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What Is an Iris Nevus?

An iris nevus is a benign proliferation of melanocytes within the iris stroma that appears as a localized pigmented spot or patch. It is sometimes described as a freckle or mole on the colored part of the eye. Iris nevi can be flat or slightly elevated and vary in color from light brown to dark brown. Most are stable and harmless, but a small fraction can transform into iris melanoma over time. Because of this, documentation and periodic observation are recommended.

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What Is an Iris Nevus?

An iris nevus is a benign proliferation of melanocytes within the iris stroma that appears as a localized pigmented spot or patch. It is sometimes described as a freckle or mole on the colored part of the eye. Iris nevi can be flat or slightly elevated and vary in color from light brown to dark brown. Most are stable and harmless, but a small fraction can transform into iris melanoma over time. Because of this, documentation and periodic observation are recommended.

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Appearance and Variants

Iris nevi may be solitary or multiple and can occur anywhere on the iris surface. Some have well defined borders, while others blend more gradually into surrounding tissue. They may cause focal distortion of the iris architecture, such as crypt changes or localized ectropion uveae. Sectoral nevi can involve a wedge shaped portion of the iris, and some are associated with localized heterochromia. Nevi near the pupil margin can affect pupillary shape slightly but usually do not disturb vision.

Risk Features and Complications

Most iris nevi remain stable for years, but certain features raise concern about possible melanoma transformation. These include documented growth, prominent vascularity, seeding of tumor cells onto the iris surface or into the angle, and elevated intraocular pressure. Secondary glaucoma can occur if pigment or tumor tissue obstructs the trabecular meshwork. Rarely, large or malignant lesions can cause visible distortion of the pupil or anterior chamber angle. Careful slit lamp examination and gonioscopy help detect these changes.

Diagnosis and Monitoring

Diagnosis is usually clinical, made by observing a characteristic iris lesion on slit lamp examination. Baseline photography documents size, color, and configuration for future comparison. Ultrasound biomicroscopy can measure lesion thickness and assess angle involvement when needed. Follow up intervals depend on size and risk features but commonly range from yearly to more frequent in suspicious cases. Referral to an ocular oncologist is considered when melanoma is suspected or when worrisome change is documented.

Management and When to Treat

Most iris nevi are simply observed without intervention. Patients are advised to report any noticeable change in size, color, or associated symptoms such as pain or visual disturbance. When melanoma is diagnosed or strongly suspected, treatment options include surgical excision, iridectomy, plaque radiotherapy, or other oncology guided approaches. The goal is to remove or control malignant tissue while preserving as much normal iris and visual function as possible. Prognosis for small, well managed iris melanomas is generally favorable.

FAQs About Iris Nevi

Is an iris nevus the same as a freckle?

It is similar to a freckle or mole on the skin but located in the iris tissue, and it usually behaves in a benign way.

Can iris nevi turn into cancer?

Malignant transformation is uncommon but possible, which is why growth and other risk signs are monitored.

Do iris nevi affect vision?

Most do not affect vision, though very large or strategically placed lesions can disturb the pupil or angle.

How often should an iris nevus be checked?

Many are reviewed annually, with more frequent visits if there are concerning features or documented change.

References

American Academy of Ophthalmology (EyeNet). ?Differentiating Iris Pigmented Lesions: A Primer.? https://www.aao.org/eyenet/article/differentiating-iris-pigmented-lesions

PubMed. ?Iris nevus growth into melanoma: analysis of 1611 consecutive eyes: the ABCDEF guide.? https://pubmed.ncbi.nlm.nih.gov/23290981/

American Academy of Ophthalmology. ?Clinical Update: Oncology (PDF) - Differentiating Iris Pigmented Lesions.? https://www.aao.org/Assets/c0ad02f8-09d8-451a-8d92-db2c439b8a40/637152405743970000/february-2020-clinical-update-oncology-pdf

University of Iowa (EyeRounds). ?Differential diagnosis of a heavily pigmented iris lesion.? https://webeye.ophth.uiowa.edu/eyeforum/atlas/pages/differential-diagnosis-of-a-heavily-pigmented-iris-lesion.html

American Academy of Ophthalmology (Ophthalmology Journal). ?Iris Nevus Growth into Melanoma (Abstract).? https://www.aaojournal.org/article/S0161-6420%2812%2900954-2/abstract