Purpose:
To describe longitudinal ciliary muscle growth (changes in thickness) and determine how axial elongation affects the growth process.
Methods:
The cyclopleged, right eyes of 106 children (mean ± SD age = 8.9 ± 1.3 years) were measured on two different occasions separated by one year. The ciliary muscle was imaged with the Visante Anterior Segment OCT, and its thickness was measured at 1 mm (CMT1), 2 mm (CMT2) and 3 mm (CMT3) posterior to the scleral spur. The statistical significance of one-year changes in axial length (IOLMaster), spherical equivalent refractive error (Grand Seiko autorefractor), and ciliary muscle thickness was determined for all eyes, eyes with fast growth (axial length change ≥ 0.25 mm), and eyes with slow growth (axial length change < 0.25 mm). Correlations between changes in axial length and CMT1, 2 and 3 were calculated.
Results:
No significant correlations between changes in axial length and ciliary muscle thickness were found (CMT1: r = –0.02, CMT2: r = –0.2, CMT3: r = –0.02, all p > 0.10). Statistically-significant changes in axial length, refractive error, and ciliary muscle thickness were observed over the one year period (Table 1) for all groups. The magnitude of change in CMT2 and CMT3 was remarkably similar for fast-growing and slow-growing eyes, supporting the lack of correlation between changes in axial length and CMT1, 2, and 3.
Conclusions:
While previous studies have shown that myopic eyes have a thicker ciliary muscle, it does not appear that this occurs simply because myopic eyes grow more and are longer. Other etiological explanations as well as the ability of ciliary muscle thickness to predict myopia should be explored.
Keywords: ciliary muscle • myopia • refractive error development