Ophthalmology – Iris Nevus

Basics

Description

An iris nevus is a benign melanocytic tumor arising from the iris stroma. Iris melanocytic lesions form a spectrum ranging from harmless freckles and nevi to malignant iris melanoma.

Iris nevi can vary considerably in:

• Size
• Shape
• Thickness
• Degree of pigmentation
• Circumscribed versus diffuse appearance

A key distinction is that an iris nevus distorts or replaces the normal iris stromal architecture, whereas an iris freckle is a superficial area of pigmentation that does not alter the underlying iris structure.

Iris freckles are extremely common and have essentially no malignant potential.

Iris nevi usually become clinically apparent during childhood, puberty, or young adulthood and often remain stable for many years.

Alert

A pigmented iris lesion showing documented progressive enlargement should raise concern for iris melanoma.

Other concerning features include:

• Secondary glaucoma
• Angle involvement
• Tumor seeding
• Prominent intrinsic vessels
• Hyphema
• Increasing thickness

Special Variant – Iris Melanocytoma

Iris melanocytoma is a deeply pigmented variant of melanocytic nevus.

It is usually benign but may undergo spontaneous necrosis.

Necrotic tumor cells and pigment can disperse into the anterior chamber and obstruct the trabecular meshwork, producing secondary glaucoma. This is sometimes called melanocytomalytic glaucoma.

Melanocytoma may also have an associated ciliary body component.

Malignant transformation is possible but uncommon.

Pediatric Considerations

Iris nevi are often first detected during childhood, particularly in the preteen or adolescent years.

Most remain stable into adulthood.

Because many lesions are discovered incidentally, baseline photography is particularly valuable in children to allow accurate comparison over time.

Geriatric Considerations

An iris nevus discovered in an older patient may have been present for decades.

A newly noticed lesion in an older adult is not automatically malignant, but suspicious features or documented growth deserve careful evaluation.

Epidemiology

Iris freckles are very common and can be seen in approximately half or more of the general population.

True iris nevi are less common, occurring in roughly 5% of individuals.

Most are benign and remain stable.

Risk Factors

Reported associations include:

• White race
• Light iris color, particularly blue, gray, or green
• Inferior location of the lesion

Most iris nevi and many iris melanomas are located in the inferior half of the iris.

Sectoral iris nevi may be associated with ocular melanocytosis.

General Prevention

There is no proven method to prevent iris nevi.

Reasonable preventive measures include:

• Limiting excessive ultraviolet exposure
• Wearing UV-protective sunglasses
• Regular ophthalmic follow-up for suspicious lesions

The most important strategy is documenting a lesion early so that subsequent growth can be recognized.

Etiology

The exact cause is unknown.

Iris nevi arise from benign proliferation of melanocytes within the iris stroma.

Commonly Associated Conditions

Most iris nevi occur in otherwise normal eyes.

Some may be associated with:

• Sectoral ocular melanocytosis
• Iris pigment epithelial cysts
• Secondary cataract
• Rare secondary glaucoma

Diagnosis

History

Most patients are asymptomatic.

The lesion may be:

• Noticed by the patient
• Noticed by a family member
• Found incidentally during a routine ophthalmic examination

Important historical questions include:

• How long has the lesion been present?
• Has its size or color changed?
• Is there a previous photograph?
• Has there been pain, redness, or blurred vision?
• Has the patient ever been told the IOP is elevated?
• Is there a history of ocular melanoma or melanocytosis?

Documented stability strongly favors a benign nevus.

Physical Examination

Iris nevi have a broad range of appearances.

They may be:

• Small or large
• Flat or mildly elevated
• Dome-shaped
• Circumscribed or sectoral
• Pigmented or nonpigmented
• Uniform or heterogeneous in coloration

Possible secondary changes include:

• Corectopia
• Ectropion uveae
• Localized cataract
• Associated iris pigment epithelial cyst
• Intrinsic vascularity

Some benign nevi may have visible vessels, so vascularity alone does not establish malignancy.

Secondary Glaucoma

Glaucoma is uncommon with a simple iris nevus.

Therefore, elevated IOP in an eye with a melanocytic iris lesion should raise suspicion for:

• Iris melanoma
• Angle involvement
• Tumor seeding
• Melanocytoma with pigment dispersion

Unilateral unexplained glaucoma in association with an iris lesion warrants careful gonioscopy.

Sector Iris Nevus

A sector nevus extends radially from the pupillary margin toward the anterior chamber angle.

It may involve one or several clock hours.

Some authors consider this a localized manifestation of ocular melanocytosis.

Tapioca Nevus

A tapioca nevus has a multinodular surface composed of multiple small pale or pigmented elevations resembling tapioca pudding.

This appearance can resemble tapioca melanoma, so documentation of stability is particularly important.

Diffuse Iris Nevus and Cogan–Reese Syndrome

The term “diffuse iris nevus” has sometimes been used in connection with Cogan–Reese syndrome.

However, Cogan–Reese syndrome is part of iridocorneal endothelial syndrome and is not a true melanocytic nevus.

Diagnostic Tests and Interpretation

Slit-Lamp Examination

Slit-lamp examination evaluates:

• Pigmentation
• Thickness
• Surface architecture
• Intrinsic vessels
• Corectopia
• Ectropion uveae
• Hyphema
• Tumor seeding

Careful serial examinations are essential.

Anterior Segment Photography

Baseline photography is one of the most useful tools in managing an iris nevus.

Serial photographs allow detection of subtle:

• Growth
• Shape change
• Color change
• New vascularity
• Pupillary distortion

Documented enlargement is one of the strongest indicators of malignant transformation.

