Abstract
Abstract: :
Purpose: Hartmann–Shack aberrometry provides more precise measurements of astigmatism in small chick eyes than previous capabilities would allow. We wish to track astigmatism in normally developing eyes and in eyes with lens induced myopia. Methods: On the first day post–hatching, 16 chicks were unilaterally fitted with minus 15D goggles. The other eye acted as a control. On days 0, 2, 4, 7, 9, 10, and 14, goggles were removed for brief periods of time for Hartmann–Shack wavefront measurements (633nm light) and retinoscopy. Both eyes were measured in six additional birds allowed to develop without goggles. Hartmann–Shack images chosen for analysis corresponded to larger pupils and were presumed to be unaccommodated. Astigmatism was calculated for 1.6 mm pupils. Results: In chicks, Hartmann–Shack measurements are able to repeatedly measure cylinders within 0.25D. In birds without goggles, smaller amounts of cylinder did not change significantly with growth. In the control eyes of the goggled birds, initially higher values of cylinder decreased significantly (p<0.02) with age to values not different from the control birds on day 7. The standard errors of the means significantly (p<0.01) decreased exponentially with age. Cylinder values in the treated eyes of the goggled birds did not change significantly with age and the standard errors of the means did not decrease significantly. The oblique Jackson cross cylinder (JCC45) terms were not significantly different between eyes in the goggled birds on day 0. By day 14, the JCC45 terms were significantly smaller in the control eyes (p=0.01). With age, the larger JCC0 terms of the control eyes of the goggled birds decreased significantly (p<0.02) to values not significantly different from eyes of ungoggled birds. Neither JCC term changed significantly with age in the goggled eyes. The standard errors of the mean were consistently higher in the older goggled eyes than in eyes that were not goggled. Conclusions: These results are consistent with the emmetropization of astigmatism in chick eyes without goggles. Lens induction of myopia causes changes in the optical components of the treated eye relative to the control eye in goggled birds and relative to the eyes of birds without goggles. Lens induction of myopia interferes with the emmetropization of astigmatism.
Keywords: astigmatism • optical properties • myopia