Non polarized dermoscopy
Non-polarizied dermoscopes
A dermoscope (or dermatoscope) is a
the handheld device, equipped with a magnification lens and a light source. It enables the visualization of the subsurface morphology of cutaneous lesions, down to the depth of the superficial dermis. It reveals colors and structures that are normally not visible to the unaided eye and improves the diagnostic accuracy and confidence level of experienced users, for both pigmented and non-pigmented skin lesions.
Non-polarized dermoscopes (NPD) are equipped with a magnification lens and light-emitting diodes to provide illumination. They require direct contact of the glass plate with the skin surface and the presence of a liquid interface with a refractive index equal to or closely matching that of the skin. Different immersion liquids can be used: 70% alcohol, gel (i.e., ultrasound gel, antibacterial gel), water or mineral oil. Air bubbles between the dermoscope’s glass plate, the immersion liquid, and the skin surface create a skin–air interface. The interface causes a back-scatter of light and precludes the observer from visualizing structures below the stratum corneum. Thus, air bubbles should be eliminated.
NPD allows visualization of subsurface structures located in the epidermis and the dermal-epidermal junction (DEJ), but can hardly visualize structures deeper than the DEJ.
Optical properties of light during the use of NPD
- The Surface glare is eliminated by matching the refractive indexes of the NPD's glass plate, the immersion medium, and the skin.
- Superficial penetrating light is the main source of contrast when using NPD. The light that enters the skin is absorbed (e.g. by melanin) or reflected back (e.g. by keratin in milia-like cysts) at the layers of the epidermis and the DEJ. The superficial penetrating light undergoes minimal scattering events and is, therefore, the main source of light that reflects back to the NPD lens.
- Deep penetrating light contributes only a small fraction of back-reflected light detected with NPD. This is due to the decay of light by multiple scattering events, as it goes deeper into the skin.
Melanoma, as it appears clinically (insert) and on NPD:
Globular nevus as it appears clinically (insert) and on NPD:
- An Atlas of Dermoscopy, Second Edition. Marghoob A. et al. CRC Press; 2012.
- Benvenuto-Andrade, C., Dusza, S.W., Agero, A.L., Scope, A., Rajadhyaksha, M., Halpern, A.C. & Marghoob, A.A., 2007, Differences between polarized light dermoscopy and immersion contact dermoscopy for the evaluation of skin lesions. Arch Dermatol, 143, 329–38.
- Gewirtzman, A.J., Saurat, J.H. & Braun, R.P., 2003, An evaluation of dermoscopy fluids and application techniques. Br J Dermatol, 149, 59–63.
- Marghoob, A.A., Cowell, L., Kopf, A.W. & Scope, A., 2009, Observation of chrysalis structures with polarized dermoscopy. Arch Dermatol, 145, 618.
- Pan, Y., Gareau, D.S., Scope, A., Rajadhyaksha, M., Mullani, N.A. & Marghoob, A.A., 2008, Polarized and nonpolarized dermoscopy: the explanation for the observed differences. Arch Dermatol, 144, 828–9.
- Wang, S.Q., Dusza, S.W., Scope, A., Braun, R.P., Kopf, A.W. & Marghoob, A.A., 2008, Differences in dermoscopic images from nonpolarized dermoscope and polarized dermoscope influence the diagnostic accuracy and confidence level: a pilot study. Dermatol Surg, 34, 1389–95.
