Diseases of the Eye and Ear

Chapter 29 Diseases of the Eye and Ear



THE EYE


The structures of the eye in the bird are similar to those in mammals. Upper and lower eyelids and a nictitating membrane are present. Modified feathers called filoplumes are present at the margins of the lids and function like eyelashes, for protection and tactile stimulation. The leading edge of the nictitans is pigmented. The harderian gland, the major source of tear production, is located at the base of the nictitating membrane.


The cornea resembles that of the mammalian animal. The iris of most birds is brown, although other colors may be seen. The iris of cockatoos is sexually dimorphic, with female birds having red irises and male birds having brown ones. Young African gray parrots have brown irises whereas those of adults are more grayish. Young Amazons will have brown irises that become red–orange as they age, and macaws have brown irises that become gray between 1 and 3 years of age, then turn yellow in older birds. Direct pupillary light reflexes are demonstrable, but consensual reflexes are absent in the avian. The vitreous body is large and transparent. The fundus is usually gray or red. The optic disk is elongated and barely visible because of the presence of the pecten. The pecten is a vascular structure believed to be involved in the nutritional support of the retina, in the acid-base balance of the inner eye, and it may agitate the vitreous during eye movement. No tapetum is present in the avian retina. Color vision is well developed in pet birds.



Aug 31, 2016 | Posted by in GENERAL | Comments Off on Diseases of the Eye and Ear
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