Age dependence of the average refractive index of the isolated human crystalline lens

Abstract

Purpose : To study the age-dependence of the human lens refractive index (RI) and its implication for the refractive index profile.

Methods : Measurements were taken on 91 isolated lenses from 91 human donors (age: 0.03 to 55 years). Lenses were immersed in balance salt solution (BSS) in the test chamber of an 880nm spectral-domain Optical Coherence Tomography (OCT) system. 3D images of the lens were acquired. The average group refractive index (RI) was calculated using the method of Uhlhorn et al (Vis Res 2008). The axial pixel coordinates of the anterior lens (AL), posterior lens (PL), unshifted cell window (W1) and shifted cell window (W2) from the central B-scan were recorded using Image J (Figure A). The average group RI was calculated using the equation n=nW/(1-(W2-W1)/(PL-AL)), where nW=1.341 is the group RI of BSS. The measurement uncertainty is ±0.004. The group RI at 880nm was converted to phase RI at 589 nm using the dispersion equation of water. The outcomes were compared to a prediction drawn using a model with a central RI plateau in the nucleus and a linear variation of the RI in the cortex. We used RI values of the nucleus and outer cortex from Kasthurirangan et al (IOVS 2008) and age-dependent thickness of the cortex and nucleus from Dubbleman et al (Vis Res 2003).

Results : From 2 to 55 years, the mean value of the average group RI at 880nm was 1.412±0.002 (Figure B), independent of age (p=0.95). Two lenses from donors of age 0.33 and 3 months had significantly lower RI (1.403 and 1.401). The average phase RI at 589 nm is 1.404±0.002. The model predicts an average phase RI ranging from 1.403 to 1.405, in close agreement with our measurements.

Conclusions : From age 2 to 55 years the average lens RI is constant with age within the measurement uncertainty (±0.004). These results are consistent with the progressive formation of a central RI plateau with age.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.

 

Figure A. OCT image showing the anterior lens (AL), posterior lens (PL), unshifted cell window right (W1, left and right) and shifted lens window (W2). W1 was calculated by taking the average of W1 left and W1 right.

 

Figure B. Scatterplot shows the age-dependence of the average group RI.