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Movement of the accommodative structures and anterior/posterior segment fluid exchange

Poster Details

First Author: M.Croft USA

Co Author(s):    J. McDonald   A. Katz   T. Nork   J. Kiland   P. Kaufman   E. Lütjen-Drecoll

Abstract Details



Purpose:

After pars plana vitrectomy in human patients there is a loss of accommodative ability of 2.25 diopters.Smith R.C. et al 1990 [Eye] Earlier research [Coleman et al 1985] points to a role for the vitreous in accommodation and presbyopia. More recent findings also indicate a role for the vitreous but not as proposed in the earlier research [Croft and Kaufman et al IOVS 2013] and now this role is further elucidated. Our group has developed a technique to visualize fluid movement and the structures/strands within the vitreous compartment at rest and during accommodation in the rhesus monkey eye. Our goal was to determine the accommodative function of the vitreous membranes and the intravitreal compartments (lacunae) in both young and aging rhesus monkey eyes and the relationship to other accommodative intraocular structures.

Setting:

Department of Ophthalmology and Visual Sciences, University of Wisconsin-Madison, USA.

Methods:

Seven iridectomized rhesus monkeys ranging in age from 5 years to 25 years old were selected and a stimulating electrode was inserted into the Edinger-Westphal nucleus (midbrain) to induce accommodation. A Hartinger coincidence refractometer was used to measure accommodative amplitude.Ultrasound biomicroscopy (UBM; 50, 35, 20 MHz) was used to image the vitreous membrane, the entire extent of the ciliary body, the anterior and posterior lens surfaces, and the zonula during accommodation. A 50 µl intravitreal injection of triamcinolone was used to enhance visualization of intravitreal structures by UBM. Distances between various other intraocular accommodative structures were measured. An endoscopic camera was used to image the intraocular structures inside the vitreous during accommodation. A 50 µl intravitreal injection of 0.02% aminofluorescein dye was used to enhance visualization of intravitreal structures by endoscopy. Four rhesus monkeys underwent unilateral extracapsular lens extraction and the eyes were imaged by UBM before and after lens extraction.

Results:

The triamcinolone particles were suspended in the vitreous fluid and also clung to the vitreous membranes/strands as visualized by UBM. During accommodation the anterior hyaloid membrane and the capsule bowed backward. The fluid and the vitreous structures/strands located in the central vitreous also moved posteriorly as the peripheral vitreous attached to the vitreous zonule was pulled forward by the contraction of the ciliary muscle. Intravitreal lacunae could be visualized beginning in the mid-region of the vitreous and the peripheral edge of these lacunae extended to and were adjacent to the vitreous zonule. 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 was pulled forward. Triamcinolone particles were also observed in the anterior chamber and during accommodation these particles were observed to move 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 of the vitreous compartment. The reverse was true during disaccommodation. These movements decline with age. The endoscopy results confirm the images seen using the UBM

Conclusions:

The posterior/anterior fluid flow between the anterior chamber and the vitreous compartments during accommodation/disaccommodation represents fluid displacement in response to the lens thickening and muscle contraction. This 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. There is fluid movement during the accommodative response which is in the posterior direction in the mid-central region of the vitreous while the peripheral vitreous/fluid adjacent to the vitreous zonule moves forward. The vitreous lacunae move during the accommodative/disaccommodative response and may play a role in the fluid redistribution/dynamics during accommodation. Future descriptions of the mechanism of accommodation and presbyopia therapy should take these findings into account. FINANCIAL INTEREST: One of more of the authors... research is funded, fully or partially, by a company producing, developing or supplying the product or procedure presented

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