Scotopic sensitivity: relation to age, dietary patterns, and smoking status.

PURPOSE: Although previous data suggest that rod-mediated sensitivity decreases with age, this decrease may be insignificant when only healthy individuals younger than 65 years are considered. In this study, we assess the relationship between age and scotopic sensitivity loss in subjects younger than 65 years to determine whether scotopic sensitivity losses can be detected when confounding factors are considered (including iris color, smoking status, and dietary patterns) and a large sample size is used.
METHODS: A total of 121 subjects (aged 20 to 63 years) were tested under dark-adapted (scotopic) conditions. Scotopic sensitivity was measured as absolute thresholds to a 2.8 degree, 550-nm test presented at 6 degrees in the temporal hemiretina. Stimuli were presented in Maxwellian view.
RESULTS: When all the subjects were considered together, there was a slight nonsignificant trend for scotopic sensitivity to decline with age (p < 0.11). This tendency was largely driven by the older (45 to 63 years) past and never smokers and was statistically significant (p < 0.024 and p < 0.05, respectively) when those two groups were analyzed separately. Scotopic sensitivity for the younger (20 to 44 years) past, current, and never smokers did not decline with age. When all the variables were considered in a general model, dietary intake of vitamin E explained a significant amount of the variation in scotopic sensitivity (p < 0.03). No relationships were found between scotopic sensitivity and iris color.
CONCLUSIONS: Age-related losses in scotopic sensitivity before age 65 are slow. Moreover, individual variations in scotopic sensitivity for younger subjects is minimal, even in the presence of dramatic stressors such as long-term, heavy exposure to cigarette smoke. These data suggest that measurements of scotopic sensitivity may not be good indicators of the retinal health of individuals younger than 65 years.