Effect of Surface Dissolution on Dislocation Activation in Stressed FeSi6.5 Steel.

The effects of surface dissolution on dislocation activation in FeSi6.5 steel are quantitatively studied by analyzing the stress relaxation data using the thermal activation theory of dislocation. The stressed FeSi6.5 steel sample in acid solutions (H2SO4 or HCl) exhibits a much higher rate of stress reduction with time compared with that in air or deionized water. As the stress relaxation time is prolonged to 20 min, the relaxation rates are 0.055 MPa·min-1 in water and 0.074, 0.1, 0.11 MPa·min-1 in H2SO4 solutions with pH 4, 3, and 2, respectively. In a NaCl solution, a slight increase in the relaxation rate compared with air was found. Higher acidity (lower pH) of the solution inducing higher stress relaxation rate implies the softening is associated with the anodic dissolution of the surface layer and the accelerated (additional) flow of dislocations. The analyses using the thermal activation theory of dislocation during relaxation reveal the mechanism for the accelerated plastic flow induced by the corrosive medium. The variations of these parameters are related to the relaxation of the stress field of dislocations and the weakening of interaction between slip dislocations and short-range obstacles. The chemomechanical effect, including a reduction in apparent activation energy and a decrease in waiting time for dislocation to obtain sufficient thermal activation energy to cross obstacles, causes an increase in the stress relaxation rate (plastic strain rate). The study confirms that surface dissolution accelerates the plastic flow of metals and supports the view that surface dissolution facilitates dislocation slip. It is helpful to improve the formability of brittle metals.

Comment on "Surface elastic constants of a soft solid" by Q. Xu, R. W. Style and E. R. Dufresne, Soft Matter, 2018, 14, 916.

The commented article represents one of the attempts to use the Shuttleworth equation for predicting surface stresses in a soft material. However, this led to the definition of surface stress in terms of the total surface energy instead of the density of this energy. This contradicts the theory of elasticity and is the result of mathematical defects made in the derivation of the above equation.

Driving behaviour and visual compensation in glaucoma patients: Evaluation on a driving simulator.

BACKGROUND: To assess the driving performance and both the visual scanning and driving compensations of glaucoma patients. METHODS: In this case-control pilot study, the driving behaviour and performance of 14 patients with glaucoma and nine healthy age- and sex-similar control subjects were compared in a fixed-base driving simulator. All subjects performed in four scenarios with one to two hazardous situations on urban streets, for a total of five hazards. Measurements taken during the tests included reaction times, longitudinal regulation, lateral control and eye and head movements. RESULTS: Glaucoma patients showed poor driving performance with longer reaction time to hazardous situations than control subjects: pedestrians crossing the road from the left (p < 0.022) or from the right (p = 0.013), and vehicles coming from the left (p = 0.002). Their mean duration of lateral excursion was longer (p = 0.045), and they showed more lane excursions in a wide left curve (p = 0.045). Glaucoma patients also showed a higher standard deviation of time-headway (p = 0.048) with preceding vehicles. Analyses of driving behavioural compensations on curved roads showed that glaucoma patients stayed closer to the centre line in large (p = 0.006) and small (p = 0.025) left curves and on small right curves (p = 0.041). Additionally, on straight roads, as compared to control subjects, glaucoma patients showed longer mean time-headway (p = 0.032) and lower mean speed (p = 0.04). Finally, the glaucoma group exhibited a larger standard deviation of horizontal gaze (p = 0.034) than the control subjects. CONCLUSIONS: In a virtual driving environment, glaucoma patients exhibited unsafe driving behaviours, despite their driving and eye-scanning compensations.

Partial recovery of visual function in a blind patient after optogenetic therapy.

Optogenetics may enable mutation-independent, circuit-specific restoration of neuronal function in neurological diseases. Retinitis pigmentosa is a neurodegenerative eye disease where loss of photoreceptors can lead to complete blindness. In a blind patient, we combined intraocular injection of an adeno-associated viral vector encoding ChrimsonR with light stimulation via engineered goggles. The goggles detect local changes in light intensity and project corresponding light pulses onto the retina in real time to activate optogenetically transduced retinal ganglion cells. The patient perceived, located, counted and touched different objects using the vector-treated eye alone while wearing the goggles. During visual perception, multichannel electroencephalographic recordings revealed object-related activity above the visual cortex. The patient could not visually detect any objects before injection with or without the goggles or after injection without the goggles. This is the first reported case of partial functional recovery in a neurodegenerative disease after optogenetic therapy.

