Equine glaucoma: a histopathologic retrospective study (1999-2012).

This study conducted a retrospective review of histopathologic findings in equine globes enucleated due to glaucoma, with the medical records at The Ohio State University from 1999 to 2012 being analyzed. The findings show that equine glaucoma most often strikes as a secondary condition to uveitis, specifically in Appaloosas and elder horses, and shares histopathologic similarities to chronic glaucoma.

Methods

• The team behind the study reviewed past medical records at the Ohio State University. The timeframe of these records spanned from 1999 to 2012.
• The researchers analyzed data related to the horses’ signalment, history, and treatment. They also examined histologic slides of enucleated globes and kept a record of the lesions found.

Results

• A total of 23 eyes from 23 different horses were deemed eligible for inclusion in this study. The majority of these horses were over the age of 15.
• The ages of the horses included in the study ranged from 5 to 35 years, with the mean age coming in at 17.4.
• On breakdown of the affected eyes, 10 cases involved the left eye whilst 13 cases concerned the right eye.
• Of the total cases, 56% were mares and 44% were geldings.
• Various breeds were included in the research, the most common being Quarter Horses (30%), followed by Appaloosas (26%), and Thoroughbreds (22%).

Common Histopathologic Changes

• Hypercellularity of the optic nerve in 93% of cases
• Retinal atrophy in 89% of cases
• Corneal vascularization and descemetization of pectinate ligaments each in 83% of cases
• Hypercellularity of the anterior corneal stroma in 75% of cases
• Posterior bowing of the iris base and ciliary body atrophy each in 74% of cases
• Corneal striae in 70% of cases
• Pars plana elongation in 60% of cases
• Cataract in 53% of cases
• Collapsed ciliary cleft/trabecular meshwork in 52% of cases

Secondary Evidence of Uveitis

• Evidence of uveitis was present in 87% of eyes, identified by cataracts, lymphoplasmacytic infiltration of the uvea, and/or anterior or posterior synechiae.
• The main conclusion that can be drawn from this is that equine glaucoma most frequently occurs secondary to uveitis, particularly in Appaloosas and older horses.

Additional Findings

• The histologic changes witnessed in this study mirror prior reports on chronic glaucoma.
• Finding special mention were indications not previously seen in horses – posterior bowing of the iris base and the superior retina escaping atrophy related to increased intraocular pressure.