Electroretinography changes in carriers of X-chromosomal retinitis pigmentosa

Out of five families with pedigrees typical for X-linked retinitis pigmentosa (RP) the authors examined eight definite and eight possible female carriers. Subjective symptoms were mild and variable, consisting mainly of relative nyctalopia. Ophthalmoscopic examination revealed a normal fundus, or mild changes suggestive of RP, or even marked changes. Perimetry (Goldmann) revealed some narrowing of the outer isopter corresponding to a significant reduction in visual field area. In testing dark adaptation, the final rod threshold was slightly elevated in five out of 16 subjects. Ganzfeld-electroretinography using matched band filters in conditions of dark and light adaptation to selectively stimulate rod and cone signals revealed reduced b-wave amplitudes in most cases. White stimuli, applied in dark adaptation, generated ERGs with less abnormality than the selective rod and cone ERGs. Peak times of the cone b-waves were prolonged in most cases. The ERG abnormalities were more pronounced in definite carriers and in advanced age. In some cases remarkable differences were noted between the two eyes as regards fundus morphology and ERG responses. The authors conclude that the possibility of improved genetic and educational counseling in families afflicted by X-linked RP justifies the considerable diagnostic effort involved in such examinations.