Ocular diseases unique to the feline patient (Proceedings)

Many ocular conditions seen in cats are identical to those in other domestic species however there are eye diseases which are only seen with any frequency in cats (eyelid agenesis, diffuse iris melanoma) or which have common and unique presentations in the cat compared with other species (immune mediated uveitis and ocular eosinophilic disease).

Eyelid agenesis or coloboma is the most commonly reported eyelid developmental abnormality. Usually the upper lateral eyelid is poorly developed with skin and eyelid hair directly abutting the conjunctival and corneal surface resulting in chronic irritation, increase lacrimation, blepharospasm, and keratitis. Treatments have involved localized cilia cryothermy or skin grafting procedures for large lid defects.

Entropion may occur as a congenital condition (often in brachycephalic reeds) or develop in association with inflammatory disease of the eyelids or cornea. Surgical repair is usually straightforward.

Blepharitis is seen less commonly in cats than dogs. Causes include bacterial infections (Staphylococcus), mange, dermatomycosis, and immune mediated disease. Eyelid neoplasia in cats differs from the types seen in dogs. Squamous cell carcinoma is common in white cats from UVL exposure. Surgical excision (or debulking) of squamous cell carcinoma often requires other adjunctive treatment to effectively limit progression of the disease. Mast cell tumors may involve the lid including the margin – excision is often effective in treating the disease.

The third eyelid may be involved in inflammatory disease of the conjunctiva (see below). Prolapsed of the gland of the third eyelid occurs infrequently with a predisposition in the Burmese. Surgical repositioning in usually curative.

Third eyelid protrusion is seen in young cats with enteritis, weight loss. It must be differentiated from orbital mass (exophthalmos, globe deviation, failure to retropulse, Horner's syndrome (enophthalmos, miosis and ptosis), microphthalmos, and phthisis bulbi. Neoplasia of the third eyelid is not common in the cat – swelling of the nictitans may occur with eosinophilic infiltrative disease.

Conjunctivitis is probably the most commonly seen feline ocular disease in general practice. The etiologies include feline herpesvirus, chlamydophila felis, less commonly mycoplasma, calicivirus and allergic (immune mediated disease). Determining a definitive etiology is difficult. Culture of the conjunctiva is usually meaningless; cytology may help differentiate herpesvirus form eosinophilic infiltrative disease or neoplasia. PCR for herpesvirus or Chlamydophila is rarely of value diagnostically.

Clinical sign are ocular discharge (often accompanied in cases of viral disease by signs of upper respiratory tract infection), conjunctival hyperemia, eyelid edema and chemosis Conjunctivitis may be accompanied by corneal ulceration in herpesvirus infection. Change from a serous to mucopurulent discharge will accompany secondary bacterial infection. Chronic conjunctivitis (especially associated with herpesvirus infection results in symblepharon with adhesions forming between the palpebral and bulbar conjunctiva and cornea and scaring the nasolacrimal duct. The most common sequel to conjunctivitis in the cat is chronic epiphora.

Treatment is supportive in most cases – topical antibiotics q8-6h (neomycin, polymixin, gramicidin, tetracycline or ofloxacin), NSAIDs ( flurbiprofen or diclofenac Na), systemic antibiotics (for secondary infections), nebulization and fluid and parenteral nutrition in severe cases of URT infection, oral L-Lysine 500 mg PO daily. Systemic use of anti-viral drugs may be helpful – in most cases famcyclovir is the drug of choice. Chronic symblepharon can be treated surgically but requires cautious dissection of scarred tissue combined with vigorous herpesvirus and anti-inflammatory therapy.

Corneal ulceration occurs in the cat in for many of the same reasons in dogs (trauma) but in all cases the possibility of herpesvirus infection should be considered in the differential diagnoses. Typical dendritic staining patterns with rose Bengal and Fluorescein stain is diagnostic however when larger more geographic ulcers are seen herpesvirus should still remain the number one differential. For this reason in any ulcers which fail to heal within a few days in the absence of obvious causes of irritation, herpesvirus therapy should be considered. For simple superficial abrasions and ulcer topical antibiotic therapy (possibly combined with limited use of cycloplegic) is adequate initially - recheck within 4-5 days – if the lesion is not healed add herpesvirus therapy. In most cases suspected herpesvirus keratitis is treated with topical idoxuridine, trifluridine or cidofovir q4-6h and may be supplemented with systemic famcyclovir and L-lysine orally.

