Pterygium

Pterygium

Definition  Triangular fold of conjunctiva that usually grows from the medial portion of the palpebral fissure toward the cornea.

Epidemiology: Pterygium is especially prevalent in southern countries dueto increased exposure to intense sunlight.

Etiology: Histologically, a pterygium is identical to a pinguecula. However, itdiffers in that it can grow on to the cornea; the gray head of the pterygium will grow gradually toward the center of the cornea (Fig. 4.3a). This progression is presumably the result of a disorder of Bowman’s layer of the cornea, which pro-vides the necessary growth substrate for the pterygium.

Symptoms and diagnostic considerations: A pterygium only producessymptoms when its head threatens the center of the cornea and with it the visual axis (Fig. 4.3b). Tensile forces acting on the cornea can cause severe corneal astigmatism. A steadily advancing pterygium that includes scarred conjunctival tissue can also gradually impair ocular motility; the patient will then experience double vision in abduction.

Differential diagnosis: A pterygium is an unequivocal finding.

Treatment: Treatment is only necessary when the pterygium produces thesymptoms discussed above. Surgical removal is indicated in such cases. The head and body of the pterygium are largely removed, and the sclera is left open at the site. The cornea is then smoothed with a diamond reamer or an excimer laser (a special laser that operates in the ultraviolet range at a wavelength of 193 nm).

Clinical course and prognosis: Pterygia tend to recur. Keratoplasty is indi-cated in such cases to replace the diseased Bowman’s layer with normal tissue. Otherwise the diseased Bowman’s layer will continue to provide a growth substrate for a recurrent pterygium.