Morphology and Accommodative Function of the Vitreous Zonule in Human and Monkey Eyes

Abstract

Purpose To explore the attachments of the posterior zonule and vitreous in relation to accommodation and presbyopia in monkeys and humans. Methods We used novel SEM and UBM techniques to visualize the anterior, intermediate and posterior vitreous zonule and their connections to the ciliary body, vitreous membrane, lens capsule and ora serrata, and to characterize their age-related changes and correlate them with loss of accommodative forward movement of the ciliary body. We injected α-chymotrypsin focally to lyse the vitreous zonule and determined the effect on movement of the accommodative apparatus in monkeys. Results The vitreous attaches to the peripheral lens capsule and the ora serrata directly. The pars plana zonule and the posterior tines of the anterior zonule are separated from the vitreous membrane except for strategically placed attachments, collectively termed “vitreous zonule,” that might modulate and smooth the forward and backward movements of the entire system. Age-dependent changes in these relationships correlated significantly with loss of accommodative amplitude. Lysis of the intermediate vitreous zonule partially restored accommodative movement. Conclusions The vitreous zonule system may help to smoothly translate to the lens the driving forces for accommodation and disaccommodation generated by the ciliary muscle, while maintaining visual focus and protecting the lens capsule and ora serrata from acute tractional forces. Stiffening of the vitreous zonular system may contribute to age-related loss of accommodation and offer a therapeutic target for presbyopia.

Computer-animated model of accommodation and presbyopia

“…The posterior vitreous zonular fibers (off-white) form a sponge-like structure at the vitreous base with obliquely crossing fibers forming a network capable of dampening the forces of accommodation and preventing trauma to the peripheral retina, as suggested by L€ utjen-Drecoll et al 8 As a group, the posterior zonular fibers, in concert with the anterior zonular fibers, create the reciprocal zonular action that occurs during accommodation and disaccommodation. The posterior zonular fibers transfer tension and release from the ciliary muscle to the elastic foundation in the choroid.…”

“…In 2010, L€ utjen-Drecoll et al 8 identified 3 elements of vitreous zonular fibers in addition to the pars plana zonule. The classification of zonular fibers as anterior/ posterior or as lenticular/vitreous/pars plana is confusing, Using model-based cognitive thinking, a new classification based on structure and function is proposed.…”

“…4 As many investigators have noted, the architecture of the zonular fibers determines the way the forces of ciliary-body contraction are distributed in shaping the lens during accommodation and disaccommodation. The recent studies by Bernal et al, 5 Nankivil et al, 6 Croft et al, 7 and L€ utjen-Drecoll et al 8 include new understanding of the zonular anatomy, and this has been incorporated into the first version of the computer-animated model. In 2013, in landmark studies, a team of Americans and Europeans described an additional zonular fiber and documented movements of the zonular fibers, anterior hyaloid, choroid, and sclera with endoscopy and video UBM.…”

Restoration of accommodation: new perspectives

“…As the same time the anterior zonules relax, reducing their tension on the lens such that the lens changes shape anteriorly, the posterior zonules contract, moving the posterior capsule backward. This vitreal-zonular complex stiffens with age, losing its elasticity (1)(2)(3) . The age-related changes in these structures and their biomechanical interactions with the ciliary-lens complex may contribute to presbyopia (3).…”

“…This vitreal-zonular complex stiffens with age, losing its elasticity (1)(2)(3) . The age-related changes in these structures and their biomechanical interactions with the ciliary-lens complex may contribute to presbyopia (3). It has been newly discovered that there are also changes in extralenticular structures which may have an impact on the loss of accommodation which were previously deemed to be of very little importance, namely the sclera and choroid (2) .…”