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 Table of Contents  
Year : 2017  |  Volume : 4  |  Issue : 2  |  Page : 27-30

Dermatoscopy: Physics and principles

Department of Dermatology, Velammal Medical College and Research Institute, Madurai, Tamil Nadu, India

Date of Web Publication17-Nov-2017

Correspondence Address:
Balakrishnan Nirmal
Assistant Professor and Consultant, Department of Dermatology, Velammal Medical College and Research Institute, Madurai, Tamil Nadu
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ijdpdd.ijdpdd_13_17

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Dermatoscopy is an in vivo noninvasive technique used to examine pigmented and amelanotic skin lesions. The technique is performed using a hand-held self-illuminating device called dermatoscope that visualizes features present under the skin surface that are not normally visible to unaided eye. The images from the dermatoscope can be digitally photographed or recorded for future reference. Nonpolarized dermatoscopy requires contact with the skin surface and interface fluid between glass and skin surface. Polarized light penetrates deeper than the nonpolarized light and does not require contact fluids.

Keywords: Dermatoscopy, nonpolarized, polarized

How to cite this article:
Nirmal B. Dermatoscopy: Physics and principles. Indian J Dermatopathol Diagn Dermatol 2017;4:27-30

How to cite this URL:
Nirmal B. Dermatoscopy: Physics and principles. Indian J Dermatopathol Diagn Dermatol [serial online] 2017 [cited 2023 Mar 24];4:27-30. Available from: https://www.ijdpdd.com/text.asp?2017/4/2/27/218537

  Introduction Top

Skin surface microscopy was first performed in the early 20th century by Johann Saphier (1920) using a binocular microscope having an inbuilt light source. Leon Goldman (1951), also known as father of dermatoscopy, used the technique for the evaluation of pigmented lesions. MacKie (1971) used the technique for the assessment of pigmented lesions before surgery. From then, dermatoscopy was recognized as a noninvasive technology used to visualize subsurface features including epidermis, dermoepidermal junction, and superficial dermis that are not visible to the naked eye.[1]

  Terminology Top

Dermatoscopy is also known as dermoscopy, skin surface microscopy, epiluminescence microscopy, and incident light microscopy.[2] However, the consensus with regard to the correct terminology for the technology is still debatable. While the term “dermoscopy” is popular, “dermatoscopy” is more traditional and correct.[3] The specialty is correctly termed as dermatology not dermology.[4] Hence, it is always better to use the correct terminology rather than using shorter popular terms.

  Components of Dermatoscope Top

The essential components of a dermatoscope include as follows:

  1. Illumination system
  2. Achromatic lens
  3. Contact plate
  4. Power supply.

Older dermatoscopes used halogen lamp illumination system which rendered a yellowish hue to the images. The present dermatoscopes utilize white-light-emitting diodes as light source which consumes less power when compared to the halogen lamps. Power source is rechargeable lithium battery, AA battery, and lithium-ion battery. The achromatic lens usually provides a magnification of ×10 in most standard dermatoscopes. Contact plates are multicoated silicone glass and either graduated or nongraduated. Graduated plates have a scale inscribed to measure the dimensions of the lesion examined.[5]

  Magnified Light Top

Natural light when incident on objects is reflected, absorbed, or scattered. Light incident on the skin surface normally is reflected back. This phenomenon is called glare or specular reflectance [Figure 1]. Light is reflected back because the stratum corneum has a higher refractive index of 1.55 as compared to 1.0 of air. Thus, most of the light incident on the skin surface is reflected when visualized with a magnifying glass, and hence, dermatoscope is not a magnifying glass.
Figure 1: Magnified light: (a) Incident light is reflected back from skin surface, (b) Normal skin showing surface markings (×10)

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  Nonpolarized Dermatoscopy Top

To visualize deeper skin structures, this specular reflectance has to be reduced. This can be achieved when a glass plate with a refractive index of 1.52 comes in contact with the stratum corneum (1.55) with an interface fluid in between both the surfaces [Figure 2]. The refractive index of the fluid interface should ideally be equal to that of the skin to match it optically and minimize glare, allowing more light to penetrate through the stratum corneum.[6]
Figure 2: Nonpolarized dermatoscopy: (a) Incident light in the presence of interface fluid penetrates the superficial layers of the skin, (b) Normal skin showing light brown reticular pattern (×10)

