Measurements were taken of the various intraocular distances within the UBM images (
Fig. 1), and comparisons were made between the images in the unaccommodated and accommodated states. The lens thickness and the width of the ciliary muscle apex were measured (
Fig. 1), with the latter measurements analogous to those taken from histologic sections by Tamm et al.
55 The distance measured from the scleral spur to the posterior insertion zone of the vitreous zonule was designated Spur-to-VZ insertion (
Fig. 1A). The distance from the muscle apex to the posterior insertion zone of the vitreous zonule was designated as the length of the vitreous zonule (
Fig. 1A), because the location of the zonular plexus
2 was best represented by the clearly defined muscle apex in the UBM images. Additional measurements included the circumlental space (CLS,
Fig. 1B), the distance between the vitreous zonule insertion zone and the peripheral lens equator (PVZ INS-LE,
Fig. 1A), and the distance between the scleral spur and lens equator (centripetal lens equator position,
Fig. 1B). We used the scleral spur as a reference point from which to gauge accommodative forward movement of the posterior insertion zone of the vitreous zonule. Forward movement was defined as anterior movement; in the above instance, it would be anterior movement of the insertion zone toward the scleral spur or toward the cornea. The lens equator was the point of the lens that was closest in distance to the ciliary processes (i.e., where the CLS is narrowest) in the UBM image (
Fig. 1). The UBM probe was oriented into a position that allowed us to visualize and record the outermost portion of the lens equator edge and an entire ciliary process ridge, all within the same image. In all subjects, images were selected that showed the narrowest CLS (
Fig. 1). The lens equator appeared at a modest angle to the sclera and not quite parallel to the axis symmetry of the eye. Nonetheless, we know this to be the lens equator as we positioned the UBM probe to detect the narrowest point between the lens and ciliary process ridge (as evidenced by the presence of anterior zonule,
Fig. 1D,
Supplementary Fig. S2) and then the position of the UBM probe was fine-tuned to include the vitreous zonule.