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 can result in neonatal ocular disorders with conjunctivitis, keratitis and discharge (neonatal ophthalmia).Young cats show conjunctivitis with serous to purulent discharge. Keratitis with superficial ulcers (typical dendritic ulcers) occur more frequently in older cats.

 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.

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

 Feline Immunodeficiency Virus mainly produces anterior uveitis.

 Feline calicivirus is currently thought to be responsible for 90% of upper respiratory tract infections in cats. The virus can be the cause of conjunctivitis, but the conjunctival disorders appear rarely without other signs of the disease.

Bacterial infections

Chlamydia psittaci is the second most common cause of conjunctivitis in cats. The first is the feline herpesvirus.

Protozoal infections

Ocular toxoplasmosis is an important disease 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.

Fungal infections

Fungal infections are not very frequent in cats. 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. 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. 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-Unfrequent