Clinical and electroretinographic findings of progressive retinal atrophy in miniature schnauzer dogs of South Korea

Abstract

The purpose of the study was to describe the clinical and electroretinographic features of clinical cases of progressive retinal atrophy (PRA) in miniature schnauzer (MS) of South Korea. Sixty-six MS (14 normal and 52 affected) were included. All animals underwent routine ocular examinations. Electroretinogram (ERG) was recorded in the 14 normal and 15 affected dogs. For normal dogs, the mean age ± SD was 4.1 ± 2.4 years (1 to 9 years), and there were no ocular abnormalities on the basis of ocular examinations and ERG results. For the PRA-affected dogs, it was shown that the mean age ± SD was 4.3 ± 1.1 years (2 to 7 years), and 44 dogs (84.6%) were 3 to 5 years old. Most of the PRA-affected dogs had abnormal menace responses (98.1%) and pupillary light reflexes (PLRs, 88.5%); some dogs showed normal menace response (1.9%) and PLRs (11.5%). Ophthalmoscopic abnormalities in the affected group included one or more of the following changes: hyperreflectivity and discoloration of the tapetal area, attenuation of retinal vessels, depigmentation in non-tapetal area and optic disc atrophy. ERG in the affected dogs showed non-recordable responses in all cases tested with clinical signs of PRA. The present study showed that PRA in MS was mainly observed between the age of 3 to 5 years. ERG revealed abnormal rod and cone responses in affected dogs at the ages studied.

Fig. 1.

Fundus photographs of PRA-affected miniature schnauzers at 2 years (a), 4 years (b) and 6 years (c) of age. The fundus abnormalities observed in the affected dogs are: diffuse hyperreflectivity (in a and b) and severe vascular attenuation (in a, b and c).

Fig. 2.

Representative ERG waveforms recorded using the dog protocol in 4 years old normal and PRA-affected MS. The waveforms of each column were obtained from same MS dogs. Scotopic ERGs (a and b, e and f) and photopic ERGs (c and d, g and h) are shown. R responses (0.025 cd·sec/m², a and e), were designated R1 (1 min), R5 (5 min), R10 (10 min), R15 (15 min) and R20 (20 min) after the initiation of dark adaptation (from top to bottom in a and e), and MRC responses (2.5 cd·sec/m², b and f). The C responses (2.5 cd·sec/m², c and g) and CF responses (2.5 cd·sec/m², d and h) were obtained after 10 min of light adaptation using 25 cd/m² of background light. The light stimulus coincides with the y-axis of each recording. Please note that the time scale varies between some of the photopic recordings.