A new approach for quantifying epithelial and stromal thickness changes after orthokeratology contact lens wear

The aim of the study was to develop an automatic segmentation approach to optical coherence tomography (OCT) images and to investigate the changes in epithelial and stromal thickness profile and radius of curvature after the use of orthokeratology (Ortho-K) contact lenses. A total of 45 right eyes from 52 participants were monitored before, and after one month of, uninterrupted overnight Ortho-K lens wear. The tomography of their right eyes was obtained using optical OCT and rotating Scheimpflug imaging (OCULUS Pentacam). A custom-built MATLAB code for automatic segmentation of corneal OCT images was created and used to assess changes in epithelial thickness, stromal thickness, corneal and stromal profiles and radii of curvature before, and after one month of, uninterrupted overnight wear of Ortho-K lenses. In the central area (0–2 mm diameter), the epithelium thinned by 12.8 ± 6.0 µm (23.8% on average, p < 0.01) after one month of Ortho-K lens wear. In the paracentral area (2–5 mm diameter), the epithelium thinned nasally and temporally (by 2.4 ± 5.9 µm, 4.5% on average, p = 0.031). The stroma thickness increased in the central area (by 4.8 ± 16.1 µm, p = 0.005). The radius of curvature of the central corneal anterior surface increased by 0.24 ± 0.26 mm (3.1%, p < 0.01) along the horizontal meridian and by 0.34 ± 0.18 mm (4.2%, p < 0.01) along the vertical meridian. There were no significant changes in the anterior and posterior stromal radius of curvature. This study introduced a new method to automatically detect the anterior corneal surface, the epithelial posterior surface and the posterior corneal surface in OCT scans. Overnight wear of Ortho-K lenses caused thinning of the central corneal epithelium. The anterior corneal surface became flattered while the anterior and posterior surfaces of the stroma did not undergo significant changes. The results are consistent with the changes reported in previous studies. The reduction in myopic refractive error caused by Ortho-K lens wear was mainly due to changes in corneal epithelium thickness profile.

Conformality of atomic layer deposition in microchannels: impact of process parameters on the simulated thickness profile

Unparalleled conformality is driving ever new applications for atomic layer deposition (ALD), a thin film growth method based on repeated self-terminating gas-solid reactions. In this work, we re-implemented a diffusion-reaction model from the literature to simulate the propagation of film growth in wide microchannels and used that model to explore trends in both the thickness profile as a function of process parameters and different diffusion regimes. In the model, partial pressure of ALD reactant was analytically approximated. Simulations were made as function of kinetic and process parameters such as temperature, (lumped) sticking coefficient, molar mass of the ALD reactant, reactant’s exposure time and pressure, total pressure, density of the grown material, and growth per cycle (GPC) of the ALD process. Increasing the molar mass and the GPC, for example, resulted in a decreasing penetration depth into the microchannel. The influence of the mass and size of the inert gas molecules on the thickness profile depended on the diffusion regime (free molecular flow vs. transition flow). The modelling was compared to a recent slope method to extract the sticking coefficient. The slope method gave systematically somewhat higher sticking coefficient values compared to the input sticking coefficient values; potential reasons behind the observed differences are discussed.

Mathematical formulation of the film thickness in a multi-pad externally adjustable hydrodynamic bearing using the transformation technique

Instability problem of a hydrodynamic plain journal bearing at higher speeds is conventionally resolved by using the non-circular bearings. High speed precision rotating shafts demands accurate positioning of the journal centres. A multi-pad adjustable bearing is a non-circular bearing, provides a fine-tuning option of the journal centre by continuously changing the bearing profile. In the present study, the bearing has a configuration of four bearing pads that are adjustable both in the radial and tilt directions. The fluid film thickness profile is conventionally obtained using the trigonometric relations, which has computational limitations, especially in multi-pad adjustable bearings. In this investigation, the film thickness profile of a multi-pad adjustable bearing is mathematically formulated using the transformation technique. The results obtained are compared with those available in the literature for a similar bearing. The observation shows that transformation technique eliminates the projection approximation error present in the conventional technique.

