How do you differentiate pterygium from pseudo-pterygium in a patient, particularly considering their medical history and potential exposure to ultraviolet (UV) radiation?

Distinguishing Pterygium from Pseudo-pterygium

The key distinguishing feature is that a true pterygium is firmly adherent to the underlying cornea and cannot be moved with a probe, while a pseudo-pterygium is mobile and can be separated from the cornea because it results from conjunctival scarring that has secondarily adhered to a corneal defect. 1

Clinical History Assessment

True Pterygium Risk Factors

• Chronic UV exposure is the most critical risk factor, particularly in patients with occupational sun exposure (farming, construction) or leisure activities (boating, golfing) 2
• Low humidity environments and modest air movement exposure 2
• Geographic location in high UV-exposure regions 3
• Typically bilateral presentation, though may be asymmetric 3
• Gradual onset without preceding trauma 1

Pseudo-pterygium Risk Factors

• History of ocular trauma (blunt or penetrating injury, chemical burns, forceps delivery) 2
• Previous ocular surgery or inflammation 1
• History of corneal ulceration or infection 1
• Typically unilateral presentation 1
• Acute onset following a specific inciting event 1

Physical Examination Findings

Slit-lamp Biomicroscopy Features

Perform detailed slit-lamp examination to evaluate location, depth, elevation, and vascular characteristics of the lesion 4

True Pterygium Characteristics:

• Fibrovascular tissue originating from the nasal or temporal bulbar conjunctiva that extends onto the cornea in a triangular configuration 3, 5
• Firmly adherent to underlying cornea—cannot be moved with a probe 1
• Progressive growth pattern toward the optical axis 5
• Associated with Stocker's line (iron deposition at the leading edge) 3
• May cause irregular astigmatism as it approaches the visual axis 3, 5

Pseudo-pterygium Characteristics:

• Mobile tissue that can be separated from the cornea with a probe—this is the pathognomonic finding 1
• Conjunctival tissue adherent to a pre-existing corneal defect or scar 1
• May originate from any quadrant (not limited to nasal/temporal) 1
• Associated conjunctival scarring visible on examination 2
• History of preceding corneal pathology 1

Diagnostic Algorithm

1. Obtain detailed history focusing on UV exposure patterns, ocular trauma, previous infections, and chemical exposures 2, 1

2. Perform slit-lamp biomicroscopy to assess:

   • Location and pattern of conjunctival involvement 4
   • Presence of underlying corneal scarring or defects 1
   • Vascular pattern and tissue characteristics 4

3. Perform probe test: Attempt to gently pass a probe beneath the lesion

   • If immobile and firmly adherent = True pterygium 1
   • If mobile and can be separated = Pseudo-pterygium 1

4. Assess for bilateral involvement: True pterygium is typically bilateral (though asymmetric), while pseudo-pterygium is usually unilateral 3, 1

Critical Pitfalls to Avoid

• Do not assume all triangular conjunctival lesions are pterygium—always perform the probe test to differentiate from pseudo-pterygium 1
• Exclude malignancy in atypical presentations, particularly yellowish or brownish lesions with irregular borders, as conjunctival melanoma, sebaceous carcinoma, or metastatic disease can mimic pterygium 4, 6
• Consider biopsy for lesions with atypical features, rapid growth, or recurrence in elderly patients 4
• Do not misdiagnose chronic blepharoconjunctivitis when sebaceous carcinoma or metastatic disease is present, as this delays appropriate treatment 6

Additional Considerations

• True pterygium requires surgical excision when it causes reduced visual acuity, progressive astigmatism, or approaches the optical axis 5
• Pseudo-pterygium management focuses on treating the underlying cause and may not require excision unless symptomatic 1
• Both conditions benefit from UV protection, but this is particularly critical for preventing true pterygium progression and recurrence 5