Abstract

Although not an uncommon clinical entity in reptiles, there is a paucity of published information on the etiology, pathogenesis, clinical manifestations and treatment of cataracts in reptiles. Lenticular degeneration with opacification, or cataract formation, probably occurs in reptiles for similar reasons as in mammals and birds. Cataracts are usually classified by age of onset (congenital, juvenile, senile), anatomic location, cause, degree of opacification (incipient, immature, mature, hypermature), and shape. Cataracts may be inherited (particularly in dogs) but other etiologies include diabetes mellitus, malnutrition, radiation, inflammation, and trauma. Cataracts may be unilateral or bilateral depending on the etiology, and the rate of cataract formation may be different in each eye. Most cataracts result in impaired vision to a greater or lesser degree. Vision may be regained in young animals when cataracts undergo sufficient spontaneous resorption, and congenital nuclear cataracts in young animals may reduce in size with the growth of the lens, restoring vision as the animal grows.^1,6

Lenticular sclerosis characterized by variable degrees of central fiber compaction in the substance of the crystalline lens has been reported in reptiles.² This causes the lens to appear slightly silver-grey but does not seem to impair vision. The etiology of cataracts in reptiles is often obscure. In those few cases where an etiology could be surmised, it was usually secondary to uveitis or trauma. Nutritional and environmental factors have also been implicated in some cases. They have been reported and observed in a wide range of reptile species.⁴ Lens opacity may vary from small, focal nuclear or cortical opacities to dense cataracts. Cataracts have been reported in reptiles at various ages with some being evident at birth.⁴ Juvenile cataracts have been reported in young varanid lizards.² The etiology is unclear, although a genetic predisposition has been suggested. Senile cataracts in aged captive reptiles have been reported. Post-hibernation blindness in European tortoises due to cataract development, vitreal opacification, and central nervous system, deficits is a well-recognized syndrome.^2,3

At present the only definitive therapy for cataracts is surgical removal of the lens. Early cataract removal using current surgical techniques (phacofragmentation) has high success rates in other species.⁵ There are no reports in the readily available literature of cataract extraction in a reptile. This paper reports successful bilateral phacofragmentation with restoration of vision in an adult male Komodo dragon (Varanus komodoensis).

Case Report

An 18-yr-old, 85.6-kg, male Komodo dragon (Varanus komodoensis) was noted to have progressive loss of vision in the right eye over a period of approximately 3 mo. Ophthalmic examination included slit lamp biomicroscopy and indirect ophthalmoscopy. The right eye had a mature cataract. There was no menace response, but the eye was light perceptive. The lens of the left eye had mild opacity on the anterior and posterior lens capsule. Fundic examination was normal for the left eye. Vision from this eye was not impaired. The animal was physically restrained and anesthetized using isoflurane in oxygen administered via a face mask, intubated with a size 10 endotracheal tube, and maintained on isoflurane in oxygen using intermittent positive pressure ventilation at four breaths per min. An attempt to dilate the pupil with intracameral pancuronium (Pavulon, Organon Teknika, Baulkham Hills, NSW, Australia) was unsuccessful.

A 3.2-mm incision was made at the dorsal limbus using a 45°, matte finish, bevel-up keratome blade (Becton Dickinson and Co., Franklin Lakes, NJ, USA). Air was injected into the anterior chamber, thereby displacing the aqueous fluid. A capsule-specific dye (Vision Blue, Dutch Ophthalmic Research Centre, Zuidland, The Netherlands) was used to stain the lens capsule and facilitate the lens capsule removal. A continuous curvilinear capsulorhexis was then performed (4.0 mm diameter). The lens nucleus and cortex were then removed almost exclusively by aspiration via the phacofragmentation unit (Phacoplus, Allergan Medical Optics, Gordon, NSW, Australia). The corneal incision was sutured using 8/0 Ethilon on a spatula needle (Ethicon, Johnson and Johnson, Somerville, NJ, USA) in a single interrupted pattern. The globe was reinflated with an air bubble.

