Comparison of pterygium head quantification methodologies based on color photography of primary pterygia

Abstract

Purpose : To compare and validate two grading methods for quantification of pterygium size and surface area based on color photos of primary pterygia.

Methods : Color photographs of 164 eyes with primary pterygia taken in primary gaze with a modified single lens reflex camera system (Canfield Scientific Inc, Fairfield, NJ, USA) were analyzed. Utilizing ImageJ (National Institutes of Health, Bethesda, MD USA) software, three size parameters of the head of the pterygium were quantified included length (mm), width (mm), and surface area (mm²) of the pterygium head. Two grading methodologies were compared using differing strategies to demarcate the head of the ptergygium. The first method defined the head of the pterygium as any fibrovascular tissue crossing the corneal limbus, including any associated corneal opacity. The second grading method defined the pterygium head as any vascularized tissue past the corneal limbus with discernable active blood flow; any avascular fibrous tissue or opacity on the cornea was excluded.

Results : Paired t test was used to assess the validation of the two pterygium grading methods. The results from the first pterygium grading method yielded mean measurements for width, length and surface area of pterygia head as follows: 3.97 ± 1.02 mm (1.65-6.22 mm), 2.41 ± 1.16 mm (0.65-5.37 mm) and 7.27 ± 4.65 mm² (0.89-18.39 mm²) respectively.
The results from the second pterygium grading method yielded mean measurements for width, length and surface area of pterygia head as follows: 4.49 ± 1.33 mm (0.72- 7.50 mm), 2.22 ± 1.04 mm (0.57-5.23mm) and 7.39 ± 5.12 mm² (0.37-24.12 mm²) respectively.
Results showed a significant difference in width of the pterygium (p=0.0001) when comparing the two methods of grading, however there was no significant difference in the length (p=0.08) and area (p=0.41) of the pterygium.

Conclusions : Two grading methodologies are presented, demonstrating strategies for reproducibly quantifying the size of pterygium head based on two dimensional color photographs of the eye taken in primary gaze with a simple set focus camera. With both methods, measurements of the width, length and surface area of the corneal portion of the pterygium can be quantified using objective grading criteria. Such methodologies can be used to standardize our evaluation of pterygia in clinical research and clinical trials.

This abstract was presented at the 2019 ARVO Imaging in the Eye Conference, held in Vancouver, Canada, April 26-27, 2019.