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OP3.5 | Pterygium — SDL Guide

Learning Objectives

• Describe the aetiology, pathophysiology, and ocular features of pterygium
• Distinguish pterygium from pseudopterygium, pinguecula, and other conjunctival lesions
• Outline the indications for surgical management and describe the surgical options with their recurrence rates
• Identify Stocker's line as a pathognomonic feature of pterygium

INSTRUCTIONS

Pterygium is a common conjunctival condition in tropical and subtropical regions, including India, where prolonged UV-B exposure, dust, and outdoor work contribute to its prevalence. It presents as a visible fleshy triangular growth on the white of the eye and can reduce vision through corneal invasion or induced astigmatism. The NMC OP3.5 competency requires you to understand the full clinical picture — from its benign stable form to the progressive form requiring surgery — and to distinguish it from conditions that mimic its appearance, particularly pseudopterygium.

References

• AK Khurana — Comprehensive Ophthalmology, 7th ed., Ch. 6: Diseases of Conjunctiva (textbook)
• Parsons' Diseases of the Eye, 23rd ed., Ch. 8: Diseases of the Conjunctiva (textbook)

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Version 2.0 | NMC CBUC 2024

The Fleshy Growth on the Eye — Clinical Presentation of Pterygium

Pterygium (Greek: pteryx = wing) is a wing-shaped fibrovascular growth of bulbar conjunctival tissue that extends across the limbus onto the corneal surface. It is almost invariably located on the nasal side of the eye — the nasal conjunctiva receives the maximum UV-B exposure (from light reflecting off the nasal bridge and the narrow angle between the lid margin and the eyeball). Temporal pterygium is much rarer. Bilateral pterygium in both nasal quadrants can occur.

The typical patient is a middle-aged or older person from a tropical or subtropical region with a history of prolonged outdoor UV exposure — agriculture, fishing, construction, or military service. In India, pterygium is particularly prevalent in coastal and dry-land farming populations. Men are more commonly affected than women, likely due to greater outdoor work exposure.

Clinical presentation:
- The patient notices a visible pinkish-red fleshy lesion on the white of the eye, often remarked upon by family members before symptoms appear.
- Redness and irritation — the vascularised body of the pterygium causes chronic conjunctival hyperaemia.
- Foreign body sensation — from disruption of the tear film by the tissue on the cornea.
- Visual disturbance — as the pterygium advances onto the cornea, it distorts the corneal curvature, inducing irregular astigmatism that causes blurring not correctable with pinhole. When the pterygium covers the visual axis, visual acuity is directly reduced.
- Restricted eye movement — large pterygium can limit abduction (as the nasal conjunctiva is tethered to the nasal fornix by the pterygium body).

Pterygium: Anatomy and Limbal Invasion

Pathogenesis: UV Damage, Limbal Stem Cells, and Fibrovascular Invasion

The pathogenesis of pterygium is most coherently explained by the limbal stem cell failure hypothesis, supported by the observation that UV-B radiation is the dominant environmental risk factor and that pterygium tissue represents conjunctival (not corneal) epithelium that has breached the limbal barrier.

Normal limbal stem cells form a functional boundary at the corneoscleral junction that prevents conjunctival epithelium from invading the cornea. Chronic UV-B exposure damages the DNA of these limbal stem cells through oxidative stress and the formation of pyrimidine dimers, impairing their proliferative and barrier functions. Once the barrier is compromised, the conjunctival epithelium — with its subepithelial fibroblasts — begins to migrate centripetally onto the corneal surface. The clinical implication of this pathogenetic model is important: pterygium is a disease of limbal barrier failure driven by cumulative UV-B dose, not a simple inflammatory or neoplastic process. This is why UV-B protection (sunglasses with UV400 rating, wide-brimmed hats) is the only evidence-based preventive measure, and why recurrence after surgical excision is so common — if the UV-B exposure continues and the limbal stem cell dysfunction persists, the barrier will fail again and the tissue will regrow. The three components of the invading tissue are described below.

The migrating tissue has several components:
1. Abnormally active fibroblasts — which lay down disorganised extracellular matrix (fibronectin, tenascin, matrix metalloproteinases). The expression of matrix metalloproteinases (particularly MMP-2 and MMP-9) by pterygium fibroblasts is responsible for the dissolution of Bowman's layer (the acellular zone beneath the corneal epithelium) as the pterygium head advances.
2. Vascular component — the pterygium body is richly vascularised (hence its pink-red colour), fed by dilated conjunctival vessels from the body and neck that branch to supply the advancing head.
3. Inflammatory cell infiltration — mast cells, lymphocytes, and macrophages are present in the pterygium stroma; UV-B induces the production of pro-inflammatory cytokines (VEGF, TGF-β) that sustain the fibrovascular proliferation.

Other risk factors that compound UV-B exposure: dusty environments (chronic ocular surface irritation), dry climates, low altitude (higher UV levels at equatorial latitudes), lack of UV-protective eyewear.

Stocker's line: At the leading edge of the pterygium head, a brownish horizontal line of iron (haemosiderin) deposits in the corneal epithelium — the Stocker's line — is pathognomonic of pterygium. It forms from tear-film iron deposits at the epithelial margin of the pterygium-cornea interface and is best seen under slit-lamp examination with a yellow filter.

Examining and Grading a Pterygium

Clinical examination of a pterygium requires documentation of four parameters that determine the management decision: the anatomy of the pterygium components, the extent of corneal involvement, the visual acuity, and the activity (progressive vs stationary). This structured approach prevents the common clinical error of simply noting 'pterygium present' without quantifying the key variables that inform the decision to observe versus refer for surgery. The single most clinically critical measurement is the distance of the pterygium head from the pupillary margin — a pterygium that has reached within 2–3 mm of the pupil will threaten the visual axis within months in an active growing pterygium, while one 5–6 mm away in a stationary thin pterygium may be safely watched for years. Documentation of these parameters at each visit also allows detection of progression by serial comparison, which is the only reliable way to identify an active pterygium in an otherwise quiet eye.

Anatomy — three parts of a pterygium:
- Head (cap): The most advanced part, sitting on the cornea; the apex of the triangular wing. Examine the cornea immediately ahead of the head for Stocker's line.
- Neck: The narrowest part at the limbus, where the corneal and conjunctival portions meet.
- Body: The broad triangular conjunctival portion; shows the vascular pattern; may have dilated 'feeder vessels' from the conjunctiva.

Grading by corneal extent:
The most clinically important measurement is how far the head has advanced onto the cornea, measured in millimetres from the limbus:
- Grade 1 (T1): thin, transparent — only slightly overlapping the cornea, able to see corneal vessels through the tissue.
- Grade 2 (T2): intermediate — partially obscuring the corneal surface.
- Grade 3 (T3): thick, opaque — completely obscuring the corneal vessels beneath; near the visual axis.
Surgery is generally indicated when the pterygium approaches within 2–3 mm of the pupillary margin or has reached Grade 3.

Visual acuity and refraction:
Test VA in both eyes. If VA is reduced and the pterygium overlies the cornea, try to determine whether the reduction is from induced astigmatism (the pterygium flattens the corneal curvature in the horizontal meridian as it invades) or from direct visual-axis coverage. Importantly, pterygium-induced astigmatism does NOT improve with pinhole (because it is corneal distortion, not simple refractive error).

Activity assessment:
Signs of an active (progressive) pterygium: prominent vascularity of the body, thick head, Stocker's line close behind the head (indicating recent advance). A stationary pterygium is avascular, thin, and translucent.