Modelling eye lengths and refractions in the periphery

Purpose To create a simplified model of the eye by which we can specify a key optical characteristic of the crystalline lens, namely its power. Methods Cycloplegic refraction and axial length were obtained in 60 eyes of 30 healthy subjects at eccentricities spanning 40° nasal to 40° temporal and were fitted with a three‐dimensional parabolic model. Keratometric values and geometric distances to the cornea, lens and retina from 45 eyes supplied a numerical ray tracing model. Posterior lens curvature (PLC) was found by optimising the refractive data using a fixed lens equivalent refractive index (neq). Then, neq was found using a fixed PLC. Results Eccentric refractive errors were relatively hyperopic in eyes with central refractions ≤−1.44 D but relatively myopic in emmetropes and hyperopes. Posterior lens power, which cannot be measured directly, was derived from the optimised model lens. There was a weak, negative association between derived PLC and central spherical equivalent refraction. Regardless of refractive error, the posterior retinal curvature remained fixed. Conclusions By combining both on‐ and off‐axis refractions and eye length measurements, this simplified model enabled the specification of posterior lens power and captured off‐axis lenticular characteristics. The broad distribution in off‐axis lens power represents a notable contrast to the relative stability of retinal curvature.