Intraocular Pressure

IOP should be measured at every evaluation.

New or progressive elevation should prompt investigation for angle involvement or malignant transformation.

Gonioscopy

Gonioscopy is used to assess:

• Extension into the anterior chamber angle
• Abnormal pigmentation of the trabecular meshwork
• Tumor seeding
• Associated angle mass

Angle involvement is an important feature distinguishing a suspicious lesion from an uncomplicated nevus.

Transillumination

Transillumination helps assess whether the apparent iris lesion extends posteriorly into the ciliary body.

This is particularly important for thicker or peripheral tumors.

Ultrasound Biomicroscopy

UBM is useful for:

• Measuring lesion thickness
• Determining posterior extent
• Detecting ciliary body involvement
• Distinguishing a solid nevus from a cystic lesion
• Providing a baseline for future comparison

It is especially useful for larger or more heavily pigmented lesions.

Anterior-Segment OCT

AS-OCT can image smaller, superficial iris lesions.

It is particularly helpful for lightly pigmented or nonpigmented lesions.

However, deeply pigmented or thick lesions may cause significant posterior shadowing, limiting assessment of their full depth.

Fine-Needle Aspiration Biopsy

FNAB is not needed for routine stable iris nevi.

It may be considered when:

• The diagnosis remains uncertain
• The lesion has suspicious features
• Differentiation from melanoma would alter management

Because low-grade melanoma can resemble a nevus cytologically, samples should be interpreted by an experienced ocular cytopathologist.

Pathological Findings

Iris nevi are usually composed predominantly of low-grade spindle melanocytic cells.

Some borderline lesions are difficult to distinguish histologically from low-grade melanoma.

For this reason, clinical behavior over time, especially documented growth, remains extremely important.

Differential Diagnosis

Important differential diagnoses include:

• Iris melanoma
• Iris melanocytoma
• Ocular melanocytosis
• Iris pigment epithelial cyst
• Adenoma of the iris pigment epithelium
• ICE syndrome
• Iris lymphoma
• Iris metastasis
• Iris granuloma
• Juvenile xanthogranuloma
• Retained anterior chamber foreign body

The most clinically important distinction is between iris nevus and iris melanoma.

Features Suggesting Melanoma Rather Than Nevus

Concern for melanoma increases with:

• Documented growth
• Increasing thickness
• Secondary glaucoma
• Angle involvement
• Tumor seeding
• Prominent intrinsic or feeder vessels
• Spontaneous hyphema
• Increasing pupillary distortion
• Progressive ectropion uveae

A stable lesion without these features is much more likely to remain benign.

Treatment

Medication

There is no medication required for an uncomplicated iris nevus.

Observation

Observation is the standard management.

Baseline assessment should ideally include:

• Slit-lamp examination
• Anterior segment photography
• IOP measurement
• Gonioscopy
• UBM when appropriate
• Transillumination
• AS-OCT in selected lesions

Follow-up is then used to establish whether the lesion remains stable.

Follow-Up Interval

A suspicious or newly documented lesion may initially be reassessed at approximately 6 months.

Once long-term stability is established, follow-up can often be extended to 6–12 month intervals, depending on its characteristics.

Higher-risk lesions require closer surveillance.

Documented Growth

If a melanocytic iris lesion shows unequivocal progressive growth, it should no longer be managed as a simple nevus.

The patient should be evaluated for iris melanoma and referred to an ocular oncologist when appropriate.

Management of Elevated IOP

Topical glaucoma medications may be used if IOP elevation occurs.

However, because secondary glaucoma is unusual with a benign nevus, the lesion must be reassessed carefully for malignant transformation or angle involvement.

Associated Hyphema

If inflammation or hyphema accompanies a lesion, cycloplegics and topical anti-inflammatory therapy may be used when appropriate.

The cause of the bleeding must still be investigated.

Surgery

Routine surgical excision is not indicated for a stable iris nevus.

Treatment is reserved for lesions that:

• Demonstrate documented growth
• Develop convincing malignant features
• Produce significant complications requiring intervention

Such lesions should be managed according to principles used for iris melanoma.

Ongoing Care

Follow-Up Recommendations

Patients should undergo periodic ophthalmic examinations.

Monitoring may include:

• Slit-lamp examination
• Anterior segment photography
• Gonioscopy
• IOP measurement
• UBM
• Transillumination
• AS-OCT when useful

The precise testing schedule depends on the lesion’s size, location, and level of suspicion.

Patient Education

Patients should understand that most iris nevi are benign and remain stable throughout life.

They should also understand why periodic monitoring is important.

They should return earlier than scheduled if they notice:

• Increase in size
• Change in pupil shape
• New pain
• Blurred vision
• Redness
• Visible bleeding in the eye

Avoiding excessive sun exposure and using UV-protective eyewear is reasonable.

Prognosis

The overall prognosis is excellent.

Most iris nevi remain stable and never become malignant.

A small proportion of suspicious or borderline lesions may enlarge over time and ultimately prove to be melanoma.

Therefore, the goal of management is not to remove every iris nevus, but to document stability and promptly identify the uncommon lesion that begins to grow.

Complications

Possible complications include:

• Secondary cataract
• Pupillary distortion
• Ectropion uveae
• Rare secondary glaucoma
• Pigment dispersion from melanocytoma
• Rare malignant transformation into iris melanoma

The most important clinical principle is: a stable iris nevus is usually benign, but documented progressive growth or secondary glaucoma should prompt evaluation for iris melanoma.