Evaluation and management of unilateral ptosis and avoiding contralateral ptosis.

Treating unilateral ptosis can be challenging and a proper preoperative evaluation may help prevent unexpected outcomes on the contralateral lid. Preoperative evaluation should include testing for Hering's law, which remains useful in understanding the phenomenon of induced contralateral eyelid retraction in the context of ptosis. Approximately 10% to 20% of patients with unilateral ptosis have some degree of induced retraction on clinical evaluation in the contralateral lid. When there is a positive Hering's test on preoperative examination, the surgeon should consider a bilateral ptosis procedure. The surgical approach to unilateral ptosis depends on the severity of the ptosis and its etiology, and the surgeon should be aware of which procedure is most likely to provide the best outcome in selected instances.