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A 12-year-old girl presented with a history of repeated headaches (with no ocular symptoms) for 3 years. There was no history of ocular trauma or surgery. On ocular examination elsewhere, she was diagnosed as having intravitreal cysticercosis after observing a cyst in the left eye and was referred for vitrectomy to a tertiary eye care centre.
Her vision was 20/20 in both eyes, with no signs of ocular inflammation. Biomicroscopic examination of the left eye showed a mobile, pigmented, circular cyst in the anterior vitreous, but it was not blocking the pupillary axis (figure 1). Intraocular pressure and fundus examination of both eyes was normal. Ultrasonography revealed a free-floating cyst with no scolex in the anterior vitreous. Ultrasound biomicroscopy did not show any other cyst or mass in the iris and ciliary body. Non-contrast head CT of the brain and orbit ruled out intracranial cysticercosis. The headaches were attributed to convergence insufficiency and the patient was advised orthoptic exercises.
It is easy for a floating iris cyst to mimic intraocular cysticercosis, as it is a common diagnosis, and also, most surgeons are unaware about iris cysts. Often, neuroimaging is normal and adds to the diagnostic dilemma. Although both appear quite similar, the classic pigmentation on the cyst wall, lack of ocular inflammation and lack of scolex on USG help confirm diagnosis of the floating iris cyst.
Shield1 postulated that epithelial cysts arise between the pigmented epithelial layers of the iris, and often break free and migrate into the vitreous chamber, and these are called dislodged cysts. Lois et al2 reported that 12% of primary iris pigment epithelium cysts were vitreous cysts. Sugar et al3 suggest it is important to distinguish retrolental iris cysts (between lens and anterior hyaloid) from anterior vitreous cysts—as retrolental cysts may cause visual disturbance and may be associated with posterior lenticular opacities.
Free-floating iris cysts in the vitreous are uncommon, yet they are commonly confused with more serious conditions, but require no treatment.
In the differential diagnosis of any intraocular cyst, a high index of suspicion should be kept for benign dislodged iris cysts.
Competing interests None declared.
Patient consent Obtained.
Provenance and peer review Not commissioned; externally peer reviewed.