Continuing Education Activity

Iris cysts may occur as a primary or secondary process. These can have variable disease courses and severity, potentially affecting an individual's vision and quality of life. This activity highlights the role of the interprofessional team in the evaluation and treatment of patients with iris cysts.

Objectives:

• Describe a common classification system of iris cysts.
• Identify a differential diagnosis for iris cysts.
• Review various imaging modalities used to investigate iris cysts.
• Outline an approach for the treatment of iris cysts.

Introduction

Iris cysts are not common and can provide a challenge for clinicians in terms of diagnosis and management. Iris is the colored muscular diaphragm with a circular central aperture forming the pupil. It is uveal tissue composed of stroma anteriorly and two layers of pigment epithelial cells posteriorly.

Primary cysts can arise from both the pigment epithelium and stroma. Secondary cysts may arise from the iris tissue or the implantation of other material. Knowledge of the condition and the method of evaluating iris cysts is important to making the correct diagnosis. There are controversies regarding the best management, and often treatments are advised in a step-wise fashion in terms of invasiveness. Treatment is sometimes indicated to prevent secondary complications.

Etiology

Iris cysts can be classified into primary and secondary cysts. Primary cysts do not have a recognizable etiology, while secondary cysts do. Shields et al. have proposed a classification system.[1] Furthermore, they can be classified according to the tissue of origin.

Primary cysts can arise from iris pigment epithelium or iris stroma. Iris pigment epithelium cysts are further subdivided according to their location. Examples include pupillary/central, mid-zonal, peripheral, dislodged, free-floating in the anterior chamber or vitreous chamber. Stromal cysts develop within the iris tissue and can cause iris deformation. Free-floating cysts can also occur and are epithelial in origin. Stromal cysts can be congenital or acquired.

Secondary cysts are subdivided according to the pathophysiology. Implantation cysts can occur due to the presence of a foreign body in the iris or by epithelial downgrowth following an ocular surgery or trauma.

Drug-induced cysts are also recognized, and these are associated with miotics such as phospholine iodide, pilocarpine, and the prostaglandin analog latanoprost.[2][3] These are rare side-effects.

Inflammation and uveitis are rare causes of iris cysts. They have been noted in Fuch heterochromic iridocyclitis, herpes zoster ophthalmicus, and other cases of non-granulomatous anterior uveitis.[4][5]

Parasites are very rare causes of iris cysts, and cysticercosis is the most commonly associated pathogen.[6]

Intraocular tumors can present with cysts, which may be from a primary uveal tumor-like uveal melanoma or nevus, and the extension of periocular tumors and metastasis.[7][8]

Epidemiology

Iris cysts are uncommon lesions. There is no population-based study available to estimate the prevalence or incidence of these lesions. The largest case series of 3,690 iris lesions managed at a single center by Shields et al. showed 21% of them were cystic.[9] Of those, 87% were pigment epithelial cysts. Among the iris stromal cysts, congenital stromal cysts were more common in children.[9]

Secondary cysts are more common than primary cysts. The secondary cysts are more common in males, which is likely linked to trauma and implantation cysts.[10]

Histopathology

The type of iris cyst determines the histology seen. Central and mid-zonal iris pigment epithelium cysts comprise heavily pigmented columnar cells and do not transilluminate, whereas peripheral iris pigment epithelium cysts are partly lined by non-pigmented epithelium and usually transilluminate.[11]

Stromal cysts have an epithelial lining that may be made of the stratified squamous epithelium to mono-layered cuboidal cells.[12] In the majority, they also have goblet cells. These features are typical of surface epithelium and suggest surface ectodermal origin. It is postulated that during embryogenesis, surface ectodermal cells may have been trapped in the iris stroma.[13]

Implantation cysts require epithelial cells to enter the anterior chamber. These may proliferate to form secondary iris cysts. The classic appearance is of concentric layers of stratified squamous epithelium.[11] They may contain goblet cells. These may or may not show a connection to the wound.

History and Physical

With primary iris cysts, they are often found incidentally. Many are asymptomatic unless they have enlarged to obscure the visual axis or cause other secondary complications.[14] In children, stromal cysts tend to enlarge and may cause amblyopia or strabismus, but stromal cysts usually remain stable in adults.[15]

Central posterior pigment cysts are found between the pupillary margin and the iris root. Midzonal cysts can present between the iris root and the ciliary body. Peripheral cysts occur in the iridociliary sulcus. 

Stromal cysts arise inside the iris tissue and often cause iris deformation. Congenital cysts are present before ten years of age and are usually unilateral and solitary. Acquired cysts present later in life and seldom require treatment.

Free-floating cysts may appear in the anterior chamber or the vitreous cavity.

Secondary cysts may have clues in the history, which may aid in classifying the lesion. It is not uncommon for patients to present with symptoms from secondary iritis, glaucoma (open and closed-angle), and cataract.[11]

Parasitic cysts may be asymptomatic or have low-grade iritis. These cysts may contain clear fluid or suspended particles or freely moving scolex.[6]

Evaluation

To evaluate an iris cyst, it is essential to perform a complete ocular examination of the anterior segment, including the gonioscopy and posterior segment.  