Postoperative treatment included carprofen (Rimadyl, Pfizer Animal Health, West Ryde, NSW, Australia) at 3.5 mg/kg SID, SC, doxycycline (Vibravet 100 Paste, Pfizer Animal Health, West Ryde, NSW, Australia) at 10.0 mg/kg SID, PO, chloramphenicol plus polymixin B (Opticin eye ointment, Ilium Veterinary Products, Smithfield, NSW, Australia) topically TID, and dexamethasone (Maxidex eye drops, Alcon Laboratories, Frenchs Forest, NSW, Australia) topically TID. Four days postsurgery, the cornea was generally clear with a small area of local corneal edema around the suture line. A small amount of white flocculent material was present in the anterior chamber. The doxycycline, topical antibiotics, and dexamethasone were continued for 2 wk postsurgery and carprofen was continued for 3 wk. At 16 days postsurgery, the eye was open, the cornea clear, and the white flocculent material in the anterior chamber had disappeared. It did seem, however, that the animal was irritated by the eye, as he was rubbing it, resulting in ulceration of the skin over the eyebrow ridge. Although there was no apparent cause for the irritation, a mild uveitis was suspected. Oral doxycycline was recommenced and continued for a further 7 days. At 22 days postsurgery, all treatment ceased and by 30 days the eye appeared normal. There was no apparent irritation and vision in the eye appeared to have been restored.

One and a half months after surgery on the right eye, the lens of the left eye had become completely opaque and vision was impaired. Four months after the first surgery, the animal was again anesthetized and the left lens removed as previously described. Postoperative treatment included carprofen at 4.0 mg/kg IV once, then 4.0 mg/kg SID, PO for 5 days, then 2.0 mg/kg SID, PO for 9 days, then 2.0 mg/kg every 48 h for 7 days, and enrofloxacin (Baytril, Bayer, Pymble, NSW, Australia) at 5 mg/kg SID, PO for 7 days. A combination antibiotic and corticosteroid (neomycin, polymixin B, sulfacetamide, prednisolone) ointment (Amacin, Jurox, Rutherford, NSW, Australia) was used topically BID in the eye for 5 days. At 1 wk postsurgery, some white flocculent material was noted in the anterior chamber but no other abnormalities were detected. Recovery was more rapid after the second surgery and the eye appeared normal and vision restored by 3 wk postsurgery. One year after the procedures, the animal is normal and appears to have vision comparable to that prior to the development of cataracts.

Discussion

This patient represented a unique opportunity to use a well-established surgical technique to restore vision in a non-mammalian species. Limitations of cataract surgery in this species mainly involved the inability to establish mydriasis using previously reported techniques. Although not specifically reported in this species, the assumption made was that like other reptiles, the iris would be made of skeletal muscle. The lack of response to skeletal muscle blockade using pancuronium is hard to explain. However, in the author’s experience with other reptiles there does not appear to be a uniform response to intracameral skeletal muscle blockers. The possibility certainly exists that there could be a smooth muscle component to the iris musculature in Komodo dragons.

Some interesting observations can be made in comparing the surgical procedure between reptiles and mammals. Ocular physiologic phenomenon between mammalian and reptilian eyes has been previously investigated.⁷ The surgical procedure itself was remarkably easy compared to similar-aged domestic mammals. Of particular note is that the lens itself was incredibly soft, and required little if any phacofragmentation time. In fact, the lens removal was similar in nature to that of a juvenile cataract in a mammal requiring aspiration only. Also, in spite of the age of the animal, the lens capsule itself was very elastic, with no capsular fibrosis. There was also no need for capsular vacuuming after lens extraction, as there were no residual lens epithelial cells seen through the operating microscope. These differences could be accounted for by intrinsic anatomic differences, or the fact that aging proceeds at a rate more typical of humans.

In hindsight, a clear corneal incision for entry into the anterior chamber would have been preferable, as closure of the limbal incision was difficult owing to the presence of scleral ossicles. Hyaline cartilage is present in the sclera of lizards and chelonians from the equator to the posterior pole, with scleral ossicles extending anteriorly from the equator to the limbus.³ This meant that the needle used was quickly dulled and difficult to pass.

Postoperative care was aimed at controlling uveitis. The presence of some flocculent material postoperatively may have been lens material inadvertently missed (especially in light of the lack of mydriasis), or more likely a sterile inflammatory reaction. It did not seem to have a detrimental effect on the final outcome. The use of topical and systemic anti-inflammatory drugs no doubt greatly helped in control of postoperative inflammation. The success of bilateral phacofragmentation in this Komodo dragon suggests that cataract removal in other reptilian species is a viable option.

Acknowledgments

The authors thank Taronga Zoo’s reptile keepers and veterinary nurses for their care and dedication to this case and Ms. Natalie Brock (ophthalmic nurse) for her assistance during the surgical procedures.

Literature Cited

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