Ciliary Zonule of the Human Eye: Structural and Mechanical Aspects

Purpose: The ciliary zonule of the human eye plays a central role in accommodation. The purpose of this study was to better define its three-dimensional organization and biomechanical properties. Methods: The structural organization of the zonule was visualized in semi-intact donor globes using fluorescent Lens culinaris agglutinin to label zonular fibers. Individual fibers were isolated and subjected to mechanical testing using a custom-built force probe. Results: The number, size, and orientation of zonular fibers were quantified, and their relationships to one another, the anterior hyaloid, and the adjacent ocular surfaces were documented. In most donor eyes, a population of circumferential fibers derived from radial fiber tracts was identified. The circumferential fibers, together with the innermost radial fibers, supported the anterior hyaloid. Zonular fibers exhibited viscoelastic behavior and could be elongated to more than three times their initial length before failure. The fibers had a Poisson's ratio of 0.37 and demonstrated strain-dependent stiffening. The effective elastic modulus, calculated at physiological strains, was approximately 1.3 MPa. Zonule biometric data were incorporated into a three-dimensional digital model of the eye. Conclusions: This analysis provides a comprehensive structural and biomechanical characterization of the human ciliary zonule and establishes a quantitative framework for modeling the accommodative mechanism.