Accommodative movements of the lens/capsule and the strand that extends between the posterior vitreous zonule insertion zone & the lens equator, in relation to the vitreous face and aging

Abstract

Purpose To elucidate the dynamic accommodative movements of the lens capsule, posterior lens and the strand that attaches to the posterior vitreous zonule insertion zone and posterior lens equator (PVZ INS-LE), and their age-related changes. Methods Twelve human subjects (ages 19–65 years) and twelve rhesus monkeys (ages 6–27 years) were studied. Accommodation was induced pharmacologically (humans) or by central electrical stimulation (monkeys). Ultrasound biomicroscopy was used to image intraocular structures in both species. Surgical procedures and contrast agents were utilized in the monkey eyes to elucidate function and allow visualization of the intraocular accommodative structures. Results Human: The posterior pole of the lens moves posteriorly during accommodation in proportion to accommodative amplitude and ciliary muscle movement. Monkey: Similar accommodative movements of the posterior lens pole were seen in the monkey eyes. Following extracapsular lens extraction (ECLE), the central capsule bows backward during accommodation in proportion to accommodative amplitude and ciliary muscle movement, while the peripheral capsule moves forward. During accommodation the ciliary muscle moved forward by ~1.0 mm, pulling forward the vitreous zonule and the PVZ INS-LE structure. During the accommodative response the PVZ INS-LE structure moved forward when the lens was intact and when the lens substance and capsule were removed. In both the monkey and the human eyes these movements declined with age. Conclusions The accommodative shape change of the central capsule may be due to the elastic properties of the capsule itself. For these capsule/lens accommodative posterior movements to occur, the vitreous face must either allow for it or facilitate it. The PVZ INS-LE structure may act as a “strut” to the posterior lens equator (pushing the lens equator forward) and thereby facilitate accommodative forward lens equator movement and lens thickening. The age-related posterior restriction of the ciliary muscle, vitreous zonule and the PVZ-INS LE structure dampens the accommodative lens shape change. Future descriptions of the accommodative mechanism, and approaches to presbyopia therapy, may need to incorporate these findings.

Presbyopia and Glaucoma: Two Diseases, One Pathophysiology? The 2017 Friedenwald Lecture

“…5–9 Posteriorly, the CM is also tethered by true elastic tendons inserting into the elastic lamina of Bruch's membrane at the ora serrata (Figs. 2–4),5,10 where the pars plana zonules, the intermediate vitreous zonules,11 and the posterior vitreous zonule insertion to lens equator (PVZ INS LE) strands12 (the vitreous strands that extend from the intermediate vitreous zonule posterior insertion zone to the lens equator) all come together in a small region that we call the intermediate vitreous zonule posterior insertion zone (Fig. 3).…”

“…Thick black line (1) represents the intermediate vitreous zonule that extends between the intermediate vitreous zonule posterior insertion zone and the zonular plexus (which resides between the walls of the ciliary processes). Thick blue line (2) represents the vitreous strand that extends from the intermediate vitreous zonule posterior insertion zone and attaches to the posterior lens equator (PVZ INS-LE) 12. Thin green lines represent other vitreous strands that extend from the posterior vitreous body to the pars plana region (3) or the pars plicata region (4).…”

The importance of parameter choice in modelling dynamics of the eye lens

“…The anterior hyaloid membrane, attached to the posterior lens capsule through Wieger’s ligament 71 , was not incorporated into current models. Recent evidence showing that the posterior zonule is anchored in the hyaloid membrane instead of attaching directly to the posterior lens capsule 72 , 73 , should be considered in future modelling studies. It is acknowledged that the lens is not an isolated component but an optical element in the eye.…”

Presbyopia: Effectiveness of correction strategies

“…Therefore, contraction and relaxation of the zonules will gradually have less of an impact on crystalline lens shape with age (Koretz and Handelman, 1986). As indicated in Section 2.2, further in vivo research may also demonstrate a reduction in efficiency of zonular action with age (Croft et al, 2016).…”

“…More recent studies have also provided in vivo evidence for a new structure that extends from the posterior insertion zone of the vitreous zonule in a straight course directly to the posterior lens equator, without passing in proximity to the zonular plexus (termed PVZ INS-LE) (Croft et al, 2013a;Croft et al, 2013b). Moreover, together with the posterior/ vitreous zonule, the PVZ-INS LE structure may dampen the accommodative lens shape change in the ageing eye (Croft et al, 2016).…”