Iris Cysts
Fluid-filled cystic lesions arising from the iris pigment epithelium (IPE) or iris stroma. The majority are primary, idiopathic, and benign — remaining stable for life. Secondary cysts may arise from surgery, trauma, miotics, or parasitic infection and carry a greater risk of progression and complications.
Last updated: March 2026
Panel A — Anterior View (Slit-Lamp)
Panel B — Iris Cross-Section (Cyst Location & UBM Appearance)
Panel A: Anterior view showing dark, round primary IPE cysts at the pupillary margin and a larger pale translucent stromal cyst causing subtle pupil displacement. Panel B: Cross-section comparing IPE cyst (between PPE layers), stromal cyst (within anterior stroma), and solid iris melanoma — UBM differentiates hollow cysts from solid tumours.
Iris cysts are benign fluid-filled structures arising from the posterior (pigment epithelial) or anterior (stromal) surface of the iris. They represent one of the most common iris lesions encountered in clinical practice, with primary iris pigment epithelium (IPE) cysts being the most prevalent subtype.
Primary IPE cysts are typically bilateral, small (1–5 mm), thin-walled, and deeply pigmented (melanotic). They form between the two layers of the posterior iris pigment epithelium and are usually visible at the pupillary margin during mydriasis as dark, round lesions that appear to "roll" with eye movement. They are typically stable for life and require only periodic monitoring.
Stromal cysts are less common, usually unilateral, and occur predominantly in children. They arise from the anterior iris stroma, appear pale and translucent on slit-lamp examination, and have a greater tendency to enlarge. Enlarging stromal cysts in children may obstruct the visual axis, causing deprivation amblyopia, or compress the trabecular meshwork, causing secondary angle closure glaucoma.
Secondary iris cysts arise from extrinsic causes including prior intraocular surgery (epithelial or fibrous ingrowth), miotic medications (pilocarpine, historically used for plateau iris), and, in endemic regions, parasitic infection (ocular cysticercosis from Taenia solium).
The primary clinical concern with any iris cyst is differentiation from a solid iris tumour — particularly iris melanoma — as management differs dramatically. Ultrasound biomicroscopy (UBM) is the investigation of choice, demonstrating a cystic (hollow) internal reflectivity in contrast to the solid pattern of melanoma.
Primary Iris Cysts (Idiopathic)
- Primary IPE cysts: Idiopathic fluid accumulation between the two layers of the posterior iris pigment epithelium. May be congenital or develop in adulthood. The most common type — found in up to 2–5% of the general population.
- Primary stromal cysts: Congenital entrapment of surface epithelial cells within the developing iris stroma during embryogenesis. Predominantly present in children and young adults; may enlarge progressively.
- Dilation lag cysts (peripheral IPE cysts): Small cysts visible at the pupillary margin on dilation; particularly common in middle-aged adults; often bilateral; benign.
Secondary Iris Cysts
- Implantation cysts (post-surgical): Conjunctival or corneal epithelium dragged into the anterior chamber during intraocular surgery (cataract, penetrating keratoplasty, glaucoma surgery); forms a progressively enlarging pearl-white cyst at the surgical site or on the iris surface; may cause secondary glaucoma by obstructing the trabecular meshwork.
- Traumatic implantation cysts: Epithelium implanted via a penetrating wound; similar clinical behaviour to post-surgical implantation cysts.
- Miotic-induced IPE cysts: Historically associated with long-term pilocarpine use for plateau iris or narrow angle treatment; thought to result from stimulation of pigment epithelial proliferation by miotics.
- Parasitic cysts (ocular cysticercosis): Intraocular implantation of Taenia solium larva (cysticercus cellulosae) from contaminated food/water in endemic regions (South/Southeast Asia, Sub-Saharan Africa, Latin America); may reside in the anterior chamber or subretinal space; may be visible as a pearlescent cyst in the anterior chamber.
Primary IPE cysts: The posterior iris pigment epithelium consists of two layers of melanin-rich cells derived from the neuroectoderm of the optic cup. Cyst formation results from fluid accumulation within the potential space between these two epithelial layers, akin to a retinal detachment occurring at the level of the iris pigment epithelium. The exact stimulus for fluid accumulation is unknown in idiopathic cases. The thin, intact epithelial lining contains the fluid and transilluminates on retroillumination.
Primary stromal cysts: Thought to arise from aberrant sequestration of surface epithelial progenitor cells within the iris stroma during embryonic development, or from metaplastic change of stromal cells. The cyst lining consists of non-keratinising stratified squamous or cuboidal epithelium. As the cells proliferate and secrete fluid, the cyst enlarges. Unlike IPE cysts, stromal cysts are not pigmented and appear pale or translucent.
