Purpose: To model the cross-sectional relationship of ciliary muscle thickness (CMT) and age throughout the decades of life.
Methods: Subjects (N = 784) were ages 3 to 91 years. Measurements included distance autorefraction and Zeiss OCT imaging of the ciliary muscle in the right eye. Four ciliary muscle thickness (CMT) measurements were made at the thickest region (CMTMAX) and at 1, 2, and 3 mm from the scleral spur (CMT1, CMT2, CMT3). General linear regression models were used.
Results: Mean ± standard deviation (SD) subject age (years) was 23.4 ± 18.4 (range: 3.4 to 91). Mean ± SD spherical equivalent (D) was -0.53 ± 1.88 (range: -10.87 to +6.00). The relationship between all CMT measures and age was significant [CMTMAX: Intercept = 805.75, Age (ß = 1.04, p < 0.000001)]; CMT1: Intercept = 746.6, Age (ß = 2.3, p = 0.0003), Spherical Equivalent, M (ß = -5.8, p = 0.005), Age2 (ß = -0.02, p = 0.01), M2 (ß = -0.9, p = 0.02); CMT2: Intercept = 483.5, Age (ß = 2.4, p = 0.0007), M (ß = -17.7, p < 0.000001), Age2 (ß = -0.03, p = 0.001), M2 (ß = -1.9, p = 0.00005); CMT3: Intercept = 254.6, Age (ß = 2.8, p < 0.000001), M (ß = -13.4, p < 0.000001), Age2 (ß = -0.04, p = 0.00002), M2 (ß = -1.2, p = 0.001). The relationship between the location of the point of maximum thickness relative to the scleral spur (SStoMAX) and age was also significant (Intercept = 666.55, Age (ß = 4.5, p = 0.08), M (ß = -33.75, p < 0.000001), Age2 (ß = -0.07, p = 0.007), M2 (ß = -2.2, p = 0.06).
Discussion: These data show that the relationship between cross-sectional ciliary muscle thickness and age is positive in childhood (increasing ciliary muscle thickness with increasing age) but negative in older age (decreasing ciliary muscle thickness with older age). The point of maximum thickness increased across all decades of life and also moves posteriorly in childhood and then anteriorly in older adults. A similar relationship showing an increase in thickness in younger ages also has been found in previous studies. To the best of our knowledge, our study is the first to describe the cross-sectional relationship between ciliary muscle thickness and age as a quadratic function.