Waterloo Public Library

Purpose: In vivo measurements of photoreceptors in the chick eye, an animal model of myopia, are desirable. This longitudinal data will then be compared to various models of eye growth. Methods: Both eyes of 10 chicks were imaged in a confocal scanning laser ophthalmoscope in a 6 degree field of view between days 0 and day 14 and axial length measurements were taken using A-scan ultrasound. Angular cone densities were measured directly. Using focal length to eye length ratios from published schematic eye models, linear cone spacings on the retina were calculated. Initial measurements on myopic birds have also been performed. Results: Cones were successfully imaged in normal and myopic eyes. For normally developing chicks, there was a small but significant linear increase in angular cone density with growth. Paired t-tests showed no significant difference in angular cone density between days 0 and 14 for left or right eyes. Conclusions: We have imaged in vivo cones longitudinally in developing alert chicks. The ability to image cones in the young chick eye indicates that the optical quality is better than the retinal sampling by the observed cones. Our results are consistent with a linear expansion of the retina at the same rate or more slowly than the axial length change.