Implantation cysts: Conjunctival or corneal surface epithelial cells, when displaced into the anterior chamber during surgery or trauma, retain their growth potential in the aqueous environment. They proliferate, form an epithelial-lined cyst, and progressively enlarge. If the cyst ruptures, shed epithelial cells can coat the trabecular meshwork, corneal endothelium, and iris surface — a condition known as epithelial ingrowth — which carries a poor prognosis.
Parasitic: After ingestion of Taenia solium eggs, oncospheres hatch in the intestine, penetrate the gut wall, and disseminate haematogenously. Larvae may reach the eye via the posterior ciliary arteries, lodging in the choroid, vitreous, or anterior chamber. Larval growth forms the cysticercus, a fluid-filled bladder with an invaginated scolex.
Primary IPE Cysts
Most common; posterior iris pigment epithelium; bilateral; dark/melanotic; stable; mid-zonal, pupillary margin, or peripheral location; benign.
Primary Stromal Cysts
Less common; anterior iris stroma; usually unilateral; pale/translucent; may enlarge, especially in children; amblyopia risk in children.
Secondary: Implantation
Post-surgical or post-traumatic epithelial ingrowth; progressive; may cause glaucoma; requires surgical management. Pearl-white smooth surface.
Secondary: Miotic-Induced
Associated with long-term pilocarpine use; IPE cysts; typically regress after discontinuing the miotic agent.
Secondary: Parasitic
Cysticercosis (Taenia solium) in endemic regions; pearlescent cyst in AC or subretinal space; scolex may be visible within cyst; requires systemic evaluation.
By Location
Pupillary zone (visible at pupil margin), mid-zone (mid-iris stroma), peripheral (near angle / ciliary body). Angle involvement correlates with glaucoma risk.
- Miotic use (pilocarpine): Long-term topical pilocarpine — historically used for angle-closure prophylaxis and plateau iris; IPE cyst formation was a well-recognised side effect.
- Prior intraocular surgery: Cataract surgery, penetrating keratoplasty, glaucoma filtering surgery — all carry risk of epithelial implantation into the anterior chamber.
- Penetrating ocular trauma: Any full-thickness wound with contamination by surface epithelium risks implantation cyst formation.
- Childhood age: Primary stromal cysts predominantly present in children; progressive enlargement is more likely in younger patients.
- Residence in/travel to endemic regions: Cysticercosis — South Asia (India, Myanmar), Southeast Asia, Sub-Saharan Africa, Latin America; consumption of undercooked pork or contaminated water.
- Congenital factors: Primary IPE cysts may be identified from birth or early childhood; no specific identifiable risk factor.
- Usually asymptomatic (primary IPE cysts): The vast majority of primary IPE cysts are discovered incidentally during routine dilated eye examination; the patient is unaware of their presence.
- Visual axis obstruction: Large stromal or implantation cysts that encroach on the visual axis cause blurred vision; particularly significant in children where it causes deprivation amblyopia.
- Photophobia and glare: Large cysts may optically degrade the image; secondary glaucoma with elevated IOP may cause halos and light sensitivity.
- Symptoms of angle closure: If a large peripheral cyst occludes the iridocorneal angle — acute headache, eye pain, coloured haloes around lights, nausea, reduced vision; may mimic primary angle closure attack.
- Floaters: If a parasitic cyst ruptures in the anterior chamber or vitreous, inflammatory debris may cause floaters and significant visual disturbance.
- Cosmetic concern: Visible large anterior stromal cysts may be noticed by patients or parents as a white or glistening spot on the iris.
- Secondary angle closure glaucoma: Large peripheral iris cysts may physically touch or occlude the trabecular meshwork; acute angle closure attack with markedly elevated IOP, corneal oedema, and pain. Can become a surgical emergency.
- Deprivation amblyopia (children): Large anterior stromal cysts that cover the visual axis in infancy or early childhood deprive the visual cortex of clear retinal input, causing irreversible amblyopia if not treated promptly.
- Cyst rupture: Spontaneous or traumatic cyst rupture may release epithelial cells or cystic contents into the anterior chamber; epithelial ingrowth from implantation cyst rupture is a devastating complication causing progressive membrane formation over the corneal endothelium and trabecular meshwork.
- Progressive enlargement: Particularly primary stromal cysts and implantation cysts; may displace the lens, distort the pupil, and occlude the angle over months to years.
