In a 4-month period, 449 subjects visited the center, and all were measured. For 11 subjects, photographs for the grading of ARM were missing. One eye had AMD. Because the model analysis of its reflectance may have been unreliable because of scarring of the retina, its data were omitted. In two subjects, measurement of fundus reflectance failed, because of technical difficulties with the setup. The final study group consisted of 435 subjects, 199 men, aged 69 ± 6 years, and 236 women, aged 69 ± 6 years (
P = 0.39). Because of difficulties in the right eye (e.g., ptosis and amblyopia) in 84 subjects, the left eye was measured instead of the right. These measurements were included in the analyses, because there is a good correlation of MP optical density between both eyes.
44 MP (at 460 nm) was 0.32 ± 0.16 in men and 0.34 ± 0.15 in women (
P = 0.23). Melanin optical density (at 500 nm) was 1.20 ± 0.21 in men and 1.18 ± 0.19 in women (
P = 0.31).
Table 1 shows the gender distribution and means (±SD) for age, MP, and melanin optical density at different stages of ARM. As expected, age differed significantly between the different stages of ARM (
P < 0.001). Gender distribution (
P = 0.73) and MP and melanin optical density (0.39 and
P = 0.40, respectively) were similar for the different stages of ARM. Comparison of all pooled ARM cases with those without ARM also resulted in no differences in gender distribution (
P = 0.17), MP (
P = 0.92), and melanin optical density (
P = 0.38).
MP optical density showed a slight but significant increase with age (Pearson correlation, r = 0.15, P = 0.002, β = 0.0041 year), whereas melanin optical density showed a similar decrease (r = −0.14, P = 0.004, β = −0.0049 year). Although unlikely, this could influence the association between ARM stage, MP, and melanin optical density. Therefore, we applied a GLM analysis with MP and melanin optical density as dependent variables, age as a covariate, and ARM stage as a factor. We found no increase to a significant effect for ARM stage in the MP analysis (P = 0.30) or in the melanin analysis (P = 0.42).
To estimate the reliability of the measurements in this population of elderly subjects, fundus reflectance was measured twice in the same eye of 17 random subjects (7 men, aged 67 ± 6 years, and 10 women, aged 68 ± 5 years). The repeat measurements were performed in the same session, and subjects were repositioned. The coefficient of repeatability, twice the square root of the mean of the squared differences,
45 was 0.11 for the MP optical density and 0.13 for the melanin optical density. We found a mean relative difference between the two measurements of 10% for the MP optical density and 3% for the melanin optical density.
Table 2 shows the mean relative differences for MP and melanin optical density stratified for the different stages of ARM. There were no significant differences in both MP and melanin optical density between the different stages of ARM (one-way ANOVA,
P = 0.61 and
P = 0.18, respectively) or between the 6 persons with ARM and the 11 without (
P = 0.20 and 0.12, respectively).