The present disclosure describes a psychophysical test to assess the cone photoreceptor pathway by determining the sensitivity of the cone photoreceptors. The test may be used to determine of a subject is suffering from, or is likely to suffer from, a disease state involving the fovea, parafovea, macula, neurological pathways used by these area to communicate with the visual processing centers in the brain and cone photoreceptors and/or ganglion cells. The present disclosure also describes an apparatus for such testing purposes. Using the novel cone photoreceptor sensitivity test and apparatus, the present disclosure shows that cone photoreceptor sensitivity in subjects with primary open angle glaucoma was decreased as compared to a control group (p=0.04). This cone photoreceptor sensitivity test is shown to have excellent repeatability, can be administered in a short time, does not require extensive subject instruction and meets other limitations required for application in a clinical setting.