Gender differences in iridocorneal angle morphology: A potential explanation for the female predisposition to primary angle closure glaucoma in dogs

Abstract

Objective: Female dogs have approximately twice the risk of males for developing primary angle closure glaucoma (PACG). The cause of this gender difference is unknown, but one theory proposes that the gender differences in iridocorneal angle morphology are involved in this risk differential. Procedures: Fifty beagles (25 males, 25 females) were included into this study and had normal baseline ophthalmic examinations. Normal dogs were selected so as to avoid any potentially confounding influence of goniodysgenesis. Standardized 20-MHz high-resolution ultrasound images of the iridocorneal angle were acquired from one eye of each dog with the scan plane perpendicular to the limbus in the superior temporal quadrant. Images were imported into ImageJ, and the angle opening distance (AOD) and angle recess area (ARA) were measured by a masked observer, and the analysis of variance method was used to compare differences. Results: The mean (±SD) AOD was significantly smaller for female dogs (0.847±0.241mm) vs. male dogs (1.058±0.322mm) P-value=0.012. The mean (±SD) ARA tended to be smaller for female dogs (0.584±0.278mm) vs. male dogs (0.748±0.385mm), but this difference was not significant (P-value=0.092). Conclusions: Female dogs have a significantly smaller AOD vs. males. This difference may render the female iridocorneal angle more susceptible to closure and may partially explain the 2:1 female/male predisposition to PACG. Further studies using goniodysgenic dogs are warranted. © 2012 American College of Veterinary Ophthalmologists.