Netherlands Ophthalmological Society, 167th Meeting, Vlissingen 1972 Ophthalmologica, Basel 171: 296-305 (1975)
Cataract Extraction in the Dog J.
A. O o st e r h u is and I. G. J eltes
Ophthalmological Department of the University Hospital, Leyden
The first lens extraction in the dog was probably carried out by M oller in 1886. Intracapsular lens extraction was first described by B a r t h o l o m e w in 1936. However, reclination of the lens into the vitreous body has long been considered to be a useful method, since it was still advocated by S c h l o t t h a u e r in 1939 and M eans in 1942. Fairly recently, even the ratio nale of cataract extraction in the dog was called in question. Thus, F o r m ston stated in 1952 that 'lens extraction is fraught with difficulties and is speculative’ and that it was ‘doubtful if justifiable in the dog when the desired result cannot always be achieved and when the patient has such little respect for optical aids’. M a r k o w it z wrote in 1954 that ‘there is very little positive indication for performing the operation, unless it be for cos metic or sentimental reasons, or in cases where the economic value of the animal is particularly high.’ However, now that the results have gradually become less disappoint ing, operations for removal of the lens are no longer rejected, in spite of the fact that the success rate is still far lower than that of cataract extrac tion in man. This is clear from the analysis of 171 lens extractions in dogs performed by K n ig h t [1962] during the period 1958-1961 and of 252 intracapsular operations performed over a period of 17 years by St a r t u p [1967]. The figures presented below are seen to compare very unfavour ably with the results obtained in humans:
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Introduction
OOSTERHUIS/J ELTES
Knight, 1962 Startup, 1967
297
Number of eyes
Results, °/o good
fair
failure
171 252
26 22
24 28
50 50
Better results are claimed M agran e [1969], who had a success rate of 80 o/o in 397 extracapsular lens extractions versus only 44 °/o good results in 22 intracapsular extractions. Further details and a review of the liter ature can be found in the excellent articles of Sta r tu p [1967], The relatively small number of publications on cataract extraction in the dog as compared with those on lens extraction in man suggests that only a limited number of veterinary surgeons have acquired the skill needed for the difficult technique in the dog. Veterinary surgeons have in the past no doubt been discouraged by poor results. These may be attributed partly to unsatisfactory anaesthesia and unavailability of the expensive instruments for eye surgery, but above all to the fact that for lens extraction in the dog to be successful, much technical skill and ex perience in intraocular surgery is required and these cannot be gained by veterinary surgeons who only occasionally have the opportunity to operate on cataracts in dogs. Ophthalmic surgeons have developed this skill by operating on human patients, but it must be stressed that operations per formed by them on dogs are bound to be unsuccessful if they use the same technique as in humans. Moreover, they do not have sufficient knowledge of the pre- and post-operative care and anaesthesia of the animal. It is therefore our opinion, based on personal experience, that except in large veterinary centres where lens extractions in the dog are carried out regularly, satisfactory results can only be obtained by a very close co operation between veterinary and eye surgeons. This paper deals with our own experience of cataract extraction in the dog.
Cataract extraction is undoubtedly more difficult in the dog than in man. M agrane [1965], the most experienced veterinary surgeon in this field, states that: ‘Those who have performed intraocular surgery almost invariably have wisely solicited the aid of an ophthalmologist for their
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The Odds
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initial attempts. It is then that both the veterinarian and the medical doctor learn that the dog’s eye presents a more difficult surgical field than does the human eye.’ However, it is not sufficient to be an accomplished surgeon. A good understanding of the macroscopic and microscopic anatomy and the physiology of the dog’s eye is the first requisite. Without this knowledge, lens extractions in the dog, even when properly executed, are doomed to be unsuccessful. Thus, when one of the techniques com monly accepted in human cataract surgery is employed in the dog, the surgeon, even when prepared to spend the unusual amount of time needed for this procedure in the dog, will be constantly faced with failures. There fore, the difference in technique between man and dog will be stressed in this paper. The mode of operation described below can also be used for removing the (sub)luxated lens from the anterior chamber of the eye. It is simpler in that intracapsular extraction can be performed more easily because the suspension of the lens is more or less loosened by degeneration of the zonular fibres. On the other hand, some vitreous loss is almost unavoid able, especially when complicating glaucoma has already set in before operation. Several days of cloudiness of the cornea in the glaucomatous state may damage the cornea to such an extent that after extraction of the lens it does not regain its clarity even when tension in the eye returns to normal.
