Abstract
The purpose of this study was to provide an in-depth analysis of the ciliary muscle's (CM) morphological changes during accommodation by evaluating CM thickness (CMT) profiles. The CM of 15 near-emmetropic subjects (age 20-39) was imaged via optical coherence tomography (OCT) during far (0 D) and near vision (3 D). A custom-made Java-based program was used for semi-automatic CM segmentation and thickness measurements. CMT profiles were generated to determine regions of the largest shape changes. The results revealed on average a thinning within the first 0.25 mm and a thickening from 0.36 to 1.48 mm posterior to scleral spur when accommodating from 0 to 3 D. In contrast to previous analyses, this method offers pixel-wise reconstruction of CM shapes and quantification of accommodative change across the entire muscle boundary.
Highlights
Accommodation is the process by which the eye changes the crystalline lens’ refractive power to maintain a clear image of objects at different viewing distances
Interest in ciliary muscle biometry has increased during the last decade, especially in presbyopia and myopia research – the former because of new approaches for artificial accommodation using the ciliary muscle’s contraction in intraocular lens designs [4,5], the latter because myopia development is thought to be related to near-vision behavior [6,7,8,9]
Refractive power measurements by eccentric photorefraction were not possible in two subjects because of difficulties with pupil tracking: the eyelid either partly covered the pupil or the pupil diameter was considerably reduced during near accommodation, both preventing reliable measurements of refractive power by photorefraction. 3.1 Repeatability analysis 3.1.1 Intra-examiner repeatability The averaged ciliary muscle area (CMA), calculated for each subject at both distances, was significantly different between the two successively performed ciliary muscle segmentations
Summary
Accommodation is the process by which the eye changes the crystalline lens’ refractive power to maintain a clear image of objects at different viewing distances. The ciliary muscle, a smooth muscle that consists of three types of muscle fibers [1] is the only active element of this mechanism. It is responsible for changing the shape of the eye lens by reducing the tension of the anterior zonules [2]. As to differences depending on the refractive error, it was found that an increased thickness of the ciliary muscle is associated with myopia [11,14,15,16,22] and that in the unaccommodated state, the ciliary muscle is significantly longer in eyes with greater axial length [24]. It has been hypothesized that the increased ciliary muscle thickness changes the mechanical properties that impede equatorial stretch, promoting myopic development [8]
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