic disease who have adjusted reasonably well to their visual impairment, the complications of anesthesia should be weighed against the benefits of vision. Philosophies of Cataract Surgery With rare exceptions, I perform cataract surgery on one eye only, because of the ability of a pet to function well with monocular vision, lower cost to the owner, and the reduced insult to the patient in terms of anesthesia time and postoperative discomfort. It also is reassuring to know that, in case of failure, one has an alternative to offer the client in terms of operation on the fellow eye. Of course, both cataracts may be removed at one or two sittings at the owner's insistence or if acute visual function is necessary, as in retrievers or obedience dogs. The procedure for cataract removal, when performed with appropriate preoperative treatment and instrumentation, is not difficult. However, the incidence of intraoperative or postoperative complications is high compared to those for other procedures, and these complications frequently have disastrous effects on the visual outcome. With experience and greater understanding of ocular anatomy, physiology, and pathology, the recognition and management of complications are facilitated with resultant improved success. The results of my series of cataract extractions reflects a progressive increase in success rate commensurate with experience and refinement of technique (Table I). These data support the concept that results are most likely to be rewarding in the hands of an experienced cataract surgeon. Routine Procedures and Techniques Adequate preoperative preparation will mrmmize intraoperative and postoperative complications. The canine eye responds to even meticulous surgery with intraoperative constriction of the pupil, which necessitates increased intraocular manipulation which hampers exposure and intensifies postoperative inflammation. I have found that treatment with oral corticosteroids and aspirin and topical antibiotic-corticosteroid solutions for two days prior to surgery will minimize these problems. Prostaglandins play a role in both of these phenomena, and aspirin, which inhibits synthesis of prostaglandin, provides results superior to the use of corticosteroids alone. Planned extracapsular extraction is the rule. The posterior capsule and the hyaloid membrane of the anterior vitreous are intimately
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Table 1. Outcome of Surgical Procedures for Cataracts Performed by the Author YEAR
NUMBER OF EYES OPERATED
1974 1975 1976 1977 1978 1979 Total
6 24 29 31 46 83 219
NUMBER OF EYES SUCCESSFUL*(%)
3 17 23 26 39 76 184
(50) (71) (79) (84) (85) (92) (84)
*Success was defined as adequate visual function (as determined by owner), the ability to negotiate an obstacle course, and a normal fundus four weeks after surgery.
associated, and intracapsular extraction or tearing of the posterior capsule is invariably associated with vitreous presentation. While not always disastrous, vitreous presentation adds an undesirable challenge that frequently precipitates other complications. In addition, enzymatic dissolution of the zonules is unreliable in the dog, and intracapsular extraction results in excessive traction on the ciliary processes. Stable, deep anesthesia is important. Under light anesthesia, the animal may move when the iris is touched and intraocular pressure may increase owing to extraocular muscle contraction. The stability of anesthesia induced with methoxyflurane is preferred over that induced with fluothane, but the usually quieter recovery from fluothane anesthesia reduces the likelihood of trauma inflicted by thrashing about during recovery. The positioning of the patient is crucial to the success of the procedure. The muzzle should be elevated to enable the surgeon to visualize the iris and lens surface in a horizontal plane. A traction suture of 4-0 silk placed through the conjunctiva under the insertion of the superior uveitis muscle may be necessary to achieve this end. The incision, which also is crucial, should be a minimum of 180°. It is difficult to accurately predict lens size prior to surgery, and attempting to deliver an intumescent lens through a small incision will result in undue trauma and residual lens material in the anterior chamber. I prefer to utilize a limbal-based flap because ( 1) the incision heals more rapidly than a clear corneal incision, (2) corneal scarring at the incision site is minimized, (3) accurate apposition of the surgical wound margin is facilitated, (4) if corneal dehiscence occurs, the intraocular contents are not exposed to the environment, and (5) adsorbable suture knots may be covered by the flap so that postoperative irritation does not occur. These advantages more than offset the additional three to five minutes it takes to dissect the flap and control the minimal hemorrhage associated with the corneoscleral incision. Preplaced sutures hinder exposure and manage-
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ability, and I prefer to have unobstructed access to the anterior segment should complications arise. Capsulectomy is performed with a cryoprobe or a capsule forceps. While it is easier to obtain a good equatorial capsular tear with t he former, the incidence of posterior capsule disruption increases. I prefer to grasp the capsule as superficially and as widely as the dilated pupil will allow without compromising visu alization of the forceps teeth. The forceps are closed and elevated minutely but sha rply. The lens cortex and nucleus a re removed in toto; liquified or residual cortex m ay be gently irrigated or aspirated with a blunt needle. If a pupil of less than 3 mm has resulted, sphincter iridectomy is performed. This is the exceptional circumstance, h owever. Closure is achieved with 7-0 polyglactin 910 in a simple interrupted or with 9-0 nylon in a continuous "boot lace" pattern. Postoperative care is critical and is titered to temper inflammation and to maintain pupil size. Triamcinolone acetonide (0.5 ml) is administered subconjunctivally in the inferior quadrants. Oral corticosteroids are continued for three to five days . Topical I per cent atropine sulfate, 10 per ce nt phenylephrine, and antibiotic-corticosteroid solutions are applied every two hours daily for the first three days, which is the critical period for control of pupillary size. Bandages are not utilized as the surgery is tolerated remarkably well. Atropine a nd topical corticosteroids are continued until the inflammation has subsided, usually at four weeks. The patient is re-examined at 2, 4, 12, and 24 weeks and 1 year after surgery.
