To report a case of a 59-year-old female with a free-floating monolateral vitreous cyst localized in the posterior vitreous in the left eye.

A 59-year-old female who complained of an intermittent floater in the left eye for 3 months visited our clinic. She had been suffering from visual disturbance for approximately 3 months. There was no previous history of trauma, infection, or inflammatory disorders. The best corrected visual acuity was 20/20 in both eyes. On fundoscopic exam, a 3-4 disc diameter (DD) sized, brown-colored pigmented vitreous cyst was detected at the inferior temporal side of the posterior vitreous in her left eye. B-scan ultrasound confirmed the presence of an echo-free cystic formation that was free from surrounding vitreous strands or other adhesions located at the posterior vitreous. No specific findings or leakage were observed on fluorescein angiography. We followed-up the patient periodically (1 month, 3 months, and 6 months after the initial visit) and monitored whether the size or location of the cyst had changed. At every follow-up exam, the size or location of the cyst was stationary and the patient's visual acuity was 20/20 in the affected eye, thus we suggested she should be followed-up periodically for her cyst without any intervention.

We report a case of a patient with no previous ocular history or impaired vision who had a free-floating vitreous cyst localized in the posterior vitreous in the left eye. The disease did not appear to progress or become aggravated over a short-term follow-up period and no specific treatment was required.