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  Polarized Dermatoscopy Top

Specular reflectance reduction is also achieved by a technology called polarized dermatoscopy which utilizes two filters held orthogonally at 90°. Polarizers are widely used in the field of photography to reduce glare.[7] Polarized light incident on the stratum corneum is partly reflected from the surface and the rest enters the skin. The part which is reflected from the skin surface maintains its polarization and is blocked by the second filter. The part which penetrates the skin surface loses its polarization and hence is allowed to pass the second filter. The polarized light penetrates 60–100 μm deep into the skin surface [Figure 3]. This technology which allows the light which has lost its polarization to pass through the second filter whereas blocking the light which maintains its polarization is known as cross-polarization.[8]
Figure 3: Polarized dermatoscopy: (a) Incident polarized light penetrates deeper, loses polarization and is allowed to the eyepiece by the cross-polarizer, (b) Normal skin showing dark brown reticular pattern (×10)

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  Nonpolarized Versus Polarized Dermatoscopy Top

Nonpolarized dermatoscopy requires contact with the skin surface and interface fluid, whereas polarized dermatoscopy neither requires contact nor fluid. Nonpolarized dermatoscopy helps in better visualization of superficial structures such as comedo-like openings, milia-like cyst, crypts, fissures, and scales [Figure 4]. Deeper structures such as white, shiny streaks, vessels [Figure 5], and pigment network [Figure 6] are more conspicuous with polarized dermatoscopy.[9] Hence, nonpolarized and polarized dermatoscopy techniques are complementary to each other, with structures more apparent with one mode not being clearly visible in the other mode. These structures blink when toggled between both these modes in hybrid dermatoscopes possessing both these modes.[10]
Figure 4: Dermatoscopy of acanthosis nigrigans (×10): Crypts and fissures are more prominent in nonpolarized dermatoscopy (a) when compared to polarized dermatoscopy (b). (Image courtesy: Department of Dermatology, CMC, Vellore)

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Figure 5: Dermatoscopy of psoriasis (×10): When compared to nonpolarized dermatoscopy (a) regular red dots are clearly visualized in polarized dermatoscopy. (Image cour tesy: Depar tment of Dermatology, CMC, Vellore)

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Figure 6: Dermatoscopy of melasma (×10): When compared to nonpolarized dermatoscopy (a) accentuated reticular pattern seen more darker with polarized dermatoscopy (b). (Image courtesy: Department of Dermatology, CMC, Vellore)

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  Interface Fluids Top

The penetration of light from a dermatoscope is increased by the application of clear interface fluids. Few early studies have reported the use of immersion oil as contact fluid and have fallen out of favor subsequently due to carcinogenic and fetotoxic properties of chlorinated paraffin and dibutyl phthalate.[11] The various interface fluids used currently in dermatoscopy include alcoholic disinfectant, aqueous disinfectant, 70% ethanol, 90% isopropanol, liquid paraffin, water, and ultrasound gel.[12] Air inclusions are an issue when contact fluids are used and the number of inclusions is the highest for liquid paraffin. Ultrasound gel though slightly blurry is the fluid of choice in nails [Figure 7], mucosa, and periorbital region where other fluids will flow off. Alcohols have good clarity, low viscosity, and disinfectant properties. Nosocomial infection is a matter of concern with contact dermatoscopy. It has decreased significantly with the use of disposable covers for contact plates and disinfection with 70% isopropyl alcohol.[13]
Figure 7: Nailfold capillaroscopy of systemic sclerosis (×10) with ultrasound gel as interface fluid. (Image courtesy: Department of Dermatology, CMC, Vellore)

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  Colors Top

Melanin is the most important chromophore in pigmented lesions, and the color of melanin under dermatoscopy depends on its depth of location in the skin and its concentration. Melanin is black under dermatoscopy when present in the stratum corneum or upper epidermis, brown at the dermoepidermal junction, gray at papillary dermis, and blue when present in the reticular dermis [Figure 8].
Figure 8: Color of melanin under dermatoscopy when present in (a) basal layer (melasma): Brown, (b) superficial dermis (lichen planus pigmentosus): Gray, (c) deep dermis (congenital melanocytic nevus): Blue. (Image courtesy: Department of Dermatology, CMC, Vellore)

