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E. M. Alsaleh, G. Wilson, D. Horner; Corneal Curvature at Different Stages of Pterygium. Invest. Ophthalmol. Vis. Sci. 2008;49(13):6033. doi: https://doi.org/.
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To investigate the effect of pterygium on corneal curvature.
Corneal topography was determined using a portable Keratron Scout (EyeQuip Company, Florida, USA). Nineteen points at equal intervals along the horizontal corneal meridian were selected to represent instantaneous corneal curvature from limbus to limbus. Photographs of the central, nasal and temporal aspects of the eye were taken using a Nikon D200 digital camera with a Micro-Nikkor 105 mm lens equipped with a close-up flash system. From the photographs the percentage of the corneal diameter occupied by the pterygium was determined and the pterygium graded: Grade 1 (conjunctival), Grade 2 (up to 10%), Grade 3 (>10% to 20%), up to Grade 6. Subjects were volunteers from the clinic at the Indiana University Eye Care Center, Guanajuato, Mexico. This is a region with a high prevalence of pterygium due to altitude, clear skies and an outdoor lifestyle. The age range was 18 to 87 years (27 men and 53 women, mean = 49.3 years). Of the 80 subjects, 73 had a pterygium in at least one eye (6 had one eye affected, 67 had both eyes affected). A total of 154 eyes were enrolled. 57 eyes had almost the same grade of pterygium in both nasal and temporal sides (bilateral), and 77 eyes had pterygium limited to one side of the cornea (unilateral). 20 eyes had minimal conjunctival changes, and they were used as controls.
All unilateral pterygia were nasal. The measured mean ± SD of the instantaneous curvatures (diopters) for the controls and 65 eyes with unilateral pterygia covering Grades 2, 3 and 4 are shown in the table:
Pterygium causes flattening of the nasal cornea but no change temporally. Pterygium usually does not affect the curvature of the central cornea.
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