As the disease progresses, some cone function may still be recorded after the rod response is extinguished. Leber's congenital amaurosis is an inherited retinal disorder characterized by diffuse photoreceptor cell disease. Once poor vision is suspected, an ERG showing markedly reduced amplitudes will indicate this disorder. This may spare the patient and family costly neurologic and radiologic examinations looking for a central visual disorder. These dystrophies are inherited through autosomal dominant, autosomal recessive, and X-linked recessive mechanisms.
Patients usually manifest with loss of acuity, central scotomata, and defective color vision .
In patients with cone dystrophy, cone ERG recordings are attenuated or extinguished, however rod ERG recordings may be minimally affected in the early stages of the disease. Patients with cone-rod dystrophies will show markedly reduced or absent cone ERGs and reduced rod ERGs. In many forms of congenital stationary night blindness, the patient presents with poor night vision and is myopic. However, some patients with both the autosomal recessive and X-linked forms do not exhibit myopia, and have normal visual acuity. Further, some patients do not complain of night blindness.