Section 03 of 10

How the dermatoscope creates its view

Understanding the instrument helps you interpret its output.

Cutaway diagram of a dermatoscope showing the LED light ring, polarising filter, magnification lens, glass contact plate, and battery housing.

Internal components of a typical polarised dermatoscope.

Real dermatoscopes vary in shape and size between manufacturers. The image you see through the lens will also differ depending on whether you use polarised or non-polarised (contact) mode — both are covered later in this section.

Magnification

Standard dermatoscopes provide 10× magnification. This makes features visible that are invisible to the naked eye, but it also changes your spatial reference. A structure that appears 2mm across in the dermatoscope is actually 0.2mm in reality.

Train yourself to think in dermoscopic scale. "Small" and "large" take on different meanings at 10× magnification.

Light penetration

Light enters the skin and interacts with structures at different depths:

Surface structures reflect light directly — they appear bright and well-defined
Mid-depth structures scatter light — they appear softer, with gradients
Deep structures absorb light selectively — they appear as colour shifts (blue-grey tones)

Cross-section diagram showing how light penetrates skin at three depths: surface structures appearing bright and crisp, mid-depth structures appearing softer with gradients, and deep structures appearing blue-grey due to the Tyndall effect.

Light penetration at three depths — surface (bright, crisp), mid-depth (softer, scattered), and deep (blue-grey colour shift).

The colour–depth relationship shown here is a useful guide, not a precise rule. In practice, lesion type, thickness, and your dermoscopic technique all influence the colours you see.

Colour is a depth cue. Brown at the surface looks different from brown at the junction, which looks different from pigment in the dermis. Learning to read these differences is at the heart of dermoscopy.

Polarised vs non-polarised

Non-polarised (contact) dermoscopy requires gel or fluid and shows surface features well
Polarised (non-contact) dermoscopy eliminates surface reflection and reveals deeper structures

Many dermatoscopes offer both modes. Learning to interpret each takes practice.

Side-by-side comparison of contact and polarised dermoscopy. Contact dermoscopy uses a glass plate with immersion fluid to reduce surface reflection. Polarised dermoscopy uses cross-polarised filters to eliminate surface glare and visualise deeper structures without skin contact.

Contact vs polarised dermoscopy — two approaches to eliminating surface reflection and revealing subsurface structures.

Both modes can reveal overlapping features. Polarised dermoscopy does not literally see deeper layers — it reduces surface glare, making structures visible that contact dermoscopy may obscure.

Knowledge check2 of 5

A structure appears bright, well-defined, and crisp through the dermatoscope. What does this suggest about where it sits?