Laser light is a useful tool for destroying tissue, stimulating blood flow, and determining diagnosis. The resolution and depth of penetration may be limiting factors for use depending on the light. As resolution is clearer, depth is lost and vice versa.

There are two main devices that can provide quality visualization of the tissue in depth and resolution: optical coherence tomography (OCT) and reflectance confocal microscopy (RCM).

OCT has a resolution of 6 µm and a depth of 2 mm (field of view 16 mm). OCT can also provide details into the vascular pattern as the light can generate a visualization of moving components, such as blood flow. The ability to visualize and monitor blood flow is also significant, since many abnormalities of the skin are accompanied by a deviation from normal levels of vascular activity.¹

RCM provides much better resolution (1 µm) than OCT but has less depth (200-250 µm) of imaging (field of view 1-8 mm). RCM allows the horizontal visualization of the epidermis and the superficial dermis and the observation of cell morphology with a nearly histological resolution.²

Non-invasive diagnostic tools can be applied in different dermatologic areas. One use is to quantify and identify the changes in the skin after treatment with a fractionated carbon dioxide laser and to see the effect of skin remodeling induced by the laser treatment.³ For example, when lasers are used for skin rejuvenation, a clear remodeling process can be seen at 3 and 6 weeks post treatment with RCM. The steps involve the removal/reduction of pigmentation and keratinocyte alterations (epidermal effect) as well as the deposition of new collagen in parallel-oriented horizontal fibers that are responsible for tightening the skin (dermal effect).

Chronological aging and photoaging can be assessed by means of RCM or OCT.^4,5

Skin care products reduce keratinocyte alterations and pigmentation (cytological improvement) while reducing hyperplasia, inducing more regular (trophic) epidermis, and new collagen deposition in small bright fibrillae (architectural effect).

Patients with melasma and age-freckles are good candidates for depigmentation therapy. With the use of RCM, the layers of the skin can be viewed to determine the different levels of pigment involvement (mottled pigmentation (epidermis); increased brightness of rings, bright polycyclic papillary contours and dendritic-shaped melanocytes (dermo-epidermal junction level); melanophages [dermis]).

When dealing with flat lesions on the face, it is important to perform a thorough differential diagnosis in order to avoid mistakes before laser treatments. Features that provide clues to a diagnosis of lentigo maligna include:

• The presence of blue-gray dots or circles around the hair follicle.
• RCM presence of dendritic cells around the hair follicle.
• The golden rule: “if you see grey don’t spray”.

The combination of OCT and RCM enables the repeated non-invasive observation of skin morphology in vivo at quasi-histologic resolution combining cytological and architectural information.