Dynamic wavefront measurement of accommodation and pupil area in response to electric stimulation of ciliary nerve in cats

Abstract

Purpose: To investigate the changes of accommodation and pupil area elicited by electrical stimulation of the ciliary nerve, we analyzed the wavefront aberrations (WAs) and the pupil size with a Shack-Hartmann wavefront aberrometer (SHWA) before, during, and after the stimulation.

Methods: Six eyes of six cats were studied under general anesthesia. Trains of monophasic pulse (current, 0.1 to 2.0 mA; duration, 0.5 ms/phase; frequency, 5 to 40 Hz) were applied to either the lateral or medial branch of the short ciliary nerve (Kuchiiwa, 1990). Hook-shaped bipolar stimulating electrodes were made of stainless steel with a diameter of 0.3 mm and were hooked onto the short ciliary nerve about 5 mm from the scleral surface. We measured the wavefront aberration for 2 seconds before, 8 seconds during, and for 20 seconds after the electrical stimulation with a compact wavefront aberrometer (Aston University and Topcon Co). The pupillary images were simultaneously photographed during the wavefront measurements. The wavefront aberrations and the pupil images were recorded at 10 Hz.

Results: The pupil dilated asymmetrically when one side of the ciliary nerve was stimulated and dilated symmetrically when both sides of the ciliary nerves were stimulated. The pupil was never constricted by any stimulating parameters. Although asymmetrical pupil dilation occurred by unilateral ciliary nerve stimulation, no asymmetrical terms of the WAs were found. The accommodative responses had an implicit time of 2 to 6 sec and an amplitude of 1 to 2 diopters. The implicit times were slower than that in humans (0.4 second, F. W. Campbell, 1960) and the cat’s response to electrical stimulation of the LS area (1.0 second, K. Ohtsuka, 1996). After the stimulation, accommodation decreased slowly to the original state taking >10 sec. The latencies of the accommodative responses were always shorter than the detection limit (<100 ms).

Conclusions: The pupillary dilation was asymmetrical to the optical axis following unilateral ciliary nerve stimulation but no asymmetrical aberration change was found. The discrepancy may stem from the fact that the crystalline lens has a viscoelastic property and the asymmetric contraction of ciliary muscle might not cause the optical asymmetry.

Keywords: 404 accommodation • 667 pupil • 508 electrophysiology: non-clinical