To report a case of congenital idiopathic microcoria corrected with pupilloplasty and amblyopia treatment.

A 4-year-old girl was referred for pupillary abnormality of the left eye. Her mother experienced no problems during gestation, and the patient was born at full term. On initial examination, visual acuity was 20/25 in the right eye and counting finger at 50 cm in the left eye. Slit lamp examination revealed that the left pupil was displaced superonasally. A band of fibrous tissue extended across the left pupil and there was no red reflex. There was very slight reaction to mydriatics. Using 23-gauge vitrectomy scissors, a pupilloplasty was performed, and the synechiae are removed. Postoperatively, the pupillary light reflex was brisk, and occlusion therapy was initiated. After 3 months, the visual acuity of the left eye improved to 20/30.

In our case, although microcoria was diagnosed at a relatively old age, the patient's clinical features were consistent with congenital idiopathic microcoria. Therefore, we diagnosed the patient with gradually progressed congenital idiopathic microcoria. In the case of typical congenital idiopathic microcoria, the red-reflex is absent at birth because of the small pupil. However, as in our case, it is possible that the pupil can contract gradually due to movement of the fibrous strand. The point must be considered in such patients.