Conjunctival pterygia. Mechanism of corneal topographic changes.

Pterygia induce irregular corneal astigmatism that sometimes necessitates surgical removal before the lesion has advanced close to the visual axis. This astigmatism may occur either due to traction generated by the pterygium mechanically pulling on and distorting the cornea, or by the pooling of tears in advance of the pterygium, or both. To evaluate the effect of localized tear pooling on pterygium-induced astigmatism, corneoscope photographs were obtained before and after absorbing excess tears at the pterygium-corneal interface with a cellulose sponge. Pterygia from these patients were then excised and examined with transmission electron microscopy for the presence of myofibroblasts. The absence of myofibroblasts in these lesions as well as the alterations in corneoscopy induced by localized removal of tears at the advancing edge of the pterygia suggest that corneal distortion in the presence of pterygia is caused in part by local changes in the tear film.