Reduction in axial length with age: an emmetropizing mechanism for the adult eye?

Mechanisms accounting for the fact that the eye tends to become and remain emmetropic have been proposed for the developing eye, but no such mechanisms have been proposed for the adult eye. In the study reported here, refractive component data published by Sorsby and his co-workers were reanalyzed in terms of the variations in these components with age. Included in the analysis are component data for one eye of each of 271 subjects from age 4 to age 70 years, whose ocular refraction was between plano and +2.00 D. The results of this analysis show that the axial length of the eye appears to decrease during the adult years of life, concurrently with a decrease in anterior chamber depth and an increase in the refractive power of both the cornea and the lens. It is proposed that a reduction in the axial length of the adult eye serves as an emmetropizing mechanism, occurring in harmony with the increase in the refracting power of the eye, which would otherwise cause the refraction of the eye to move in the myopic direction.