Superficial non-healing ulcers occur in cats and may behave the same way as in dogs. Treatment is by epithelial debridement and application of a soft contact lens to the cornea. Grid keratotomy is contra-indicated in this species. Corneal sequestra are probably the feline version of the canine non-healing ulcer. These are treated with superficial keratectomy with contact lens support or by an advancement corneal graft or support with a synthetic graft material.

Deep corneal ulcers may heal with medical therapy but often need usually need surgical care to ensure adequate support and blood supply for healing and maintenance of vision. This can be provided with a pedicle conjunctival graft or a cornea-conjunctival transposition. Fortunately feline corneas have an amazing capacity to heal even severe lesions with limited scarring.

Non-ulcerative keratitis may occur in cats. Stromal keratitis may be due to herpesvirus infection. Lymphosarcoma may infiltrate the cornea as well as any other area of the eye. Eosinophilic keratoconjunctivitis is seen most often in cats among the domestic species. White to pink raised epithelial and stromal masses with vascularization are typical. Differentiation of the various forms of keratitis is possible by cytology of corneal scrapings. Eosinophilic keratitis responds to topical corticosteroids in most cases. Some cats require concurrent treatment for herpesvirus if the history suggests this being involved.

Uveitis is common in cats. Etiologies include trauma, infectious diseases – toxoplasmosis, systemic mycoses, feline infectious peritonitis, feline immunodeficiency virus, feline leukemia virus, Bartonella, and ocular neoplasia. In many cases the etiology goes undetermined and chronic lymphoplasmacytic inflammation is found on histopathology. These cases are difficult to manage long-term and often progress to glaucoma. An immune mediated basis is assumed although what the trigger for the disease might be is unknown. Diagnostic workup requires a minimum database, serology or PCR for known potential infectious causes, chest/abdominal radiographs and abdominal ultrasonography. Treatment with corticosteroids and NSAIDs is usual combined with specific therapy if an underlying infectious cause is identified.

The most common primary ocular tumors in cats are diffuse iris melanoma and trauma induced ocular sarcoma. Secondary ocular lymphosarcoma often involves the anterior uvea or choroid. Early enucleation is recommended since cats have a relatively high frequency of uveal neoplastic metastasis. .

Glaucoma in cats is most commonly secondary to uveitis. Primary glaucoma has been reported in Persians and Siamese cats. Cats of various breeds seem predisposed to aqueous misdirection syndrome in which aqueous humor migrates back into the vitreous humor and displaces the vitreous, iris and lens anteriorly contributing to iridocorneal angle compromise and swallowing of the anterior chamber. Treatment of glaucoma in cats is complicated in cases with concurrent uveitis. Cats do not respond to latanaprost and are poorly responsive to some carbonic anhydrase inhibitors. Topical dorzolamide and timolol may be effective in reducing pressures. Surgical therapy (lensectomy) in aqueous misdirection syndrome or lens phakoemulsification and endocyclophotoablation (ECP) and surgical options when medications alone are insufficient to control intraocular pressure. Blind eyes with high pressure are painful and should be enucleated or in select cases undergo globe evisceration and prosthesis.

Cataracts are usually seen associated with uveitis. Lens luxation is a common sequel to uveitis and/or glaucoma – surgical therapy to remove the lens may be effective so long as inflammation and intraocular pressure can be controlled. Ocular sarcoimas have been seen in cats after cataract surgery and amplify the need for long-term postoperative anti-inflammatory therapy.

Inherited retinal degenerations are seen in cats less frequently than dogs – the cause and genetics of the disease have been investigated in the Abyssinian cat. Feline central retinal degeneration associated with taurine deficiency is now seen infrequently since feline diets now supplement with taurine.

Cats are prone to retinal toxicity and degeneration due to over-dosage with enrofloxacin and other fluoroquinolones. Rapid and irreversible loss of vision occurs in cats dosed with enrofloxacin at doses higher than that recommended for cats.

Hypertensive retinopathy is a common cause of acute vision loss in older cats with underlying renal failure, cardiomyopathy or hyperthyroidism. Affected animals present with bullous retinal detachment and retinal hemorrhages or hyphema. Systolic blood pressures over 160 mmHg are considered diagnostic of systemic hypertension. Treatment is started with a calcium channel blocker – amlodipine and the cat should be investigated for the underlying cause. Vision may return if the retinal detachment is of short duration.

Optic nerve related contralateral blindness. The cat is not infrequently affected by iatrogenic optic nerve atrophy secondary to enucleation of the contralateral eye. Traction on the optic nerve of the eye being removed can cause damage to the nerve of the remaining at via the chiasm. Great care and delicate handling of the optic nerve is important when enucleating this species.