Effect of Cervical Sympathetic Stimulation on Accommodation in Monkeys An example of a beta‐adrenergic, inhibitory effect

The preganglionic cervical sympathetic nerve, of mainly cynomolgus monkeys (Macaca irus), has been stimulated electrically using different stimulation rates. The accommodative response to stimulation was a change in refraction towards hypermetropia. This response could not be inhibited by adrenergic α‐receptor antagonists, though these drugs reduced the blood volume changes in the eye upon stimulation. On the other hand, the β‐adrenergic blocker propranolol caused a complete elimination of the sympathetic stimulation response, though changes in eye volume seemed uninfluenced. The accommodative response (in diopters) to stimulation increased considerably when the eye was under strong cholinergic tone. When the animal was pretreated with a large dose of atropine. cervical sympathetic stimulation did not affect the refractive state of eye. The results indicate the presence of a β‐adrenergic, inhibitory mechanism of the ciliary muscle. Possibly this mechanism is responsible for distance accommodation (decrease in accommodation). Changes in vascular structures upon sympathetic stimulation play no practical part in regulating the accommodation.