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Maria Walker, Rebecca Kivlin, Nathan Doble; Measurement of the Photoreceptor Pointing in the Living Chick Eye. Invest. Ophthalmol. Vis. Sci. 2013;54(15):3430.
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The chick retina is a widely used animal model in the study of eye growth, in particular for the study of emmetropization and myopia. Like most eyes, the ability to image the fine retinal structure is degraded by the aberrations in the lens and cornea. In previous work, we showed in-vivo images of individual chick photoreceptors taken with an adaptive optics (AO) fundus camera (Headington et al. Current Eye Research, 2011). Here we utilize this imaging capability to examine the individual cone directionality of the chick photoreceptors.
Two White Leghorn chickens (Gallus gallus domesticus) (age 30d, approx. 650g) were anesthetized with a combination of Ketamine/Xylazine and dilated with Vecuronium Bromide suspension prior to imaging. The AO fundus camera at the New England College of Optometry was modified in order to image the smaller 3mm pupil of the chick. Translating the entrance pupil position of the imaging beam (650nm) allowed for the measurement of the individual cone pointing. Thirteen entrance pupil positions were tested to obtain 1-degree FOV retinal images; four retinal images were registered for each position. Upon compensating for the variation in incident light intensity due to light delivery optics, a centroiding algorithm was used to determine the directionality of individual cones.
Upon projection of the cone pointing toward the pupil plane, the degree of disarray was found to be slightly larger than that found in the human eye. Interestingly, our initial results show an elliptical pointing pattern in the pupil plane with major and minor axes of 0.5 and 0.2 mm respectively. The major axis was horizontal and the center of the pattern lay on average 0.5 mm from the pupil center.
Similar to the human eye, the chick photoreceptor disarray is small, implying that the receptors are aligned to maximize the signal coming through the center of the pupil aperture.
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