Introduction

The eye is often compared to "a window open to the body". It is the only part of the body where, thanks to transparent media, vessels are visible by the examiner. Many systemic diseases can have ocular manifestations. When only ocular signs are present, it is very useful for the practitioner to be able to recognize them. This allows an early diagnosis of the disease and an early control of the lesions often avoiding irreversible complications. In many ways, this section of ophthalmology can be considered as a border between ophthalmology and internal medicine. This paper focuses on the most frequent causes of ocular lesions in cats.

Viral infections

 Panleukopenia infection has been associated with retinal dysplasia and optic nerve lesions.

 Feline herpes virus (FHV-1) can result in neonatal ocular disorders with conjunctivitis, keratitis and discharge (neonatal ophthalmia). Older kittens and young cats show conjunctivitis with serous to purulent discharge. In older cats, conjunctivitis and keratitis are a result of reactivation of latent virus rather than a sign of primary infection. Keratitis with superficial ulcers (dendritic or geographic) is typical of the disease. FHV-1 may also be a cause of anterior uveitis.

 FHV-1 ocular complications. The virus is pathogen for the epithelial cells. Different ocular complications may occur after primary ocular lesions.

 Symblepharon is a conjunctival adhesion.

 Obliteration of lacrimal puncta is a cause of chronic epiphora.

 Keratoconjunctivitis sicca may be a consequence of glandular ductules obliteration.

 Stromal keratitis is secondary to an immune mediated inflammatory reaction.

 Corneal sequestrum may occur after a corneal ulcer.

 PCR is the most sensitive and specific technique for diagnosis. Treatment is based on the use of: systemic broad spectrum antibiotics (if there is respiratory involvement), topical antibiotics to prevent local bacterial infection, topical antiviral therapy. Interferon, oral L-lysine, cyclosporine and removal of corneal lesion are alternative treatments.

 Feline infectious peritonitis is caused by a coronavirus. Anterior uveitis with keratic precipitates or hypopyon may be observed. There is both vasculitis and chorioretinitis lesions associated with retinal haemorrhages or retinal detachments. The diagnosis is difficult. Seropositivity is not a proof of the aetiology, but with protein analysis can be suggestive of non effusive FIP.

 Feline leukaemia complex can affect any ocular structure. The anterior uvea is the most frequently tissue involved. Haemorrhages can appear in the anterior chamber.

 Feline Immunodeficiency Virus mainly produces anterior uveitis. Other associated infectious agent as T.gondii can be the cause of ocular signs.

 Feline calicivirus is currently thought to be responsible for 90% of upper respiratory tract infections in cats. The virus may be the cause of conjunctivitis, but the conjunctival disorders appear rarely without other signs of the disease. Conjunctival pathogenicity for conjunctival tissue is doubtful. PCR provides the most sensitive and specific test for viral identification. The treatment is based on the use of systemic and local antibiotics.

Bacterial infections

 Chlamydiosis by Chlamydiofila felis (Chlamydia psittaci) is the second most common cause of conjunctivitis in cats. The first is the feline herpesvirus. Diagnosis is made by identification of intracytoplasmic inclusion on conjunctival scrapings or better by PCR. Tetracyclines are used as treatment.

 Bartonellosis may be a cause of uveitis in cats. Doxycline is used as treatment.

 Tuberculosis can result in anterior or posterior uveitis (mainly of granulomatous type).Treatment consists of systemic penicillins.

Protozoal infections

 Toxoplasmosis is a frequent infection in the cat. T.gondii is suspected to be the cause of many cases of feline anterior uveitis. Despite the many diagnostic techniques, the definitive diagnosis of the disease remains difficult. Oral clindamycin (12,5 mg/kg-twice daily during two weeks) is the current first line treatment .

Fungal infections

Fungal infections are not very frequent in cats living in Europe. Mostly reports come from North America and concern cryptococcosis. The lesions consist of chorioretinitis or papillitis.

Cardiovascular disorders

Systemic hypertension is a common cause of intra ocular haemorrhages and retinal detachment in cats. It is unfortunately, the more frequent cause of loss of vision in old cats. The diagnosis is based on determination of systemic arterial blood pressure. The recommended procedure is to use Ultrasonic Doppler devices. Antihypertensive therapy with amlodipine is considered to be effective. Hypertension is commonly observed in cats with renal failure.

Since cataract, lens luxation, glaucoma in cats are frequently secondary to uveitis, it is advised in such cases to investigate the aetiologies of possible previous intraocular inflammation.

The different systemic diseases are summarised in the table with the prevalence of the clinical signs.

Table 1. Ocular Manifestations of Feline Systemic Diseases

Relative Prevalence of Clinical Signs

++: Frequent
+++:Very frequent
+/-: Variable-Infrequent