Taurine deficiency retinopathy

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

A feline central retinal degeneration was first reported in 1970 in New York. The aetiology was unknown but it was not originally considered to be a nutritional retinopathy. Taurine deficiency retinopathy (TCRD) is a bilateral, usually symmetrical, progressive condition that occurs in both sexes. The retinal changes are typical, unusual and highly specific for this condition, particularly  in the early stages. The first lesion appears at the area centralis, level with and temporal (lateral) to the optic disc in a region devoid of visible blood vessels. A zone of granularity has been described but the first obvious change is the presence of a horizontally oval, focal and well-demarcated millet-seed like spot of increased reflectivity. Hyperreflectivity in a tapetal region always indicates retinal thinning, i.e. retinal degeneration, whatever the cause. The affected area increases in size but remains clearly defined and horizontal and oval in shape. Ophthalmoscopically, the appearance may suggest a pigmented border particularly along the upper and lower edges. A second and similar area appears next on the nasal (medial) side of the disc. These two areas spread toward one another, meet, and fuse in a bridge immediately superior to the optic disc. Further progression occurs but until this time there has been no apparent loss of vision noticed clinically. The whole of the fundus is then affected with a generalised retinal degeneration which appears ophthalmoscopically as hyperreflectivity in the tapetal region; previously no change would have been noted except in the areas described. Finally, attenuation of blood vessels and blindness occurs.

Typical taurine deficiency in a pet cat

Histopathologically, there are no inflammatory changes; the outer retinal layers are most severely affected with loss of photoreceptors and associated nuclear layer and the inner layers remaining more normal; no changes by light microscopy have been described in the retinal pigment epithelium despite the apparently pigmented borders visible ophthalmoscopy.

The amino-sulphonic acid taurine is now recognised as essential for the cat and approximately 10mg/kg has been shown to be the daily requirement for an adult cat. However, occasional cases of naturally occurring taurine deficiency retinopathy still occur in household cats which are sometimes kept indoors and fed unusual diets including entirely dog foods (dogs are able to synthesise their own taurine).