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.
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.
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).
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.