Conjunctival Nevus

A conjunctival nevus is the most common benign melanocytic tumour of the conjunctiva, accounting for approximately 52% of all conjunctival melanocytic lesions. It arises from the proliferation of melanocytes — neural crest–derived pigment-producing cells — within the conjunctival epithelium or subepithelial stroma. The condition is broadly analogous to cutaneous melanocytic nevi but exhibits several conjunctiva-specific histological features, most notably the presence of intralesional epithelial inclusion cysts in up to 60–66% of cases, which serve as an important benign diagnostic marker.

Conjunctival nevi typically present in childhood or early adulthood (median age of onset in the first two decades), are usually located in the interpalpebral bulbar conjunctiva at or near the limbus, and in the majority of cases pursue a stable, benign clinical course. However, a small but important minority (estimated at approximately 1%) undergo malignant transformation to conjunctival melanoma — a sight-threatening and potentially life-threatening condition. This transformation risk, combined with the clinical overlap between conjunctival nevi and other conjunctival pigmented lesions (primary acquired melanosis, conjunctival melanoma), makes accurate diagnosis and diligent longitudinal monitoring critical competencies for optometrists.

The primary role of the optometrist in conjunctival nevus management is serial photodocumentation, objective assessment of lesion stability, identification of atypical features mandating urgent ophthalmological referral, and patient education regarding monitoring for change.

The etiology of conjunctival nevi is multifactorial, involving genetic predisposition, UV radiation, and developmental factors. The condition shares etiological features with cutaneous melanocytic nevi but has unique aspects related to the conjunctival microenvironment.

The pathogenesis of conjunctival nevus mirrors that of cutaneous melanocytic nevi, with the critical distinction that the conjunctival microenvironment — with its unique epithelial architecture, goblet cells, and vascular supply — produces some lesion-specific histological features.

Melanocyte proliferation and nest formation. Under the influence of BRAF or NRAS mutations, conjunctival melanocytes undergo clonal expansion. Rather than dispersing as single cells along the basal epithelial layer, these proliferating melanocytes aggregate into discrete clusters called nests or theques. The location of these nests — at the epithelial–stromal junction (junctional), in the substantia propria (subepithelial), or at both sites (compound) — determines the histological nevus type and its clinical behaviour.

Oncogene-induced senescence (OIS). Despite harbouring activating BRAF mutations, the majority of nevus cells enter a stable, non-proliferating state mediated by OIS — a cell-autonomous tumour suppressor programme triggered by sustained oncogene activation. OIS is enforced by upregulation of p16/INK4a and p21/CIP1, causing permanent cell cycle arrest. This is the fundamental molecular mechanism limiting the growth and malignant potential of most conjunctival nevi. Escape from OIS — through secondary mutations (in TERT promoter, CDKN2A, TP53, or chromosome 3 deletions) — is a critical step in progression to conjunctival melanoma.

Intralesional epithelial inclusion cysts. The epithelial cysts characteristic of conjunctival nevi are a unique feature of this anatomical site. As nevus cells proliferate and the lesion expands within the subepithelial stroma, nests of conjunctival epithelium — including goblet cells — become entrapped within the lesion, forming mucus-containing or clear cystic structures. These cysts are lined by conjunctival epithelium and contain either clear serous fluid or mucus. Their presence is strongly associated with benignity and reflects the retention of normal epithelial architecture within the lesion; malignant melanoma typically destroys this architecture.

Pigmentation variation. The degree of melanin production by nevus cells determines whether a lesion appears brown, tan, or amelanotic. Amelanotic nevi contain nevus cells with reduced melanogenic activity (low tyrosinase expression) rather than an absence of melanocytes. Increased melanin production during puberty or pregnancy reflects upregulation of melanocortin-1 receptor (MC1R) signalling and stimulated tyrosinase activity rather than cellular proliferation, which explains why hormonally driven darkening is not necessarily a sign of malignant change.

Conjunctival nevi are classified histopathologically by the location of nevus cell nests relative to the conjunctival epithelium. The WHO Classification of Tumours of the Eye (2018) provides the current standard framework.

