Progressive visual loss and severe retinal degeneration in a captive Kodiak bear (Ursus arctos mittendorfi)

Abstract

A 27-year-old female Kodiak bear displayed signs of progressive visual loss over an 18-year period. The bear was examined under general anaesthesia, where fixed mydriatic pupils, a diffusely hyper-reflective retina with vascular attenuation was observed. An electroretinogram was performed bilaterally, revealing no electrical activity associated with either retina and confirming a diagnosis of severe bilateral retinal degeneration. The bear was euthanased eight months later due to a diagnosis of a metastasised hepatic neoplasm. Histopathology of the bear’s eyes revealed marked outer layer retinal degeneration. The aetiology of this retinal degeneration could not be confirmed.

Morphology and Histology of the Orbital Region and Eye of the Asiatic Black Bear (Ursus thibetanus)—Similarities and Differences within the Caniformia Suborder

“…The literature describing the correct structure of the skull while taking into account the anatomical description of the orbital region, the eyeball and the accessory organs of the eye at the macro and microscopic level in the family Ursidae (American black bear Ursus americanus [ 23 , 24 ]; Asiatic black bear Ursus thibetanus [ 25 ]; North American brown bear or Grizzly bear Ursus arctos horribilis [ 26 , 27 ]; brown bear Ursus arctos [ 28 , 29 , 30 , 31 ], sloth bear Melursus ursinus [ 25 , 32 , 33 , 34 ]; Sun Bear Ursus malayanus [ 25 ]; polar bear Ursus maritimus [ 27 ]) are very limited. On the other hand, studies on clinical case descriptions of diseases of the eyeball and accessory organs of the eye in representatives of this family are much more frequent [ 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 ]. A review of the literature describing the morphology of the eye socket, eye tunics, eyelids and orbital glands in suborder Caniformia is presented in Table S1 .…”