Despite severe imposed astigmatic blur, chicks compensate for spectacle lenses

Purpose: Is compensation for spectacle lenses simply a special case of deprivation myopia? Using lenses with +5D in one meridian and -5D in the other (OD mean spherical power), we imposed defocus that could not be cleared by accommodation. We asked whether these lenses, like diffusers, would cause myopia and whether they would prevent lens compensation. Methods: Cornell K chicks were fitted at day 6 with these astigmatic lenses oriented with the rule, against the rule or at 45 degrees. These lenses were also combined with +6D and -6D spherical lenses. Refractive error of anesthetized chicks was measured with a Hartinger refractometer. Results: With the +5D/-5D lenses alone, there is a statistically significant trend in the hyperopic direction, in all three lens orientations. With the combined lenses compensation was unimpaired. Conclusions: Despite the lack of clear images, chicks compensate for both hyperopic blur (negative lenses) and myopic blur (positive 4 lenses). Astigmatic defocus alone caused eyes to grow toward hvoerooia. instead of towards myopia as predicted by the form-deprivation hypothesis.