Ultrastructure of the optic nerve microcirculation and lamina cribrosa in beagle dogs with hereditary primary open angle glaucoma

Mechanical and vascular theories have been proposed to explain the damage to optic nerve axons in human glaucoma. The optic nerve head tissues are structurally distorted posteriorly, both clinically and histologically, with prolonged elevation of intraocular pressure to result in axon compression and obstruction of axoplasmic flow. Optic nerve vascular antoregulatory mechanisms may also be defective and result in local ischemia from circulatory abnormalities.;Optic nerve axoplasmic flow is known to be impaired at the scleral lamina cribrosa in Beagle dogs with hereditary primary open angle glaucoma and is similar to the human condition. Trypsin and detergent digests to remove all neural, vascular and glial cellular tissue revealed a well-developed scleral lamina cribrosa in the normal dog in this study. Beagle dogs with primary open angle glaucoma demonstrated mechanical distortion of the anterior lamina cribrosa prior to the detection of ophthalmoscopic changes in the optic nerve head.;Ultrastructural examination of optic curve capillaries in the canine lamina cribrosa revealed many spherical, membrane bound, electron-dense inclusions, that closely resembled Weibel-Palade bodies, in pericytes and endothelial cells of preglaucomatous, early, moderate, and advanced glaucomatous Beagle dogs.;Scanning electron microscopy of vascular corrosion casts of the optic nerve region in normal and glaucomatous Beagle dogs demonstrated the blood supply to the canine laminar optic nerve to be derived from short posterior ciliary arteries, cilioretinal arteries and longitudinal pial vessels. No differences between the casts in normal and glaucomatous dogs were detected.;This study revealed a significant change in the supporting architecture of the optic nerve that began early and increased in severity as the disease process progressed. An ultrastructural difference between the laminar capillary endothelial cells of normal and glaucomatous Beagles could represent a functional vascular disorder, as Weibel-Palade bodies are associated with microcirculatory abnormalities. The short posterior ciliary arteries formed a ring of striated pillars around the scleral canal. No central retinal artery was present in the dog.