Figure 3. Pupilla ry mem brane with a small , occluded, u p d rawn pupil six months after extracapsula r extraction in a fi ve year old miniature Poodle.
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Figure 4. Eight weeks after extracapsular extraction with vitreous Joss and anterior vitrectomy in a two year old miniature Poodle. A, \'\Thile the ant.erior segme nt appears satisfactory (note the corneal scar at the incision site), a traction detachment of the retina with a large nasal periphera l dialysis has occurred (B).
Complications
Intraoperative complications include miosis, which can be largely prevented by adequate premedication and minimal intraocular manipulations; h e morrhage from the ciliary process while performing the capsulectomy or from the sphincterotomy incision if one is necessary; vitreous presentation; and posterior capsular opacity. A small pupil is managed by sphincterotomy and postoperative medication. Ciliary process hemorrhage occurs in only 2 per cent of the cases, iris h emorrhage will occur in approximately 20 per cent of animals su~jected to three or four quadrant sphincterotomy. In both cases, bleeding is minimal and self-limited. T he vessels are encouraged to clot on their own by delaying manipulations for three to five minutes. The blood can be irrigated or gently teased from the a nterior chamber. A small amount of residual hyphema, while not desirable, is resorbed over two to three wee ks without adverse consequences. Vitreous presentation occurred in 15 per cent (33 of 219) of planned extracapsular extractions and in all a nimals with incomplete cataract resorption (6 dogs). Vitreous presentation is managed by a n anterior chamber air bubble if the h yaloid me mbrane is intact. Unfortunately, the h yaloid m embra ne usually ruptures a nd the vitreous must be removed from the anterior chamber to reduce the likelihood of disastrous sequelae. I perform radical anterior vitrectomy with cellulose sponges, excising the gel vitreous as close to the plane of th e iris as possible, or with a disposable vitreophage (Kaufman Vitrector II, Concept, Clearwater, Florida) .5 The vitreophage is preferred because it minimizes in-
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traocular manipulation and traction in the retina. Vitrectomy is performed until the anterior chamber is completely free of vitreous and the iris plane assumes a concave appearance. Administration of preoperative mannitol does not appear to influence the incidence of vitreous presentation in the normotensive dog, with one of 12 dogs in each group developing this complication in a prospective study comparing treated and nontreated patients. In approximately 2 per cent of patients with cataracts, the posterior capsule will be translucent or opaque at the time of surgery. If the fundus cannot be visualized on the table, the capsule should be incised and/or removed. Except for a 3 mm superior opening, the incision is closed and the anterior chamber reformed with an air bubble; the posterior capsule is then incised with a hooked 23 gauge needle. The linear incision will usually widen to prevent unimpaired observation of the posterior pole. If it does not, the incised margins are grasped and the capsule teased away from the hyaloid membrane Postoperative complications in the author's series included pupillary membrane without (22 of 35) or with (7) pupillary occlusion and secondary glaucoma, and retinal detachment (6). Of the 35 failures, 20 were associated with vitreous presentation. Those not associated with vitreous presentation demonstrated intense postoperative inflammation related to residual lens material and/or excessive intraocualr manipulation. While focal opacification of the posterior capsule is not uncommon, and, if a pupil is maintained, good functional vision will persist around the secondary cataract. Coreoplasty may be performed as a salvage procedure in dogs with pupillary membranes with or without iris bombe. Vision was restored in two of seven eyes operated by the author. Presently available suctioncutting machines manipulated through the pars plana offer promise in the management of this common complication. My experiences are similar to those of Startup 5 and Magrane; 4 increased success rates may be the result of improved technology and the relatively short-term follow-up for the described series. For example, retinal detachment, may occur several months to years following surgery. Phakoemulsification
Because of the tendency of the canine ms to constrict during surgery and the density of the majority of canine cataracts, especially the nucleus, the sonication and aspiration of cataractous lenses with the instruments currently available is, in my opinion, less rewarding than the extracapsular technique described above. Intraocular Lenses
The use of intraocular plastic lenses is gaining popularity in human ophthalmology. These lenses may be clipped or sutured to the iris or
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inserted into the anterior chamber or lens capsule bag. Because of the marked inflammatory response of the canine eye, significant differences in anterior chamber and pupil size, and the ability of our patients to function well as aphakes, their routine use is not recommended.