One should beware of a faulty selection of cases as otherwise success ful surgical treatment may not be followed by the expected restoration of vision to the dog. There are some strict criteria for accepting canine cataract patients for surgery. (1) The behaviour of the dog must clearly show that he cannot nego tiate an obstacle course and cannot get along any more in unfamiliar sur roundings. The cataract must be diffuse and very dense. (2) It has been observed that even when there is a fairly dense cataract in both eyes, the dog retains a certain degree of vision. Therefore, if in a dog without visual orientation the opacification of both lenses is not dense, one should look for other causes of blindness, e.g. retinal degeneration. (3) Retinal degeneration should be minimal or absent. Cataract may be of secondary nature, associated with progressive retinal atrophy, which.
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unfortunately, is regularly encountered at an early age in several breeds such as the Miniature and the Toy Poodle, the Labrador Retriever and the Cocker Spaniel. When cataract is dense in both eyes, observation of the pupillary reflex to light as regards promptness of the reaction and the degree of narrowing of the pupil is essential. A weak reflex is indicative of possible degenerative retinal changes, which are almost certainly intense when the pupils are wide and not responsive to light. The ophthalmic examination also includes measurement of the intra ocular pressure, since glaucoma endangers the surgical outcome. One should not tamper with the eyes more than one can help, e.g. to deter mine the patency of the lacrimal ducts or to make bacterial cultures of conjunctival swabs. We have found this to be unnecessary when epiphora is absent and when broad spectrum antibiotic ointment is applied directly after the operation. Apart from an ophthalmic examination a thorough general examina tion should be made to make sure that the general physical condition of the dog allows a long operation. As this is not the task of the ophthalmic surgeon but of the cooperating veterinary surgeon, it will not be discussed in detail. Anaesthesia The operation should be carried out under general anaesthesia; the use of fluothane is to be preferred, reducing as it does the intraocular pres sure and - consequently - the risk of vitreous loss after extraction of the lens. This effect of fluothane, however, is only obtained when anaesthesia is rather deep. We have found a retrobulbar injection to be strongly con traindicated: in the small orbit of the dog, in which the eye occupies most of the space, the injection invariably leads to an increase in pressure from behind and thus greatly promotes the loss of vitreous during lens ex traction.
The dog is placed on its side on the operating table. The position of the head should be such that the optical axis of the eye to be operated on is more or less vertical. To this end the nose generally has to be elevated by means of sand bags or foamed plastic. The tracheal tube must be kept out of the surgical field.
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The area around the eye is clipped as close to the skin as possible and the eye lashes are cut when the dog is under anaesthesia and not earlier, so that one can do this properly without the risk of damaging the eye should the dog happen to move its head. Subsequently the lids and sur rounding skin are well cleansed with a disinfectant fluid, at the same time removing residual bits of cut hairs. Since mydriasis is essential for delivery of the lens, atropine is in stilled into the conjunctival sack before starting anaesthesia; if the mydria tic effect is insufficient, the instillation is repeated and combined with instillation of a 10-percent sympathico-mimetic phenylephrine solution. We arc not in favour of atropine medication for several days prior to the operation [Startup, 1967] because we want to regulate the size of the pupil prior to and during the operation to not much wider than medium size, in order to perform good iridotomies and to restrict the risk of loss of vitreous and of incarceration of the iris into the corneal wound. The dog is then covered with sterile drapes, leaving only the area of palpebral fissure and, on the temporal side, the area for the canthotomv uncovered. A canthotomy is performed, which as a rule has to be rather large in order to obtain good access to the eye and to avoid any pressure of the eyelids on the eye. Haemorrhage can be minimized by compressing the cutting area with haemostatic forceps for about 30 sec before cutting. The lid margins and edges of the canthotomy are then sutured to the margin of the opening in the sterile drape, taking care that there is no traction of the drape on the eyelids. If necessary, the opening in the sterile drape is enlarged. The sutures are not cut; haemostatic clamps are fastened to their ends and their weight is used to keep the eyelids open. We prefer this to the use of an eye speculum, which, especially when not positioned properly, may increase the intraocular pressure and. moreover, does not fit very well when a large canthotomy has been made. In the same way the nictitating membrane is kept out of the way by means of a suture with a haemostatic clamp attached to its end.
