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Phillip Buckhurst, Hetal Buckhurst, Catriona Hamer; Assessment of ciliary muscle morphology using a new Fourier domain swept source anterior chamber optical coherence tomographer. Invest. Ophthalmol. Vis. Sci. 2013;54(15):3035.
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Despite the growing interest in understanding the ciliary muscle (CM) morphology, there are no standardized ciliary muscle parameters. Uni-dimensional measures of ciliary muscle thickness (CMT) via anterior segment optical coherent tomography (AS-OCT) suggest the temporal CMT to be thicker than the nasal CMT. Such measures of thickness are limited by the accuracy in locating the scleral spur and errors introduced by using straight-line calipers along curved scleral wall. In order to overcome these limitations the study utilizes a new fourier domain swept source anterior chamber optical coherence tomographer (SSOCT) to examine measures of temporal and nasal CM thickness, cross-sectional area and their changes with accommodation.
Twenty young phakic subjects aged between 18 - 30 years were recruited with a range of refractive error (MSE (D) -1.64 ± 2.64; range -9.50 to +1.25). Using SSOCT (Casia SS-1000, Tomey) temporal and nasal ciliary muscle cross-sections were imaged in the relaxed state and at stimulus vergence levels of -2.5D and -10D. Using Casia software, manual measures of nasal and temporal CMT (NCMT and TCMT respectively) were taken in successive posterior steps from the scleral spur at 1 mm (CMT1), 2 mm (CMT2) and 3 mm (CMT3). For each accommodative target, ciliary muscle area was calculated for the nasal and temporal cross sections. Non-cycloplegic refractive error measurements were taken with a open field autorefractor (Grand Seiko Co. Ltd). Statistical comparisons and analyses were conducted using mixed repeated measures ANOVAs and Pearson’s correlation coefficient.
CMT1, CMT2 and CMT3 were thickest on the temporal side for all accommodative stimuli (p<0.05). The ciliary muscle area was greatest on the temporal side in comparison to the nasal side in the relaxed state (p<0.001) and with the -2.5D vergence (p=0.025) and -10D vergence (p=0.026).
The CM area and thickness is significantly greater on the temporal side in comparison to the nasal side. The high resolution cross sectional images of the CM provided by the Casia enables measurement of cross sectional area. This additional parameter of the CM morphology may assist with modeling the accommodative process and understanding the potential biomechanical role of the ciliary muscle in myopigenesis.
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