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Mary Ann Croft, T Michael Nork, Jared McDonald, Gregg A Heatley, Alexander Katz, Paul L Kaufman, Elke Luetjen-Drecoll; MECHANISM OF ACCOMMODATION: NEW FINDINGS AND THE IMPLICATIONS FOR PRESBYOPIA. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):3568.
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© ARVO (1962-2015); The Authors (2016-present)
To better understand the accommodative mechanism and presbyopia.
In 10 rhesus monkeys (ages 8-22 yrs), maximum accommodative responses were induced by electrical stimulation of the E-W nucleus. Ultrasound biomicroscopy (UBM; 50 MHz, 35 MHz) images were collected in the region of lens, ciliary muscle (CM), and zonular attachments during the accommodative response. Images were collected before & after lens extraction. Various contrast agents (i.e., triamcinolone, fluorescent microspheres) were used to enhance visualization of the intraocular structures and fluid movements during accommodation.
PVZ INS-LE structure (which is attached directly to the posterior lens equator and to the posterior insertion zone of the vitreous zonule) remained straight during the accommodative response (i.e., it did not relax). The anterior end of the PVZ INS-LE moved forward during accommodation in the presence or absence of the lens/capsule, pulled/pushed forward by the CM. Intravitreal lacunae could be visualized and the mid-vitreous portion of the lacunae moved posteriorly during accommodation while the peripheral edge of the lacunae adjacent to and interconnected with the vitreous zonule were pulled forward. During accommodation there was fluid flow from the anterior chamber toward the cleft of the anterior hyaloid membrane and then further posteriorly into the cleft between the vitreous zonule and the pars plana. The reverse was true during disaccommodation. These movements declined with age. There was an age-related accumulation of vitreous membranes/fibers in the region of the vitreous zonule, the PVZ INS-LE and the ora serrata.
In the young eye, the PVZ INS-LE may act as a “strut” to the posterior lens equator, facilitating accommodative forward movement of the lens equator and thereby facilitating lens thickening. The accommodative posterior/anterior segment fluid flow/exchange represents fluid displacement in response to the lens thickening and CM contraction, and the fluid exchange may allow for the elimination of waste particles/material from the vitreous by transfer to the anterior chamber and then out through the trabecular meshwork. With age, the aggregation of vitreous fibers peripherally may contribute to the posterior restriction of the CM, the vitreous zonule, and the PVZ-INS LE and thereby dampen the accommodative lens shape change and fluid dynamics.
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