A pterygium is quite similar to a pinguecula in terms of location, and histologic features, but it encroaches onto the cornea in a winglike fashion.Epidemiology/Incidence/Prevalence
: Pterygia have been reported to occur in males twice as frequently as in females. It is the most common conjunctival specimen that we receive.Etiology:
Several surveys have shown that countries nearer the equator have higher rates of pterygia. UV (ultraviolet) B light may be a risk factor for the development of pterygia. UV B radiation may induce cellular changes in the exposed region of the cornea. Pterygia arise at the nasal or temporal limbus, almost invariably as an extension of a preceding conjunctival pinguecula. Pterygia are most likely initiated by prolonged solar exposure and appear to share many of the histologic features of solar degeneration seen in the skin.Clinical Findings:
Pterygia are usually confined to the exposed surface of the conjunctiva, and usually on the side closest to the nose. Less often, pterygium can also occur on the outer side of the cornea. One or both eyes may be involved. Pterygia may distort or obstruct vision if they grow into the visual axis or produce astigmatism.Histopathology:
Pterygia show the same consistent features as pinguecula but in addition show pannus undermining and destroying Bowman's layer.
The destruction of Bowman’s layer (arrow 1 in the figure) by the advancing fibrovascular tissue results in a corneal scar. There is accompanying pannus formation (arrow 2) and chronic inflammation (arrow 3). So called recurrent pterygia lack the histopathologic features of elastotic degeneration and are more accurately classified as exuberant granulation tissue. Ultrastructurally, a case has been made for active elastogenesis in the form of elastic fiber precursors. Newly synthesized microfibrils and amorphous elastin appear to be secreted by fibroblasts as part of the repair process.Treatment:
Pterygia that interfere with vision can be removed surgically. Following surgical removal, it is not unusual for an elevated vascularized scar (“recurrent pterygium”) to form at the excision site. All specimens removed with the clinical diagnosis of pterygium should be examined histologically because squamous carcinoma are all too often thought clinically to be pterygia.