Researchers in Brazil have found that horses affected with hereditary equine regional dermal asthenia (HERDA) have ocular differences to healthy horses.
The researchers, from three departments at the Univ Estadual Paulista, in Botucatu, São Paulo, set out to compare ocular dimensions, corneal curvature, and corneal thickness between horses with HERDA and unaffected horses.
Horses with HERDA – or hyperelastosis cutis – have a defect in their collagen fibers or in the way those fibers are structurally organized in the mid to deep dermis. The skin over the back and sides of the neck may seem to be easily torn or stretched, and it often develops seromas and hematomas (“blisters” filled with either serum or blood). Healing is usually adequate but often leaves unsightly scars.
The Brazilian researchers tested five HERDA affected quarter horses and five healthy control quarter horses, finding that the corneal region was thinner in the affected group than the control group. Significant differences in corneal thickness were only observed for the central and dorsal regions. The affected horses also exhibited significant increases in corneal curvature and corneal diameter.
Ophthalmologic examinations revealed mild corneal opacity in one eye of one affected horse and in both eyes of three affected horses.
However, there were no significant differences in tear production, intraocular pressure, or ocular dimensions in the horses.
Schirmer’s tear test, tonometry, and corneal diameter measurements were performed in both eyes of all horses before ophthalmologic examinations. Ultrasonic pachymetry was performed to measure the central, temporal, nasal, dorsal, and ventral corneal thicknesses in all horses. B-mode ultrasound scanning was performed on both eyes of each horse to determine the dimensions of the ocular structures and to calculate the corneal curvature.
The researchers said additional research wass required to determine whether the increased corneal curvature significantly impacts the visual accuracy of affected horses .
The study was published online before appearing in the journal Veterinary Opthalmology.
Ocular dimensions, corneal thickness, and corneal curvature in quarter horses with hereditary equine regional dermal asthenia
Peres R. Badial1, Luis Emiliano Cisneros-Àlvarez, Cláudia Valéria S. Brandão, José Joaquim T. Ranzani, Mayana A.R.V. Tomaz, Vania M. Machado, and Alexandre S. Borges.