Differentials
Pseudopterygium
SIGNS / SYMPTOMS
Very often history of previous infectious, chemical, thermal, or traumatic injury to the cornea.
May occur at multiple locations and is not restricted to the 3 and 9 o'clock (interpalpebral) positions.
INVESTIGATIONS
Slit-lamp exam: reveals lesion to be adhesion of a fold of conjunctiva, which has occurred as a response to a previous peripheral corneal ulcer or inflammation.
Lesion typically only fixed at its apex to the cornea so that a probe may be passed underneath its body at the limbus, while a true pterygium adheres to the underlying cornea throughout its length. Thinning of the underlying cornea may be seen at its head.
Pingueculum
SIGNS / SYMPTOMS
Does not encroach on the cornea.
INVESTIGATIONS
Slit-lamp exam: reveals exact extent and nature of lesion. A pingueculum is limited to limbus and conjunctiva and does not encroach onto the cornea.
Marginal keratitis
SIGNS / SYMPTOMS
Associated with blepharitis. Infiltrate on corneal surface is separated by a clear zone from the limbus. Typically occurs at 2, 4, 8, and 10 o'clock position. Does not have a typical pterygium shape. Often superior and inferior.
INVESTIGATIONS
Corneal swab/scraping: microscopy and culture positive for infecting organism, but infecting organisms are often not detected, as many cases are due to an inflammatory reaction to staphylococcal proteins.
Corneal micropannus
SIGNS / SYMPTOMS
History of trachoma or lack of corneal oxygenation due to excessive contact lens wear.
INVESTIGATIONS
Slit-lamp exam: reveals encroachment of fine blood vessels onto corneal surface.
Conjunctival carcinoma in situ
SIGNS / SYMPTOMS
Rare. Does not have a typical pterygium shape. Not restricted to the 3 and 9 o'clock (interpalpebral) positions and can occur at any position on the cornea.
INVESTIGATIONS
Slit-lamp exam: gelatinous-appearing mass.
Biopsy: cytologic features of a squamous cell carcinoma, but the basal membrane of the epithelium remains intact.
Squamous cell carcinoma
SIGNS / SYMPTOMS
Rare. Does not have a typical pterygium shape. Not restricted to the 3 and 9 o'clock (interpalpebral) positions and can occur at any position on the cornea. May arise from a pterygium, carcinoma in situ, or de novo.
INVESTIGATIONS
Slit-lamp exam: surface may appear keratinized and friable.
Biopsy: well-differentiated squamous cell carcinoma with invasion of the basal membrane.
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