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M. L. Kisilak, J. J. Hunter, E. L. Irving, M. C. W. Campbell; In vivo Imaging of Photoreceptors in the Alert Chicken. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1191.
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In vivo measurements of photoreceptors in the chick eye are desirable given in vitro measurements in the literature, which suggest changes in cone morphology with the induction of myopia. In vivo images would allow longitudinal measurements of the angular photoreceptor spacing in the growing chick eye and during the induction of refractive errors. This data could then be compared to various models of eye growth. There have been very few objective measures of the retinal morphology in the growing chick eye and no in vivo measurements.
Both eyes of 4 chickens (21 days old Ross Ross) were imaged in a confocal scanning laser ophthalmoscope in a 6 degree field of view (633nm light). The right eyes of these birds had recovered from lens-induced hyperopia. Angular photoreceptor spacing was measured directly and Fourier transforms were performed on sub-regions of averaged images. Hartmann-Shack wavefront measurements (633nm light) and ultrasound were performed following the imaging session. Hartmann-Shack images were analyzed for the largest common pupil size among birds. Imaging was also attempted on a subsequent set of younger birds.
A moderately-sized confocal pinhole produced high contrast real-time images of photoreceptors in eyes of alert chicks. Axial length measurements showed no significant differences between left and right eyes (paired t-test). Photoreceptors were successfully imaged in six of the eight eyes (day 21). Hartmann-Shack measurements confirmed that the two eyes that were not successfully imaged had poorer optical quality. Direct measurements of photoreceptor diameters were consistent with known in vitro morphology. Photoreceptor spacing given by both Fourier transforms (Yellott’s ring) and direct measurements were consistent with literature data suggesting that we imaged more than one photoreceptor class. Photoreceptors were also imaged in alert 2 day old chicks.
We have successfully imaged in vivo photoreceptors in alert chick eyes (day 2 and day 21). These measurements are not confounded by the artifacts found with in vitro measurements (for example shrinkage) and will allow for longitudinal tracking of developmental changes in photoreceptor sampling within a single eye.
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