Figures 1 2to
3show the distributions of annual rate of change by ocular function and genotype. The
x-axes are all spaced in intervals of 0.1 log
e unit (i.e., ∼10%) and, for a given measure of ocular function, span the same range. The modal values provide a gauge of the variation in rate of change and represent 60.6% to 61.8% of cases for visual acuity, 47.6% to 54.7% of cases for visual field area, and 33.3% to 40.4% of cases for cone ERG amplitude. Even though these modal values, on average, represent only about half of each group of change scores, it is still possible to discern differences in these distributions that parallel the mean differences cited. With the location of the mode on the
x-axis for the
USH2A patients as reference, the cumulative percentage of cases to the left of this value (i.e., associated with faster progression) for visual acuity is 9.9% in
USH2A patients, 6.7% in
RHO patients, and 19.5% in
RPGR patients. The cumulative percentage of cases to the left of the
USH2A mode for visual field area is 31.2% in
USH2A patients, 11% in
RHO patients, and 19.5% in
RPGR patients. The cumulative percentage of cases to the left of the
USH2A mode for cone ERG amplitude is 37.6% in
USH2A patients, 12.3% in
RHO patients, and 15.1% in
RPGR patients. Thus, the visual acuity distribution in the
USH2A patients tends to lie between those of the
RHO patients and
RPGR patients, whereas the visual field and ERG distributions in the
USH2A patients tend to be to the left of the corresponding distributions for the
RHO and the
RPGR patients—similar to that observed for mean rates of change.