It is beyond the scope of this paper to discuss the many variations employed in cataract extraction in the dog; for this the interested reader should consult the publications mentioned in the list of references. We
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shall only describe the technique which in our hands has proved to give satisfactory results. This by no means excludes the possibility of modifica tions giving as favourable, if not better results. After bringing the dog into a suitable position, performing canthotomy and obtaining suitable retraction of the lids and the nictitating membrane, as described above, one may find access to the inner eye still difficult. Therefore, three traction sutures are made through the conjunctiva and sclera along the upper half of the limbus, the nasally and temporally located sutures lying in a more or less diametrical position. The traction sutures are very important for gently moving and/or rotating the eye with out elevating the intraocular pressure when making an incision or suturing the relatively large corneal incision in the small orbital aperture. To the end of the sutures small clamps (bulldogs) are fastened (the small type arterial clamps are too heavy and may cause an increase in intraocular pressure). An incision of about 180 is then made 1.5 mm centrally of the limbus in the superior half of the cornea and about two-thirds of the thickness of the cornea deep. At first we used to make - as in the human eye - a limbus-based conjunctival flap and a corneo-scleral incision, but we abandoned this technique, since cutting into the limbal vascular network resulted in two complications. First, haemorrhages may develop during surgery or in the first few days after the operation [D arraspen et al., 1961; Startup. 1967], which may be fatal [Smythe, 1958], Secondly, it was our experience that damage to the dense limbal vasculature inter fered with a proper nutrition of the cornea, thus resulting in a greater swelling and cloudiness of the cornea in the first week after the operation than after a corneal incision. The cornea sometimes even failed to clear at all and permanent scarring impeded recuperation of good vision. The corneal incision should not be made less than 1.5 mm from the limbus, so as to restrict the development of goniosynechiae and to avoid damage to the limbal vessels by suturing. Two virgin silk sutures are then placed in the corneal wound dividing the length of the incision into about three equal parts. The anterior chamber is opened, using, as for the initial corneal incision, an ordinary razor blade fragment or a Pierce-Hoskin pre-formed razor blade fragment. With Castroviejo scissors the incision is enlarged, the pre-formed incision guiding the scissors and restricting squashing of the corneal tissue between the scissor blades. We then perform several iridotomies using Vannas scissors, about one
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Cataract Extraction in the Dog
OOSTF.RHUIS/J El. ITS
in each quadrant, taking care to cut only the sphincter part of the iris. Thus, the pupil, being slightly dilated when the anterior chamber is opened, is enlarged to such an extent that it will not interfere with the extraction of the lens, which is much larger than the human lens. Another major advantage of the iridotomies is that post-operative con striction of the pupil is prevented. This complication, which can lead to pupillary obstruction, development of a membrane in the pupil, iris bombans and glaucoma, is often the cause of failure in the post-operative period, even when strong mydriatics are given conscientiously [St a r t u p . 19671. The importance of this complication is apparent from the follow-up study of M agrank [1969] after 429 cataract extractions in the dog: of the 77 ultimate failures 32 were mainly due to iris bombans and/or pupillary seclusion, complicated by glaucoma in 16 eyes. After extracapsular extrac tion the wide pupil guarantees good accessibility of the lens material to the aqueous, promoting dissolution of the residual lens material. It is a well-known fact that an iridectomy should never be performed, as this inevitably leads to excessive and prolonged bleeding. Therefore, M a c r a n e [1969] only performs an iridectomy if more working room is needed for the extraction and for this purpose he uses an electroscalpel in order to restrict complicating haemorrhages. In iridotomy, however, bleed ing is absent or minimal as long as cutting into the thick, highly vascular basal part of the iris is carefully avoided and only the thin, not very vas cular sphincter part of the iris is cut. The persistently rather large and somewhat irregular pupil is not cosmetically disturbing and, to our sur prise, has been found not to cause photophobia in the dog. After the iridotomies have been made the actual lens extraction is per formed. For both intracapsular and extracapsular extraction cryo-extraction is to be preferred to any other technique. As the zonular fibres in the dog are often difficult to break, freezing of the cryode not only to the lens capsule but also to the underlying lens substance is necessary to produce a solidification deep enough to allow lens extraction without capsular rupture. It is well known that u-chymotrypsin in a concentration of 1:5,000, as used successfully in human eyes, will not yield a lytic action of the zonular fibres in the dog. By using higher concentrations of up to 1:500 complete zonulolysis may be obtained in the dog, but according to Startup [1967] this may be responsible for post-operative pupillary ad hesions and glaucoma which he observed in these cases. «-Chymotrypsin in a concentration of 1:2,500 can be used safely, but it weakens the zonular fibres only to some extent and does not completely eliminate
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302
303
