Rosacea Subtypes Visually and Optically Distinct When Viewed with Parallel-Polarized Imaging Technique

Parallel-polarized light (PPL) photography evaluates skin characteristics by analyzing light reflections from the skin surface.

The aim of this study was to determine the significance of quantitative analysis of PPL images in rosacea patients, and to provide a new objective evaluation method for use in clinical research and practice.

A total of 49 rosacea patients were enrolled. PPL images using green and white light emitting diodes (LEDs) were taken of the lesion and an adjacent normal area. The values from the PPL images were converted to CIELAB coordinates: L^* corresponding to the brightness, a^* to the red and green intensities, and b^* to the yellow and blue intensities.

A standard grading system showed negative correlations with L^* (r=-0.67862, p=0.0108) and b^* (r=-0.67862, p=0.0108), and a positive correlation with a^* (r=0.64194, p=0.0180) with the green LEDs for papulopustular rosacea (PPR) types. The xerosis severity scale showed a positive correlation with L^* (r=0.36709, p=0.0276) and a negative correlation with b^* (r=-0.33068, p=0.0489) with the white LEDs for erythematotelangiectatic rosacea (ETR) types. In the ETR types, there was brighter lesional and normal skin with white LEDs and a higher score on the xerosis severity scale than the PPR types.

This technique using PPL images is applicable to the quantitative and objective assessment of rosacea in clinical settings. In addition, the two main subtypes of ETR and PPR are distinct entities visually and optically.