Sixteen persons with GON were recruited for the study (10 women and 1 man of European ancestry; 2 women and 3 men of African ancestry). Demographic characteristics of the patients and controls are shown in
Table 1. The patients' average age was 63.7 years (range, 42–88 years). There were 19 control subjects (3 women and 6 men of European ancestry; 3 women and 7 men of African ancestry) with an average age of 59 years (range, 49–80 years), whose data were collected in our previous study.
13 There was no significant difference in the mean age between the two groups (
t-test,
P > 0.05). The number of subjects in the race and sex categories was not sufficient to test for differences between the two groups.
Average pupil diameters of the patients were plotted against time for both control and test stimuli (623 and 470 nm, respectively;
Fig. 1A). For comparison, pupil traces for the same stimuli in the control subjects are presented in
Figure 1C. PIPR values to both red and blue stimuli were plotted against the baseline pupil diameters (
Fig. 1B; blue light,
R 2 = 0.335,
P < 0.05; red light,
R 2 = 0.034,
P > 0.05). PIPR values for the controls subjects were also plotted as a function of baseline pupil diameter (
Fig. 1D; blue light,
R 2 = 0.303,
P < 0.05; red light,
R 2 = 0.045,
P > 0.05).
Values for the baseline pupil diameter, sustained pupil diameter, and PIPR measures for red (control) and blue (test) stimuli, respectively, of the patients and age-matched controls are shown in
Table 2. For the patient population, the mean response to the blue stimulus was 0.7 mm (SEM 0.14,
P < 0.05), with a net PIPR of 0.6 mm (SEM 0.12,
P < 0.05). For the control subjects, the mean response to the blue stimulus was 1.5 mm (SEM 0.15,
P < 0.05),) with a net PIPR of 1.3 mm (SEM 0.16,
P < 0.001).
For subsequent analyses, we used the net PIPR values.
Figures 2A and
2B show the relationship of the net PIPR (
Fig. 2A;
R 2 = 0.433,
P < 0.05) and the net PIPR change (%) (
Fig. 2B;
R 2 = 0.239,
P = 0.055) as a function of the baseline pupil diameter for the patient population.
Figures 2C and
2D show the relationship of the net PIPR (
Fig. 2C;
R 2 = 0.237,
P < 0.05) and the net PIPR change (%) (
Fig. 2D;
R 2 = 0.004,
P > 0.05) as a function of the baseline pupil diameter for the control population. It should be noted in
Figures 2B and
2D that there is no significant relationship between baseline pupil diameter and net PIPR change (%), showing that this metric effectively controls for baseline pupil diameter in both the patients and the age-matched controls.
When we compared the results from our glaucoma patients with those of the age-matched controls, we found that all PIPR measures were significantly lower (
P < 0.001) in the patient population than in the control group (
Table 3). When we compared the net PIPR change (%) among the patients and the controls (
Fig. 3), we noted that most patients had a PIPR change of <20% (
n = 16; mean, 13%), whereas most control subjects had a PIPR change of >20% (
n = 19; mean, 27%).
We then examined whether the magnitude of central visual field loss, as measured by the MD (in dB), affected the net PIPR change (%) (
Fig. 4). For this analysis we used data from all the patients whose MD values were outside the normal limits (
n = 15). We observed a tendency for baseline pupil diameter to become smaller as the visual field loss became worse (
Fig. 4A;
R 2 = 0.363,
P < 0.05). However, multiple regression analysis of visual field loss as a function of baseline pupil diameter and net PIPR change (%) indicated that visual field loss was correlated with the net PIPR change (%) (
P < 0.05) but not with the baseline pupil diameter (
P > 0.05). This latter observation is consistent with the observation that the mean and variance of the baseline pupil diameter in the age-matched controls (4.85 mm; SD, 0.99 mm) are very similar to those of the patient population (4.54 mm; SD, 1.07 mm). Given the results of the multiple regression analysis, we investigated the relationship between MD and the net PIPR change (%) with single linear regression. These data show that as visual field loss increases in severity, there is a reduction in the net PIPR change (%) (
Fig. 4B;
R 2 = 0.466,
P < 0.05). Importantly, the intercept of the regression line with the 0 dB value was at a net PIPR change (%) of 25.5%, which was similar to the value of 27.3% for the net PIPR change (%) in the age-matched controls, who had visual fields within normal limits.