ABSTRACT
PURPOSE: To report a case of bilateral Marcus Gunn syndrome, which can be easily overlooked. CASE SUMMARY: A 6-year-old boy visited our clinic complaining of right ptosis. On ocular examination, the palpebral fissure width was 4 mm in the right lid and 7 mm in the left lid. Marginal reflex distance 1 (MRD 1) was -1 mm in the right lid and 2 mm in the left lid. Bilateral levator muscle function was good. When the patient moved the jaw to the right side, the left eyelid was retracted by 2 mm, and when the jaw was moved to the left side, the right upper eyelid retracted by 4 mm, which showed a moderate bilateral jaw-winking phenomenon. There was no change in bilateral palpebral fissure width when only opening the mouth without jaw movement. CONCLUSIONS: Asymmetrical bilateral ptosis can be easily misdiagnosed for unilateral ptosis, and concurrent Marcus Gunn phenomenon can exist. Therefore, a thorough examination is necessary when examining a ptosis patient.