SELECTIVE CONE DYSTROPHY WITH PROTAN GENOTYPE

Purpose. To determine the functional defects in two male patients with progressive cone dystrophy and hybrid LM cone pigment genes. Methods, Clinical evaluation, standard electroretinography, and electrooculogr aphy were performed in two affected patients and two family members. M easurements of spectral sensitivity and transient tritanopia were made in both patients. Results. In the patients, visual acuity varied betw een 20/50 and 20/100. The electroretinogram showed reduced flicker res ponses. When light adapted, a-wave amplitudes were borderline, but b-w ave amplitudes were reduced severely. Electroretinography with chromat ic stimuli showed a difference between well-preserved responses to gre en and markedly reduced responses to red stimuli. Spectral sensitivity measurement revealed a lack of L (long-wavelength sensitive; red) con e function and normal function of the S (short-wavelength sensitive; b lue) and M (middle-wavelength sensitive; green) cones. Transient trita nopia was abnormal, indicating a severe disturbance of cone-cone inter action. Conclusions. Progressive cone dystrophy with predominant dysfu nction of L cones exists in both patients. The cone dystrophy may be c aused by a rearrangement of the X-chromosome pigment gene array that i s associated with the deletion of L-cone sequences and the formation o f hybrid L-M cone pigment genes. It cannot be excluded, however, that both patients have protanopia and that cone dystrophy developed becaus e of other causes.