To investigate the clinical features and therapeutic effects of unilateral ptosis in patients who respond to the phenylephrine (PE) test.

Patients who presented with unilateral ptosis from January 2010 to December 2014 and underwent a PE test were included in the analysis. A 2.5% ophthalmic solution of phenylephrine hydrochloride was instilled at the superior conjunctival fornix in the ptotic eye. After 10 minutes of instillation, the patients' eyelid heights were evaluated. Underlying systemic diseases were examined based on previous medical history, a blood test, neurologic examination, and radiologic imaging findings.

Twenty-six of 44 patients who underwent a PE test showed positive results. Fourteen (53.8%) patients with positive PE test had systemic disease, and 2 (11.2%) patients had systemic disease with negative PE test. In the positive PE test group, the associated systemic disease frequency was remarkably high ( p = 0.004). Myasthenia gravis (MG) was found more frequently in the positive PE test group than in the negative PE test group ( p = 0.031). After 6 months, the interpalpebral fissure height increased by 2.20 mm in the positive PE test group and 2.38 mm in the negative PE test group. Patients receiving medication treatment experienced an increase in interpalpebral fissure height of 2.00 mm in the positive PE test group and 2.50 mm in the negative PE test group. In patients undergoing observation alone, the interpalpebral fissure height increased by 1.50 mm in the positive PE test group and 0.80 mm in the negative PE test group. There was no significant difference in treatment methods (respectively, p = 0.147, p = 0.228 and p = 0.112).

The PE test can be considered to help with differential diagnosis when examining patients with mild to moderate ptosis. If the PE test is positive, underlying comorbidity including MG should be considered.