Quantification of the Anterior-Centripetal Movement of the Ciliary Muscle During Accommodation Using Dynamic OCT Imaging

Abstract

Purpose: Although the lens undoubtedly plays a major role in presbyopia, altered lens function could be in part secondary to age-related changes of the ciliary muscle. Ciliary muscle changes with accommodation have been quantified using optical coherence tomography, but so far these studies have been limited to quantifying changes in ciliary muscle thickness, mostly at static accommodative states. Quantifying ciliary muscle thickness changes does not effectively capture the dynamic anterior-centripetal movement of the ciliary muscle during accommodation. To address this issue, we present a method to quantify the movement of the ciliary muscle during accommodation using trans-scleral optical coherence tomography images obtained dynamically.

Methods: An image processing framework including distortion correction, geometric transformation, and Procrustes analysis, was used to quantify the anterior-centripetal movement of the ciliary muscle apex and centroid during accommodation. The method was applied in a preliminary study to quantify ciliary muscle displacement and its relation to lens thickness change with accommodation on two young adults and two prepresbyopes.

Results: The magnitude and the direction relative to the pupil plane of the apex/centroid displacement in response to a two diopters (2D) stimulus were 0.16/0.20 mm at 11.3°/30.5° and 0.26/0.34 mm at 6.6°/33.2° for the young adults and 0.20/0.20 mm at 29.7°/40.6° and 0.24/0.40 mm at 33.0°/31.7° for the prepresbyopes, respectively.

Conclusions: This study demonstrates the feasibility of quantifying dynamic anterior-centripetal movement of the ciliary muscle during accommodation using optical coherence tomography. The method better captures the functional response of the muscle than the quantification of thickness changes.

Translational relevance: We provide a method that holds potential to better understand the age-related changes of the ciliary muscle on presbyopia.

Figure 1.

Method to quantify the displacement of the apex and centroid of the ciliary muscle. (I) Image processing to correct for eye movement and improve image contrast. (II) Segmentation and distortion correction of the ciliary muscle and the sclera. (III) The ciliary muscle and sclera are rotated to align the iris in the same direction as in the AS image, that is, ensuring that it is aligned at 0° with respect to the lens. (IV) biometry of the ciliary muscle obtained through a statistical shape method (Procrustes analysis).

Figure 2.

(A) Ciliary muscle thickness profile in the unaccommodated and accommodated state for a 2D accommodation stimulus in participant 4. (B) Change in the ciliary muscle thickness at the point of maximum thickness (CMT_max) and at 3 mm (CMT_3mm) from the scleral spur. There is an increase of 0.10 mm of CMT_max and a decrease of −0.02 mm of CMT_3mm. (C) Change of the ciliary muscle apex (navy) and centroid (blue), together with the change in LT (red), according to time for a 2D accommodative stimulus for participant 4. The accommodation stimulus was triggered at 1.54 s. (D) Change in apex and centroid against the change in LT.

Figure 3.

Two-dimensional displacement of the apex (A) and centroid (B) of the ciliary muscle for a 2D accommodation stimulus for participant 4. The stimulus was applied at t = 1.54 seconds.

Figure 4.

Change in LT according to ciliary muscle apex (A) and centroid (B) displacement for 2D and 4D accommodation stimuli.

Figure 5.

Ciliary muscle apex (A) and centroid (B) angle of movement. Participants 1 and 2 are young participants. Participants 3 and 4 are prepresbyopic participants.