- Parasitic uveitis: Death or rupture of a cysticercus cyst releases antigenic material, provoking severe granulomatous uveitis; may cause hypopyon, posterior synechiae, and secondary glaucoma.
- IOP elevation (sub-acute): Even without frank angle closure, trabecular compression by a cyst may produce chronically elevated IOP with insidious optic nerve damage.
Ocular Cysticercosis (Taenia solium)
The most important systemic association for iris cysts. Caused by larval stage (cysticercus) of the pork tapeworm Taenia solium. The parasite gains entry to the eye via the bloodstream following ingestion of T. solium eggs (from faecally contaminated food/water — not from eating undercooked pork, which causes intestinal tapeworm rather than cysticercosis).
- Neurocysticercosis: CNS involvement (most common site); seizures, focal neurological deficits, hydrocephalus; CT/MRI brain reveals calcified or ring-enhancing lesions.
- Subcutaneous cysticercosis: Palpable nodules in subcutaneous tissue.
- Systemic evaluation: Serology (ELISA for anticysticercal antibodies), CT brain (mandatory when ocular cysticercosis is confirmed or suspected); neurology consultation.
- Treatment: Surgical removal of intraocular cysticercus before initiating systemic antiparasitic therapy (albendazole/praziquantel) to avoid severe intraocular inflammatory reaction from in-situ larval death.
Other primary iris cysts (IPE and stromal) have no associated systemic diseases. Secondary implantation cysts are purely ocular consequences of prior surgery or trauma.
- Slit-lamp biomicroscopy: Primary examination; assess cyst location, size, wall characteristics (smooth/irregular), colour (dark = IPE; pale = stromal/implantation), transillumination (hollow vs solid), effect on pupil and angle. Retroillumination is essential.
- Pharmacological dilation: Mydriasis (tropicamide 1% ± phenylephrine 2.5%) reveals peripheral IPE cysts at the pupillary margin that may not be visible in the undilated state.
- Ultrasound Biomicroscopy (UBM — 50 MHz): Gold standard for iris cyst characterisation. Demonstrates: cystic (hollow, anechoic) internal pattern vs solid (echogenic) pattern of melanoma; cyst wall thickness; relationship to the iridocorneal angle and ciliary body; posterior extension. Indispensable for any posterior or peripheral cyst not well visualised on slit-lamp.
- Anterior Segment OCT (AS-OCT): High-resolution imaging of anterior iris cysts; non-contact; good for follow-up; limited penetration for deeply posterior lesions (where UBM is superior).
- Fluorescein angiography (FFA): Iris cysts show no intrinsic vascularity and no leakage; differentiates cysts from vascular tumours (iris melanoma, haemangioma).
- B-scan ultrasound: For large posterior cysts or parasitic cysts; less resolution than UBM but broader field of view.
- IOP measurement: Goldmann applanation tonometry; elevated if angle involvement present; monitor at every visit for peripheral cysts.
- Gonioscopy: Assess angle anatomy when peripheral cysts are present; determine degree of angle compromise.
- Serology (parasitic): ELISA anticysticercal antibodies; CT brain if cysticercosis confirmed or suspected; systemic evaluation.
Primary IPE Cysts — Observation
The vast majority require no treatment. Observe with slit-lamp photography and UBM at 6–12 monthly intervals. Document size, location, and any new features at each visit. If stable over 2–3 years, annual monitoring is sufficient.
Symptomatic or Enlarging Cysts — Intervention
- Argon laser photocoagulation: For accessible IPE cysts; laser energy punctures the cyst wall, causing collapse; may recur.
- Nd:YAG laser puncture: Photodisruption of cyst wall; effective for superficial anterior stromal and IPE cysts; risk of recurrence and seeding of cyst contents.
- Surgical aspiration: Fine-needle aspiration ± excision for large stromal cysts; higher recurrence with aspiration alone; excision with cyst wall removal preferred.
- Vitrectomy: For parasitic cysts in the posterior segment or large anterior segment cysts requiring complete removal; remove intact before antiparasitic therapy.
- Miotic discontinuation: For pilocarpine-induced cysts — stop the offending agent; cysts typically regress.
- Surgical excision (implantation cysts): Progressive implantation cysts require excision of the entire cyst wall; often requires anterior vitrectomy and iris repair; risk of epithelial ingrowth if rupture occurs during surgery.
Glaucoma and Amblyopia
- Treat elevated IOP with topical agents while planning definitive cyst treatment.
- Surgical cyst removal may resolve angle closure; adjunctive filtering surgery if residual glaucoma persists.
