Selected issues in the anatomy and physiology of the avian organ of vision and eye disorders in farmed poultry

The aim of this article was to review current knowledge of the anatomy and physiology of the avian eye and ocular diseases in poultry. The avian visual organ consists of the eye and extraocular organs and, unlike the mammalian eye, is characterised by many structural and functional adaptations that enhance vision. Avian eyes do not have the same functions as mammalian eyes. Bird eyes have high sensory sensitivity and are capable of constellation recognition for star orientation and navigation; they may be regarded as the finest ocular organs in the animal kingdom. It is generally accepted that the considerable differences in the morphology and function of avian eyes are largely due to adaptations to specific activities and environmental conditions. Eye diseases are rarely diagnosed in poultry because, unlike livestock and pets, detailed ophthalmological examinations are not carried out on farmed birds. Nevertheless, poultry are frequently affected by ocular pathologies, including developmental abnormalities, infectious and non-infectious diseases, degenerative processes, tumours, injuries and pathological conditions of unknown aetiology. In poultry, ocular disease is often associated with respiratory and systemic disease. Ocular pathology in farmed birds has a complex aetiology and its incidence can be reduced by controlling the incubation parameters of hatching eggs, avoiding feeding errors in breeder flocks and rearing poultry under conditions that optimise welfare and comply with biosecurity standards.