A comparative study was performed to compare methods of quantitative evaluation of damage to photoreceptor cells in rat eyes exposed to light. Using a manual count of individual photoreceptor nuclei as the standard, the following measurements were compared: (1) outer nuclear layer column count, (2) area, (3) thickness, and (4) the number of nuclei of the outer nuclear layer of the retina using a newly developed computer program that counts a digitized image. Linear-regression analysis of the data showed that the computer method was the most accurate with a Pearson correlation coefficient of 0.9911. The other methods tested also correlated well with the manual count, with coefficients ranging from 0.9367-0.9532. All these methods were reasonably accurate measurements of photoreceptor layer integrity, with the computer count most closely approximating the values obtained by a manual count. However, the outer nuclear layer thickness measurement appeared to be the fastest and most convenient method to evaluate photoreceptor cell damage quantitatively. Computer counting could be reserved for situations in which a high degree of accuracy is required.