Assessment of crystalline lens shape during accommodation using IOLMaster 700 B-scan images

Purpose : The Zeiss IOLMaster 700® biometer offers image-based axial measurement of eye structures together with visualisation of the anatomical details in a longitudinal section. We aimed to analyse these B-scan images to determine crystalline lens shape changes induced by accommodation.

Methods : IOLMaster 700 B-scan images were acquired from 10 children (age: mean 11.1, SD 0.4 years) during 0D and 6D accommodation tasks. Scans were analysed using custom MATLAB software to determine the curvature measurements for anterior and posterior cornea and lens surfaces. The process involved segmenting the image to locate the corneal and lens surfaces (Figure 1), correcting for existing distortions in the image to reconstruct ray path distance maps, and using the maps with ray tracing to determine surface positions. Second order polynomials were fit to the surfaces to compute radii of curvature.

Results : The radius of curvature decreased significantly with accommodation for the anterior lens (t8 = 5.93, p = 0.0003) (0D accommodation: mean 13.26mm, SD 2.19mm; 6D accommodation: mean 8.87mm, SD 0.94mm) but not for posterior lens (p > 0.05) (0D accommodation: mean -5.62mm, SD 0.64mm; 6D accommodation: mean -5.11mm, SD 0.52mm), nor for anterior and posterior cornea. Results for all surfaces are shown in Figure 2 with data for one image (6D accommodation) discarded due to eye movement artefacts.

Conclusions : This is a novel analysis of the data contained in IOLMaster 700 images. The measured changes in both anterior and posterior lens surface curvature were comparable to previous studies that demonstrate its potential of measuring lens shape during accommodation. Because of the wide availability of IOLMaster 700, this may be a useful research tool for studying crystalline lens shape. Further research is required to establish repeatability and accuracy of the technique.