New Freeware for Image Analysis of Lissamine Green Conjunctival Staining.

PURPOSE: Lissamine green (LG) is often used in addition to fluorescein to assess the severity of conjunctival damage in dry eye syndrome, which is graded manually. Our purpose was to describe an algorithm designed for image analysis of LG conjunctival staining. METHODS: Twenty pictures of patients suffering from dry eye with visible LG conjunctival staining were selected. The images were taken by 2 different digital slit lamps with a white light source and a red filter transmitting over the wavelengths absorbed by LG. Conjunctival staining appeared in black on a red background. The red channel was extracted from the original image. Stained areas were then detected using a Laplacian of Gaussian filter and applying a threshold whose value was determined manually on a subset of images. The same algorithm parameters remained constant thereafter. LG-stained areas were also drawn manually by 2 experts as a reference. RESULTS: The delineation obtained by the algorithm closely matched the actual contours of the punctate dots. In 19 cases of 20 (95%), the algorithm found the same Oxford grade as the experts, even for confluent staining that was detected as a multitude of dots by the algorithm but not by the experts, resulting in a high overestimation of the total number of dots (without mismatching the Oxford grade estimated by the experts). The results were similar for the 2 slit-lamp imaging systems. CONCLUSIONS: This efficient new image-analysis algorithm yields results consistent with subjective grading and may offer advantages of automation and scalability in clinical trials.

Size of the Lesions of Superficial Punctate Keratitis in Dry Eye Syndrome Observed With a Slit Lamp.

PURPOSE: To evaluate the size distribution of epithelial lesions of superficial punctate keratitis (SPK) in dry eye after staining of the ocular surface by sodium fluorescein. METHODS: Fluorescein was instilled in 10 patients with dry eye graded using the Oxford Scheme. Pictures were taken using a standard Topcon slit lamp with cobalt blue light, without barrier filter. Two magnifications (×10 and ×16) were used and calibrated using a certified standard reference grating, allowing the diameter of the observed objects to be determined with ImageJ software. The most visible and isolated SPK lesions (green dots) were selected. The size of 254 SPK lesions was measured by tracing the irradiance profile and manually measuring the full width at half maximum. RESULTS: For all patients, with the 2 magnifications combined, the median diameter was 20.9 µm (15.2-26.6 µm, 10-90 percentile). There was a significant difference between the size of SPK lesions measured with ×10 and ×16 magnifications, respectively, 24.3 µm (18.2-29.8) versus 19.0 µm (15.2-26.6) (P < 0.001). CONCLUSIONS: Lesions seem to be smaller than normal superficial epithelial cells (which are approximately 25 × 50 µm) and might correspond to the staining of dying shrunken cells, according to recent investigations. These new quantitative data will help in developing automated recognition algorithms to obtain reliable objective classification of corneal staining.