Quantifying spherical aberration of the human crystalline lens during simulated accommodation using ray-tracing aberrometry

Abstract

Purpose : To demonstrate the viability of using a ray-tracing aberrometer to measure spherical aberration of the human crystalline lens in vitro during simulated accommodation.

Methods : A custom-made system that merges ray-tracing aberrometry and OCT (Ruggeri et al, Biomed Opt Express 2018;9:3834-51) was used to measure the optical aberrations and geometry of the human lens. Experiments were performed on 5 post-mortem lenses (Ages: 32, 34, 34, 45 and 45 y/o). The lens with its accommodative framework was mounted in a stretcher and submerged in a chamber filled with BSS. Simulated accommodation was achieved by radially stretching the globe in 2 mm increments. The aberrometer delivered a matrix of 13 × 13 rays spaced 0.5 mm apart through the lens for each stretching state. A 2D image sensor recorded images of the spots generated by the exit rays. Images of the spot patterns acquired at 9 different axial positions were processed to calculate the slope of the exit rays. Ray slopes over a 6 mm pupil were used to calculate Zernike wavefront coefficients. Lens power and spherical aberration (SA) were determined from the defocus and 4^th order Zernike terms, respectively. Lens thickness was calculated from the OCT images. The system enables measurements with a precision of 0.4 D (power), 0.06 µm (SA) and 10 µm (thickness).

Results : Zernike coefficients (defocus and SA), power and thickness are summarized in the table for each lens and stretching state. Lens power and thickness increase with simulated accommodation (decreased stretch) in the younger lenses (32 and 34 y/o), as expected. In the older lenses (45 y/o), there were no measured changes in shape and power with stretching. There were no measured changes in spherical aberration with stretching across lenses. Spherical aberration was significantly less negative in the older lenses (45 y/o), which is consistent with prior results (Smith et al, Vision Res 2001;41:235-43).

Conclusions : We assessed the feasibility of measuring spherical aberration of the human lens in vitro during simulated accommodation with a ray-tracing aberrometer. Simulated accommodation had no effect on spherical aberration in lenses older than ~30 y/o.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.