Optimized architecture for nutrition in the avascular retina of Megachiroptera.

Investigations were undertaken to evaluate the unique choroidal vascular system of the Megachiroptera (fruit bats) and its possible significance for retinal nutrition. Fluorescein angiography was performed and documented on Pteropus poliocephalus. Vascular casts were made of the eye of Pteropus scapulatus. Histologic evaluation was performed on P. scapulatus. Results confirmed that each papilla has a vascular core, and a unique vascular system emanating from the optic disc. The histological appearance of the choroid and retina of P. scapulatus confirmed a vascular core to the papillae with a thin, but definite Bruch's membrane. Megachiroptera have a unique vascular system to supply nutrition to the retina consisting of capillary loops within a dense, uniform mosaic of choroidal projections or papillae, which permit the diffusion of metabolites to the retina and a heretofore undescribed vascular tuft emanating from the optic disc. We suggest that this vascular system provides nutrition by diffusion to a thick avascular retina, without any shadowing by vessels, and allows for nocturnal visual acuity and light-gathering capabilities.

Central corneal dermoid in a Labrador retriever puppy.

An eight-week-old, male Labrador retriever puppy was presented with an abnormal appearance of the left cornea, observed after the eyelids opened in the second week of life. Ocular examination showed a large central dermoid of the left cornea. The dermoid was excised by superficial keratectomy, and healing was uneventful. The dermoid was classified as a Mann's second type. To the authors' knowledge, a Mann's second type corneal dermoid has not previously been reported in a dog.