Cataracts in cats

©Barnett, KC & Crispin, SM Feline Ophthalmology (2002) Saunders

Cataract in the cat is uncommon and, whereas in the dog many cases of cataract are presented to the veterinary ophthalmologist, opacity of the lens in the cat is a rare presentation. The difference in incidence is partially due to the fact that many cataracts in the dog have been proven to be primarily hereditary, as for example in the Golden Retriever, American Cocker Spaniel and Miniature Schnauzer. However, there are only occasional reports of feline breed-related cataract. In addition, cataract secondary to the generalised form of progressive retinal atrophy does not occur in the cat, although in the dog this form of cataract is a common, if not invariable, sequel in such breeds as the Irish Setter, Miniature Poodle, Cocker Spaniel and Labrador Retriever, for example. Cases of advanced hereditary retinal degeneration in the Abyssinian cat have been examined over several years and the lens has always remained entirely free from an opacity.

To date, there are no proven reports of primary, hereditary, non-congenital cataract in the cat. However, three cases have been reported in related Himalayan cats in which the condition was bilateral and present as early as 12 weeks and with variable expression from posterior polar through posterior subcapsular to total; progression was recorded in one case. The relationship of the cats indicated simple autosomal recessive inheritance. Another case was of primary hereditary cataract in related British blue cream cats in which the condition was bilateral and similar in two eyes, affecting the anterior and posterior poles and suture lines.

The Chediak-Higashi syndrome has been recorded in blue smoke Persian cats as an autosomal recessive condition and includes cataract in addition to thin pale irises and fundic hypopigmentation.

Feline cataract is, therefore, almost always secondary in form and can be classified under the following headings:

(1) Post-inflammatory (uveitis) - probably the most frequent and often associated with posterior synechiae

(2) Traumatic - particularly following penetrating corneal injuries involving the anterior lens capsule. These cataracts, as with the previous type, may be partial or total. Note that lens resorption does occur, particularly in young cats, both with and without damage to the anterior capsule and may itself lead to uveitis. The extent and progression of traumatic cataract in the cat is variable and adhesions to the iris are usually present.

(3) Metabolic - diabetic cataract has been described as rare in the cat and is certainly much less common than in the dog and of slower onset.

(4) Secondary to other eye disease - examples in the category include glaucoma and following lens luxation

Nutritional cataracts have been described in the feline, including a deficiency of arginine occurring in young kittens. Bilateral cataracts have also been seen in several of the big cats, e.g. tiger, cheetah, leopard and black leopard and always in animals hand-reared from birth and frequently given a variety of supplements in addition to various milk supplements.

Senile nuclear sclerosis occurs in the cat but usually only becomes evident at a more advanced age than in the dog, where it may first become noticeable as early as 6 or 7 years; in the cat it is not apparent until 10 years and older.

Cataract may also be classified according to the position of the opacity within the lens, e.g. nuclear, cortical, capsular, perinuclear, suture line, posterior polar, equatorial, cortical and focal (i.e. small and well demarcated).

The management of cataract in the cat is similar to that in the dog in that surgery is the only possible treatment. Although cataract in the cat is commonly secondary to another eye disease, although rarely to a retinal disorder, cataract surgery seldom results in severe intraocular inflammation, as is often the case in the dog; despite the fact that cataract is often secondary to uveitis. The cause of the uveitis should, if possible, be ascertained prior to surgery and any active cases of uveitis treated. A cat blind with bilateral cataract does not always adapt well and cataract surgery in this species can be particularly rewarding.