Detection of increase in corneal irregularity due to pterygium using Fourier series harmonic analyses with multiple diameters

Purpose To determine steep increase of corneal irregularity induced by advancement of pterygium. Methods A total of 456 eyes from 456 consecutive patients with primary pterygia were examined for corneal topography and advancement of pterygium with respect to the corneal diameter. Corneal irregularity induced by the pterygium advancement was evaluated by Fourier harmonic analyses of the topographic data that were modified for a series of analysis diameters from 1 mm to 6 mm. Incidences of steep increases in the asymmetry or higher-order irregularity components (inflection points) were determined by using segmented regression analysis for each analysis diameter. Results The pterygium advancement ranged from 2% to 57%, with a mean of 22.0%. Both components showed steep increases from the inflection points. The inflection points in the higher-order irregularity component altered with the analysis diameter (14.0%–30.6%), while there was no alternation in the asymmetry components (35.5%–36.8%). For the former component, the values at the inflection points were obtained in a range of 0.16 to 0.25 D. Conclusion The Fourier harmonic analyses for a series of analysis diameters revealed that the higher-order irregularity component increased with the pterygium advancement. The analysis results confirmed the precedence of corneal irregularity due to pterygium advancement.