Quantitative analysis of regular and irregular astigmatism induced by pterygium

Purpose. To quantitatively evaluate thr influence of pterygium and its remo val surgery on both regular and irregular corneal astigmatism, Methods. In 19 eyes of 19 patients undergoing pterygium surgery, videokeratographic mea surements were taken before and 1 month after surgery. Using Fourier harmon ic analysis, dioptric data on mire rings were decomposed into spherical, re gular astigmatism, and irregular astigmatism (decentration and higher order irregularity) components. The distance between the line of sight and the a dvancing edge of pterygium was measured, and the eyes were classified into two groups: large pterygium group (the distance <2.0 mm, n = 7) and small p terygium group (greater than or equal to 2.0 mm, n = 12). Fifteen eyes of 1 5 subjects served as age-matched normal control eyes. Results. Before surge ry, the magnitudes of regular astigmatism and higher order irregular astigm atism showed significant correlation with the size of pterygium. Regular as tigmatism, asymmetry, and higher order irregularity in the large pterygium group were significantly greater than those of normal control eves. The pte rygium removal surgery significantly improved these changes, but regular as tigmatism and higher order irregularity in the large pterygium group still remained significantly greater than those in the normal control eves. Concl usion. Pterygium induces a significant amount of regular and irregular asti gmatism in proportion to its size. The removal surgery can improve these ch anges, but corneal distortion does not normalize completely in eyes with ad vanced pterygium.