Optic nerves from the study patient and the age-matched RP patients demonstrated significant atrophy when compared with those of the age-matched normal patients, evident both histologically (
Fig. 3) and morphometrically in terms of total axon counts (
Fig. 4). Total axon counts using criterion 1 were 45,726 ± 3,004 in the study patient's right optic nerve; 140,393 ± 4,740 in the study patient's left optic nerve; 68,096 ± 2.873 in age-matched RP patient 1; 227,515 ± 1,559 in age-matched RP patient 2; 750,855 ± 3,983 in age-matched normal patient 1; 714,887 ± 3,852 in age-matched normal patient 2. Total axon counts using criterion 2 were 81,442 ± 4,664 in the study patient's right optic nerve; 203,401 ± 14,746 in the study patient's left optic nerve; 111,311 ± 13,000 in age-matched RP patient 1; 369,933 ± 21,613 in age-matched RP patient 2; 993,763 ± 43,741 in age-matched normal patient 1; 1,297,791 ± 42,010 in age-matched normal patient 2. Independent-samples
t-tests of optic nerve axon counts of the study patient versus the age-matched normal patients and age-matched RP patients versus age-matched normal patients yielded
P = 0.03 and = 0.01, respectively, using criterion 1 and
P = 0.03 and = 0.04, respectively, using criterion 2. There was no statistically significant difference in total axon counts between each of the study patient's optic nerves versus the two optic nerves from RP patients (
P = 0.59 and
P = 0.97 with criterion 1, and
P = 0.61 and
P = 0.89 with criterion 2, for the study patient's right and left optic nerves, respectively). No statistical analysis was performed between the study patient's implanted and nonimplanted eyes, because a
t-test cannot be performed between two groups, each having a single sample. Appropriate use of the
t-test requires a standard deviation within the groups to be compared, and with only a single eye in each group, no standard deviation can be calculated. Therefore, the only comparison that can be made between individual eyes is strictly observational. In that regard, there did appear to be a difference between the implanted and the contralateral eye in that patient, but it is not possible in this study to determine the statistical significance of that difference. Any differences between the study patient and the age-matched RP patients were small compared with the axon dropout in age-matched normal patients versus that in age-matched RP patients.