Assessing Photoreceptor Status in Retinal Dystrophies: From High-Resolution Imaging to Functional Vision.

PURPOSE: To describe the value of integrating phenotype/genotype data, disease staging, and evaluation of functional vision in patient-centered management of retinal dystrophies. METHODS: (1) Cross-sectional structure-function and retrospective longitudinal studies to assess the correlations between standard fundus autofluorescence (FAF), optical coherence tomography, visual acuity (VA), and perimetry (visual field [VF]) examinations to evaluate photoreceptor functional loss in a cohort of patients with rod-cone dystrophy (RCD); (2) flood-illumination adaptive optics (FIAO) imaging focusing on photoreceptor misalignment and orientation of outer segments; and (3) evaluation of the impact of visual impairment in daily life activities, based on functional (visual and mobility) vision assessment in a naturalistic environment in visually impaired subjects with RCD and subjects treated with LuxturnaⓇ for RPE65-related Leber congenital amaurosis before and after therapy. RESULTS: The results of the cross-sectional transversal study showed that (1) VA and macular sensitivity were weakly correlated with the structural variables; and (2) functional impairment (VF) was correlated with reduction of anatomical markers of photoreceptor structure and increased width of autofluorescent ring. The dimensions of the ring of increased FAF evolved faster. Other criteria that differed among groups were the lengths of the ellipsoid zone, the external limiting membrane, and the foveal thickness. FIAO revealed a variety of phenotypes: paradoxical visibility of foveal cones; heterogeneous brightness of cones; dim, inner segment-like, and RPE-like mosaic. Directional illumination by varying orientation of incident light (Stiles-Crawford effect) and the amount of side illumination (gaze-dependent imaging) affected photoreceptor visibility. Mobility assessment under different lighting conditions showed correlation with VF, VA, contrast sensitivity (CS), and dark adaptation, with different predictive values depending on mobility study paradigms and illumination level. At high illumination level (235 lux), VF was a predictor for all mobility performance models. Under low illumination (1 and 2 lux), VF was the most significant predictor of mobility performance variables, while CS best explained the number of collisions and segments. In subjects treated with LuxturnaⓇ, a very favorable impact on travel speed and reduction in the number of collisions, especially at low luminance, was observable 6 months following injection, in both children and adults. CONCLUSIONS: Our results suggest the benefit of development and implementation of quantitative and reproducible tools to evaluate the status of photoreceptors and the impact of both visual impairment and novel therapies in real-life conditions. NOTE: Publication of this article is sponsored by the American Ophthalmological Society.

Correlations Between Subjective Evaluation of Quality of Life, Visual Field Loss, and Performance in Simulated Activities of Daily Living in Glaucoma Patients.

PRECIS: Glaucoma patients displayed alterations in their quality of life (QoL) and their ability to perform activities of daily living. The visual field (VF) of the worse eye might serve as a good marker for QoL evaluation. PURPOSE: The purpose of this study was to explore the correlations between VF defects, performance in simulated activities of daily living, and subjective evaluation of QoL in glaucoma patients. METHODS: Thirty-two patients with glaucoma and 10 age-matched control subjects were included. All participants answered a QoL questionnaire and underwent an assessment of visual function including monocular and binocular best-corrected visual acuity, binocular contrast sensitivity test (LogCS), and monocular and binocular VF. All subjects also carried out a series of simulated activities of daily living in a controlled environment. RESULTS: Glaucoma patients had lower QoL scores compared with controls for the composite score, near and distance activities, social functioning, mental health, role difficulties, dependency, and color vision. With regard to performance in the simulated mobility task, the number of mobility incidents was higher for glaucoma patients than for control subjects. For the reaching and grasping tasks, the overall movement duration for small objects was significantly longer in glaucoma patients compared with controls. The VF mean deviation of the worse eye was correlated with most of the QoL subscores. Mobility incidents as well as the reaching and grasping task parameters were not significantly correlated with QoL scores. CONCLUSIONS: Glaucoma patients showed an alteration of performance in simulated daily living activities, associated with a decreased QoL. There was no clear correlation between alterations in QoL and ability to perform activities of daily living. The QoL related to vision was mostly correlated to the visual function of the worse eye.

