The clinical "naked eye" examination is important in the assessment of the gross morphological features of the lesion, such as size, shape, colors, contours, and surface topography.
Since the refractive index of the stratum corneum (surface layer of the skin) is higher than that of air, much of the incident light is reflected off the surface of the skin and causes the surface glare, as the reflected light overwhelms the retina and precludes the observer from visualizing the light reflected from the deeper layers of the skin. Thus, clinical "naked eye" examination mainly allows the assessment of morphological features of the surface layer of the skin (stratum corneum), and to a much lesser extent, the colors and structures of the deeper layers of the epidermis and the superficial dermis.
In body areas with a thick stratum corneum (e.g. on acral surfaces), there is a greater back-scatter of the light and the skin appears more opaque. In body areas with a thin stratum corneum (e.g., eyelids), the skin appears more translucent.
This figure shows the clinical examination of a pigmented lesion showing the surface glare. The interpretation of the lesion is very limited and difficult.