Detection using the multifocal electroretinogram of mosaic retinal dysfunction in carriers of X-linked retinitis pigmentosa

Purpose: To examine whether a mosaic pattern of retinal dysfunction in obligate carriers of X-linked retinitis pigmentosa (XLRP) could be observed in local electroretinographic responses obtained with the multifocal electroretinogram (mfERG). Design: Prospective observational case series. Participants: Five obligate carriers of XLRP (mean age, 53.2 years) were recruited into the study. Methods: Examination of each subject included a complete ocular examination, Humphrey visual field, standard full-field electroretinogram (ERG), and mfERG testing. For the mfERG, we used a 103-scaled hexagonal stimulus array that subtended a retinal area of approximately 400 in diameter. The amplitudes and implicit times in each location for the mfERG was compared with the corresponding value determined for a group of normally sighted, age-corrected control subjects. Main Outcome Measures: Mapping of 103 local electroretinographic response amplitudes and implicit times within the central 400 with the multifocal electroretinogram. Results: Localized regions of reduced mfERG amplitudes and/or delayed implicit times were found in four of five carriers. In one of these four carriers, a mosaic pattern of mfERG dysfunction was present even in the absence of any clinically apparent retinal changes, retinal sensitivity losses on Humphrey field testing, or abnormal full-field cone ERG responses. However, one carrier with a typical tapetal-like reflex demonstrated no deficit on any functional tests. Conclusions: The mfERG demonstrated patchy areas of retinal dysfunction in some carriers of XLRP. This mosaic pattern of dysfunction may be observed in some patients with a normal-appearing fundus, normal psychophysical thresholds, and normal amplitude and implicit time full-field ERG cone responses. Ophthalmology 2002;109:560-568 (C) 2002 by the American Academy of Ophthalmology.