Cone photoreceptor disorders form a clinical spectrum of diseases that include progressive cone dystrophy (COD) and complete and incomplete achromatopsia (ACHM). Impairment or death of cone photoreceptor cells is the clinical hallmark of these disorders. COD is a progressive cone disorder in which patients may initially have normal cone function but develop progressive visual acuity loss, increasing photophobia, color vision disturbances, and diminished cone responses on ERG, usually in the first or second decade of life. The visual acuity of these patients generally worsens to legal blindness before the fourth decade of life. ACHM is a stationary congenital autosomal recessive cone disorder characterized by low visual acuity, photophobia, nystagmus, and severe color vision defects. Patients with the complete ACHM subtype have no cone function on electroretinography, whereas those with incomplete ACHM show residual cone function. [From OMIM]