- ICD-9 364.60
- ICD-10 H21.302
An iris cyst is an epithelial-lined space that involves a layer of the iris. A primary iris cyst does not have a recognizable etiology. A secondary iris cyst has a recognizable etiology, such as surgical or nonsurgical trauma.
Classification of Iris Cysts:
- Primary Cysts
- Iris pigment epithelium cysts
- Iris stromal cysts
- Secondary Cysts
Primary iris cysts are congenital and occur sporadically. Iris pigment epithelium cysts occur more commonly in adults while iris stromal cysts occur more in children.
Primary iris cysts are nonkeratinized squamous epithelial-lined structures that arise either from the posterior iris layer or stroma. Epithelium from stromal cysts contains goblet cells.
The pathogenesis of primary iris cysts is not entirely understood, and proposed mechanisms in the literature are controversial. Iris pigment epithelial cysts are thought to be remnants of the marginal sinus of the iris that have not been obliterated. The presence of goblet cells in iris stromal cysts suggest that they are formed by entrapped surface ectoderm tissue likely during formation of the lens vesicle (4th week of embryogenesis).
Primary iris cyst are most commonly of posterior pigment epithelial cell origin and located in the peripheral iris.
The diagnosis of iris cysts is based on the slit lamp exam and imaging by ultrasound biomicroscopy (UBM) or anterior segment optical coherence tomography (AS-OCT). Despite the high-resolution imaging of AS-OCT, UBM remains the gold-standard imaging due to ability to better characterize the interior of the cystic structurs.
Iris cysts are often found incidentally. Though they may be congenital, they may not be detected until late into the first or second decade of life. Patients may notice a “spot” on their iris.
Rare reports exist in the literature describing an inheritance pattern of iris cysts, which may present as multiple or bilateral iris cysts in successive generations.
The majority of patients are asymptomatic, however if there is progressive enlargement of the cyst, there is a higher likelihood of having symptoms. Symptoms may include blurry vision, photophobia, and eye pain.
Cysts may have a round or collapsed appearance. Iris pigment epithelial cysts can be located on the anterior or posterior surface of the iris. They have a brown/black, velvety appearance and typically do not transilluminate. Iris stromal cysts appear as clear masses on the anterior surface of the iris and do transilluminate.
Iris cysts secondary to trauma and subsequent epithelial implantation appear as serous or solid in continuity with the wound with or without membranes on the anterior iris surface.
It is important to rule out iris melanoma when evaluating an iris cyst. Iris melanomas appear as a brown lesion arising from the stroma. Unlike primary iris pigment epithelium cysts, they can be variably colored, maintain stable contour even after dilation. Presence of sentinel vessels and intrinsic vessels within the lesion are suggestive of a solid tumor rather than a benign cyst.
Depending on the size, location and compression of adjacent structures, the following complications may occur secondary to iris cysts:
- Angle-closure glaucoma
- Plateau iris syndrome
- Pigment dispersion syndrome
- Corneal edema
- Focal cataract
- Lens subluxation
Ultrasound biomicroscopy (UBM) is the gold standard for imaging large iris cysts. Iris cysts appear round or ovoid with a thin, hyperechoic wall (due to the epithelial cell lining) and a hypoechoic interior (due to its fluid contents). 
Anterior segment optical coherence tomography (AS-OCT) may be of utility for small anterior iris lesions such as iris nevi but because of increased posterior shadowing, it is inferior to UBM for visualizing iris cysts.
The following may be considered in the differential diagnosis of iris masses:
- Primary iris pigment epithelial cyst
- Primary iris stromal cyst
- Epithelial downgrowth
Iris cysts secondary to miotics (phospholine iodide) are treated with phenylephrine 2.5%. Cysts also resolve with discontinuation of phospholine iodide. 
Iris cysts that are stable and not causing symptoms or secondary complications require no treatment but should be followed regularly. Iris cysts that involve the visual axis, particularly in children at risk for amblyopia, necessitate intervention. Most authors recommend treating iris cysts using a step-wise approach, starting with less-invasive treatment prior to proceeding to surgical excision whenever possible.
- Laser Treatment
- Argon laser photocoagulation - photocoagulation of the cyst epithelium may be able to halt production of cystic fluid contents. This may be performed to shrink the cysts; though recurrence is common. Its utility is limited in cases of large cysts and when visualization is difficult.
- Nd:YAG - photodisruption (laser cystostomy) of the cyst wall may allow perforation of the cyst and release of contents into the anterior chamber.
- Cyst aspiration with injection of sclerosing agent- Aspiration of the cyst contents with subsequent injection of absolute alcohol to induce sclerosis and closure of the cystic cavity has demonstrated good success in a minimally-invasive method. Methods may vary, but a 27g infusion/aspiration needle can be used to first aspirate cyst contents, then infuse alcohol until the cyst wall turns grey, after which the alcohol is removed.  While recurrence is not common, this procedure can be repeated if it does occur. Other sclerosing agents published in the literature include trichloroacetic acid, 5-fluorouracil, and mitomycin C.
- En bloc excision - A more aggressive surgical approach is en bloc excision of the iris cyst with or without light cryotherapy. While this procedure has a good success rate, there is greater risk of causing collateral damage to ocular structures.
- Secondary iris cysts due to epithelial downgrowth may require more aggressive surgical excision and devitalization of the epithelial tissues with vitrectomy, lensectomy, and cryodestruction of residual cells at the excision site.
Post operative complications
Postoperative complications depend on the amount of tissue removed. Complications can include cataract formation, corneal edema, glaucoma, and transient anterior segment inflammation.
The prognosis of primary iris cysts is good, as the majority do not require treatment. Recurrence after excision is more common in stromal cysts than pigment epithelial cysts. The prognosis of secondary iris cysts is much more variable and those as a result of epithelial downgrowth typically carry a poor prognosis.
- Images courtesy of The Robert Cizik Eye Clinic, Houston, TX.
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