Pattern of dysfunction in progressive cone dystrophies--an extended classification.

An extended classification for progressive cone dystrophies is proposed on the basis of the retrospective analysis of the clinical and electrophysiological findings obtained in a series of 91 patients with progressive cone dystrophies and of a review of the literature. This classification depends on the different patterns of electroretinographic responses. Four main categories and ten subgroups are distinguished. Generalized cone dystrophies are most frequent (76/91), affect all types of cones, and may be subdivided according to the degree of rod involvement. In selective cone dystrophies (8/91), the three cone types are affected differently as detected with the color electroretinogram. They are subdivided on the basis of the cone type predominantly involved. Additional inner retinal transmission defects may occur in cone dystrophies (3/91). They are identified by an alteration in the b/a-wave ratio on the electroretinogram and may affect the cone or rod pathway. Localized cone dystrophies (4/91) are limited to certain retinal areas.