Correction of unilateral blepharoptosis is unexpectedly difficult because healthy eye is often affected by Hering's law.

We measured changes of marginal reflex distance (MRD1) on the unaffected eyelids between preoperative and 3-month postoperative photographs after ptosis correction. This study analyzed 134 unilateral blepharoptosis patients with ptosis correction from February 2002 to February 2011. Fifty patients among them were negative in Hering's law dependence test. From the preoperative and postoperative photographs the MRD1 of unaffected upper eyelids were measured and adjusted with the average pupil diameter of Koreans. Mean age was 34.4 and male was 30 and female was 20. Average follow-up periods were 14 months.

Thirteenth unaffected eyes (26%) showed decreased MRD1, and 3 patients (6%) showed decreased MRD1 value over 1.0 mm. Then 3 patients needed additional operations for correction of preoperatively unaffected but ptotic eyelids.

There were no meaningful data statistically in the value of MRD1 in every unaffected eye of the patients and in the difference between preoperative and postoperative MRD1 of groups divided according to severity, causes, and types of operation.