2.1.4.1　Dermoscopy

Dermoscopy is a non-invasive technique that allows microscopic visualization of subsurface skin structures not visible to the naked eye.It may be performed with manual devices and allow magnifications up to×20，or with digital systems requiring a video camera equipped with optic fibers and lenses that ensure magnifications of up to×200.Dermoscopy can eliminate the reflection，refraction，diffraction of light by adding a“clearing”medium or/and a polarized light，so as to visualize the structures of cutaneous lesions.

Dermoscope has two types：non-contact type（Figure 2-2（a））and contact type（Figure 2-2（b））.Contact dermoscopy uses a glass window with alcohol or imaging gel in contact with the skin to reduce the refractive index between the skin and dermoscope lens.In the non-contact dermoscopy，there is no contact of the lens with the skin.The cross-polarized lens absorbs all the scattered light and hence allows only light in a single plane to pass through it（Figure 2-3）.Dermoscopy can be applied to diagnose skin tumor，pigmented skin disease，inflammatory dermatosis，infectious dermatosis and autoimmune dermatosis，as well as to observe hair and nails.(https://www.daowen.com)