Ocular dimensions, corneal thickness, and corneal curvature in quarter horses with hereditary equine regional dermal asthenia.

The research focuses on comparing ocular dimensions, corneal curvature, and corneal thickness in horses affected by a condition called hereditary equine regional dermal asthenia (HERDA) and those that are unaffected.

Objective and Methods

• The aim was to understand how hereditary equine regional dermal asthenia (HERDA), a genetic skin disease, affects the eye structure in horses. The study involved five horses with HERDA and a control group of five healthy horses.
• They performed multiple tests on both eyes of all horses involved in the experiment. The Schirmer’s tear test to measure tear production, tonometry to measure eyeball pressure, and measurements of corneal diameter were conducted.
• Sophisticated methods like ultrasonic pachymetry and B-mode ultrasound scanning were conducted. The former measures the thickness of different corneal regions, while the latter helps in determining ocular structure dimensions and calculating the corneal curvature.

Results

• While it was found that corneal regions in affected horses were thinner than those in the control group, the significant differences were only for the central and dorsal regions.
• The study also revealed that horses with HERDA showed increased corneal curvature and corneal diameter compared to the healthy ones. Additionally, mild corneal opacity was observed in one eye of an affected horse and in both eyes of three horses.
• However, there were no notable differences in the Schirmer’s tear test, measurements of intraocular pressure, or ocular dimensions between the HERDA-affected and unaffected horses.

Conclusions and Further Research

• The researchers concluded that HERDA-affected horses exhibited several ocular changes such as decreased corneal thickness in certain corneal regions, increased curvature and diameter of the cornea, and mild corneal opacity.
• Despite these findings, the relationship between HERDA and its impact on a horse’s visual accuracy due to the increase in corneal curvature remains unclear and needs additional research.