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MaryAnn Croft, Julie A Kiland, Gregg A Heatley, T Michael Nork, Jared McDonald, Alexander Katz, Elke Lutjen-Drecoll, Paul L Kaufman; Accommodative Movements of the Choroid in the Region of the Optic nerve in Young and Old Eyes. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2647.
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© ARVO (1962-2015); The Authors (2016-present)
To elucidate the accommodative movements of the choroid in the region of the optic nerve (ONR) before and after lens extraction, in accommodating and presbyopic monkey eyes and to compare the data with shape changes of other ocular tissues evaluated by a newly developed computer program.
In 4 rhesus monkeys (ages 8-22 yrs), maximum accommodative responses were induced by electrical stimulation of the Edinger-Westphal nucleus. Fundus photos were taken and UBM; 50 MHz, 35 MHz; images were collected in the region of the ora serrata (ORR), the ONR, lens, ciliary body, and zonular attachments in the unaccommodated and accommodated states. The movement of the ONR was measured using distances between vessel branches on opposite sides of the nerve. Measurements were performed before and after lens extraction.
During accommodation in the young aphakic eye (n=2; age 9), the ORR moved forward by ~1 mm, the ONR 0.10 ± 0.02 mm (n=2). In the aphakic older eye (n=2; ages 17,22 yrs), these movements declined to ~0.3 mm in the ORR and to 0.02 ± 0.02 mm in the ONR. In the young phakic eye, lens thickening (0.45 ± 0.04 mm; n=2) during ~10 diopters of accommodation magnified the region of the optic nerve by ~10%, but in the phakic older eye, very little magnification was observed. The newly developed program allows individual comparisons between the measurements obtained on fundus photos and that obtained by UBM.
The accommodative movements of the ORR are nearly tenfold greater than in the ONR. They decline with age, but still are present in both regions. Thus, the stretching of the choroid during accommodation may place tensions on the ONR and contribute to the formation of extracellular material, which occurs with age and makes the old optic nerve more susceptible for glaucomatous damage. If movement of the choroid is investigated in young eyes, the magnification induced by accommodative lens thickening should be taken into consideration. These findings may also have implications for the mechanism of accommodation and presbyopia and the assessment/function of accommodating IOLs.
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