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.
Highlights
Accommodative refractive change is primarily brought about by alterations in the surface curvatures of the crystalline lens
The mean magnitude of change during accommodation as measured by the anterior segment (AS)-OCT was similar to the Dubbleman eye model [65]
The largest discrepancy between approaches appears to be lens thickness (LT) and anterior segment length chamber (ASL), where the AS optical coherence tomography (AS-OCT) appears to overestimate these components in comparison to the Scheimpflug data described by Dubbelman [19,45,46,47]
Summary
Accommodative refractive change is primarily brought about by alterations in the surface curvatures of the crystalline lens. The lens equatorial diameter decreases [7,8,9,10,11,12,13,14,15], with the associated curvature changes resulting in a reduction of the anterior chamber depth [1,16,17,18,19,20,21,22] and an increase in lens axial thickness [1,5,16,17,18,19,20,21,23,24,25,26,27]. Alterations in axial surface distances (i.e., the reduction in anterior chamber depth (ACD) and increase in crystalline lens thickness (LT)) appear to reduce accommodative response with increasing levels of accommodative demand [5,28].
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