Abstract
PurposeTo determine the biometry of anterior segment dimensions of the human eye on both horizontal and vertical meridians with extended scan depth optical coherence tomography (OCT) during accommodation.MethodsTwenty pre-presbyopic volunteers, aged between 24 and 30, were recruited. The ocular anterior segment of each subject was imaged using an extended scan depth OCT under non- and 3.0 diopters (D) of accommodative demands on both horizontal and vertical meridians. All the images were analyzed to yield the following parameters: pupil diameter (PD), anterior chamber depth (ACD), anterior and posterior surface curvatures of the crystalline lens (ASC and PSC) and the lens thickness (LT). Two consecutive measurements were performed to assess the repeatability and reproducibility of this OCT. They were evaluated by calculating the within-subject standard deviation (SD), a paired t-test, intra-class correlation coefficients (ICC) and the coefficient of repeatability/reproducibility (CoR).ResultsThere were no significant differences between two consecutive measurements on either horizontal or vertical meridians under both two different accommodative statuses (P>0.05). The ICC for all parameters ranged from 0.775 to 0.998, except for the PSC (0.550) on the horizontal meridian under the non-accommodative status. In addition, the CoR for most of the parameters were excellent (0.004% to 4.89%). In all the parameters, only PD and PSC were found different between the horizontal and vertical meridians under both accommodative statuses (P<0.05). PD, ACD, ASC and PSC under accommodative status were significantly smaller than those under the non-accommodative status, except that the PSC at the vertical meridian did not change. In addition, LT was significantly increased when accommodation.ConclusionThe extended scan depth OCT successfully measured the dimensions of the anterior eye during accommodation with good repeatability and reproducibility on both horizontal and vertical meridians. The asymmetry of lens posterior surface and oval-shaped pupil were found during accommodation.
Highlights
Accommodation is the ability of the eye to change the refractive power to focus on the objects at different distances, which is controlled by ciliary muscle contraction
Several techniques have been developed for measuring the anterior segment of the eye in vivo, such as the slitlamp assessment, [10] Scheimpflug imaging, [7,11] A scan ultrasounds,[12] ultrasound biomicroscopy (UBM), [13] and Purkinje reflexes
Reproducibility and repeatability of five anterior segment parameters were determined under the different conditions (Table 2)
Summary
Accommodation is the ability of the eye to change the refractive power to focus on the objects at different distances, which is controlled by ciliary muscle contraction. [1] Among all the accommodation theories, the Helmholtzian theory is the most widely accepted. [2] In order to allow the retina to focus on objects at near distances with clarity, the ciliary muscle contracts, zonular fibres relax, causing the thickness, curvature and position of the crystalline lens to change. [3,4] Rohen JW. et al used the anatomical method to confirm this theory and further explained the process of accommodation. [5].the ability of accommodation decreases gradually as age increases. [6] The inevitable decline in accommodative amplitude and characteristic loss of near visual function with age causes presbyopia. Accommodation is the ability of the eye to change the refractive power to focus on the objects at different distances, which is controlled by ciliary muscle contraction. [2] In order to allow the retina to focus on objects at near distances with clarity, the ciliary muscle contracts, zonular fibres relax, causing the thickness, curvature and position of the crystalline lens to change. It is essential to investigate the dynamic variations of the anterior segment configuration dimensions in understanding the characteristics of the ocular accommodation. Several techniques have been developed for measuring the anterior segment of the eye in vivo, such as the slitlamp assessment, [10] Scheimpflug imaging, [7,11] A scan ultrasounds,[12] ultrasound biomicroscopy (UBM), [13] and Purkinje reflexes. The Purkinje reflexes cannot directly reflect the ocular optic configuration dimensions
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