Egbert Lenderink

Characterization of age-related effects in human skin: A comparative study that applies confocal laser scanning microscopy and optical coherence tomography.

Skin structure and age-related changes in human skin were characterized in vivo by applying confocal laser scanning microscopy (CLSM) and optical coherence tomography (OCT). The overall effect of aging skin, derived from studies of volunteers belonging to two age groups, was found to be a significant decrease in the maximum thickness of the epidermis and flattening of the dermo-epidermal junction. At a certain depth in the dermis, well below the basal layer, a reflecting layer of fibrous structure is observed in CLSM images. The location of this layer strongly depends on age and is situated much deeper below the skin surface in younger than in older skin. In addition, large structural changes were observed with age. The OCT images show two bright reflecting layers. The first one is due to scattering at the skin surface. The second band appears to be caused by a layer of fibrous structure in the dermis. Direct comparison of CLSM and OCT suggests that the same fibrous layer is imaged by the two techniques. This layer might be due to the transition between the papillary and reticular dermis. A comparison of CLSM and OCT enables a better understanding of the images.

Optical Coherence Tomography

Dr Sebasiten Wolf describes how SD-OCT has improved the visualization of intraretinal morphologic feaures both quantatively and qualatively.

In vivo measurements of epidermal thickness with optical coherence tomography and confocal laser scanning microscopy: a comparison of methods

Two noninvasive optical techniques, optical coherence tomography (OCT) and confocal laser scanning microscopy (CLSM) were used to measure the thickness of the epidermis of volunteers. It was found that due to their different resolution and penetration behavior, these two techniques are sensitive to different markers of the epidermal-dermal boundary. In CLSM, the tops of the dermal papillae are clearly and individually visible, whereas in OCT the fibrous structures immediately below the basal cell layer show up most clearly. Image segmentation algorithms were devised for automatic epidermal thickness determination. Both techniques were applied in a study into the effects of ultraviolet irradiation on the thickness of the epidermis. After exposure to a cumulative does of 15.7 (+/- 1.0) personal minimal erythema doses over three weeks, the changes were so small that only CLSM was able to discern them, due to its superior resolution. On average, it was found that the epidermis increases in thickness by 3 micrometers (p=0.011), which could be attributed entirely to a thickening of the stratum corneum.

Optimization, sensitivity analysis, and robust design using response surface modeling

Response surface modeling (RSM) is described as a tool to perform optimizations and sensitivity analysis in optical modeling. With this method, the behavior of the system is first mapped out using a limited set of ray-tracing simulations, carefully spanning the full parameter space. This can already be done before the full merit function is known. The relation between design parameters and system performance is then approximated by fitting the simulation results to functional forms. All subsequent optimizations are then performed very time-efficiently on the functional descriptions of the dependencies. This contrasts with direct optimization, where the computationally intensive optical modeling is in the loop of the optimization algorithm, and where changes in merit function, mapping out trade-offs, and determining sensitivities, are very time consuming. The paper will discuss the advantages of RSM with respect to direct optimization and give recommendations for the type of problems that are preferentially addressed by RSM. The method will be illustrated by a case: how optical simulations were used in the design of LumiramicTM phosphor conversion components for LEDs.

In vivo imaging of human skin: a comparison of optical coherence tomography and confocal laser scanning microscopy

Optical coherence tomography (OCT) and confocal laser scanning microscopy (CLSM) were applied to characterize non-invasively and in vivo the upper layers of human skin on the back of the hand. The techniques enable a detailed determination of the thickness and location of various skin layers in the epidermis and superficial dermis. Due to differences in spatial resolution and penetration depth of these methods, OCT and CLSM give complementary information on the composition and structure of skin. OCT signals of the back of the hand show three reflecting layers at different depth in the skin. A direct comparison with CLSM enables the assignment of these layers: the first one is due to the reflection at the skin surface, the second one appears to be caused by the reflection at the basal epidermal layer and the third layer can be ascribed to reflection at fibrous structure in the upper dermis. A comparison of methods reveals a consistent interpretation of the images.