Ablative lasers such as Erbium:YAG and CO2 lasers have been successfully used for many years for the treatment of wrinkles. Following the ablation of epidermal and dermal skin layers, a wound healing process is initiated. Despite the good cosmetic outcome, this method is being used with decreasing frequency due to the risk of severe side effects and delayed wound healing. Alternative non-ablative laser methods have been developed that are less invasive, but also less effective. A new treatment method has been developed on the basis of a publication by D. Manstein et al. 2004, which propagated the idea of fractional photothermolysis, i.e. a method that does not involve the treatment of the entire skin surface, but of microscopically small areas surrounded by bridges of untreated skin. Such treatment can be carried out using both ablative and non-ablative lasers.

The goal of our study was to investigate the suitability of an Erbium:YAG handpiece for the fractional irradiation of wrinkles and scars.

1. Determination of parameters

Pre-investigations using different masks to separate the laser beam into extremely fine individual beams led to excellent results with a hole width of about 150 μm and a gutter width of 350 μm. Using photos, reflected light microscope analysis and optical coherence tomography (OCT), the effect of the laser was assessed on the forearms of two patients with a consistent fluence of 16 J/cm², but with a different number of pulses. A substance defect around 130 μm in diameter was observed, which, depending on the number of pulses used, reached a maximal depth of more than 300 μm when 8 succeeding pulses were applied (Fig. 1). More than 4 pulses resulted in the bleeding from the microdefects. The first signs of inflammation were observed after 7 hours.

Using 8 to 10 pulses, some crusty plaques in the area of the microdefects were still visible after two weeks. These are similar to the MEND (microscopic epidermal necrotic debris) resulting from the application of purely thermal fractional laser treatments. This refers to the transepidermal outward transfer of necrotic material from the skin.

Histological alterations at different points in time following laser treatment were investigated using human skin in a CAM model. With a fluence of 12 J/cm² and 12 repetitive pulses, tissue microdefects surrounded by a thermal necrosis zone that went as far down as the reticular dermis were visible after four to eight hours (Fig. 2a).

The basal cell layer of the keratinocytes was closed again after 24 hours. However, subepidermal fissures still remained visible after 48 hours (Fig. 2b).

2. Wrinkle treatment

Nine volunteers aged between 42 and 64 participated in a clinical study investigating the treatment of facial wrinkles. The volunteers were treated with a fluence of 12 J/cm² and a sequence of 12 ablative pulses. Treatment was repeated after five to seven weeks, and a control was carried out after an additional five to seven weeks. The surface relief of the treated skin areas was determined using fringe projection (PRIMOS system, GFM Messtechnik, Teltow). The measurement values were analysed using a MatLab (MathWorks Inc.) software modified by our "Measurement Technology" research group. The treated wrinkle was compared with a neighbouring untreated wrinkle in order to compensate the body's own fluctuations such as the degree of hydratisation of the skin.

The results depended on the localisation and depth of the wrinkles: the treatment of tiny wrinkles in the upper lip area led to a considerable reduction of the wrinkle depth in 3/3 volunteers. Two volunteers showed an improvement in wrinkles on the cheek. Low-grade improvements were achieved for a periorbital wrinkle and a wrinkle in the glabellar region. It was not possible to improve deeper marionette folds after two treatments. All volunteers rated the treatment as not very painful. Directly after treatment, all volunteers showed a reddening and swelling of the area which persisted for three days. In the eye area, crusts were visible for a period of five days. Infections and pigment alterations were not observed.

3. Scar treatment

Clinical investigations assessing the treatment of scars involved two volunteers who had suffered from hypotrophic scars for several years, one volunteer who had had a hypertrophic scar for two years and three volunteers with keloids. The volume of the scars in relation to the surrounding skin was determined using fringe projection. The thickness of the keloids was determined sonographically (10 MHz).

In the case of hypotrophic scars, a slight increase in the scar depth was observed after two laser treatments. The hypertrophic scar flattened, whereas the keloids did not alter after 2 to 3 laser treatments.

4. Discussion

These investigations show that fractional ablative Erbium:YAG laser treatment seems to be an effective tool for the treatment of fine wrinkles. The treatment did not appear to cause undue damage to the patients. Due to the quick re-epithelialisation, the risk of side effects was considerably reduced compared to extensively ablative methods. It was possible to carry out multiple treatments without any problem.

In terms of scar treatment, the non-ablative thermal mode of the Erbium:YAG laser (previous investigations) seems to be superior to fractional ablation.