Image analysis of conjunctival staining with Lissamine green in dry eye syndrome

Abstract

Purpose : Lissamine Green (LG) is often used in addition to fluorescein to assess the severity of conjunctival lesions during dry eye syndrome but its quantification remains manual. Aim: to describe an algorithm destined to the image analysis of LG stained conjunctival lesions.

Methods : Ten pictures of 6 patients suffering from dry eye and presenting visible LG positive conjunctival staining were selected among pre-existing data. Pictures had been taken during routine consultation, after instillation of LG, using 2 different slit-lamps with a white light source and a red filter transmitting over the wavelengths absorbed by LG. Conjunctival staining consequently appeared black against a red background. 16x magnification was used to image the entire conjunctival surface. With the ImageJ software, the red channel was extracted from the original image. Edge detection was performed using a Laplacian of Gaussian (LoG) filter. A manual threshold was determined on a subset of images in order to select only the stained areas. The same threshold remained constant thereafter. Finally, the detected areas were overlaid onto the original RGB image. The lesions were also manually outlined by two experts for comparison.

Results : In addition to enhancing the global contrast on the conjunctival surface, the red filter combined with a LoG filter allowed highlighting and localizing LG staining while avoiding the erroneous detection of blood vessels. The delineation obtained by the algorithm closely matched the actual contours of small lesions, and was therefore in good agreement with the experts. The large areas of confluent LG stained lesions were separated by the algorithm in numerous small dots, resulting in a large overestimation of the total number of dots. Nevertheless, these cases were already classified as Oxford grade V (>316 dots) and the grading was therefore not modified by the overestimation. Despite slight changes in picture quality, results were similar for both slit-lamps indicating that the algorithm was robust.

Conclusions : This new image analysis algorithm could increase the reliability (fidelity, accuracy, reproducibility) of the quantification of LG conjunctival staining, especially in clinical trials.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.

 

Delineation of LG conjunctival staining obtained through our approach thanks to a filtered image (A) and overlaid onto the RGB image (B). Scale bar: 1.25mm.