Risk factors for developing a conjunctival nevus:

• UV radiation exposure — cumulative UV-B exposure promotes melanocyte proliferation on the ocular surface; the interpalpebral location reflects zones of maximum UV exposure
• Childhood and adolescence — nevi most commonly first present in the first two decades of life; the conjunctiva has greater nevus-forming potential in younger individuals
• Fair skin and light irides — reduced constitutional melanin may alter UV exposure–related melanocyte responses; individuals with lighter complexions have a higher incidence of cutaneous nevi, which may extend to ocular surface melanocytic lesions
• Familial atypical mole syndrome (dysplastic nevus syndrome) — individuals with multiple cutaneous atypical nevi may have a higher risk of ocular melanocytic lesions
• Oculodermal melanocytosis (nevus of Ota) — congenital dermal melanocytosis affecting the periocular skin and conjunctiva; a distinct entity but associated with increased melanocytic activity on the ocular surface

Risk factors for malignant transformation of an existing nevus:

• Adult age at presentation — a conjunctival pigmented lesion first appearing in adulthood has a higher prior probability of being primary acquired melanosis (PAM) with atypia or early melanoma than a new nevus
• Junctional histological type — higher activity than compound or subepithelial nevi
• Documented growth on serial observation — any increase in size, elevation, or pigmentation beyond what is attributable to puberty/pregnancy
• Absence of intralesional cysts — cyst-free pigmented conjunctival lesions are more suspicious
• Personal or family history of cutaneous melanoma — elevated risk of ocular surface melanoma in this population
• Immunosuppression — systemic immunosuppression (organ transplant recipients, HIV/AIDS, chronic immunosuppressive therapy) is associated with increased risk of melanocytic transformation

The overwhelming majority of conjunctival nevi are entirely asymptomatic. The most common reason for presentation is a patient or parent noticing a pigmented spot on the eye, prompting attendance for reassurance.

• Asymptomatic (most common) — the lesion is discovered incidentally during routine examination or noticed by the patient or a family member as a new or changing coloured spot on the eye
• Cosmetic concern — anxiety about the appearance of a pigmented lesion on the eye; fear of cancer, especially in patients or parents aware of skin melanoma; this is often the primary driver of presentation even when the lesion is entirely benign and stable
• Mild irritation or foreign body sensation — occasional; may occur if the lesion is elevated enough to disrupt the tear film over its surface; typically intermittent and mild
• Perceived change in appearance — patients may notice a colour change (darkening during puberty or pregnancy) or an apparent change in size, which typically prompts urgent attendance; these hormonally induced changes are usually benign
• Absence of pain — pain or tenderness associated with a pigmented conjunctival lesion is not a feature of nevus; its presence should raise suspicion for an inflammatory or malignant process
• Visual symptoms — nevi do not cause visual impairment unless extremely large (rare) or involving the cornea (in which case pterygium or other diagnoses should be considered)

• Malignant transformation to conjunctival melanoma — the most significant complication; estimated lifetime risk approximately 1% for compound nevi (higher for junctional nevi, lower for subepithelial nevi). Transformation is associated with TERT promoter mutation, CDKN2A deletion, copy number abnormalities, and loss of p16 expression. Conjunctival melanoma has metastatic potential and carries a 10-year mortality of approximately 25–30%; early detection and excision are critical
• Development of primary acquired melanosis (PAM) around a nevus — PAM with atypia may develop in conjunction with or adjacent to a pre-existing nevus; this combination is associated with higher transformation risk and requires careful mapping and specialist management
• Lesion enlargement causing cosmetic distress — even benign growth (e.g., during puberty) can be alarming; clear patient communication and reassurance with documented stability is essential to prevent unnecessary patient anxiety or premature surgical intervention
• Misdiagnosis and delayed treatment of malignancy — a conjunctival melanoma or PAM with atypia incorrectly labelled as a stable nevus represents the most clinically consequential diagnostic error in conjunctival lesion management; serial photodocumentation and low threshold for referral are the primary safeguards
• Post-excision complications — excision of a benign conjunctival nevus carries risks of scarring, local recurrence (nevus cells may extend beyond the clinically visible borders), symblepharon formation, and limbal stem cell deficiency if the excision margin involves the limbus
• Psychological impact — significant patient anxiety is common with any pigmented ocular lesion; even after benign diagnosis is confirmed, some patients experience persistent anxiety that warrants clear communication and follow-up reassurance

Most conjunctival nevi are isolated ocular findings without systemic disease associations. However, several systemic and syndromic conditions are clinically relevant.

