Progressive retinal atrophy

From Cat
Appearance of the retina in feline PRA

Feline progressive retinal atrophy (PRA) is a rare autosomal[1] genetic disease retinal disease of Bengal[2], Norwegian forest, Abyssinian, Somali[3] and Persian breeds[4].

PRA is an umbrella term that refers to several types of retinal problems, all of which can cause blindness. When retinal atrophy occurs alone, it is not a painful condition and animals adjust well to blindness. Although a genetic predisposition has been found in the above breeds, cats of any breed can be affected by either sudden or progressive retinal atrophy.

Glaucoma is a common non-genetic cause of PRA[5].

In Persian breeds, no association with PKD or coat-color (especially chocolates) appears to relate to the incidence of PRA, which occurs in all color types[6].

In the Abyssinian, there are two distinctly separate forms of PRA, an autosomal recessive and an autosomal dominant form. Both are bilateral and progressive[7]. Autosomal recessive disease appears to develop later, often in cats over 12 months of age.

Clinical signs begin usually with mydriasis, starting with one eye, then both, due to reduced light responses in the affected eye(s). As symptoms progress, nystagmus becomes obvious, with intermittent, variable expression. This form of PRA is rod-cone dysplasia due to degeneration of photoreceptors occurring before maturation. Ophthalmic lesions can be viewed from 8 weeks of age. Lesions progress rapidly within 2-3 months and blindness is the invariable outcome, with little treatment afforded to delay or halt the progression of retinal disease.

Ophthalmic lesions include tapetal hyperreflectivity and attenuation of the retinal blood vessels, with loss of pigment in the nontapetal region. Over time, further nontapetal depigmentation occurs, particularly in the area centralis region. There have been no cases of a secondary cataract due to PRA, unlike dogs where it commonly occurs.

Pathology is caused by changes to retinal blood flow as PRA progresses, with severely decreased circulation at late stages of retinal degeneration. The choroidal microcirculation however, is not significantly affected by the disease, until later in the disease process.

References

  1. Rah H et al (2005) Early-onset, autosomal recessive, progressive retinal atrophy in Persian cats. Invest Ophthalmol Vis Sci 46(5):1742-1747
  2. Winn, 2012
  3. Djajadiningrat-Laanen SC et al (2002) Progressive retinal atrophy in Abyssinian and Somali cats in the Netherlands (1981-2001). Tijdschr Diergeneeskd 127(17):508-514
  4. Aiello, Susan, BS, DVM, ELS, Editor, The Merck Veterinary Manual, (Merck Handbooks, eighth edition, 1998) page 356 - 358
  5. Trost K et al (2007) Goniodysgenesis associated with primary glaucoma in an adult European Short-haired cat. Vet Ophthalmol 10:3-7
  6. Rah H et al (2006) Lack of genetic association among coat colors, progressive retinal atrophy and polycystic kidney disease in Persian cats. J Feline Med Surg 8(5):357-360
  7. Barnett, KC & Crispin, SM (2005) Feline ophthalmology, Saunders, Philadelphia, pp:162-164