Influence of pupil size, anisocoria, and ambient light on pilocarpine miosis. Implications for supersensitivity testing.

BACKGROUND

This study determines how pupil size, anisocoria, and ambient light influence miotic responses to dilute pilocarpine. The aim is to establish whether mechanical properties of the iris affect miotic behavior using a cholinergic agonist and, if so, to define a more specific clinical definition of supersensitivity testing for suspected tonic pupil disorders.

METHODS

The right pupil of 42 normal subjects was first dilated with phenylephrine to create an experimental anisocoria. Then, pilocarpine 0.1% was placed in both eyes. Net constriction of the larger right pupil was determined by subtracting the amount of pilocarpine-induced constriction of the control left pupil from the amount of pilocarpine-induced constriction of the experimental right pupil. Pupil diameters were measured in room light and darkness.

RESULTS

In only a few subjects, the larger right pupil became smaller than the left pupil after pilocarpine administration. Net constriction of the right pupil was greater when determined in room light than in darkness. The amount of net constriction of the right pupil showed good correlation with the degree of baseline anisocoria when evaluated in room light, but not so in darkness.

CONCLUSION

Pupil size, degree of anisocoria, and light conditions influence the amount of pilocarpine-induced change in anisocoria. If a patient's larger pupil becomes the smaller pupil in darkness after dilute pilocarpine is applied to both eyes, then it is likely that such a response occurred independent of mechanical properties of the iris, and likely represents a supersensitive response. Ophthalmology.