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

The research examines the effects of the PMEL17 (Silver) mutant gene on ocular anomalies in horses, using both ultrasonography and ophthalmoscopy, with results indicating ultrasonography as more effective in identifying certain conditions.

Research Methods

• The study focused on 67 Comtois and 18 Rocky Mountain horses, grouping them into carriers and noncarriers of the PMEL17 mutant gene. This classification was based on their coat color or through genetic testing.
• Every horse underwent direct ophthalmoscopy, a common method for examining the interior of the eye, followed by a standardized ultrasonographic examination, a non-invasive procedure that uses sound waves to create images of the eye’s internal structure.

Key Findings

• Out of the 85 horses, 75 (approximately 88.24%) carried at least one copy of the PMEL17 (Silver) mutant allele, a variation of a gene associated with certain ocular anomalies.
• The ultrasonographic examination revealed various malformations typically associated with this gene such as cornea globosa (a bulbous cornea), severe iridal hypoplasia (underdevelopment of the iris), uveal cysts (fluid-filled sacs in the uvea), cataracts, and retinal detachment.
• Statistical analysis showed that horses carrying the PMEL17 mutant gene had a significantly increased depth of the front chamber of the eye (anterior chamber) and a decreased thickness of the anterior uvea compared to noncarriers.
• The uveal cysts in the carrier horses varied widely in terms of location and ultrasonographic appearances. Additionally, in almost 70% of the carrier horses, ultrasonography detected ciliary cysts (cysts in the ciliary body of the eye) that were not identified during the direct ophthalmoscopy.

Conclusion

• The study concluded that ultrasonography is effective in detecting uveal cysts in horses carrying the PMEL17 mutant gene and in assessing the depth of the anterior chamber of the eye. These results suggest that ultrasonography may be a more effective tool than direct ophthalmoscopy for detecting ocular conditions in these specific cases.