Representative maps of CS obtained for the two stimuli conditions (LSF and ISF) from representative (close to the median) patients with STGD, morphologically unaffected relatives, and control subjects are shown in
Figures 3 and 4 . As expected from known relative cone distributions, CS was higher in central locations than in the more peripheral regions for both CS methods. The LSF task yielded higher CS than did the ISF-task in all groups (in age-matched control subjects mean CS was 29.4 ± 3.4 dB in the LSF-condition and 25.2 ± 7.2 dB in the ISF perimetric tests). Three patients with STGD were excluded (of 27) due to unstable fixation.
LSF-biased perimetry revealed significant impairment in patients with STGD in comparison to their relatives and control subjects (P < 0.0001 for both comparisons). Of note, the patients’ performance was significantly impaired across the whole visual field and not only at the central-most regions (P < 0.0001 for zones 0, 1 and 2, for both CS methods). For the ISF task the deterioration of CS function in patients with STGD was even more evident (patients’ mean CS was 17.3 ± 8.7 and 10.8 ± 7.7 dB for the LSF and ISF tasks, respectively).
Concerning morphologically unaffected relatives, LSF perimetry showed, as expected, significantly better performance than in patients with STGD for all tested zones (P = 0.0008 for zone 0; P < 0.0001 for zones 1, 2). However, we were surprised to find significant differences between these morphologically unaffected relatives and control subjects across the whole visual field (P < 0.0013, P = 0.0045, and P = 0.0009, for zones 0, 1 and 2, respectively). Again, similar results were obtained with the ISF test (P < 0.0187, P < 0.0001, and P = 0.0012 for zones 0, 1, and 2, respectively). These asymptomatic relatives had CS performances that were between the patients with STGD and the control group, for both CS tasks (mean CS was 26.5 ± 5.3 and 21.0 ± 8.2 dB for the LSF and ISF conditions, respectively). In summary, STGD relatives seem to be relatively impaired in both CS tasks. In other words, morphologically unaffected relatives might represent a pre-STGD stage with CS impairment (also discussed later in the article).