A possible change of refractive index with age and its relevance to chromatic aberration.

The Purkinje-Sanson images of the eyes were photographed in red and blue light in two groups of subjects, young (19-38 years) and old (52-63 years). Densitometric examination of the negatives showed a significant increase in the amount of red light and a significant decrease in the amount of blue light reflected from the anterior surface of the lens (third image) in the group of old subjects as compared to the group of young persons. There is also a significant decline in the blue light reflected from the posterior surface of the lens (fourth image) but no change in the red light in old versus young eyes. From these results it is suggested that the index of refraction of the lens increases for red (nC) and decreases for blue light (nF) in the aging eye and similarly the index of the vitreous varies differentially in blue and red light. These specific changes in the indices of the lens and vitreous are believed to account for the large decline of axial chromatic aberration of the aging eye. In addition, the examination of the first Purkinje-Sanson image tends to indicate that the index of refraction of the cornea does not vary with age.