Anterior Segment Measurements Using Digital Photography: A Simple Technique

Abstract

The purpose of this study is to describe a simple method of measuring anterior segment lesions from digital slit lamp images and confirm reliability of the technique. Ten reference photos were taken of a PD ruler, refocusing on the ruler for each photo. Using Adobe Photoshop, the number of pixels per millimeter squared (area) and 1 mm (linear) were recorded for each photo. An Excel spreadsheet was set up to convert pixels to millimeters and millimeters squared. Interrater reliability was determined by two observers who independently calculated the area of 69 epithelial defects. A Bland and Altman plot was used to demonstrate the agreement between the two doctors. Interrater reliability was excellent as measured by an intraclass correlation coefficient (ICC 2,1) = 0.99. From the Bland and Altman plot it was determined that in 95% of cases, the area of the epithelial defect measured by provider 2 may be as much as 1.17 mm less than or 1.09 mm greater than that measured by provider 1. This simple method, which allows accurate measurements from digital images using common off-the-shelf software, is a valuable tool for clinical documentation as well as for research purposes.