None of the ERG parameters (
Table 2) changed with age (1–15 years), and all were within the range reported for an older sample.
7 Furthermore, the mean amplitudes of the a-waves in dark-adapted XLRS eyes were lower than in controls throughout the stimulus range (
Fig. 2) that covers the range of stimuli used in previous studies.
4,6,7 The saturated amplitude of the rod photoresponse,
RROD (derived from the a-wave responses to the brightest flashes [
Equation 1]) was significantly below that in the controls—our values of XLRS R
ROD, at 31% to 92% of the normal mean, overlap broadly those of Khan et al.
7 (54%–123% of the normal mean). Despite the similar values, Khan et al.
7 found that the mean XLRS
RROD did not differ significantly between XLRS and their controls. These a-waves from the dark-adapted eye must be rod-dominated, although some cone contamination cannot be excluded.
27 Because our
RROD values were low, even in our youngest participants and even in those tested awake without anesthesia, compromise of the dark-adapted a-wave response, the
RROD parameter, and explicitly rod activity, may be an inherent dysfunction of the XLRS retina. Interestingly, the patients on dorzolamide had among the largest
RROD values; however, in another study of carbonic anhydrase inhibitor on isolated retina, saturated rod photoresponse amplitude was decreased.
28