Visual cues for depth perception

The brain uses several cues to reconstruct three dimensions from a flat image. In dermoscopy, the most useful are:

1. Colour gradients

Melanin appears different colours depending on its depth within the skin:

This gradient isn't absolute — other factors matter — but it provides a reliable starting framework.

Common pitfall: Assuming all brown is the same. A brown that "feels" flat versus one that "feels" deep often reflects this gradient at work.

2. Sharpness and blur

Structures at the surface appear sharp and well-defined. Structures deeper in the skin appear softer, with less distinct edges.

Think of looking through water: the bottom of a shallow pool is crisp; the bottom of a deep pool is hazy. The same principle applies to dermoscopy.

3. Shadow and highlight

Raised structures cast subtle shadows. Vessels appear as linear red structures because they sit within tissue that scatters light around them.

The "shiny white structures" seen in some lesions reflect light in a way that indicates they sit at a specific optical interface — they are only visible under polarised light.

4. Vessel behaviour

Vessels live in the dermis. Their visibility and pattern provide information about depth and tissue architecture:

• Fine vessels near the surface — thin-walled, superficial
• Arborising (tree-like) vessels — branching through the papillary dermis
• Dotted vessels — cross-sections of vertical vessels seen from above
• Linear or serpentine vessels — horizontal orientation within the dermis