The purpose of the proposed research is to develop a model of myopia that could be used to evaluate treatment techniques for ultimate application to humans. Our preliminary experiments have indicated that defocus of the retinal image in domestic chicks for the first three weeks of life results in an increase in the diameter of the globe of the eye that is suggestive of myopia.
The specific aims of the proposed research are to replicate our preliminary findings using more precisely defined optical devices and then to use behavioral techniques to assess the degree of myopia. The myopia will be calculated from a comparison of the far point of accommodation in treated and untreated chicks. Visual acuity and intensity difference thresholds will be determined in order to assess whether the defocussing procedure has produced impairments of visual information processing either in the retina or centrally. If myopia is present in the chicks, an attempt will be made to correct the defect by interposing an optometric trial lens between the cornea and the target. Finally, an attempt will be made to evaluate the hypothesis that a cause of myopia is intensive and prolonged inspection of the spatial properties of visual stimuli close to the near point of accommodation by comparing the eyes of untreated subjects in visual acuity tests with the eyes of another group of chicks that have had equivalent experience with a test of comparable difficulty, but in which the spatial properties of the stimulus are irrelevant. The advantages of such a model are (1) very low expense, (2) very rapid development and (3) suitability for the evaluation of mechanical and surgical treatments for myopia, such as orthokeratosis, radial keratotomy, keratomileusis, hydrogel lenticular implantation, etc.