the necessity of instrumental zonulotomy in order to avoid rupture of the lens capsule. There is no consensus of opinion as to whether intracapsular or extracapsular extraction of the lens should be preferred. M agrane [ 19691 greatly favours extracapsular extraction since in his series twice as many were successful as compared with the intracapsular ones. However, with due attention to some technical details, the intracapsular extraction will be a rather safe procedure. The main problem is vitreous loss; in extracap sular extraction of the lens its occurrence is very much restricted by the fact that the posterior capsule is left intact. In intracapsular extraction there is no barrier left between vitreous and anterior chamber, since in the dog the hyaloid membrane adheres firmly to the posterior surface of the lens. Therefore, the vitreous adhering to the lens must be cut off with fine scissors, e.g. De Wecker's spring scissors, before the lens is delivered. At this moment the danger of vitreous loss is greatest. However, with proper precautions as previously described and especially with a relatively deep fluothane anaesthesia, inducing complete relaxation of the eye, the risk of loss of vitreous - the main complication in the series of M agrane [1969] - is reduced considerably, making intracapsular extraction a re liable method. In less experienced hands the extracapsular method is still the safest procedure. Care must be taken to remove the relatively strong anterior capsule completely. We freeze the capsule at its centre to the cryoextractor and then cut it around the tip of the cryo-extractor as periph erally as the pupil allows, almost along the equator. This can be done easily when multiple iridotomies have been made. Like a lid the anterior capsule is then lifted from the lens. Subsequently, the lenticular mass is easily removed and the subcapsular remnants of the lenticular cortex are washed out. This has to be done carefully, since lenticular debris is more toxic in the dog than in man and, if not properly removed, may even lead to failure. After the lens has been delivered, the corneal incision is closed by means of the two pre-placed sutures, taking care that incarceration of vitreous into the wound is avoided. If this occurs, the vitreous should be removed in the same way as in human eye surgery. Subsequently, air is introduced into the anterior chamber, restoring the eye to its original shape and preventing incarceration of the iris during suturing of the corneal wound. For closure of the corneal wound we have long been using another
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8 to 10 virgin silk sutures. However, we observed that, in contrast to what usually happens in man, virgin silk gave rise to a rather intense granu lomatous reaction in the dog’s cornea at the end of the first week after operation with ingrowth of vessels from the limbal area to the wound site and cloudiness of the superior half of the cornea. These signs could be relieved by removing the corneal sutures, which we did approximately on the 10th day. We now prefer to close the corneal wound with a running 9/0 perlon atraumatic suture; this material is finer and more inert and in initial results did not produce the side effects just mentioned. Inadequate suturing of the wound may easily lead to iris prolapse |S t a r t u p , 1967],
Adequate post-operative care is of paramount importance. Self-mutila tion, which may even result in the ultimate loss of the eye, is an ever present hazard. Due to lack of facilities we do not hospitalize the patients but give detailed instructions to the owners how to take care of their dogs. The operated eye is bandaged in a special way. Firstly, we wind sur gical tape around neck and head without covering the eye. A convex eye shield is then placed over the eye and fastened with short strips of surgical tape which can easily be loosened, even several times a day. for inspection of the eye or for the application of eye drops and/or ointment. A thick, soft foamed plastic ’collar' protects the eye further from any attempts of the dog to rub it. Antibiotics are given parenterally for 5 days after the operation. Daily inspection is necessary in the first post-operative week. Constric tion of the pupil, posterior synechiac and iris bombé have not been ob served any more since multiple iridotomies were incorporated in the technique. Atropine eye drops are instilled several times a day, steroid eye drops are given when, mostly on approximately the 5th day, a haziness of the cornea develops; the cornea then usually clears. The eye shield and the surgical tape around the head are removed a few days after the sutures have been taken out, provided the corneal wound has healed sufficiently and the dog is no longer trying to rub his eye. It is remarkable how well a dog with aphakic eye(s) can negotiate an ob stacle course and get along in unfamiliar surroundings again without correc tion of his aphakia. It is often a pleasure to sec how the dog has regained his activity, to the satisfaction of both the owner and the eye surgeon.
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Summary Problems and technique of cataract extraction in the dog are discussed. Details are given of the selection of cases, anaesthesia, pre-operative preparation and the surgical technique, which is in many ways different from that employed in cataract extraction in man. The importance of adequate post-operative care is stressed.
References Bartholomew , A. C.: Vet. J. 92: 262 (1936). D arraspen, E. et al.: Bull. Soc. fr. Ophtal. 74: 521 (1961). F ormston , C.: Vet. Rec. 64: 47 (1952).
Prof. Dr. J. A. O ostf. rhuis , Ooghcelkundige Klinick, Academisch Ziekenhuis, Leiden (The Netherlands)
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K night, G. C.: Vet. Rec. 69: 318 (1957). K night , G. C.: Vet. Rec. 74: 1065 (1962). M agrane, W. G.: Canine ophthalmology (Lea & Febiger, Philadelphia 1965). M agrane, W. G.: J. small Anim. Pract. 10: 545 (1969). M arkowitz, J.: Experimental surgery (Baillière, Tindall & Cox, London 1954). M eans, T. L: J. Am. vet. mcd. Ass. 100: 151 (1942). M öller , H.: Z. vergl. Augenheilk. 4: 138 (1886). Schlotthauer, C. F.: J. Am. vet. mcd. Ass. 94: 404 (1939). Smythe, R. H.: Veterinary ophthalmology (Baillière, Tindall & Cox, London 1958). Startup , F. G.: J. small Anim. Pract. 8: 667, 671, 675, 681. 685, 689, 693 and 697 (1967).
Cataract Extraction in the Dog J.
