Lower eyelid with "tarsus," no meibomian glands. Palpebra inferior larger than palpebra superior (exclusive owls). Tubular type (nocturnal birds, for example strigiformes). Conical type (diurnal birds with broad heads, for example falconiformes).ĭ. Flat type (diurnal birds with narrow heads, for example columbifomes).Ĭ. Determination by anulus ossicularis sclerae (10-10 single bony platelets). 12 % (juv.) compared to overall head weight.Ī. Weight (Oculus sinister (OS) and oculus dexter (OD) in man 1 %, Fowl 7 % (adult) resp. Axial length 8 mm (Kiwi, Aptery sp.) up to 50 mm (Ostrich, Struthio camelus).ī. Some anatomical peculiarities with relevance for the ophthalmologist are:Ī. Though there exist numerous anatomical and physiological difference-like the striated rather than smooth intraocular musculature, the anangiotic fundus oculi, the pecten oculi-basically the approach to avian ophthalmology is quite similar to that employed in mammalian ophthalmology. Thus, canaries, suffering from blindness due to cataract formation-a condition which occurs quite often in this species-act normal, as long birds as long as the interior of the cage or aviary is not modified. On the other hand, even complete blindness is not a reason for euthanasia in pet birds. It should be recognized that ultraviolet-perception (UV-perception between 320 and 680 nm), an ability common in diurnal birds bound to special UV-sensitive rods within the retina and an aspect not investigated very well to date, plays a probably plays a very important role in inter- and intraspecific communication based on plumage-UV-reflection, even in birds which appear monomorphic for the human eye, for the identification/assessment of fruit ripeness based on varying UV-reflection of fruit wax layers, for phenomena of camouflage, orientation other. Thus visual acuity is 2 to 8 times higher compared to mammals, visual fields are up to 360°, stereopsis ranges from 0° to 70°, maximum spatial frequency (the ability to resolve a certain movement into single frames) is up to 160 frames/sec (10-15 in man) and minimum detection of movements is up to 15°/hour (very slow movements). The eye as the main sense organ in birds and its visual capacities have no general superiority compared to mammals but shows a highly specialization as an adaptation to living conditions. Visual function in birds is essential for flying, surviving in the wild and reproduction. Regarding to these facts avian ophthalmology is not a highly specific working field within avian medicine but it should be an integral part of the general examination procedure. Ophthalmoscopy, i.e., examination of the posterior eye segment, therefore is obligatory in traumatized birds. Thus, the avian eye may be seen-in a much larger extent than in mammals-as a "diagnostic window." On an average, up to 35 % of all traumatized birds (incidence generally higher in raptors than in pet birds) are suffering from ocular lesions, which are most often hidden within the inner structures of the eye. The ocular symptomatology frequently enables specific conclusions to be drawn on suspected disorders or it may even be pathognomonic for a certain disease. Since ocular lesions in birds are an expression of systemic disorders more than in mammals, they represent an important diagnostic criterion. Books & VINcyclopedia of Diseases (Formerly Associate).VINcyclopedia of Diseases (Formerly Associate).
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