Sloan Letter Visual Acuity Charts and computer monitor pixilation

Purpose This research investigates how pixilation of computer monitors affects visual acuity measurement. Methods Stimuli were presented on a computer monitor as 8 lines of 5 Sloan letter optotypes in standard logarithmic progression format, ranging in size from -0.4 to 0.3 logMAR. Test distance was varied so that pixels on the monitor subtended different angles: 0.125, 0.200, 0.315, 0.50, 0.79, 1.25, 1.97 minutes of arc. Two pixel-sampling strategies were used: unfiltered sampling in which each pixel was rendered either black or white; or filtered sampling, in which pixel brightness was taken as the average letter brightness integrated across a pixel-sized aperture (i.e. grey-scale smoothing of letter edges). Binocular acuity was measured at each distance on 10 participants aged 19 to 38 years (mean 27.9 ± 7.0) using their best spectacle correction. Results Each observer’s logMAR acuity v log pixel size data was fitted with a broken line function, in which LogMAR acuity was described by a horizontal straight line below a critical pixel size (Pcrit) and by a linear relationship between acuity and pixel size above Pcrit. For small pixels sizes (below Pcrit), average asymptotic thresholds were a mean of -0.209 logMAR (SD 0.06) for the filtered letters, just slightly but significantly better than for the unfiltered letters with a mean -0.184 logMAR (SD 0.06) (t9 = 2.26, p = 0.050). Average Pcrit was significantly (p Conclusion For the purposes of visual acuity measurement, Sloan letters can be well rendered by relatively coarse sampling. Filtered letters (i.e. with grey-scale smoothed edges) can be rendered with much coarser (apparently sub-Nyquist) pixel sampling than unfiltered letters

Valores de normalidad en parámetros oculares en niños caucásicos españoles

Objetivo: cuantificar los parámetros biométricos oculares, las propiedades biomecánicas corneales, la configuración anatómica del nervio óptico y la capa de fibras nerviosas de la retina (CFNR) en un grupo de niños, mediante técnicas no invasivas. Material y métodos: se realizó un estudio transversal, descriptivo y no aleatorio en 293 niños sanos caucásicos con edades entre 6 y 17 años. Resultados: se encontró una correlación estadísticamente significativa entre la longitud axial (LA) y la histéresis corneal (CH) (p < 0,001). También se encontró disminución de la CH con el incremento de la miopía y el aumento de esta con el incremento de la hipermetropía (p < 0,001). En el segmento posterior, se evidenció correlación positiva entre el espesor medio de la CFNR y la CH (p = 0,01). Asimismo, se apreció disminución del espesor medio de la CFNR con el incremento de la LA (p < 0,001) y de la miopía (p < 0,0001). Conclusiones: la resistencia mecánica del segmento anterior del ojo está comprometida en miopes en edades tempranas y en miopías elevadas, independientemente de la edad. Valores más bajos de CH, además de una reducción en la capacidad de amortiguación viscoelástica corneal, indican la existencia de un nervio óptico más fácilmente deformable, acompañado de un adelgazamiento de la CFNR, sobre todo en niños miopes. Este estudio permite dar unos valores de normalidad de dichos parámetros y correlacionarlos con los errores refractivos

The effect of interrupted defocus on blur adaptation

YesPurpose - Blur adaptation occurs when an observer is exposed to continuous defocus. However, it is unclear whether adaptation requires constant defocus, or whether the effect can still be achieved when the adaptation period is interrupted by short periods of clear vision. Methods - The study included 12 emmetropes and 12 myopes. All observers wore full refractive correction throughout the experiment. 1D and 3D of myopic defocus was introduced using spherical convex lenses. An automated system was used to place the blurring lens before the RE for varying periods of blurred and clear vision during adaptation. Participants watched a DVD at 3 m during each 15 min trial. Visual acuity was measured using Test Chart 2000 before and after adaptation. Results - Blur adaptation occurs to varying degrees depending on the periods of incremental blur exposure. Significant improvements in defocused visual acuity occur with continuous blur, equal blur and clear periods, as well as for longer blur periods. However, longer clear periods showed reduced adaptation and this trial is significantly different to the other three trials for both defocus levels (p < 0.001). No refractive group differences were observed for neither 1D nor 3D defocus (p = 0.58 and p = 0.19 respectively). Conclusions - Intervening periods of clear vision cause minimal disruption to improvements in defocused visual acuity after adaptation, indicating that blur adaptation is a robust phenomenon. However, when the exposure to clear vision exceeds the defocused periods, adaptation is inhibited. This gives insight into the effects of real-world tasks on adaptation to blur.Ms Kiren A. Khan was supported by a School of Optometry and Vision Science PhD studentship

Human Vitamin B12 Absorption and Metabolism are Measured by Accelerator Mass Spectrometry Using Specifically Labeled 14C-Cobalamin

