Age-dependence of the peripheral defocus of the isolated human crystalline lens

Abstract

Purpose : Recent studies suggest that peripheral refraction may be a factor in myopia onset and progression. Age-related changes in lens shape and refractive index gradient due to continuous lens growth with age may produce changes in the peripheral optics of the whole eye. The purpose of this study was to quantify the peripheral defocus of the isolated human crystalline lens and its age-dependence.

Methods : Data were acquired on 12 isolated human lenses obtained from the Ramayamma International Eye-Bank, Hyderabad, India (age: 6 to 56 years, post-mortem time: 1 to 5 days). The lenses were placed in a custom-built combined Laser-Ray Tracing and Optical Coherence Tomography system that measures the slopes of rays refracted through the lens for on-axis and off-axis incidence (Manns et al, ARVO 2016). Ray slope is measured directly by recording spot patterns as a function of axial position using an imaging sensor mounted on a motorized positioning stage below the lens. The wavelength of the incident beam is 880 nm. Experiments were performed with a raster scan with a spacing of 0.5 mm. The lens power was calculated for incidence angles ranging from -30^o to +30^o in 5^o increments. At each angle, lens power was calculated by finding the axial position that minimizes the root-mean-square diameter of the spot pattern formed by the rays. The 49 central rays of the raster scan were used for the analysis, corresponding to a central 3 mm zone on axis. The age dependence of the on- and off-axis power and peripheral defocus (difference between off-axis and on axis power) was quantified.

Results : At all incidence angles, isolated lens power decreased significantly with age (Figure 1A). In all lenses, the lens power was found to increase as the incidence angle increases, corresponding to myopic peripheral defocus (Figure 1B). There was a statistically significant decrease of the peripheral defocus with age (Figure 2).

Conclusions : The results suggest that the continuous growth of the lens contributes significantly to the age-related changes in the peripheral optical performance of the whole eye.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.

 

Figure 1: (A) Isolated lens power as a function of age for 0^o, 10^o , 20^o and 30^o incidence angle. (B) Angular dependence of the lens power for 3 representative lenses (child, adolescent, adult).

 

Figure 2: Age-dependence of lens peripheral defocus at 25^o and 30^o.