Ocular findings in Quarter Horses with hereditary equine regional dermal asthenia.
OBJECTIVE
To compare ocular structures of Quarter Horses homozygous for hereditary equine regional dermal asthenia (HERDA) with those of Quarter Horses not affected by HERDA (control horses) and to determine the frequency of new corneal ulcers for horses with and without HERDA during a 4-year period.


METHODS
Cohort study of ocular structures and retrospective case series of horses with and without HERDA.


METHODS
The cohort portion of the study involved 10 Quarter Horses with HERDA and 10 Quarter Horses without HERDA; the retrospective case series involved 28 horses with HERDA and 291 horses without HERDA.


METHODS
Ophthalmic examinations, Schirmer tear tests, tonometry, corneal pachymetry, histologic examinations, and scanning electron microscopy (SEM) were performed in cohorts of Quarter Horses with and without HERDA. Records were reviewed to determine the incidence of corneal ulcers in horses with and without HERDA during a 4-year period.


RESULTS
Corneal thickness of horses with HERDA was significantly less than that of control horses, but tear production of horses with HERDA was significantly greater than that of control horses. Results of SEM revealed zones of disorganized, haphazardly arranged collagen fibrils in corneas of horses with HERDA that were not evident in corneas of control horses. The incidence of corneal ulcers was significantly greater for horses with HERDA than for horses without HERDA during the 4-year period.


CONCLUSIONS
Alterations in corneal thickness, arrangement of collagen fibers, and incidence of corneal ulcers indicated that abnormalities in horses with HERDA were not limited to the skin.
Mochal
Cathleen A
CA
Department of Clinical Sciences, College of Veterinary Medicine, Mississippi State University, Mississippi State, MS 39762, USA.
Miller
William W
WW
Cooley
A James
AJ
Linford
Robert L
RL
Ryan
Peter L
PL
Rashmir-Raven
Ann M
AM
D000818:Animals; D001247:Asthenia / Q000235:genetics / Q000662:veterinary*; D015331:Cohort Studies; D003315:Cornea / Q000648:ultrastructure; D003320:Corneal Ulcer / Q000209:etiology / Q000662:veterinary; D005128:Eye Diseases / Q000209:etiology / Q000662:veterinary*; D005260:Female; D020022:Genetic Predisposition to Disease; D006734:Horse Diseases / Q000235:genetics / Q000473:pathology*; D006736:Horses; D008297:Male; D012189:Retrospective Studies; D012873:Skin Diseases, Genetic / Q000150:complications / Q000662:veterinary*