Purchase this article with an account.
Xiaoying Zhu, Ashmeet Sidhu, Naomi R. Cernota, Josh Wallman; The Effect of Eye Size on Lens-Compensation in Chicks. Invest. Ophthalmol. Vis. Sci. 2012;53(14):3441.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
The size of all body-parts is regulated by homeostatic developmental mechanisms, generally poorly understood (here referred to "shape-factor"). Eyes have an additional, visual, homeostatic mechanism, permitting compensation for superimposed defocus. These mechanisms can work in opposite directions (as when emmetropic eyes of normal dimensions elongate in compensation for spectacle lenses) or in the same direction (as when eyes made elongated and myopic by spectacle lenses have the lenses removed). We ask whether the visual mechanism entirely dominates compensation for spectacle lenses or whether the shape-factor is also operative.
In one experiment, chicks first wore +7D lenses over one eye for 5 days (to ensure full compensation), then +15D lenses for 5 days, so that eyes (already shorter than fellow eyes) experienced 8D of myopic defocus at the time of switching. For comparison, other chicks had a similar degree of myopia from the removal of -7D lenses. In another experiment, chicks first wore -5D lenses over one eye for 7 days, then -10D lenses for 4 more days, so that eyes (already longer than fellow eyes) experienced 5D of hyperopic defocus at the time of switching. For comparison, other chicks had a similar degree of hyperopia from the removal of +7D lenses.
Eyes in which the visual and shape-factors were in the same direction (removal of spectacle lenses) showed greater changes in choroidal thickness than those in which lens-compensation required further deviations from normal eye dimensions. In terms of refractions, chick eyes fully compensated for +15D lenses after they have compensated for +7D lenses, despite having reduced ocular length (8.5 mm, 500 µm shorter than fellow eyes) at the time of switching, suggesting that myopic defocus dominated the eye-shape factor in these abnormally short eyes. On the other hand, chick eyes did not fully compensate for -10D lenses after having compensated for -5D lenses, which resulted in their eyes having been longer (9.2 mm, 100 µm longer than the fellow eyes) at the time of switching. This suggests that abnormally elongated eyes are restrained in their further elongation despite the same degree of defocus experienced.
The shape-factor influences lens-compensation. Abnormally long eyes seem more influenced by the shape-factor than abnormally short eyes.
This PDF is available to Subscribers Only