- Children with stromal cysts occluding the visual axis require urgent cyst excision followed by aggressive amblyopia therapy (patching).
Singapore Optometry Scope Note: Optometrists should document and photograph any iris lesion identified on slit-lamp at the first encounter. Perform transillumination (retroillumination) as part of routine iris assessment to help distinguish cystic from solid lesions. Refer for UBM to confirm the cystic nature of any lesion where doubt exists — this is the critical step in ruling out iris melanoma. Measure IOP at every visit for patients with known peripheral iris cysts, given the risk of secondary angle closure. In Singapore, where travel to cysticercosis-endemic regions (India, Myanmar, Southeast Asia) is common, consider parasitic aetiology in any unusual anterior chamber cyst with inflammatory activity, especially in patients from or with travel history to endemic areas. Do not initiate pilocarpine for iris-related conditions without awareness of the IPE cyst association. Refer promptly for ophthalmological assessment if a cyst is enlarging, causing visual axis obstruction in a child, or is associated with elevated IOP.
Primary IPE cysts carry an excellent long-term prognosis. The overwhelming majority remain stable for life without causing any visual impairment or secondary complications. Spontaneous resolution can occur.
Primary stromal cysts have a more variable prognosis. Although benign, they may enlarge — particularly in children — and cause amblyopia or secondary glaucoma if not monitored and treated in a timely manner. After successful excision, recurrence rates are approximately 10–30%, and follow-up is recommended.
Implantation cysts carry a more guarded prognosis due to their progressive nature and the risk of epithelial ingrowth if the cyst ruptures. Complete surgical excision is the goal but can be technically challenging; recurrence and persistent IOP elevation are possible.
Parasitic cysts (cysticercosis) have a good visual prognosis after intact surgical removal, provided the procedure is performed before severe uveitis or retinal damage develops. Systemic neurocysticercosis requires separate neurological management and may have independent impact on quality of life.
| Condition | Key Differentiator |
|---|---|
| Iris melanoma | Solid on UBM (echogenic internal pattern); intrinsic vascularity on FFA; feeder vessels visible on slit-lamp; documented growth; ectropion uveae; angle seeding. Does NOT transilluminate. |
| Iris naevus | Flat, macular or minimally elevated pigmented lesion; no cystic component; solid on UBM; stable; no transillumination. |
| Iris melanocytoma | Very dark (jet-black), densely pigmented solid lesion; rare; solid on UBM; may shed pigment granules into AC; benign but malignant transformation possible. |
| Ciliary body cyst | Located posterior to the iris on UBM; may displace iris anteriorly mimicking plateau iris; cystic on UBM; no direct slit-lamp visibility without gonioscopy/UBM. |
| Uveal effusion | Choroidal/ciliary body detachment; flat anterior chamber; not a cystic iris lesion; different presentation entirely. |
| Iris haemangioma | Vascular lesion; prominent vascularity on FFA; not cystic; may be associated with Sturge-Weber syndrome. |
- Shields CL, Arepalli S, Lally EB, Lally SE, Shields JA. Iris stromal cyst management with absolute alcohol-induced sclerosis in 16 consecutive patients. JAMA Ophthalmol. 2014;132(6):703–708. doi:10.1001/jamaophthalmol.2014.101
- Lois N, Shields CL, Shields JA, Mercado G. Primary iris stromal cysts. A report of 17 cases. Ophthalmology. 1998;105(7):1317–1322. doi:10.1016/S0161-6420(98)97039-3
- Marigo FA, Finger PT, McCormick SA, Iezzi R, Esaki K, Ishikawa H. Iris and ciliary body melanomas: ultrasound biomicroscopy with histopathologic correlation. Arch Ophthalmol. 2000;118(11):1515–1521. doi:10.1001/archopht.118.11.1515
- Shields JA. Primary cysts of the iris. Trans Am Ophthalmol Soc. 1981;79:771–809.
- Kaushik S, Ichhpujani P, Ramasubramanian A, Pandav SS. Occult intraocular foreign body: ultrasound biomicroscopy holds the key. Eye (Lond). 2008;22(7):978–980.
- Narang S, Gupta V, Gupta A, Dogra MR, Pandav SS, Das A. Role of ultrasound biomicroscopy in anterior segment evaluation of ocular cysticercosis. Eye (Lond). 2007;21(2):174–179. doi:10.1038/sj.eye.6702155
- Shields MB. Textbook of Glaucoma. 4th ed. Williams & Wilkins; 1998. Iris cysts, pp. 168–175.