Subjects in group 1 (
n = 20) had a median age of 15.6 years (interquartile range, 12.3, 15.5; range, 8.9 to 47.4) years and subjects in group 2 (
n = 14) had a median age of 42.1 years (interquartile range, 33.7, 48.4; range, 21.6 to 65.0). Summary characteristics of best and worst visual acuity, width of horizontal gaze with best visual acuity, and GDFVS over 60° horizontal gaze in 10° steps test–retest are found in
Table 1. The mean difference in test–retest visual acuity is found in
Table 2. On average, subjects in both group 1 and group 2 had a mean difference in visual acuity of less than 0.1 logMAR at each gaze position. The intraclass correlation coefficients were high in both group 1 (≥0.97) and group 2 (≥0.88) for all gaze positions (
Table 2). As seen in
Figure 3, there were no significant differences in visual acuity test–retest detected between groups (
P = 0.053) or gaze positions (
P = 0.266). There was also no evidence of an association between the differences in test–retest visual acuity and gaze position (
P = 0.79). Additionally, a significant association was not detected between age and the difference in GDFVS (95% CI: −0.07 to 0.03;
P = 0.492).
On average, the absolute mean difference in GDFVS for the 60° of horizontal gaze evaluated between test–retest in group 1 was 2.0 ± 1.56 logMAR
2/degrees and 1.96 ± 1.51 logMAR
2/degrees for group 2. To apply the test–retest GDFVS results of experiment 1 to the subjects in the INS treatment study, the mean difference in the test–retest group was recalculated using only 40° of horizontal gaze, similar to that measured in the subjects in the INS treatment study to determine the appropriate 95% limits of agreement. The Bland-Altman plot is shown in
Figure 4. On average, the absolute mean difference in GDFVS for the 40° of horizontal gaze tested between test and retest was 1.53 ± 1.11 logMAR
2/degrees for group 1 and 1.50 ± 1.06 logMAR
2/degrees for group 2. The 95% limits of agreement in subjects with INS was [−4.14 to 3.08], and the 95% limits of agreement for the control subjects without INS and typical vision was [−4.38 to 2.98].