A. O o st e r h u is and I. G. J eltes
Ophthalmological Department of the University Hospital, Leyden
The first lens extraction in the dog was probably carried out by M oller in 1886. Intracapsular lens extraction was first described by B a r t h o l o m e w in 1936. However, reclination of the lens into the vitreous body has long been considered to be a useful method, since it was still advocated by S c h l o t t h a u e r in 1939 and M eans in 1942. Fairly recently, even the ratio nale of cataract extraction in the dog was called in question. Thus, F o r m ston stated in 1952 that 'lens extraction is fraught with difficulties and is speculative’ and that it was ‘doubtful if justifiable in the dog when the desired result cannot always be achieved and when the patient has such little respect for optical aids’. M a r k o w it z wrote in 1954 that ‘there is very little positive indication for performing the operation, unless it be for cos metic or sentimental reasons, or in cases where the economic value of the animal is particularly high.’ However, now that the results have gradually become less disappoint ing, operations for removal of the lens are no longer rejected, in spite of the fact that the success rate is still far lower than that of cataract extrac tion in man. This is clear from the analysis of 171 lens extractions in dogs performed by K n ig h t [1962] during the period 1958-1961 and of 252 intracapsular operations performed over a period of 17 years by St a r t u p [1967]. The figures presented below are seen to compare very unfavour ably with the results obtained in humans:
Downloaded by: Univ. of California Santa Barbara 128.111.121.42 - 3/7/2018 11:31:54 PM
Introduction
OOSTERHUIS/J ELTES
Knight, 1962 Startup, 1967
297
Number of eyes
Results, °/o good
fair
failure
171 252
26 22
24 28
50 50
Better results are claimed M agran e [1969], who had a success rate of 80 o/o in 397 extracapsular lens extractions versus only 44 °/o good results in 22 intracapsular extractions. Further details and a review of the liter ature can be found in the excellent articles of Sta r tu p [1967], The relatively small number of publications on cataract extraction in the dog as compared with those on lens extraction in man suggests that only a limited number of veterinary surgeons have acquired the skill needed for the difficult technique in the dog. Veterinary surgeons have in the past no doubt been discouraged by poor results. These may be attributed partly to unsatisfactory anaesthesia and unavailability of the expensive instruments for eye surgery, but above all to the fact that for lens extraction in the dog to be successful, much technical skill and ex perience in intraocular surgery is required and these cannot be gained by veterinary surgeons who only occasionally have the opportunity to operate on cataracts in dogs. Ophthalmic surgeons have developed this skill by operating on human patients, but it must be stressed that operations per formed by them on dogs are bound to be unsuccessful if they use the same technique as in humans. Moreover, they do not have sufficient knowledge of the pre- and post-operative care and anaesthesia of the animal. It is therefore our opinion, based on personal experience, that except in large veterinary centres where lens extractions in the dog are carried out regularly, satisfactory results can only be obtained by a very close co operation between veterinary and eye surgeons. This paper deals with our own experience of cataract extraction in the dog.
Cataract extraction is undoubtedly more difficult in the dog than in man. M agrane [1965], the most experienced veterinary surgeon in this field, states that: ‘Those who have performed intraocular surgery almost invariably have wisely solicited the aid of an ophthalmologist for their
Downloaded by: Univ. of California Santa Barbara 128.111.121.42 - 3/7/2018 11:31:54 PM
The Odds
298
Oosterhuis/J ei.tes
initial attempts. It is then that both the veterinarian and the medical doctor learn that the dog’s eye presents a more difficult surgical field than does the human eye.’ However, it is not sufficient to be an accomplished surgeon. A good understanding of the macroscopic and microscopic anatomy and the physiology of the dog’s eye is the first requisite. Without this knowledge, lens extractions in the dog, even when properly executed, are doomed to be unsuccessful. Thus, when one of the techniques com monly accepted in human cataract surgery is employed in the dog, the surgeon, even when prepared to spend the unusual amount of time needed for this procedure in the dog, will be constantly faced with failures. There fore, the difference in technique between man and dog will be stressed in this paper. The mode of operation described below can also be used for removing the (sub)luxated lens from the anterior chamber of the eye. It is simpler in that intracapsular extraction can be performed more easily because the suspension of the lens is more or less loosened by degeneration of the zonular fibres. On the other hand, some vitreous loss is almost unavoid able, especially when complicating glaucoma has already set in before operation. Several days of cloudiness of the cornea in the glaucomatous state may damage the cornea to such an extent that after extraction of the lens it does not regain its clarity even when tension in the eye returns to normal.
