Abstract

BackgroundThe prospective observation study aimed to evaluate changes in corneal higher-order aberrations induced by advancement of pterygium using an anterior-segment optical coherence tomography (AS-OCT) and Zernike aberration analysis.MethodsThe corneal topography of 284 eyes with primary pterygia originating from the nasal region was measured using an AS-OCT (SS-1000, Tomey). With anterior corneal elevation data, Zernike polynomial coefficients were calculated in diameters of 1.0, 3.0, and 5.0 mm, and the coma, spherical, coma-like, spherical-like, and total higher-order aberrations were obtained. Pterygium size was also measured as a ratio of positions of the pterygium end with respect to the corneal diameter and categorized in eight classes: less than 15%, 15–20%, 20–25%, 25–30%, 30–35%, 35–40%, 40–45, and 45% or larger. Increases in the aberrations were analyzed with reference to those in eyes with pterygium size < 15%.ResultsThe mean age of the participants was 69.3 years, and the pterygium size ranged from 2 to 57% (mean: 28.8%). The coma aberration significantly increased when the pterygium size was 45% or larger in 1.0 and 3.0 mm diameters and over 25–30% in 5.0 mm diameter. Similar increases were found in the pterygium sizes exceeding 45, 40, and 25%, respectively, in the coma-like, spherical-like, and total higher-order aberrations. On contrast, there was no increase in the spherical aberration.ConclusionIncreases in higher-order aberrations reflected the pterygium size, and significant aberrations were induced in 5.0 mm diameter when the end exceeded 25% of corneal diameter. The use of AS-OCT and Zernike analysis could enable objective grading of pterygium advancement based on changes in corneal optics.

Highlights

  • The prospective observation study aimed to evaluate changes in corneal higher-order aberrations induced by advancement of pterygium using an anterior-segment optical coherence tomography (AS-OCT) and Zernike aberration analysis

  • All aberrations increased with the pterygium size (P < 0.01, linear regression analysis) except for the spherical aberration in 5.0 mm diameter (P = 0.083)

  • The coma aberration showed significant increases when the pterygium size was over 45% in 1.0 and 3.0 mm diameters and 25–30% or larger in 5.0 mm diameter, whereas there was no increase in the spherical aberration

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Summary

Introduction

The prospective observation study aimed to evaluate changes in corneal higher-order aberrations induced by advancement of pterygium using an anterior-segment optical coherence tomography (AS-OCT) and Zernike aberration analysis. The surface regularity index (SRI) [1, 2], higher-order irregularity (HOI) in Fourier harmonic analysis of topographic data [3, 4], and higher-order Zernike coefficients [5, 6] increase with the advancement of a pterygium. The use of anterior-segment optical coherence tomography (AS-OCT) enables accurate measurement of the anterior corneal elevation of abnormal eyes [10]. The measured AS-OCT topography could be analyzed using the Zernike polynomial expansion [11], which is more representative of optical aberrations of the cornea

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