Conjunctival nevus is primarily a clinical diagnosis based on characteristic slit-lamp features, supported by serial photodocumentation. Definitive histopathological diagnosis requires excision biopsy, which is reserved for atypical or progressive lesions.

The prognosis of conjunctival nevus is excellent in the vast majority of cases. Compound nevi — the most common type — have low malignant transformation rates and a benign clinical course when appropriately monitored.

• Malignant transformation rate — approximately 1% lifetime risk for the overall conjunctival nevus population; this rate is higher for lesions with junctional activity, absence of cysts, or atypical clinical features. Any documented growth or change in a previously stable nevus must be treated as possible early transformation until proven otherwise by histopathology
• Stability — the majority of compound nevi remain stable in size throughout adult life after the transient activity of puberty; serial documentation of stability over 2–3 years is strongly reassuring
• Recurrence after excision — local recurrence after complete excision with clear histological margins is uncommon (approximately 5–10%); incomplete excision carries a substantially higher recurrence rate, and recurrent lesions may show increased atypia
• Visual prognosis — excellent; benign nevi do not affect visual acuity or cause corneal involvement and therefore do not threaten vision
• Conjunctival melanoma prognosis (if transformation occurs) — the 5-year melanoma-specific survival for conjunctival melanoma is approximately 70–80%; however, metastatic disease — particularly to regional lymph nodes, liver, and brain — carries a significantly worse prognosis. This underscores the critical importance of early detection and referral before transformation occurs
• Follow-up duration — lifelong annual review is recommended for all documented conjunctival nevi; the risk of transformation, while low, persists throughout life and cannot be considered eliminated by a period of stability

• Cysts are the single most reassuring benign sign. When high-magnification slit-lamp examination confirms intralesional clear cysts, the probability of conjunctival melanoma drops substantially. Actively search for cysts in every pigmented conjunctival lesion using retroillumination and high magnification — they may be subtle and small.
• Photograph every pigmented conjunctival lesion at baseline. A clinical description alone is insufficient for long-term monitoring. Baseline anterior segment photography with a standardised protocol (magnification, gaze position, illumination) is essential for objectively comparing lesion size and morphology at future visits.
• A new pigmented lesion in an adult should not be presumed to be a nevus. Conjunctival nevi predominantly present in childhood. A discrete pigmented conjunctival lesion first appearing after age 30–40 without any previous documentation should be considered PAM or early melanoma until proven otherwise. Refer to ophthalmology for evaluation.
• Darkening during puberty or pregnancy is usually benign. Reassure the patient but increase monitoring frequency temporarily (3–4-monthly) to document that the change stabilises. If the lesion continues to grow or develop new vascularity beyond the hormonal context, refer urgently.
• Mobility confirms conjunctival origin. A lesion that moves freely with the conjunctiva when the patient looks in different directions is conjunctival; a lesion that remains fixed while the conjunctiva moves over it is likely episcleral or scleral (consider blue nevus, osteoma, or ciliary body tumour).
• Measure in two dimensions at every visit. Record the greatest horizontal and vertical diameter (in millimetres) using the slit-lamp reticule at every review visit. A change of ≥0.5 mm in any dimension over 6–12 months is clinically significant and warrants referral.
• Nevus of Ota is common in Singapore — know its implications. Slate-grey conjunctival and periocular skin pigmentation in a Southeast Asian or East Asian patient is frequently oculodermal melanocytosis. These patients require annual ophthalmological surveillance for uveal melanoma throughout their lifetime. Do not manage this as a routine conjunctival nevus.
• Excision biopsy is the only definitive diagnostic test. Clinical diagnosis of conjunctival nevus carries an inherent uncertainty, particularly for amelanotic lesions and those lacking cysts. When in doubt, a conservative "excise and examine" strategy provides both diagnosis and treatment with low morbidity for typical small lesions.