Does pterygium morphology affect corneal astigmatism?

Abstract

Purpose: The purpose of this study was to evaluate the correlation between corneal astigmatism and the morphology of pterygium with anterior segment optic coherence tomography (AS-OCT).

Material and methods: The size of pterygium (horizontal length, vertical width) was measured manually; pterygium area and percentage extension of the pterygium onto the cornea were calculated. Anterior and posterior corneal astigmatism, Sim K, K1, K2 were measured using a dual Scheimpflug analyzer. Morphological patterns of the pterygium analyzed with AS-OCT were determined according to the extension of the pterygium apex below the corneal epithelium. Two tomographic patterns were identified: continuous and nodular. Correlation between anterior corneal astigmatism and pterygium size, percentage extension of the pterygium, and morphological pattern of the pterygium was analyzed.

Results: The mean ages of the 47 patients were 49.4 ± 16.6 (22-80) years. Mean horizontal pterygium length, vertical width, pterygium area, and percentage extension of the pterygium were 2.8 ± 1.2 mm, 4.8 ± 1.6 mm, 7.42 ± 5.6 mm² and 24.5 ± 10.4%, respectively. Mean anterior corneal astigmatism was 2.3 ± 2.3 D and simulated keratometry was 43.4 ± 2.02 D. In terms of the morphological pattern of the pterygium, 24 eyes had continuous, 23 eyes had a nodular pattern and the median (interquartile range) anterior corneal astigmatism was 1.87 (1.01-3.80) and 1.22 D (0.58-2.35), respectively (p = 0.102). Other topographic and pterygium size parameters were similar between groups. Analyzing the correlations in groups separately, a positive moderate statistically significant correlation was present between vertical width, percentage extension, pterygium area, and anterior corneal astigmatism in both continuous and nodular groups.

Conclusions: Although not statistically significant, anterior corneal astigmatism was higher in continuous group. Using AS-OCT to standardize the morphology of pterygium could provide additional clinical information.

Keywords: anterior segment optic coherence tomography; astigmatism; morphology; pterygium.

Figure 1.

Anterior segment image of the pterygium depicting pterygium sizes. Horizontal length was defined as the line between the apex of the pterygium and nasal limbus. Vertical width was defined as the dashed line between the two limbal points where pterygium intersects the corneal limbus.

Figure 2.

(a) Anterior segment photograph of pterygium with nodular pattern. (b) Anterior segment optical coherence tomography horizontal scans of nodular pattern with well delineated masses of pterygium tissue bulging the ocular surface contour and with less advanced and creeping extension of the apex below the corneal epithelium. (c) Anterior segment photograph of pterygium with continuous morphology. (d) Anterior segment optical coherence tomography horizontal scans of continuous morphology pattern with more extension and creeping of the end of the pterygium apex below the corneal epithelium.

Figure 3.

Distribution of corneal astigmatism according to pterygium morphology.

Figure 4.

Correlation analysis between pterygium parameters and corneal astigmatism.