A methodology for evaluating pterygium measurements expressed as a percentage of corneal size based on standardized color photography

Abstract

Purpose : To describe and validate a methodology to assess the corneal extent of pterygia using standardized color photography.

Methods : 25 photographs of 21 eyes of 19 patients with nasal pterygium were included in this study. All images were taken in primary gaze using a single lens reflex camera system (Canfield Scientific, Inc., Fairfield, NJ), using fixed focus parameters under consistent lighting conditions. Using Image J (NIH, Bethesda, MD) software, the images were retrospectively and independently analyzed by two masked graders. The portion of the pterygium extending past the corneal limbus was identified and its borders were demarcated. The corneal diameter and perimeter were also demarcated. These measurements were then used to calculate the length and surface area of the head of the pterygium expressed as a percentage of the corneal length and surface area, respectively. Intraclass correlation coefficient (ICC) was calculated to assess inter- and intra- grader agreement.

Results : All 25 images could be analyzed using the methodology described, including in cases where portions of the corneal limbus were obscured, and without the need for eyelid retraction. In this cohort, the intra-grader mean percent surface area (+/- SD) and mean percent length (+/- SD) were 11.608 (+/- 7.284) mm² and 23.913 (+/- 12.152) mm, respectively. The average range of the percent surface area was (2.665, 30.392) mm² and the percent length was (8.629, 50.704) mm. The inter-grader mean percent surface area (+/- SD) and mean percent length (+/- SD) were 11.419 (+/- 7.482) mm² and 23.491 (+/- 12.302) mm, respectively. The average range of the percent surface area was (1.946, 30.613) mm² and the percent length was (7.224, 50.568) mm. The intra-grader ICCs for the percentage of pterygium to corneal surface area and length were 0.979 and 0.995, accordingly. The inter-grader ICCs for percentage of pterygium to corneal surface area and length were 0.986 and 0.984, respectively.

Conclusions : A methodology for pterygia size quantification relative to the corneal size is described and validated using color photographs of the eye taken in primary gaze with a simple set focus camera. The reproducibility of this analysis method is high and may be used to standardize evaluation of pterygia in clinical research and clinical trials.

This is a 2020 ARVO Annual Meeting abstract.