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  Concluding Remarks Top

Histopathologic examination is the gold standard of diagnosis in dermatology. Dermatoscopy is never an alternative or competitive method to histopathology, but a complementary tool that adds important clues to the diagnosis.[14] However, proper knowledge about the physics of the device and dermatoscopic patterns is extremely important to use this technique efficiently. Diagnostic accuracy of dermatoscopy correlates with the experience of the physician, and those not formally trained have decreased diagnostic performance.[15]

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Conflicts of interest

There are no conflicts of interest.

  References Top

Paech V, Schulz H, Argenyi Z, Gambichler T, Altmeyer P, editors. Introduction. Compendium of Surface Microscopic and Dermoscopic Features. Berlin: Springer; 2008. p. VII-IX.  Back to cited text no. 1
Kaliyadan F. The scope of the dermoscope. Indian Dermatol Online J 2016;7:359-63.  Back to cited text no. 2
[PUBMED]  [Full text]  
Kittler H, Marghoob AA, Argenziano G, Carrera C, Curiel-Lewandrowski C, Hofmann-Wellenhof R, et al. Standardization of terminology in dermoscopy/dermatoscopy: Results of the third consensus conference of the international society of dermoscopy. J Am Acad Dermatol 2016;74:1093-106.  Back to cited text no. 3
Ackerman AB. Dermatoscopy, not dermoscopy! J Am Acad Dermatol 2006;55:728.  Back to cited text no. 4
Nischal KC, Khopkar U. Dermoscope. Indian J Dermatol Venereol Leprol 2005;71:300-3.  Back to cited text no. 5
[PUBMED]  [Full text]  
Wang SQ, Dusza SW, Scope A, Braun RP, Kopf AW, Marghoob AA, et al. Differences in dermoscopic images from nonpolarized dermoscope and polarized dermoscope influence the diagnostic accuracy and confidence level: A pilot study. Dermatol Surg 2008;34:1389-95.  Back to cited text no. 6
Pan Y, Gareau DS, Scope A, Rajadhyaksha M, Mullani NA, Marghoob AA, et al. Polarized and nonpolarized dermoscopy: The explanation for the observed differences. Arch Dermatol 2008;144:828-9.  Back to cited text no. 7
Anderson RR. Polarized light examination and photography of the skin. Arch Dermatol 1991;127:1000-5.  Back to cited text no. 8
Benvenuto-Andrade C, Dusza SW, Agero AL, Scope A, Rajadhyaksha M, Halpern AC, et al. Differences between polarized light dermoscopy and immersion contact dermoscopy for the evaluation of skin lesions. Arch Dermatol 2007;143:329-38.  Back to cited text no. 9
Braun RP, Scope A, Marghoob AA. The “blink sign” in dermoscopy. Arch Dermatol 2011;147:520.  Back to cited text no. 10
Binder M, Kittler H, Pehamberger H, Wolff K. Possible hazard to patients from immersion oil used for epiluminescence microscopy. J Am Acad Dermatol 1999;40:499.  Back to cited text no. 11
Gewirtzman AJ, Saurat JH, Braun RP. An evaluation of dermoscopy fluids and application techniques. Br J Dermatol 2003;149:59-63.  Back to cited text no. 12
Stauffer F, Kittler H, Forstinger C, Binder M. The dermatoscope: A potential source of nosocomial infection? Melanoma Res 2001;11:153-6.  Back to cited text no. 13
Lallas A, Argenziano G. Dermatoscope – The dermatologist's stethoscope. Indian J Dermatol Venereol Leprol 2014;80:493-4.  Back to cited text no. 14
[PUBMED]  [Full text]  
Yucel A, Gunasti S, Aksungur VL. The influence of training on the recognition of gross features of dermoscopy images. Indian J Dermatol Venereol Leprol 2010;76:132-7.  Back to cited text no. 15
[PUBMED]  [Full text]  


  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8]

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Components of De...
Magnified Light
Nonpolarized Der...
Polarized Dermat...
Nonpolarized Ver...
Interface Fluids
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