Correlation Between Visual Function and Performance of Simulated Daily Living Activities in Glaucomatous Patients.

PURPOSE: To analyze the correlations between functional clinical tests and the performance of glaucoma patients in simulated daily living activities. PATIENTS AND METHODS: Thirty-two patients with chronic glaucoma, followed at the Quinze-Vingts National Ophthalmology Hospital, were included. All patients had a clinical evaluation of visual function including best-corrected visual acuity, contrast sensitivity, and monocular and binocular visual field (VF) tests. Four different simulated activities of daily living were evaluated in standardized artificial platforms (StreetLab and HomeLab): "mobility" and an obstacle avoidance task in an artificial street, "reaching and grasping" large and small objects on a kitchen work surface, "localization of people" and "face orientation recognition." Patient performance in the different tasks was correlated with VF evaluation including integrated binocular visual field (IVF), VF mean deviation (MD) of the better and the worse eye, Esterman binocular VF, best-corrected visual acuity, and contrast sensitivity. RESULTS: The IVF score was significantly correlated with "localization of people" time (r=0.49; P=0.003), "face orientation recognition" time (r=0.50; P=0.002), and "movement onset" for reaching and grasping small objects (r=0.38; P=0.029). The MD of the better eye appeared significantly correlated with "face orientation recognition" time (r=-0.44; P=0.009) and "localization of people" time (r=-0.46; P=0.005). The Esterman score appeared significantly correlated with "mobility time" (r=-0.40; P=0.018), "localization of people" (r=-0.37; P=0.030), "face orientation recognition" times (r=-0.39; P=0.024), and "movement onset" for reaching and grasping large objects (r=-0.43; P=0.015). CONCLUSIONS: The IVF score and the MD of the better eye appeared to better evaluate "reaching and grasping," "face orientation recognition," and "localization of people" simulated tasks, whereas for the "mobility" task, the Esterman VF seemed more useful. The precise evaluation of the glaucoma patient's ability to perform everyday life tasks is complex and may require both monocular and binocular VF tests.

Phototoxic action spectrum on a retinal pigment epithelium model of age-related macular degeneration exposed to sunlight normalized conditions.

Among the identified risk factors of age-related macular degeneration, sunlight is known to induce cumulative damage to the retina. A photosensitive derivative of the visual pigment, N-retinylidene-N-retinylethanolamine (A2E), may be involved in this phototoxicity. The high energy visible light between 380 nm and 500 nm (blue light) is incriminated. Our aim was to define the most toxic wavelengths in the blue-green range on an in vitro model of the disease. Primary cultures of porcine retinal pigment epithelium cells were incubated for 6 hours with different A2E concentrations and exposed for 18 hours to 10 nm illumination bands centered from 380 to 520 nm in 10 nm increments. Light irradiances were normalized with respect to the natural sunlight reaching the retina. Six hours after light exposure, cell viability, necrosis and apoptosis were assessed using the Apotox-Glo Triplex™ assay. Retinal pigment epithelium cells incubated with A2E displayed fluorescent bodies within the cytoplasm. Their absorption and emission spectra were similar to those of A2E. Exposure to 10 nm illumination bands induced a loss in cell viability with a dose dependence upon A2E concentrations. Irrespective of A2E concentration, the loss of cell viability was maximal for wavelengths from 415 to 455 nm. Cell viability decrease was correlated to an increase in cell apoptosis indicated by caspase-3/7 activities in the same spectral range. No light-elicited necrosis was measured as compared to control cells maintained in darkness. Our results defined the precise spectrum of light retinal toxicity in physiological irradiance conditions on an in vitro model of age-related macular degeneration. Surprisingly, a narrow bandwidth in blue light generated the greatest phototoxic risk to retinal pigment epithelium cells. This phototoxic spectrum may be advantageously valued in designing selective photoprotection ophthalmic filters, without disrupting essential visual and non-visual functions of the eye.