We present a novel method to quantitatively analyze confocal microscope images of retinas. We automatically detect nuclei within the outer nuclear layer (ONL) in a retinal image. Based on nuclei detection results, we also automatically measure the thickness of the ONL and the local cell density within the ONL. These measurements provide the first thorough quantitative analysis of retinal images. Our results not only verify previous conclusions about retinal restructuring during detachment, but also provide biologists with significant information about the regional responses in the ONL.