In vivo biomechanical property detection of the ciliary muscle based on optical coherence tomography and digital image correlation technology.

BACKGROUND

This study aimed to develop and validate a digital image correlation (DIC) methodology based on swept-source optical coherence tomography (SS-OCT) for quantifying in vivo ciliary muscle (CM) deformation and strain during accommodation.

METHODS

This study was comprised of three phases. First, the measurement performance was examined across two SS-OCT systems (CASIA2 and VG200D) and four scanning modes (R1, R8, R16, and R64) by comparing the DIC-derived displacements with the simulated ground-truth fields. Second, reliability was validated using a "cross-image" strategy, in which artificial deformations were applied to biological images to assess tracking accuracy under realistic speckle noise. Third, 23 subjects were recruited and divided into three groups: control group (CN, n = 7), high myopia group (HM, n = 7), and elderly group (n = 9). Macroscopic morphological parameters (anterior CM length change and maximum CM thickness change) and biomechanical parameters (e.g., equivalent strain) were extracted synchronously.

RESULTS

The R8 scanning mode in the CASIA2 device exhibited the most stable acquisition configuration. The robustness of the ncorr‑DIC algorithm was verified through the second-step experiment. Under the accommodative stimulus of - 5.0 D, the effective strain exhibited a highly significant graded attenuation among groups: CN (0.28 ± 0.06) > HM (0.20 ± 0.03) > Elderly (0.16 ± 0.05) (P = 0.002). Morphological changes were consistent with this finding, and CM thickening was significantly greater in the CN group than in the other two groups (P = 0.003). Combined analysis revealed that the mean effective strain was not only significantly positively correlated with macroscopic muscle thickening (r = 0.70, P < 0.001) but was also highly correlated with accommodation amplitude (r = 0.69, P < 0.001).

CONCLUSION

DIC-based OCT analysis is feasible for assessing the biomechanical response of CM. By quantifying mechanical attenuation associated with HM and age-related decline, this method provides a new functional biomarker for investigating the mechanisms of accommodation dysfunction and guiding clinical interventions.