1997 Volume 16 Issue 3-4 Pages 3-4_73-3-4_85
Objective: Trypsin digestion and scanning electron microscopy techniques were utilized in conjunction with computerized image analysis to examine the surface of the scleral lamina cribrosa in normal and glaucomatous horse eyes.
Sample Population: Six normal horse eyes were compared to eight glaucomatous equine eyes.
Procedure: The trypsin digestion procedure enzymatically removed all neural, vascular and glial components of the optic nerve leaving only the connective tissue framework of the scleral lamina cribrosa. Measurements of the vitreal surface of the scleral lamina cribrosa were made of individual laminar pore areas, total laminar pore number, and individual pore form factor for each eye.
Results: Statistical results demonstrated that the glaucomatous equine lamina cribrosa had a significantly higher mean total pore count (glaucoma: 959±218 pores vs. normal: 560±258 pores; p=.01), a larger mean sectional pore density (glaucoma: 70±20 pores/mm2 vs. normal: 43±25 pores/mm2; p=.04), smaller individual mean median pore areas (glaucoma: 1,952±544μm2 vs. normal: 5,282±2,089μm2; p=.0005), and a more circular, or less flattened, pore shape (p=.004), especially near the center, when compared to laminar pores of the normal equine lamina cribrosa. The intralaminar optic nerves of glaucomatous horses contain a higher percentage of connective tissue (74.2%) than the optic nerves of normal horses (67.4%).
Conclusions: The intralaminar optic nerve of glaucomatous horses contains a significantly larger total number of laminar pores, pores of significantly smaller individual area, and pores of rounder shape than the intralaminar optic nerve of normal horses. These differences may represent an anatomic variation found in horses predisposed to develop glaucoma, as well as changes resulting from intraocular pressure-induced radial stress forces causing stretching of the scleral lamina cribrosa.
Clinical Relevance: Morphologic information is provided that may partially explain the ability of the horse eye to retain vision in spite of sustained elevated intraocular pressure.
