Design: This study will be comprised of three related projects. For Aim 1, color discrimination thresholds (CCT and LvCCT) and assessments of retinal structure (imaging) and function (perimetry/microperimetry and electroretinogram) will be measured in 144 IRD participants with varying retinal phenotypes and visual acuities. IRD participants will be divided into four major categories: 1) cone & cone-rod dystrophies, 2) rod-cone dystrophies, 3) inherited maculopathies, and 4) inherited retinal dysfunction syndromes. The fourth category will be used for IRDs that do not match the description for categories 1-3 (i.e., x-linked retinoschisis, congenital stationary night blindness). Degree of severity of retinal dysfunction in IRD participants will be determined relative to the normal ranges obtained from the healthy volunteers (see Aim 3a below). For Aim 2 color discrimination thresholds (CCT and LvCCT) will be measured in one eye from 12 healthy volunteers in order to examine the effects of eccentric fixation and reduced visual acuity on color thresholds independent of retinal pathology. Between one and three study visits will be required for this aim. Aim 3 will be comprised of two parts. For Aim 3a, color thresholds will be collected from both eyes (for intraocular variability) of 35 healthy volunteers age 5 or older. For Aim 3B, color discrimination thresholds (CCT and LvCCT) will measured from 12 healthy volunteers twice in one session and then again at a second visit occurring within two months of the initial visit to determine intra-session and inter-session variability.