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Ye Jin Shin, Kevin Bui, Tyler Brown, Yue Shi, SriniVas Sadda, Olivia L Lee; Pterygium surface area quantification stratified by extension past the corneal limbus. Invest. Ophthalmol. Vis. Sci. 2020;61(9):PB0092.
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To describe and validate a methodology to assess the pterygium surface area extending beyond the corneal limbus expressed as a percentage of the corneal surface area segmented into three anatomical zones (central, mid-periphery, and periphery) based on standardized color photography.
Primary gaze images were taken using a single lens reflex camera system (Canfield Scientific, Inc., Fairfield, NJ), using fixed parameters under consistent lighting conditions. 25 photographs of 21 eyes of 19 patients with nasal pterygium were included in this study. Using Image J (NIH, Bethesda, MD) software, the images were retrospectively and independently analyzed by two masked graders. The corneal limbus was identified and demarcated 360 degrees (to the extent visible without eyelid retraction) to define the corneal circumference. Based on the circumference designating the outermost ring, two additional concentric rings of the same shape were drawn to divide the cornea into thirds. The resulting three rings demarcate the following three zones: central, mid-periphery, and periphery. The portion of the pterygium extending into each zone was identified and its borders were outlined. The pterygium surface area was calculated as a percentage of the corneal area per anatomical zone. Intraclass correlation coefficient (ICC) was calculated for inter and intra grading agreement.
All 25 images were able to be analyzed using the methodology described, even with portions of the corneal limbus obscured. The intragrader ICC for percentage of pterygium to corneal surface area for central, mid-periphery, and periphery zones were 0.980, 0.995, and 0.842, respectively. The intergrader ICC for central, mid-periphery, and periphery zones were 0.889, 0.994, and 0.861, respectively.
A methodology for pterygia size quantification relative to the corneal size divided into anatomical zones is described and validated using primary gaze color photographs taken with a simple set focus camera. Pterygia that extend into the central zone are cosmetically, visually, and optically more significant because of the involvement of the visual and pupillary axis. This quantification method allows for weighted assessment of pterygia surface area stratified by extension past the corneal limbus. The reproducibility of this method is high and can be used to standardize evaluation of pterygia in clinical research and clinical trials.
This is a 2020 Imaging in the Eye Conference abstract.
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