How is pterygium classified?

Pterygium Classification

Pterygium is classified based on multiple clinical parameters including size, vascularity, thickness, corneal involvement, and associated features, with the most validated contemporary system being the SLIT2 grading system that evaluates eight distinct components on a 1-4 severity scale.

Modern Classification Systems

SLIT2 Grading System (Recommended)

The SLIT2 system represents the most recently validated classification approach, demonstrating excellent reliability for clinical and research applications 1. This system evaluates eight parameters, each scored from 1 (normal) to 4 (severe):

Conjunctival Assessment:

• Size at limbus - demonstrates excellent inter-rater reliability (κ=0.86) 1
• Body Length - shows moderate inter-rater reliability (κ=0.54-0.57) 1
• Body Injection/vascularity - demonstrates substantial inter-rater reliability (κ=0.66-0.75) 1
• Body Thickness - shows substantial inter-rater reliability (κ=0.72-0.73) 1

Corneal Assessment:

• Stocker's line presence - demonstrates substantial inter-rater reliability (κ=0.79-0.80) 1
• Head Length - shows excellent inter-rater reliability (κ=0.86-0.87) 1
• Head Injection/vascularity - demonstrates substantial-to-excellent inter-rater reliability (κ=0.78-0.82) 1
• Head Thickness - shows substantial inter-rater reliability (κ=0.67-0.69) 1

Traditional Classification Parameters

Size and Corneal Involvement:

• Grading based on extent of corneal encroachment correlates significantly with recurrence risk (p=0.01) 2
• Higher grades of corneal involvement at presentation predict increased recurrence rates after surgical excision 2
• Classification considers the rate of fibrovascular growth and progressive potential 3

Clinical Characteristics:

• Pterygium represents fibrovascular outgrowth of conjunctiva over the cornea 3
• Assessment includes body thickness, vascularity, and length of tissue extension 1
• Histological features are incorporated into comprehensive classification systems 3

Clinical Implications of Classification

Surgical Planning:

• Higher grade pterygium at presentation leads to increased recurrence rates, supporting early surgical intervention for lower-grade lesions 2
• Classification guides selection of surgical technique and adjunctive therapies 4
• Grading systems standardize reporting of disease severity and recurrence for both clinical management and research 1

Recurrence Risk Stratification:

• Overall recurrence rate of 6.7% at one-year follow-up has been reported with adjunctive mitomycin-C use 2
• Significant correlation exists between higher corneal involvement grade and recurrence (p=0.01) 2
• Florid scarring associated with recurrence can cause ocular motility problems 5

Important Caveats

Complications Related to Classification:

• Diplopia can occur as a complication of pterygium surgery due to medial rectus damage or scarring 5
• Exotropia from medial rectus damage and esotropic restrictive non-comitant strabismus from scarring are potential complications 5
• Retrobulbar anesthesia increases postoperative diplopia risk compared to topical anesthesia 5