![]() Second, as the bird retina is cone dominated, any deficits in albino strains may be relatively minor. Although there is a common time table for the development of the mammalian visual system when expressed in terms of the caecal period, which is between conception and eye opening, the pace of retinal development in birds is accelerated, which may alter interactions between these regions. Albino mammals have specific deficits in their retinae and in the pattern of decussation at theiroptic chiasm, demonstrating that a melanin-related agent is crucial for normal development of thevisual system.Although much attention has been paid to the chiasmatic abnormality over the past30 years, little progress has been made in understanding t. First, normal mammalian retinal development may depend partly on time-dependent interactions in the maturation of the retinal pigment epithelium and the neural retina. There are two possible explanations for this result. Consequently, the underdevelopment of the central retina seen in hypopigmented mammals does not occur in this bird. Although there were variations in the measurements undertaken between the strains, none were pigment related or consistent with the abnormality found in the central retina in albino mammals. po0.05 was considered statistically allows an independent approach regardless of the density of significant. Each strain of bird had an area of increased retinal layer thickness in dorso-temporal regions, but not a fovea. Student’s t-test or Mann- approach is independent of a weight reduction in the albino Whitney rank sum test was employed to compare pigmen- retina as well as of the protein content 12 and, therefore, ted vs albino retinae. Estimates of cone numbers were also made. Measurements of layer thickness, cell density and cell size were made at a range of locations in the ganglion cell layer and in the inner and the outer nuclear layers. Retinae from normally pigmented and two forms of hypopigmented budgerigars (Melopsittacus undulatus) were studied. Also if one of the primary effects of albinism is centred on rods, then albino birds may not show a deficit, because their retinae are cone dominated. Consequently, examination of the retinae of hypopigmented birds will reveal whether there is a relationship between the two abnormalities. Birds have a highly developed central retina, but unlike most mammals they do not have a significant uncrossed retinal projection. This study addresses the question of whether pigment-related abnormalities occur in the central retina of a non-mammal, the bird. Also, many ganglion cells in temporal regions project inappropriately to the contralateral hemisphere. In the outer retina this deficit is confined to rods. The central retina in hypopigmented mammals is underdeveloped.
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