There are two types of skin ageing,’chronic ageing’ and ‘photoageing’. The importance of photoageing which occurs due to exposure of skin to sun have been well recognised and studied.
Repeated exposure to sunlight over the years results in gradual degradation of human skin and the appearance of an assortment of unwelcome signs of photoageing such as dyspigmentation, wrinkling, roughness, dullness, yellowness and laxity. The gradual changes in skin caused by cumulative sun exposure throughout one’s life appear more prominently on the parts of skin which are relatively more exposed to the sun. We have studied the photodamaged skin using an array of biophysical techniques. In the past, we have shown the effects of sun damage in cross-sectional images obtained by Optical Coherence Tomography (OCT) and ultrasonography. Confocal microscopy (horizontal sections) also showed features of sun damage.
Elastosis and topography of skin have been studied using a number of techniques. Fluorescence photography was also helpful in showing signs of photo damage. Dyspigmentation have been documented, some years ago, using Ultraviolet Light Photography, but later, techniques were developed using filtered digital photography and videomicroscopy. Recently, some more methodologies were developed to study skin dyspigmentation. A procedure utilising ‘RGB splitting’ and ‘tonal adjustment’ was used to study the hyperpigmented lesions of skin. Hyperpigmented spots, freckles and solar lentigos are shown much more clearly in these photos. Image analysis procedures quantify the hyperpigmentation.
Cross-polarised, colour photos were obtained using a digital camera, with polariser filters mounted on the flash light as well as on the lens. Using an image processing software, splitting of the RGB channels was done and the grey image of the blue-channel was saved. After tonal adjustment a final picture was obtained, clearly showing the pigment distribution. An image analysis program was developed to calculate various dyspigmentation parameters such as Luminance variance, count and degrees of pigmentation. Quantitative values, proportional to the degree of photoageing were shown. Qualitatively, the processed photos showed the hyper-pigmented lesions more vividly. We have illustrated in this study how this technique may be utilised to measure the hyperpigmentation of skin and show subtle differences.
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