Abstract
Custom high-resolution high-speed anterior segment spectral domain Optical Coherence Tomography (OCT) provided with automatic quantification and distortion correction algorithms was used to characterize three-dimensionally (3-D) the human crystalline lens in vivo in four subjects, for accommodative demands between 0 to 6 D in 1 D steps. Anterior and posterior lens radii of curvature decreased with accommodative demand at rates of 0.73 and 0.20 mm/D, resulting in an increase of the estimated optical power of the eye of 0.62 D per diopter of accommodative demand. Dynamic fluctuations in crystalline lens radii of curvature, anterior chamber depth and lens thickness were also estimated from dynamic 2-D OCT images (14 Hz), acquired during 5-s of steady fixation, for different accommodative demands. Estimates of the eye power from dynamical geometrical measurements revealed an increase of the fluctuations of the accommodative response from 0.07 D to 0.47 D between 0 and 6 D (0.044 D per D of accommodative demand). A sensitivity analysis showed that the fluctuations of accommodation were driven by dynamic changes in the lens surfaces, particularly in the posterior lens surface.
Highlights
Focusing of objects at different distances by the young human eye is enabled by modification of the shape of the crystalline lens by action of the ciliary muscle, which changes the tension applied on the zonulae attached to the capsular bag surrounding the lens in response to an accommodation stimulus
The accommodative response of the lens is typically measured by monitoring refractive changes of the eye, using techniques such as dynamic retinoscopy [1], open-field autorefractometry [2], and aberrometry [3,4,5,6,7]
Several strategies have been proposed to overcome these limitations: doubling of the axial range by complex conjugate images removal [33], dual channel Optical Coherence Tomography (OCT) systems that combine two sOCT systems focused at different planes [34,35,36], merging of images obtained focusing at different planes [28], optical switch to focus at different planes [37], ultralong scan depth OCT [38], and increased coherence length of swept sources [39,40]
Summary
Focusing of objects at different distances by the young human eye is enabled by modification of the shape of the crystalline lens by action of the ciliary muscle, which changes the tension applied on the zonulae attached to the capsular bag surrounding the lens in response to an accommodation stimulus. Several strategies have been proposed to overcome these limitations: doubling of the axial range by complex conjugate images removal [33], dual channel OCT systems that combine two sOCT systems focused at different planes [34,35,36], merging of images obtained focusing at different planes [28], optical switch to focus at different planes [37], ultralong scan depth OCT [38], and increased coherence length of swept sources [39,40] Some of these techniques have been successfully used to quantify the 3-D geometry of the anterior segment of the eye [30,39]. We estimated the dynamic fluctuations of crystalline lens geometry under steady fixation for different accommodative stimuli, to isolate the crystalline lens contributions to the dynamics of accommodation
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