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Retinal Degeneration in Cats

The retina is the tissue that lines the inner surface of the eye, and is the light sensitive part of the eye that acts as the brain's camera, transmitting images through the rods and cones that are part of its structure, thus enabling the experience of vision. The retina is part of the central nervous system (CNS) and the only part of the CNS that can be easily imaged and examined. In retinal degeneration, the cells of the retina begin to decline in function, thereby leading to impaired vision or even blindness. There are many causes for retinal degeneration.

Symptoms and Types

• Night blindness that progresses to blindness in light as well
• Dilated pupils
• Inability to see clearly in bright light
• In some conditions, only central vision may be lost and the cat may still retain peripheral vision
• The pupil (opening of the eye) has abnormal reactions to light
• The retinal structure appears abnormal when a doctor examines it with an ophthalmoscope; cataract may be observed
• The liver may also be affected, obesity may be observed

Cats

• Progressive retinal atrophy (PRA)
• Abnormal development of the light-sensitive cells in the retina is seen in Abyssinians
• Young Persians, Siamese, and domestic shorthairs may also develop this
• Vision loss that becomes worse over time (may be caused by certain enzymes)

Mean Age and Range

• Early progressive retinal atrophy may occur at three to four months of age up to two years of age
• Clinical signs of late progressive retinal atrophy are seen in cats older than four to six years of age

Causes

Genetic

• Hereditary degeneration is rarely seen in cats due to better nutrition
• Rod cone dysplasia in Abyssinians – presents around four months old
• Characterized by the formation and development of a faulty group of cells, which gradually worsen in function over life
• Rod cone degeneration in Abyssinians – presents around two years of age
• Also reported in Persians and domestic shorthair breeds

Degenerative

• Long-term glaucoma, scarring inflammation or separation of the retina due to trauma

Abnormal structure

• Abnormal structure at birth or abnormal development of the retina with age

Metabolic

• Insufficient or excess amounts of certain enzymes

Cancer

• Cancer from other parts of the body that has spread to the retina

Nutritional

• Deficiency of Vitamin A or E
• Taurine deficiency has been found to be a factor in cats

Infectious/Immune

• Infections of the retina or infections that spread from other parts of the body

Toxic

• Adverse Reactions to specific drugs

Diagnosis

You will need to give a thorough history of your cat's health, onset of symptoms, and possible incidents that might have led to this condition, such as trauma or exposure to toxic substances. Your cat's diet will also be taken into consideration, since this may be a supporting cause. Taurine is now added to cat food, but because there is a history of retinal degeneration due to lack of taurine in the diet, your veterinarian will want to ensure that your cat is receiving sufficient levels in its diet.

Your veterinarian will perform a complete physical exam on your cat, taking into consideration your cat's lineage and whether there might be a genetic link. Standard laboratory tests include a blood chemical profile, a complete blood count, an electrolyte panel and a urinalysis, in order to rule out other causes of disease.

The physical exam will entail a full ophthalmic exam using a slit lamp microscope. During this exam, the retina at the back of the eye will be closely observed for abnormalities and the electrical activity of the retina will also be measured.

Genetic testing may also be done if your cat belongs to a breed that is prone to familial retinal disease. Additionally, hormonal causes may bring about retinal disease, and this will be considered as well. X-rays, computed tomography (CT) and magnetic resonance imaging (MRI) can be used effectively to screen for the effects of hormonal abnormalities.