LENS DISLOCATION Dislocation of the lens in the dog is almost invariably associated with secondary glaucoma. The mechanisms of the glaucoma are poorly defined and may involve narrowing of the iridocorneal angle related to anterior movement of the vitreous, pupillary block by the vitreous and/or the dislocated lens or both. Regardless of the cause, prevention or effective management of the glaucoma demands removal of the lens, ideally prior to the onset of glaucoma. Intracapsular cryoextraction is the procedure of choice. To enhance exposure, I prefer a broad (up to 240° with posterior luxation) corneoscleral incision initiated with a keratome and extended with corneoscleral scissors. All vitreous that is encountered sh
ACKNOWLEDGMENT
The author gratefully acknowledges the talents of Michael Schenk, the veterinary medical illustrator of the University of Minnesota College of Veterinary Medicine, for providing the line drawings.
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REFERENCES 1. Bedford, P. G.: The surgical treatment of canine glaucoma. ]. Small Anim. Pract., 18:713-730, 1977. 2. Brightman, A. H., Magrane, W. F., Huff, R. W., eta!.: Intraocular prosthesis in the dog.]. A. A. H. A., 13:481, 1977. 3. Kolker, A. E., and Hetherington, J.: Becker-Shaffers' Diagnosis and Therapy of the Glaucomas. St. Louis, C. V. Mosby Co., 1970. 4. Magrane, W. G.: Canine Ophthalmology. Edition 3. Philadelphia, Lea and Febiger, 1977. 5. Magrane, W. G.: Cataract extraction: A follow-up study (439 cases).]. Small Anim. Pract., 10:545-553, 1969. 6. Peiffer, R. L., Jr., Gwin, R. M., Gelatt, K. N., eta!.: Combined posterior sclerectomy, Lyclodialysis and trans-scleral iridencleisis in the management of primary glaucoma. Canine Pract., 4:54-61, 1977. 7. Peiffer, R. L., and Weintraub, B. A.: Clinical and histopathologic effects oflensectomy and anterior vitrectomy in the canine eye.]. A. A. H. A., 15:421--432, 1979. 8. Scheie, H. G.: Peripheral iridectomy with scleral cautery for glaucoma. Am. J. Ophthalmol., 45:220-229, 1958. 9. Stack, W. R.: Treatment of glaucoma: Posterior sclerotomy. J.A. V.M.A., 136:453--455, 1960. 10. Startup, F. G.: Cataract surgery in the dog. ]. Small Anim. Pract., 10:457--460, 1969. 11. Vainisi, S. J.: The diagnosis and therapy of glaucoma. VET. CLIN. NoRTH AM., 3:453--465, 1973. 12. Vierheller, R. C.: Surgery for glaucoma: An analysis of technics. Mod. Vet. Pract., 49:46-68, 1968. 13. Vierheller, R. C.: Surgical treatment of glaucoma: Reappraisal of recommended operative techniques in veterinary practice. Proceedings Am. Soc. Vet. Ophthal., pp. 20-27, 1967. Department of Ophthalmology School of Medicine University of North Carolina Chapel Hill, North Carolina 27514