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Andrew D. Pucker, Loraine T. Sinnott, Chiu-Yen Kao, Melissa D. Bailey; Paradoxical Relationships between Refractive Error and Ciliary Muscle Thickness in Children. Invest. Ophthalmol. Vis. Sci. 2012;53(14):149.
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To determine if there is relationship between refractive error and ciliary muscle thickness in various anatomical regions of the muscle.
A total of 270 children (mean ± SD age = 8.70 ± 1.51 years) were recruited. Cycloplegic ciliary muscle thickness measurements were taken with a Visante™ Anterior Segment OCT at 1 mm (CMT1), 2 mm (CMT2) and 3 mm (CMT3) posterior to the scleral spur; maximum (CMTMAX) thickness was also assessed. Cycloplegic spherical equivalent refractive error (SPHEQ) was determined with a Grand Seiko autorefractor. To isolate an area of presumed circular fibers from radial and longitudinal fibers, CMT2 values were subtracted from the corresponding CMT1 and CMTMAX. Multilevel regression models were used to determine the relationship between ciliary muscle thickness and refractive error. All models were controlled for age and gender.
The following mean ± SD ciliary muscle thickness measurements were found: CMTMAX = 809.35 ± 67.67 μm, CMT1 = 778.50 ± 65.04 μm, CMT2 = 527.39 ± 73.41 μm, and CMT3 = 280.18 ± 56.52 μm. The mean SPHEQ was 0.42 ± 1.29 D (range = -4.01 D to +7.76 D). In linear models with ciliary muscle thicknesses and SPHEQ, SPHEQ was only significantly associated with CMT2 (β = -11.77, p=0.0005) and CMT3 (β = -7.90, p=0.0023). When corresponding values of CMT2 were subtracted from CMT1 and CMTMAX, CMT1 (β = 15.22, p<0.0001) and CMTMAX (β = 19.03, p<0.0001) had a significant relationship to SPHEQ.
These data indicate that the ciliary muscle is thicker in the region of the longitudinal and radial muscle fibers with increasing amounts of myopia, but paradoxically, the region where circular muscle fibers reside is thicker in hyperopic subjects. This may be the first evidence that the workload associated with the increased accommodative demand in hyperopic subjects selectively causes thickening of the circular ciliary muscle fibers.
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