Edinger-Westphal and pharmacologically stimulated accommodative refractive changes and lens and ciliary process movements in rhesus monkeys

Abstract

During accommodation, the refractive changes occur when the ciliary muscle contracts, releasing resting zonular tension and allowing the lens capsule to mold the lens into an accommodated form. This results in centripetal movement of the ciliary processes and lens edge. The goal of this study was to understand the relationship between accommodative refractive changes, ciliary process movements and lens edge movements during Edinger-Westphal (EW) and pharmacologically stimulated accommodation in adolescent rhesus monkeys. Experiments were performed on one eye each of three rhesus monkeys with permanent indwelling electrodes in the EW nucleus of the midbrain. EW stimulated accommodative refractive changes were measured with infrared photorefraction, and ciliary process and lens edge movements were measured with slit-lamp goniovideography on the temporal aspect of the eye. Images were 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 during EW stimulated accommodation and after carbachol iontophoresis to determine drug induced accommodative movements. Maximum EW stimulated accommodation was 7.36+/-0.49 D and pharmacologically stimulated accommodation was 14.44+/-1.21 D. During EW stimulated accommodation, the ciliary processes and lens edge moved centripetally linearly by 0.030+/-0.001 mm/D and 0.027+/-0.001 mm/D, with a total movement of 0.219+/-0.034 mm and 0.189+/-0.023 mm, respectively. There was no significant nasal/temporal difference in ciliary process or lens edge movements. 30-40 min after pharmacologically stimulated accommodation, 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 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 both supramaximal EW and pharmacologically stimulated accommodation. In conclusion, this study shows, for the first time, that the ciliary processes and lens edge move centripetally, linearly with refraction during EW stimulated accommodation. During pharmacological stimulation, the ciliary processes move to a greater extent than the lens edge, confirming that in adolescent monkeys, lens movement limits the accommodative optical change in the eye.

Figure 1

Slit-lamp goniovideography images of (A) an unaccommodated and (B) maximally EW stimulated accommodated eye, and (C) an unaccommodated and (D) maximally pharmacologically stimulated accommodated eye. The black crosses mark the edge of the corneal tattoo, the white crosses mark five corresponding ciliary process peaks, and the vertical white line marks the 9 o'clock equatorial edge of the lens.

Figure 2

(A, B) Ciliary process and (C, D) lens edge accommodative movement for increasing stimulus current amplitudes for the (A, C) temporal and (B, D) nasal aspects of one eye (monkey #111) spanning the full accommodative range available. For clarity, only every second data point is shown. The bottom traces show the onset of the stimulus.

Figure 3

(A) Ciliary process and lens edge movements were linearly related to accommodation for all amplitudes spanning the full accommodative range, shown for the temporal aspect of monkey #111, vertically offset for visibility. Accommodative stimuli ranged from 300 to 1400 μA. For the maximum amplitude for all monkeys, (B) ciliary process movement occurs at a rate of 0.030 mm/D, and (C) lens edge movement occurs at a rate of 0.026 mm/D. Linear regression line shown with 95% confidence intervals.

Figure 4

Ciliary process movement and lens edge movement are similar for low accommodative amplitudes in all monkeys. Ciliary process movement was greater than lens edge movement at high amplitudes in (A) monkey #54 and (B) monkey #58, and similar at all amplitudes in (C) monkey #58 and (D) monkey #111.

Figure 5

(A) During maximal EW stimulated accommodation, the circumlental space remained constant in monkeys #58a and #111, and decreased in monkeys #54 and #58b. (B) Circumlental space decreased with time after carbachol iontophoresis. For monkeys #54 and #58, circumlental space decreased to nearly zero.

Figure 6

The slope of the main sequence relationship for (A) ciliary process movement and (B) lens edge movement were not statistically different. (C) Main sequence relationship for accommodation.

Figure 7

Ciliary process movement was greater for supramaximal EW stimulation (A, closed symbols) than for maximal EW stimulation (A, open symbols). Ciliary process movement was greater than lens edge movement during (A) supramaximal EW stimulated accommodation and (C) pharmacologically stimulated accommodation. Ciliary process peak movement was slightly greater than ciliary process valley movement during (B) supramaximal EW stimulated accommodation and (D) pharmacologically stimulated accommodation.

Figure 8

Ciliary process and lens edge movement with time after carbachol iontophoresis for (A) monkey #54, (B) monkey #58, and (C, D) monkey #111. A second dose of carbachol was delivered (at arrows) after 30 minutes in monkeys #54, #58 and #111 (C) to ensure a maximal accommodative response had been induced.