Preoperative pupil fatigue.

Pupils are frequently dilated on the day before cataract surgery and for retinal detachment surgery so the fundus can be examined. This may, however, interfere with pupil mydriasis on the day of surgery. This study looked at the effect of pupil dilation with tropicamide 1% and with cyclopentolate 1% on pupil mydriasis 24 hours later, using phenylephrine 10% and cyclopentolate 1%, in 40 cataract patients. The pupils dilated with cyclopentolate one day previously demonstrated a mean reduction in subsequent mydriasis of 0.73 mm compared with pupils that had been dilated with tropicamide (P less than .0001). The magnitude of this difference was not related to the patient age (P = .12) or to iris color (P = .21). If it is necessary to dilate pupils on the day before surgery, tropicamide 1% rather than cyclopentolate 1% should be used, as it is less likely to interfere with the pupil mydriasis produced with cyclopentolate 1% and phenylephrine 10% on the day of surgery.