With the number of models available, this can seem to be a difficult decision. Whilst the amount of choice appears confusing, an understanding of some basic principles can assist. There are 2 main types of light used in dermoscopy, polarised and non-polarised.
Polarised or Non-Polarised?
Before answering this question, a look at how the dermatoscope works is helpful. The dermatoscope allows us to see the colours and microstructures of epidermis, dermo-epidermal junction and the papillary dermis, which are not visible to the naked eye. It does this in one of 2 ways.
Non-polarised light source. By using a fluid between a glass plate and the skin, reflection of light from the surface of the skin is eliminated, allowing visualisation of deeper structures. The first generation of dermatoscopes used this method and much of the early research was done in Europe using this method.
Polarised light source and a polarising filter at 90 degrees (cross polarisation). Reflected light from the surface is blocked, and light reflected from deeper structures is clearly seen. More recent research, especially that from Australia, used this method, discovering new structures which can only be seen using cross-polarisation.
Which is better?
There is no simple answer; both have their advantages and disadvantages.
The main drawback of non-polarised dermoscopy is that it requires contact with the skin and the use of a fluid. With polarised dermoscopy, both are optional, but for photography, contact eliminates camera-shake, and fluid may improve image quality. There are some important features which are better visualised with non-polarised, and others seen better with polarised dermoscopy. Some structures can only be seen with one type. In addition, vessels can be squashed using contact dermoscopy.
Why not have the best of both worlds?
In conclusion, if you are serious about dermoscopy, use a hybrid model. These are dermatoscopes which have both non-polarised and polarised light settings, and the ability to toggle between them.
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Haspeslagh M. Rosettes and other white shiny structures in polarized dermoscopy: histological correlate and optical explanation. J Eur Acad Dermatol Venereol. 2016 Feb;30(2):311-3.