Relationship of the cornea and globe dimensions to the changes of human crystalline lens diameter and power with age

Abstract

Purpose : It is well known that human crystalline lens biometry and optical properties change throughout life with age and influence whole eye refraction. However, it is not clear if lens equatorial diameter (LD) and lens power (LP) are associated with corneal and globe biometry. The purpose of the present study is to investigate the relationship between corneal and external globe dimensions and LD and LP. This would help in understanding if external factors influence lens growth.

Methods : Postmortem human eyes (n = 104, age = 9-56 years) were obtained from the Ramayamma International Eye Bank, Hyderabad, India. Globe antero-posterior length (GAPL) and mean (average of horizontal and vertical) diameters of cornea (MCD) and globe (MGD) were measured using digital calipers. Eyes were dissected to produce specimens that contain lens maintained in its accommodating framework, including intact zonules, ciliary body and sections of sclera. Specimens were mounted in a mechanical lens stretching system (EVAS I, IOVS 2007;48:3260-8) and sclera was stretched 2 mm radially. LD was measured using high magnification retroillumination photography and LP by an optical system based on Scheiner principle, both in unstretched (accommodated) and stretched (unaccommodated) states. Relationships between external globe and corneal dimensions and LD and LP were assessed by multivariate regression analysis.

Results : Age (0.017±0.002 mm/year; p<0.0001) and GAPL (0.14±0.03 mm/mm; p<0.0001) were predictors (p<0.0001; R²=0.54) for unstretched (accommodated) LD. Similarly, age (0.012±0.003 mm/year; p<0.0001) and GAPL (0.15±0.04 mm/mm; p=0.001) were predictors (p<0.0001; R²=0.34) for stretched (unaccommodated) LD. After adjusting for age-related increase, LD appears to be positively correlated to GAPL. Only age was the predictor for both unstretched/accommodated (-0.23±0.03 D/year; p<0.0001; R²=0.44) and stretched/unaccommodated (-0.12±0.03 D/year; p=0.0006; R²=0.20) LP. External globe or corneal dimension did not have an association with LP that decreased with age.

Conclusions : The results suggest that, apart from aging, lens size appears to be associated with external factor such as antero-posterior length of the eye globe. Lens optical properties seem not to be related to ocular biometry and the observed changes can be attributed to changes in lens shape and gradient refractive index throughout life.

This is a 2020 ARVO Annual Meeting abstract.