Lack of oblique astigmatism in the chicken eye

AbstractPrimate eyes display considerable oblique off-axis astigmatism which could provide information on the sign of defocus that is needed for emmetropization. The pattern of peripheral astigmatism is not known in the chicken eye, a common model of myopia. Peripheral astigmatism was mapped out over the horizontal visual field in three chickens, 43days old, and in three near emmetropic human subjects, average age 34.7years, using infrared photoretinoscopy. There were no differences in astigmatism between humans and chickens in the central visual field (chicks −0.35D, humans −0.65D, n.s.) but large differences in the periphery (i.e. astigmatism at 40° in the temporal visual field: humans −4.21D, chicks −0.63D, p