Nine patients diagnosed with multiple personality disorder (MPD) and nine control subjects role-playing MPD were given complete ophthalmological examinations to test whether the MPD subjects would show greater variability in visual functioning across alter personalities than would control subjects role-playing MPD. An analysis of variability of eight optical measures in four prominent areas of vision was performed by comparing two covariance matrices for equality. The test on the equality of the two covariance matrices showed that the two groups were significantly different (p less than .05). That is, MPD subjects had significantly more variability in visual functioning across alter personalities than did control subjects. Because the test of equality of the two covariance matrices rejected the null hypothesis, univariate analyses of variance were performed on the eight individual ophthalmological measures that comprised the matrix. The results of these analyses showed that MPD subjects had significantly more variability across alter personalities than did their control counterparts on measures of visual acuity with correction, visual acuity without correction, visual fields, manifest refraction, and eye muscle balance. The data were also analyzed for clinical significance. Blind ratings of the data were performed by comparing the results of the individual dependent measures across the alter personalities of individual MPD and control subjects according to established ophthalmological criteria. The ratings for clinical significance showed that the MPD subjects had 4.5 times the average number of changes in optical functioning between alter personalities of the control subjects, with a mean of 2.56 clinically significant changes for the MPD subjects and .55 clinically significant changes for the control subjects. This difference was also statistically significant (p less than .01).