One should beware of a faulty selection of cases as otherwise success ful surgical treatment may not be followed by the expected restoration of vision to the dog. There are some strict criteria for accepting canine cataract patients for surgery. (1) The behaviour of the dog must clearly show that he cannot nego tiate an obstacle course and cannot get along any more in unfamiliar sur roundings. The cataract must be diffuse and very dense. (2) It has been observed that even when there is a fairly dense cataract in both eyes, the dog retains a certain degree of vision. Therefore, if in a dog without visual orientation the opacification of both lenses is not dense, one should look for other causes of blindness, e.g. retinal degeneration. (3) Retinal degeneration should be minimal or absent. Cataract may be of secondary nature, associated with progressive retinal atrophy, which.
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Selection of Cases and Pre-Operative Examination
Cataract Extraction in the Dog
299
unfortunately, is regularly encountered at an early age in several breeds such as the Miniature and the Toy Poodle, the Labrador Retriever and the Cocker Spaniel. When cataract is dense in both eyes, observation of the pupillary reflex to light as regards promptness of the reaction and the degree of narrowing of the pupil is essential. A weak reflex is indicative of possible degenerative retinal changes, which are almost certainly intense when the pupils are wide and not responsive to light. The ophthalmic examination also includes measurement of the intra ocular pressure, since glaucoma endangers the surgical outcome. One should not tamper with the eyes more than one can help, e.g. to deter mine the patency of the lacrimal ducts or to make bacterial cultures of conjunctival swabs. We have found this to be unnecessary when epiphora is absent and when broad spectrum antibiotic ointment is applied directly after the operation. Apart from an ophthalmic examination a thorough general examina tion should be made to make sure that the general physical condition of the dog allows a long operation. As this is not the task of the ophthalmic surgeon but of the cooperating veterinary surgeon, it will not be discussed in detail. Anaesthesia The operation should be carried out under general anaesthesia; the use of fluothane is to be preferred, reducing as it does the intraocular pres sure and - consequently - the risk of vitreous loss after extraction of the lens. This effect of fluothane, however, is only obtained when anaesthesia is rather deep. We have found a retrobulbar injection to be strongly con traindicated: in the small orbit of the dog, in which the eye occupies most of the space, the injection invariably leads to an increase in pressure from behind and thus greatly promotes the loss of vitreous during lens ex traction.
The dog is placed on its side on the operating table. The position of the head should be such that the optical axis of the eye to be operated on is more or less vertical. To this end the nose generally has to be elevated by means of sand bags or foamed plastic. The tracheal tube must be kept out of the surgical field.
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Pre-Operative Preparation
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The area around the eye is clipped as close to the skin as possible and the eye lashes are cut when the dog is under anaesthesia and not earlier, so that one can do this properly without the risk of damaging the eye should the dog happen to move its head. Subsequently the lids and sur rounding skin are well cleansed with a disinfectant fluid, at the same time removing residual bits of cut hairs. Since mydriasis is essential for delivery of the lens, atropine is in stilled into the conjunctival sack before starting anaesthesia; if the mydria tic effect is insufficient, the instillation is repeated and combined with instillation of a 10-percent sympathico-mimetic phenylephrine solution. We arc not in favour of atropine medication for several days prior to the operation [Startup, 1967] because we want to regulate the size of the pupil prior to and during the operation to not much wider than medium size, in order to perform good iridotomies and to restrict the risk of loss of vitreous and of incarceration of the iris into the corneal wound. The dog is then covered with sterile drapes, leaving only the area of palpebral fissure and, on the temporal side, the area for the canthotomv uncovered. A canthotomy is performed, which as a rule has to be rather large in order to obtain good access to the eye and to avoid any pressure of the eyelids on the eye. Haemorrhage can be minimized by compressing the cutting area with haemostatic forceps for about 30 sec before cutting. The lid margins and edges of the canthotomy are then sutured to the margin of the opening in the sterile drape, taking care that there is no traction of the drape on the eyelids. If necessary, the opening in the sterile drape is enlarged. The sutures are not cut; haemostatic clamps are fastened to their ends and their weight is used to keep the eyelids open. We prefer this to the use of an eye speculum, which, especially when not positioned properly, may increase the intraocular pressure and. moreover, does not fit very well when a large canthotomy has been made. In the same way the nictitating membrane is kept out of the way by means of a suture with a haemostatic clamp attached to its end.