There is need for an improved test of human ability to assimilate dietary vitamin B{sub 12}. Assaying and understanding absorption and uptake of B{sub 12} is important because defects can lead to hematological and neurological complications. Accelerator mass spectrometry (AMS) is uniquely suited for assessing absorption and kinetics of {sup 14}C-labeled substances after oral ingestion because it is more sensitive than decay counting and can measure levels of carbon-14 ({sup 14}C) in microliter volumes of biological samples, with negligible exposure of subjects to radioactivity. The test we describe employs amounts of B{sub 12} in the range of normal dietary intake. The B{sub 12} used was quantitatively labeled with {sup 14}C at one particular atom of the DMB moiety by exploiting idiosyncrasies of Salmonellametabolism. In order to grow aerobically on ethanolamine, S. entericamust be provided with either pre-formed B{sub 12} or two of its precursors: cobinamide and dimethylbenzimidazole (DMB). When provided with {sup 14}C-DMB specifically labeled in the C2 position, cells produced {sup 14}C-B{sub 12} of high specific activity (2.1 GBq/mmol, 58 mCi/mmol) and no detectable dilution of label from endogenous DMB synthesis. In a human kinetic study, a physiological dose (1.5 mg, 2.2 KBq/59 nCi) of purified {sup 14}C-B{sub 12} was administered and showed plasma appearance and clearance curves consistent with the predicted behavior of the pure vitamin. This method opens new avenues for study of B{sub 12} assimilation

Freeze-dried strawberry powder improves lipid profile and lipid peroxidation in women with metabolic syndrome: baseline and post intervention effects

<p>Abstract</p> <p>Background</p> <p>Strawberry flavonoids are potent antioxidants and anti-inflammatory agents that have been shown to reduce cardiovascular disease risk factors in prospective cohort studies. Effects of strawberry supplementation on metabolic risk factors have not been studied in obese populations. We tested the hypothesis that freeze-dried strawberry powder (FSP) will lower fasting lipids and biomarkers of oxidative stress and inflammation at four weeks compared to baseline. We also tested the tolerability and safety of FSP in subjects with metabolic syndrome. FSP is a concentrated source of polyphenolic flavonoids, fiber and phytosterols.</p> <p>Methods</p> <p>Females (n = 16) with 3 features of metabolic syndrome (waist circumference >35 inches, triglycerides > 150 mg/dL, fasting glucose > 100 mg/dL and < 126 mg/dL, HDL <50 mg/dL, or blood pressure >130/85 mm Hg) were enrolled in the study. Subjects consumed two cups of the strawberry drink daily for four weeks. Each cup had 25 g FSP blended in water. Fasting blood draws, anthropometrics, dietary analyses, and blood pressure measurements were done at baseline and 4 weeks. Biomarkers of oxidative stress and inflammation were measured using ELISA techniques. Plasma ellagic acid was measured using HPLC-UV techniques.</p> <p>Results</p> <p>Total cholesterol and LDL-cholesterol levels were significantly lower at 4 weeks versus baseline (-5% and -6%, respectively, p < 0.05), as was lipid peroxidation in the form of malondialdehyde and hydroxynonenal (-14%, p < 0.01). Oxidized-LDL showed a decreasing trend at 4 weeks (p = 0.123). No effects were noted on markers of inflammation including C-reactive protein and adiponectin. A significant number of subjects (13/16) showed an increase in plasma ellagic acid at four weeks versus baseline, while no significant differences were noted in dietary intakes at four weeks versus baseline. Thus, short-term supplementation of freeze-dried strawberries appeared to exert hypocholesterolemic effects and decrease lipid peroxidation in women with metabolic syndrome.</p

Rehabilitation needs and activity limitations of adults with a visual impairment entering a low vision rehabilitation service in England

Purpose- To evaluate outcome measures of the Participation and Activity Inventory (PAI) in a sample of adults with acquired visual impairment entering vision rehabilitation. Both Priority Scores, indicating level of rehabilitative need, and Person Measures, indicating goal difficulty, were considered. Methods- Participants were newly registered adults with visual impairment within Leicestershire, United Kingdom. The importance and difficulty of 48 goals of the PAI were assessed, as were demographic factors, clinical visual function (visual acuity, contrast sensitivity, reading function) and psychosocial function (adjustment to visual loss, depression, anxiety and fear of falling). Priority scores were calculated as the product of importance and difficulty of each goal. All questionnaires were Rasch analysed, and person and item measures of perceived difficulty with goals were derived. Results- Sixty people (mean age ± S.D. = 75.8 ± 13.8 years) took part. PAI goals with greatest rehabilitative need were reading (6.82 ± 2.91), mobility outdoors (6.55 ± 3.92), mobility indoors within an unfamiliar environment (5.52 ± 3.93) and writing (5.27 ± 3.02). Greater rehabilitative need was associated with younger age (β = −0.46, p < 0.001), and with higher depressive symptomatology (β = 0.35, p < 0.01; model R2 34%). Goals with greatest difficulty were mending clothing (−1.95 ± 0.35 logits) and hobbies and crafts (−1.32 ± 0.23 logits). Greater difficulty was associated with higher depressive symptomatology (β = 0.39, p < 0.001), lower visual acuity (β = 0.42, p < 0.001) and lower adjustment of visual loss (β = 0.31, p < 0.01; model R2 53%). Conclusions- Key rehabilitation needs for adults at entry to services require both optical and non-optical interventions. As rehabilitative need was not associated with the level of visual impairment, eyecare professionals should not wait until the end of medical treatment before referral for support. Similarly, rehabilitative need was associated with younger age, indicating the importance to refer younger people with sight loss at an early stage. The use of structured assessment, such as the PAI, ensures goals that have an impact upon quality of life are specifically identified. Depression screening on entry to rehabilitation is relevant as it predicts both perceived difficulty and rehabilitative need