HISTORY

The affected dog, female, two years old; was visited in our hospital for sudden blindness in daylight. The complete eye examination showed: macroblefaron, trichiasis, distichiasis, pupillary light reflexes (direct and consensual ) normal; menace reflex absent; Schirmer's tear test OD : 18mm , OS : 19mm ; tonometry ( Tonopen XL ) - IOP OD : 20 / 21 / 20 mm Hg (5%), OS : 21 / 22 / 21 (5%). After 15 minutes instill midriatic (1% tropicamide) the examination with slit-lamp biomicroscope is normal. The posterior segment examination by direct and indirect ophthalmoscopy showed no abnormal findings (possible slight attenuation of the retinal vessels).

B-scan ultrasonography using a probe of 7.5 Hz detected no abnormalities. No responses in the cotton ball test with bright light and had no difficulty avoiding obstacles indoors or out when ambient illumination was low. The electroretinography (ERG) revealed the absence of cone function whereas rods continue to function normally. The flicker response (stimulus of 20/30 Hz and intensity of 0 db) was abnormal.

DISCUSSION

The day blindness or hemeralopia not been reported in the literature in the Shih-tzu. The references describe the hemeralopia in the Alaskan Malamute and the Poodle. The studies in the Alaskan Malamute are considered as a recessive inherited disease. This case may be a new disease in this breed or an accidental discovery.