It is beyond the scope of this paper to discuss the many variations employed in cataract extraction in the dog; for this the interested reader should consult the publications mentioned in the list of references. We
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shall only describe the technique which in our hands has proved to give satisfactory results. This by no means excludes the possibility of modifica tions giving as favourable, if not better results. After bringing the dog into a suitable position, performing canthotomy and obtaining suitable retraction of the lids and the nictitating membrane, as described above, one may find access to the inner eye still difficult. Therefore, three traction sutures are made through the conjunctiva and sclera along the upper half of the limbus, the nasally and temporally located sutures lying in a more or less diametrical position. The traction sutures are very important for gently moving and/or rotating the eye with out elevating the intraocular pressure when making an incision or suturing the relatively large corneal incision in the small orbital aperture. To the end of the sutures small clamps (bulldogs) are fastened (the small type arterial clamps are too heavy and may cause an increase in intraocular pressure). An incision of about 180 is then made 1.5 mm centrally of the limbus in the superior half of the cornea and about two-thirds of the thickness of the cornea deep. At first we used to make - as in the human eye - a limbus-based conjunctival flap and a corneo-scleral incision, but we abandoned this technique, since cutting into the limbal vascular network resulted in two complications. First, haemorrhages may develop during surgery or in the first few days after the operation [D arraspen et al., 1961; Startup. 1967], which may be fatal [Smythe, 1958], Secondly, it was our experience that damage to the dense limbal vasculature inter fered with a proper nutrition of the cornea, thus resulting in a greater swelling and cloudiness of the cornea in the first week after the operation than after a corneal incision. The cornea sometimes even failed to clear at all and permanent scarring impeded recuperation of good vision. The corneal incision should not be made less than 1.5 mm from the limbus, so as to restrict the development of goniosynechiae and to avoid damage to the limbal vessels by suturing. Two virgin silk sutures are then placed in the corneal wound dividing the length of the incision into about three equal parts. The anterior chamber is opened, using, as for the initial corneal incision, an ordinary razor blade fragment or a Pierce-Hoskin pre-formed razor blade fragment. With Castroviejo scissors the incision is enlarged, the pre-formed incision guiding the scissors and restricting squashing of the corneal tissue between the scissor blades. We then perform several iridotomies using Vannas scissors, about one
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in each quadrant, taking care to cut only the sphincter part of the iris. Thus, the pupil, being slightly dilated when the anterior chamber is opened, is enlarged to such an extent that it will not interfere with the extraction of the lens, which is much larger than the human lens. Another major advantage of the iridotomies is that post-operative con striction of the pupil is prevented. This complication, which can lead to pupillary obstruction, development of a membrane in the pupil, iris bombans and glaucoma, is often the cause of failure in the post-operative period, even when strong mydriatics are given conscientiously [St a r t u p . 19671. The importance of this complication is apparent from the follow-up study of M agrank [1969] after 429 cataract extractions in the dog: of the 77 ultimate failures 32 were mainly due to iris bombans and/or pupillary seclusion, complicated by glaucoma in 16 eyes. After extracapsular extrac tion the wide pupil guarantees good accessibility of the lens material to the aqueous, promoting dissolution of the residual lens material. It is a well-known fact that an iridectomy should never be performed, as this inevitably leads to excessive and prolonged bleeding. Therefore, M a c r a n e [1969] only performs an iridectomy if more working room is needed for the extraction and for this purpose he uses an electroscalpel in order to restrict complicating haemorrhages. In iridotomy, however, bleed ing is absent or minimal as long as cutting into the thick, highly vascular basal part of the iris is carefully avoided and only the thin, not very vas cular sphincter part of the iris is cut. The persistently rather large and somewhat irregular pupil is not cosmetically disturbing and, to our sur prise, has been found not to cause photophobia in the dog. After the iridotomies have been made the actual lens extraction is per formed. For both intracapsular and extracapsular extraction cryo-extraction is to be preferred to any other technique. As the zonular fibres in the dog are often difficult to break, freezing of the cryode not only to the lens capsule but also to the underlying lens substance is necessary to produce a solidification deep enough to allow lens extraction without capsular rupture. It is well known that u-chymotrypsin in a concentration of 1:5,000, as used successfully in human eyes, will not yield a lytic action of the zonular fibres in the dog. By using higher concentrations of up to 1:500 complete zonulolysis may be obtained in the dog, but according to Startup [1967] this may be responsible for post-operative pupillary ad hesions and glaucoma which he observed in these cases. «-Chymotrypsin in a concentration of 1:2,500 can be used safely, but it weakens the zonular fibres only to some extent and does not completely eliminate
