Isolated human crystalline lens spherical aberration: Experimental measurements and predictions from OCT-based geometry

Abstract

Purpose : To investigate age-related changes to the geometry and optical properties of the isolated human crystalline lenses and understand the sources of spherical aberration (SA).

Methods : A combined ray tracing aberrometry–OCT system (Ruggeri et al, Biomed Opt Express 2018;9:3834-51) was used to perform experiments on 58 human donor lenses (age: newborn – 56 yrs). The probing beam was sequentially delivered using a raster scan (6 x 6 mm; 0.5 mm spacing). The incident rays were centered on the lens apex. A camera captured the exit rays at different axial positions. Custom software was used for the centroid detection, slope calculation and wavefront reconstruction. Zernike wavefront coefficients (SA in particular) were determined using ray slopes over a 6 mm pupil. Lens shape (anterior and posterior lens radii and asphericity, Ra, Rp, Qa, Qp and lens thickness, LT) was quantified from the OCT images by custom algorithms for image segmentation and distortion correction. For prediction, computational ray tracing (Zemax) was performed using lens OCT-based geometry and the calculated group refractive index (RI).

Results : From 0-20 years, Ra (0.07 mm/yr; r=0.58;p=0.007) increased; Qa (-0.36 yr^-1; r=-0.81;p<0.0001), LT (-0.03 mm/yr; r=-0.72;p<0.0001) & Qp (-0.11 yr^-1; r=-0.83;p<0.0001) decreased; Rp & RI remained constant (p>0.05). Above 20 years, Ra (0.07 mm/yr; r=0.51;p=0.004), Rp (0.03 mm/yr; r=0.36;p=0.04) & LT (0.02 mm/yr; r=0.72;p<0.0001) increased, RI (-0.0001 yr^-1; r=-0.42;p=0.004) decreased; Qa & Qp remained constant (p>0.05). From 0-20 years, measured (m) and predicted (p) SA shifted to negative values reaching a minimum at ~20 years with different slopes (mSA: -0.0575 µm/yr; r=-0.48;p=0.03; pSA: -0.1999 µm/yr; r=-0.85;p<0.0001). Above 20 years, SA shifted towards less negative values with mSA generally more negative than pSA (mean, -0.7767 vs -0.3190), particularly in younger adults and with steeper changes with age (mSA: 0.0352 µm/yr; r=0.59;p<0.0001; pSA: 0.0241 µm/yr; r=0.40;p=0.03).

Conclusions : Changes in lens shape during childhood growth seem to produce age-related changes in lens spherical aberration that may influence emmetropization. The differences in the predicted and measured aberrations suggest an age-dependence of the contribution of shape and refractive index gradient to the lens optical properties, with GRIN playing a larger role in children and young adults.

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