Morphological skin ageing criteria by multiphoton laser scanning tomography: non-invasive in vivo scoring of the dermal fibre network.

Background: Morphological changes in the dermal collagen and elastin fibre network are characteristic for skin ageing and for pathological skin conditions of the dermis.

Objectives: To characterize pathological and physiological conditions by multiphoton laser scanning tomography (MLT) in vivo, it is necessary to investigate and identify morphological alterations related to ageing.

Methods: In vivo MLT was used to image two-photon excited autofluorescence (AF) and second harmonics generation (SHG) in human dermis of 18 volunteers of different ages. Criteria for the evaluation of age-dependent morphological changes in MLT images were fibre tension and morphology, network pattern, clot formation and image homogeneity. These criteria were weighted and a score was calculated.

Results: The resulting MLT-based Dermis Morphology Score is correlated with age (R2 = -0.90) and with the previously published SHG to AF Ageing Index of Dermis (R2 = 0.66). The two groups of young (age 21-38) and old (age 66-84) volunteers showed a significant difference in MLT score values (P < 0.001).

Conclusions: We could demonstrate an in vivo relationship between morphological characteristics of human dermis assessed by MLT and age. The present score allows the semi-quantitative evaluation of specific morphological changes of the dermal fibre network in ageing skin by in vivo AF and SHG imaging. This method will be useful for diagnostics of pathological conditions and their differentiation from ageing effects.