Abstract
Purpose: :
During accommodation, ciliary muscle contraction leads to physical changes in the ciliary body and crystalline lens, including centripetal ciliary body movement, a decrease in lens equatorial diameter and increase in lens surface curvatures, which result in ocular refractive changes. The goal of this study was to understand the relationship between lens and ciliary body physical movements with refractive changes during centrally and pharmacologically stimulated accommodation in adolescent rhesus monkeys.
Methods: :
Experiments were performed on one eye each of 3 rhesus monkeys (ages 6, 8 and 8 yrs) with permanent indwelling electrodes in the Edinger–Westphal (EW) nucleus. Refractive changes were measured dynamically with infrared photorefraction, and ciliary process and lens edge movements were measured dynamically with slit–lamp goniovideography on the temporal aspect of the eye. Accommodation was stimulated with increasing stimulus current amplitudes to the EW nucleus and pharmacologically stimulated with carbachol iontophoresis. Images were also recorded on the nasal aspect for one eye during EW stimulation. Image analysis was performed off–line at 30 Hz to determine refractive changes and ciliary body and lens edge movements.
Results: :
Maximum EW stimulated accommodation was 7.36 ± 0.49 D (mean ± SEM) and maximum pharmacologically stimulated accommodation was 14.44 ± 1.21 D. During EW stimulated accommodation, the ciliary processes moved centripetally 0.219 ± 0.034 mm, linearly at a rate of 0.030 ± 0.001 mm/D, and the lens edge moved centripetally 0.189 ± 0.023 mm, linearly at a rate of 0.027 ± 0.001 mm/D. There was no nasal/temporal difference in ciliary process or lens edge movements. After carbachol iontophoresis, the ciliary processes moved centripetally a total of 0.411 ± 0.048 mm, or 0.030 ± 0.005 mm/D, and the lens edge moved centripetally a total of 0.258 ± 0.014 mm, or 0.019 ± 0.003 mm/D. The peaks and valleys of the ciliary processes moved by similar amounts during accommodation.
Conclusions: :
The ciliary processes and lens edge move centripetally linearly with the change in refraction during EW stimulated accommodation. During pharmacological stimulation, the ciliary processes move to a greater extent than during EW stimulation and also to a greater extent than the lens edge, confirming that in adolescent monkeys, lens movement limits the accommodative optical change in the eye.
Keywords: ciliary body • crystalline lens • presbyopia