Although oxidative stress may play an important role in the development of age-related cataract, the degree of protection reported for antioxidant vitamins and carotenoids has been inconsistent across studies. These varied results may be due in part to the lack of good biomarkers for measuring the long-term nutritional status of the eye. The present experiments investigated the relationship between retinal carotenoids (i.e., macular pigment), used as a long-term measure of tissue carotenoids, and lens optical density, used as an indicator of lens health.
Macular pigment (460 nm) and lens (440, 500, and 550 nm) optical density were measured psychophysically in the same individuals. Groups of younger subjects—7 females (ages 24 to 36 years), and 5 males (ages 24 to 31 years)—were compared with older subjects—23 older females (ages 55 to 78 years), and 16 older males (ages 48 to 82 years).
Lens density (440 nm) increased as a function of age (r=0.65, p<0.001), as expected. For the oldest group, a significant inverse relationship (y=1.53−0.83x, r=−0.47, p<0.001) was found between macular pigment density (440 nm) and lens density (440 nm). No relationship was found for the youngest group (p<0.42).
The main finding of this study was an age-dependent, inverse relationship between macular pigment density and lens density. Macular pigment is composed of lutein and zeaxanthin, the only two carotenoids that have been identified in the human lens. Thus, an inverse relationship between these two variables suggests that lutein and zeaxanthin, or other dietary factors with which they are correlated, may retard age-related increases in lens density.