Peripheral defocus of the crystalline lens in a lens stretcher

Abstract

Purpose : There has been considerable interest in studying the peripheral optics of the eye due to its potential association with refractive error development. There is some evidence that changes in the lens with age or accommodation have an effect on peripheral defocus. The purpose of this study was to quantify the peripheral defocus of the crystalline lens and its changes during simulation of accommodation in a lens stretching system.

Methods : Measurements were performed on 13 lenses from 8 cynomolgus monkey eyes obtained as part of a tissue-sharing protocol (age: 5.7 to 12.4 years, post-mortem time: 37+/-17 hours). The lenses were mounted in a motorized miniature lens stretching system (Bioniko, Miami, FL) that simulates accommodation by radial stretching. The mounted lenses were placed in a custom-built Laser-Ray Tracing (LRT) system designed to measure the lens power and aberrations on-axis and off-axis (Maceo Heilman et al, ARVO 2015). The LRT scanned a narrow 880 nm super-luminescent diode beam through the lens. An imaging sensor mounted on a motorized positioning stage below the lens recorded the spot produced by the refracted beam. Spot positions measured for 16 vertical heights along the beam were used to reconstruct the ray path and calculate lens power from the ray slopes. The LRT delivered 27 equally-spaced parallel rays over a 6-mm diameter zone along a single meridional plane. The beam delivery optics were mounted on a motorized rotation stage that pivoted around the lens to allow acquisition of off-axis spot patterns along the same meridional plane. The lens power was measured in the unstretched and fully stretched state at incidence angles ranging from -20° to +20° in 2° or 5° increments.

Results : The on-axis lens power was 52.0+/-4.4D in the unstretched state and 32.7+/-6.1D in the stretched state. In both unstretched and stretched states, peripheral defocus was found to increase with increasing incidence angle. The peripheral defocus at 5°, 10°, 15° and 20° in the unstretched and stretched state is shown in Table 1.

Conclusions : The lens power increases peripherally. Stretching decreases the variation in power across the field. The results suggest that the lens contributes significantly to the peripheral optical performance of the whole eye and that accommodation changes the peripheral defocus of the lens.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.

 

Table 1: Average peripheral defocus (+/- SD).