Secondary instability in thin film flows under an inclined plane: growth of lenses on spatially developing rivulets

The response of a thin film flowing under an inclined plane, modelled using the lubrication equation, is studied. The flow at the inlet is perturbed by the superimposition of a spanwise-periodic steady modulation and a decoupled temporally periodic but spatially homogeneous perturbation. As the consequence of the spanwise inlet forcing, the so-called rivulets grow downstream and eventually reach a streamwise-invariant state, modulated along the direction perpendicular to the flow. The linearized dynamics in the presence of a time-harmonic inlet forcing shows the emergence of a time-periodic flow characterized by drop-like structures (so-called lenses) that travel on the rivulet. The spatial evolution is rationalized by a weakly non-parallel stability analysis. The occurrence of the lenses, their spacing and thickness profile, is controlled by the inclination angle, flow rate, and the frequency and amplitude of the time-harmonic inlet forcing. The faithfulness of the linear analyses is verified by nonlinear simulations. The results of the linear simulations with inlet forcing are combined with the computations of nonlinear travelling lenses solutions in a double-periodic domain to obtain an estimate of the dripping length, for a large range of conditions.

Cortical and Subcortical Neuroanatomical Signatures of Schizotypy in 3,004 Individuals Assessed in a Worldwide ENIGMA Study

Neuroanatomical abnormalities have been reported along a continuum from at-risk stages, including high schizotypy, to early and chronic psychosis. However, a comprehensive neuroanatomical mapping of schizotypy remains to be established. The authors conducted the first large-scale meta-analyses of cortical and subcortical morphometric patterns of schizotypy in healthy individuals, and compared these patterns with neuroanatomical abnormalities observed in major psychiatric disorders. The sample comprised 3,004 unmedicated healthy individuals (12-68 years, 46.5% male) from 29 cohorts of the worldwide ENIGMA Schizotypy working group. Cortical and subcortical effect size maps with schizotypy scores were generated using standardized methods. Pattern similarities were assessed between the schizotypy-related cortical and subcortical maps and effect size maps from comparisons of schizophrenia (SZ), bipolar disorder (BD) and major depression (MDD) patients with controls. Thicker right medial orbitofrontal/ventromedial prefrontal cortex (mOFC/vmPFC) was associated with higher schizotypy scores (r=.07, pFDR=.02). The cortical thickness profile in schizotypy was positively correlated with cortical abnormalities in SZ (r=.33, pspin=.01), but not BD (r=.19, pspin=.16) or MDD (r=-.22, pspin=.10). The schizotypy-related subcortical volume pattern was negatively correlated with subcortical abnormalities in SZ (rho=-.65, pspin=.01), BD (rho=-.63, pspin=.01), and MDD (rho=-.69, pspin=.004). Comprehensive mapping of schizotypy-related brain morphometry in the general population revealed a significant relationship between higher schizotypy and thicker mOFC/vmPFC, in the absence of confounding effects due to antipsychotic medication or disease chronicity. The cortical pattern similarity between schizotypy and schizophrenia yields new insights into a dimensional neurobiological continuity across the extended psychosis phenotype.

Corneal epithelial map after Photorefractive Keratectomy with and without mitomycin-C

Purpose: To compare epithelial thickness before and after photorefractive keratectomy (PRK) with and without mitomycin-C (MMC).Methods: Forty eyes treated with PRK for low myopia (less than -4.00 D) and low astigmatism (less than -2.00) were included in this interventional case series. The right eye of each patient assigned to receive intraoperative topical MMC% 0.02 for 15 to 30 seconds and other eye received equally balanced salt solution (control group). Epithelial thickness profile was analyzed before and 6 months postoperatively.Results: Epithelial thickness map was analyzed in superior and inferior of the cornea within central 7 mm diameter. Maximum and minimum thickness was measured and the data were compared before and after PRK. The Superior, the inferior and the maximum epithelial thickness were significantly increased after surgery in both groups (p<0.05). There was no significant difference in epithelial thickness profile between case and control group at baseline and 6-month post PRK. Final distance corrected visual acuity was similar in two groups. No case of corneal haze was observed during 6 months follow up visits.Conclusion: Intraoperative MMC% 0.02 in PRK for low myopia patients did not change the epithelial thickness profile and refractive results, when compared with matched control eyes in 6 months follow up. It seems that MMC doesn’t have a statistically significant impact in epithelial remodeling based on this data set.