Ocular findings in Quarter Horses with hereditary equine regional dermal asthenia.

The study investigates the differences in ocular structures between Quarter Horses that have hereditary equine regional dermal asthenia (HERDA) and those that do not. The researchers found significant differences in corneal thickness, collagen fiber arrangement, and occurrences of corneal ulcers, suggesting that HERDA can also affect the eyes, not just the skin.

Methods

• The researchers conducted a cohort study and a retrospective case series involving Quarter Horses with and without HERDA. The cohort study consisted of 10 Quarter Horses with HERDA (a genetic skin disease) and 10 without; the retrospective case series included a larger population of horses – 28 with HERDA and 291 without.
• The horses underwent various examinations and tests, such as ophthalmic examinations, Schirmer tear tests (measures tear production), tonometry (measures pressure inside the eye), corneal pachymetry (measures corneal thickness), and histologic examinations (examines cells and tissues under a microscope).
• Scanning electron microscopy (SEM) was used to view structures at a higher resolution, specifically to detect any differences in the collagen fibrils within the corneas of HERDA and non-HERDA horses.
• Lastly, the researchers reviewed medical records over a four-year period, looking for any incidents of corneal ulcers in horses with and without HERDA.

Results

• The findings revealed distinct disparities between HERDA and non-HERDA horses. Horses with HERDA had significantly thinner corneas compared to those without HERDA. However, their tear production was surprisingly higher.
• The SEM results demonstrated disorganized and randomly arranged collagen fibrils in the corneas of horses with HERDA. Such abnormalities were not present in the corneas of control horses.
• The review of medical records over the four-year period showed a significantly higher incidence of corneal ulcers in horses with HERDA compared to those without.

Conclusions

• The research concluded that horses with HERDA not only exhibit skin abnormalities but also have significant differences in their eye structures compared to horses without HERDA. This included alterations in corneal thickness, collagen fiber arrangement, and a higher incidence of corneal ulcers.
• This finds importance as it suggests that HERDA impacts multiple body systems, not just the skin as previously understood. Therefore, better comprehensive care can be provided to such horses considering these findings.