To compare the effects on the postnatal development of the eye of both total and partial form deprivation in diurnally reared chicks and of dark-rearing, chicks were reared with occluders covering one eye from hatching for up to 6 weeks. In diurnally reared birds, both total and partial form deprivation resulted in severe axial myopia and increased eye size. These effects were greatest for the eyes of chicks raised with total form deprivation; they had highly curved corneas and very deep anterior and vitreous chambers. In addition, the amount of myopia produced in eyes with total form deprivation was the same at 2 and 6 weeks, whereas eyes with partial form deprivation showed substantial remission even with the occluders left on. The partially deprived eyes developed a striking shape asymmetry: the posterior globe only became enlarged in the deprived region of the retina. The eyes of dark-reared chicks, regardless of whether or not an occluder was worn, also were enlarged but were hyperopic owing to a severe flattening of the cornea. This hyperopia was slow to develop compared to the myopia produced in the diurnally reared visually restricted eyes. Finally, the shape of the posterior globe of these hyperopic eyes was no different from that of normal eyes.
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