Ultrasonographic features of PMEL17 (Silver) mutant gene–associated multiple congenital ocular anomalies (MCOA) in Comtois and Rocky Mountain horses




(1) To describe the ultrasonographic appearance of multiple congenital ocular anomalies (MCOA) in the eyes of horses with the PMEL17 (Silver) mutant gene. (2) To compare the accuracy of B-mode ocular ultrasound to conventional direct ophthalmoscopy.

Animals studied

Sixty-seven Comtois and 18 Rocky Mountain horses were included in the study.


Horses were classified as being carriers or noncarriers of the PMEL17 mutant allele based on coat color or genetic testing. Direct ophthalmoscopy followed by standardized ultrasonographic examination was performed in all horses.


Seventy-five of 85 horses (88.24%) carried at least one copy of the Silver mutant allele. Cornea globosa, severe iridal hypoplasia, uveal cysts, cataracts, and retinal detachment could be appreciated with ultrasound. Carrier horses had statistically significantly increased anterior chamber depth and decreased thickness of anterior uvea compared with noncarriers (P < 0.05). Uveal cysts had a wide range of location and ultrasonographic appearances. In 51/73 (69.86%) carrier horses, ultrasound detected ciliary cysts that were missed with direct ophthalmoscopy.


In this study, ultrasonography was useful to identify uveal cysts in PMEL17 mutant carriers and to assess anterior chamber depth.