Ultrasound B-scan using a 10MHz probe can assess the lesion, including its cystic structure and posterior extension.[16] The immersion B-scan technique is more useful in evaluating the anterior segment.

Ultrasound biomicroscopy (UBM) utilizes a higher frequency (50 to 100 MHz) and offers a higher resolution of images but limited tissue penetration up to 4 mm. It is an invaluable tool in evaluating an iris cyst and differentiating it from solid uveal tumors. UBM is useful in determining the anatomical structures and relationship of the lesion.[17]

 Anterior segment optical coherence tomography (AS-OCT) has been gaining traction in clinical use and assessing anterior segment lesions, including iris cysts. It produces an image with a higher resolution than ultrasounds. However, its major drawback in this setting is shadowing caused by iris pigment epithelium and stroma, reducing the ability to discriminate cystic lesions from solid tumors in some cases.[18]

Fine needle aspirate (FNA) may be indicated when other non-invasive evaluation does not establish a diagnosis.[11]

Given the options, UBM is the gold standard in imaging an iris lesion. It is important to perform adequate documentation so that progression can be carefully monitored.

Treatment / Management

In general, iris cysts that are stable and do not cause symptoms or secondary complications can be observed. If an intervention is required, a step-wise approach in terms of invasiveness is recommended.[11]

Laser treatment may be performed, making use of the laser properties of photocoagulation (argon) or photodisruption (neodymium in yttrium aluminum garnet (Nd: YAG)).[19][20] Argon laser can be applied to the cystic wall and may stop the production of intracystic fluid. Nd: YAG laser can be used to perforate the cystic wall. The combination of the two lasers has been used by some clinicians successfully.

Another effective treatment is fine-needle aspiration and injection of a sclerosing agent. The sclerosing agents include ethanol, mitomycin C and 5-fluorouracil.[21][22] The agents will devitalize the cystic epithelium and goblet cells. These can either stabilize or involute the disease. 

One of the complications from fine-needle aspiration is when cystic contents are released in the anterior chamber, as this can cause severe inflammation. In addition, recurrence of cysts and intraocular epithelialization could occur. 

Other surgical options include excision of the cyst alone or as part of a sector iridectomy or iridocyclectomy, depending on the location of the cyst.  Surgical excision is a more definitive treatment and has the advantage of obtaining a tissue sample for histological analysis. The surgery can be done with a limbal approach or pars plana approach. However, it can be accompanied by serious complications and is usually reserved as a last resort.[11] 

The etiology of the iris cysts can also affect the management. With drug-induced cysts, discontinuation is often an effective treatment, and the cyst will resolve. In cysts secondary to a miotic (phospholine iodide), phenylephrine eye drops can be used.[23] With secondary cysts due to epithelial ingrowth, aggressive surgical intervention is often necessary.

Differential Diagnosis

It is important to differentiate different types of iris cysts, and most importantly, to rule out an intraocular tumor. A complete clinical examination and utilization of various imaging techniques as outlined above are paramount. There are a few distinguishing features between iris cysts and intraocular malignancy.[5] Malignancy tends to be solid, with irregular borders and a rough surface. They usually have surface vessels. On UBM, their walls are thicker and may have suspended particles. The posterior extension is common, as well as angle distortion.

The differential diagnosis of iris lesion includes iris nevus, Lisch nodules, melanoma, iris pigment epithelium adenoma, and metastatic iris lesions.[5][11]

Prognosis

The prognosis depends on the nature and the size of the iris cyst. Generally, primary cysts have a better prognosis than secondary cysts. Of the primary cysts, pigment epithelial cysts have a better prognosis than stromal cysts. Other factors for poor prognosis include large size (occupying more than 50% of anterior chamber), young age at presentation, apposition to cornea or lens, and reduced visual acuity at presentation.[10] There are no racial and sex-related differences affecting the prognosis.[5]

Complications

Complications depend on the size, location, and relationship with other ocular structures. Recognized complications include but are not limited to obstruction of the visual axis, mechanical corneal decompensation, glaucoma (both open and closed-angle), recurrent iritis, and cataract.[11] In children, the complications can lead to strabismus and amblyopia.[11] Rare complications reported include vitreous hemorrhage and scleral cyst formation.[24][25]

Deterrence and Patient Education

Patients can be educated regarding the prognosis of the condition and the need for regular monitoring of any changes. They should be instructed to return immediately to note any significant new symptoms or changes in their vision.

Enhancing Healthcare Team Outcomes

Iris cysts may often first be detected by an optometrist or general ophthalmologist.  Adequate documentation in the early stages of diagnosis is vital to monitor progression by their eye care provider or by a specialist over time. Documentation should include both written and photo documentation to allow for comparison as needed.  Secure storage of digital information such as photographs, UBM, and OCT is recommended.