Electromechanical reshaping (EMR) has the potential to change corneal shape to correct refractive errors without altering the mechanical properties of the cornea. Using acoustic radiation force (ARF) to stimulate the cornea of ex vivo New Zealand white rabbit globes and optical coherence elastography (OCE) to detect corneal response, the cornea’s elasticity was quantitatively determined pre- and post-EMR treatment. In addition, an optical coherence tomography (OCT) system was used to determine changes in corneal curvature. Ultimately, EMR treatment induced a shape change in the cornea and the elasticity of the cornea was similar before and after EMR treatment, indicating minimal damage.
Absorption of light by epidermal melanin can confound light-based measurements of tissue oxygenation, reducing the ability of these technologies to reliably identify hypoxia. Spatial frequency domain imaging (SFDI) may help address this critical concern, because the different spatial frequencies of light penetrate different depths into the tissue, facilitating separation between contributions of different tissue layers to the detected signal. Here, we rigorously investigate the relationship between the skin tone of healthy subjects and the tissue oxygen saturation (StO2) measured with multispectral SFDI. This study helps to quantify the degree to which skin tone influences SFDI measurements of tissue oxygenation.
Spatial Frequency Domain Imaging (SFDI) is a non-invasive diffuse optical imaging technology that quantifies tissue optical properties by projecting spatially modulated light onto a region of interest. By detecting and fitting the diffuse reflectance to a light transport model, tissue absorption (μa) and scattering (μs') coefficients are calculated. However, when measuring skin, bulk μa and μs' from a homogeneous light transport model may not correspond with the actual properties of individual skin layers, especially for highly pigmented skin. To obtain physiologically accurate skin optical property values, we propose an iterative method based on a two- layered Monte Carlo model. We initially assume that μs' in darker skin is the same as that in lighter skin, and set the epidermal a as the free parameter when fitting the diffuse reflectance. To test this algorithm, we analyzed data from the forearms of 6 subjects having various levels of pigmentation, at 8 visible-to-near-infrared wavelengths. We compared the measured reflectance to both the homogeneous model and our layered model to quantify fit accuracy. At 471 nm and 526 nm for patients of Fitzpatrick skin types IV-VI (relatively dark skin), the two-layered model provided a 10-20% improvement in fit to the AC reflectance as a function of spatial frequency, compared to the homogeneous model. These improved fits yielded epidermal absorption coefficients that were notably higher than the bulk μa from the homogeneous model. Fitting the extracted epidermal μa to a melanin extinction spectrum1 enabled estimation of the melanin concentration in the epidermis.
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