Optical Coherence Tomography Reveals Sigmoidal Crystalline Lens Changes during Accommodation

Abstract

This study aimed to quantify biometric modifications of the anterior segment (AS) during accommodation and to compare them against changes in both accommodative demand and response. Thirty adults, aged 18–25 years were rendered functionally emmetropic with contact lenses. AS optical coherence tomography (AS-OCT) images were captured along the 180° meridian (Visante, Zeiss Meditec, Jena, Germany) under stimulated accommodative demands (0–4 D). Images were analysed and lens thickness (LT) was measured, applying a refractive index correction of 1.00. Accommodative responses were also measured sequentially through a Badal optical system fitted to an autorefractor (Shin Nippon NVision-K 5001, Rexxam, Japan). Data were compared with Dubbelman schematic eye calculations. Significant changes occurred in LT, anterior chamber depth (ACD), lens centroid (i.e., ACD + LT/2), and AS length (ASL = ACD + LT) with accommodation (all p < 0.01). There was no significant change in CT with accommodation (p = 0.81). Measured CT, ACD, and lens centroid values were similar to Dubbelman modelled parameters, however AS-OCT overestimated LT and ASL. As expected, the accommodative response was less than the demand. Interestingly, up until approximately 1.5 D of response (2.0 D demand), the anterior crystalline lens surface appears to be the primary correlate. Beyond this point, the posterior lens surface moves posteriorly resulting in an over-all sigmoidal trajectory. he posterior crystalline lens surface demonstrates a sigmoidal response with increasing accommodative effort.

New insights in presbyopia: impact of correction strategies

“…To determine whether a restorative method has led to a physical biometric change (for example changes in anterior chamber depth, crystalline lens thickness, intraocular lens position or lens surface curvature), studies should use imaging techniques to quantify the underpinning morphological adaptations. Instruments that can be used include ultrasound biomicroscopy,161 OCT,162 163 Scheimpflug photography,164 partial coherence interferometry,165 optical low coherence reflectometry166 and MRI 167. An appropriate battery of objective (static and dynamic) and subjective tests to be used in clinical trials to assess the efficacy of methods to restore ocular accommodation or ameliorate the symptoms of presbyopia have been proposed for different management approached 4…”