Quantification of age-related and per diopter accommodative changes of the lens and ciliary muscle in the emmetropic human eye

Abstract

Purpose: To calculate age-related and per diopter (D) accommodative changes in crystalline lens and ciliary muscle dimensions in vivo in a single cohort of emmetropic human adults ages 30 to 50 years.

Methods: The right eyes of 26 emmetropic adults were examined using ultrasonography, phakometry, anterior segment optical coherence tomography, and high resolution magnetic resonance imaging. Accommodation was measured both subjectively and objectively.

Results: In agreement with previous research, older age was linearly correlated with a thicker lens, steeper anterior lens curvature, shallower anterior chamber, and lower lens equivalent refractive index (all P < 0.01). Age was not related to ciliary muscle ring diameter (CMRD) or lens equatorial diameter (LED). With accommodation, lens thickness increased (+0.064 mm/D, P < 0.001), LED decreased (-0.075 mm/D, P < 0.001), CMRD decreased (-0.105 mm/D, P < 0.001), and the ciliary muscle thickened anteriorly (+0.013 to +0.026 mm/D, P < 0.001) and thinned posteriorly (-0.011 to -0.015, P < 0.01). The changes per diopter of accommodation in LED, CMRD, and ciliary muscle thickness were not related to subject age.

Conclusions: The per diopter ciliary muscle contraction is age independent, even as total accommodative amplitude declines. Quantifying normal biometric dimensions of the accommodative structures and changes with age and accommodative effort will further the development of new IOLs designed to harness ciliary muscle forces.

Figure 1.

OCT images of the crystalline lens (top) and ciliary muscle (middle), and MR imaging of eye (bottom). Ciliary muscle image analysis shows cross-sectional CMT at 1, 2, and 3 mm posterior to the scleral spur as well as maximum thickness.

Figure 2.

Accommodative response to 0-, 2-, 4-, and 6-D targets with the Auto-Refractor (left) and PowerRefractor (right). Black dashed lines: 30- < 35-year-old subjects; blue solid lines: 35- < 40-year-old subjects; green solid lines: 40- < 45-year-old subjects; red dashed lines 45- < 50-year-old subjects.

Figure 3.

Statistically significant differences with age. Regression lines fitted to the following equations with age referenced to 30 years and 95% CI for slope in brackets: lens thickness by ultrasound (mm): 3.67 + 0.031 × Age [0.019 to 0.042], P < 0.001; OCT (mm): 3.65 + 0.031 × Age [0.021 to 0.042], P < 0.001; and MRI (mm): 3.68 + 0.027 × Age [0.014 to 0.039], P < 0.001; anterior lens radius of curvature by phakometry (mm): 11.82 − 0.11 × Age [−0.17 to −0.05], P = 0.001; anterior chamber depth by ultrasound (mm): 3.85 − 0.029 × Age [−0.045 to −0.012], P = 0.001; and lens equivalent refractive index (RI) by phakometry: 1.457 − 0.001 × Age [−0.001 to 0.000], P = 0.002.

Figure 4.

Lens thickness (LT) with accommodation. Black lines fitted to the regression equation for OCT data with age fixed at 30 years (solid line), 40 years (dashed line), and 50 years (dotted line) and 95% CI in brackets: LT by OCT (mm) = 3.67 + 0.065 × Acc Resp + 0.032 × (Age − 30) [Acc Resp = 0.057 to 0.072, Age − 0.020 to 0.043]; P_AccResp < 0.001, P_Age < 0.001. MRI regression equation is similar and not plotted: LT by MRI (mm) = 3.68 + 0.055 × Acc Resp + 0.028 × (Age − 30) [Acc Resp = 0.039 to 0.071, Age = 0.016 to 0.041], P_AccResp < 0.001, P_Age < 0.001.

Figure 5.

Ciliary muscle thickness with accommodation at points 1, 2, and 3 mm posterior to the scleral spur (CMT1, CMT2, CMT3) and the site of maximum width (CMTMAX). Lines fitted to regression equations with 95% CI in brackets: CMTMAX (mm) = 0.832 + 0.026 × Acc Resp [0.013 to 0.039], P < 0.001; CMT1 (mm) = 0.765 + 0.013 × Acc Resp [0.004 to 0.022], P = 0.005; CMT2 (mm) = 0.498 − 0.011 × Acc Resp [−0.003 to −0.019], P = 0.005; CMT3 (mm) = 0.282 − 0.015 × Acc Resp [−0.009 to −0.022], P < 0.001.

Figure 6.

LED and CBRD with accommodation. Lines fitted to regression equations with 95% CI in brackets: LED (mm) = 9.39 − 0.075 × Acc Resp [−0.099 to −0.053], P < 0.001; CBRD (mm) = 11.80 − 0.105 × Acc Resp [−0.149 to −0.062], P < 0.001.

Figure 7.

Change in LED with CMRD contraction for 2-D (top), 4-D (middle), and 6-D (bottom) stimuli. Circles: 30- to 35-year-old subjects; squares: 35- to 45-year-old subjects; diamonds: 45- < 50-year-old subjects.