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the necessity of instrumental zonulotomy in order to avoid rupture of the lens capsule. There is no consensus of opinion as to whether intracapsular or extracapsular extraction of the lens should be preferred. M agrane [ 19691 greatly favours extracapsular extraction since in his series twice as many were successful as compared with the intracapsular ones. However, with due attention to some technical details, the intracapsular extraction will be a rather safe procedure. The main problem is vitreous loss; in extracap sular extraction of the lens its occurrence is very much restricted by the fact that the posterior capsule is left intact. In intracapsular extraction there is no barrier left between vitreous and anterior chamber, since in the dog the hyaloid membrane adheres firmly to the posterior surface of the lens. Therefore, the vitreous adhering to the lens must be cut off with fine scissors, e.g. De Wecker's spring scissors, before the lens is delivered. At this moment the danger of vitreous loss is greatest. However, with proper precautions as previously described and especially with a relatively deep fluothane anaesthesia, inducing complete relaxation of the eye, the risk of loss of vitreous - the main complication in the series of M agrane [1969] - is reduced considerably, making intracapsular extraction a re liable method. In less experienced hands the extracapsular method is still the safest procedure. Care must be taken to remove the relatively strong anterior capsule completely. We freeze the capsule at its centre to the cryoextractor and then cut it around the tip of the cryo-extractor as periph erally as the pupil allows, almost along the equator. This can be done easily when multiple iridotomies have been made. Like a lid the anterior capsule is then lifted from the lens. Subsequently, the lenticular mass is easily removed and the subcapsular remnants of the lenticular cortex are washed out. This has to be done carefully, since lenticular debris is more toxic in the dog than in man and, if not properly removed, may even lead to failure. After the lens has been delivered, the corneal incision is closed by means of the two pre-placed sutures, taking care that incarceration of vitreous into the wound is avoided. If this occurs, the vitreous should be removed in the same way as in human eye surgery. Subsequently, air is introduced into the anterior chamber, restoring the eye to its original shape and preventing incarceration of the iris during suturing of the corneal wound. For closure of the corneal wound we have long been using another
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8 to 10 virgin silk sutures. However, we observed that, in contrast to what usually happens in man, virgin silk gave rise to a rather intense granu lomatous reaction in the dog’s cornea at the end of the first week after operation with ingrowth of vessels from the limbal area to the wound site and cloudiness of the superior half of the cornea. These signs could be relieved by removing the corneal sutures, which we did approximately on the 10th day. We now prefer to close the corneal wound with a running 9/0 perlon atraumatic suture; this material is finer and more inert and in initial results did not produce the side effects just mentioned. Inadequate suturing of the wound may easily lead to iris prolapse |S t a r t u p , 1967],
Adequate post-operative care is of paramount importance. Self-mutila tion, which may even result in the ultimate loss of the eye, is an ever present hazard. Due to lack of facilities we do not hospitalize the patients but give detailed instructions to the owners how to take care of their dogs. The operated eye is bandaged in a special way. Firstly, we wind sur gical tape around neck and head without covering the eye. A convex eye shield is then placed over the eye and fastened with short strips of surgical tape which can easily be loosened, even several times a day. for inspection of the eye or for the application of eye drops and/or ointment. A thick, soft foamed plastic ’collar' protects the eye further from any attempts of the dog to rub it. Antibiotics are given parenterally for 5 days after the operation. Daily inspection is necessary in the first post-operative week. Constric tion of the pupil, posterior synechiac and iris bombé have not been ob served any more since multiple iridotomies were incorporated in the technique. Atropine eye drops are instilled several times a day, steroid eye drops are given when, mostly on approximately the 5th day, a haziness of the cornea develops; the cornea then usually clears. The eye shield and the surgical tape around the head are removed a few days after the sutures have been taken out, provided the corneal wound has healed sufficiently and the dog is no longer trying to rub his eye. It is remarkable how well a dog with aphakic eye(s) can negotiate an ob stacle course and get along in unfamiliar surroundings again without correc tion of his aphakia. It is often a pleasure to sec how the dog has regained his activity, to the satisfaction of both the owner and the eye surgeon.
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Summary Problems and technique of cataract extraction in the dog are discussed. Details are given of the selection of cases, anaesthesia, pre-operative preparation and the surgical technique, which is in many ways different from that employed in cataract extraction in man. The importance of adequate post-operative care is stressed.
References Bartholomew , A. C.: Vet. J. 92: 262 (1936). D arraspen, E. et al.: Bull. Soc. fr. Ophtal. 74: 521 (1961). F ormston , C.: Vet. Rec. 64: 47 (1952).
Prof. Dr. J. A. O ostf. rhuis , Ooghcelkundige Klinick, Academisch Ziekenhuis, Leiden (The Netherlands)
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K night, G. C.: Vet. Rec. 69: 318 (1957). K night , G. C.: Vet. Rec. 74: 1065 (1962). M agrane, W. G.: Canine ophthalmology (Lea & Febiger, Philadelphia 1965). M agrane, W. G.: J. small Anim. Pract. 10: 545 (1969). M arkowitz, J.: Experimental surgery (Baillière, Tindall & Cox, London 1954). M eans, T. L: J. Am. vet. mcd. Ass. 100: 151 (1942). M öller , H.: Z. vergl. Augenheilk. 4: 138 (1886). Schlotthauer, C. F.: J. Am. vet. mcd. Ass. 94: 404 (1939). Smythe, R. H.: Veterinary ophthalmology (Baillière, Tindall & Cox, London 1958). Startup , F. G.: J. small Anim. Pract. 8: 667, 671, 675, 681. 685, 689, 693 and 697 (1967).
