Visual acuity in normal and diseased eyes using high-pass filtered optotypes

The most common clinical test of visual function is visual acuity (VA) measurement. Acuity tests have evolved slowly, incorporating chart design features aimed at improving measurement accuracy and minimising test variability. However, with current gold standard logMAR charts, measurements can still be affected by testing and scoring methods, possibly attributable to variations in relative legibility between conventional letters. This limits the test sensitivity and specificity in detecting a change in clinical status. Furthermore, conventional letter charts have demonstrated an insensitivity to early visual system neural deficits. High-pass filtered letters have a design in which low spatial frequencies, where conventional letters typically vary, are removed. Constructed with a dark core and light edges, the mean letter luminance matches their grey background. This results in similar detection and recognition thresholds with foveal viewing in normal subjects such that letters appear to vanish when the resolution threshold is reached. Under extra-foveal viewing, these thresholds are seen to separate, indicating the neural sampling limited nature of resolution. This thesis investigates the functional characteristics and limits to performance of high-pass filtered letters. In laboratory-based studies, high-pass VA thresholds were found to display lower between-letter threshold variability, be more robust to the number of alternative letter choices and more resistant to optical degradations including defocus and simulated lens ageing compared to conventional letters. When a novel high-pass chart, the Moorfields Acuity Chart, was employed in clinical studies, it displayed VA scores and variability less affected by termination and scoring rules in normal subjects with uncorrected refractive error, whilst better revealing functional loss in age-related macular degeneration (AMD). Thus, it appears that high-pass letters can be incorporated in a clinical test chart offering lower variability and in which recognition thresholds are better correlated with early neural deficits in AMD, in a task already familiar to patients

Management issues regarding e-commerce and the internet: 20 critical questions managers should ask before plunging into e-commerce!

The drivers for electronic commerce are both technological (under the tremendous pressure of innovation) and business oriented. The authors have found technological issues drive most industrialists, with the business drivers being vague. However both technology and business drivers should play an important part. As Cathy Benko (Deloitte consulting) had said, “for more than two centuries the industrial business model has used a single linear approach to change, predict what customers will want, design resources and organize people to serve those wants, then implement according to management’s plan and design. Today this model of Predict-design-implement is no longer viable- in fact, it is dead.” [ 11 This paper will identify managerial issues regarding ecommerce and the Internet. Chan and Swatmann [2] noted that management involvement is imperative for the success of electronic commerce implementation. The size and popularity of the lntemet have grown enormously during the past few years and continue to grow at phenomenal rates. The risk of entering ecommerce is many and it is important that the issues are understood. This paper has identified the issues, which need to be considered and 20 key questions, which need to be addressed before entering into ecommerce

The ethics of electronic monitoring within the workplace.

This paper shows that electronic monitoring of employees’ use of e-mail and the World Wide Web can be beneficial to a company and even to its employees. However, the use of monitoring and the resulting intrusion into personal privacy can also have adverse affects. Ideally, monitoring should only be used to increase the efficiency of the organisation. This would lead to a far-relaxed attitude to be monitored within the work place. It is difficult for companies to obtain the right balance between private and work-related Internet use. A solution to this problem is to contract an independent outside party to undertake the monitoring process. This paper suggests guidelines for establishing an agreed electronic monitoring policy which should enable increased productivity from better use of electronic facilities yet still be acceptable to employees. The greater acceptability of independent monitoring and the more relaxed atmosphere of a not too restrictive policy on email and Internet use will increase the overall company morale which, in turn, will produce a happier, more productive environment that will benefit both employees and managers alike

The Effect of Induced Intraocular Stray Light on Recognition Thresholds for Pseudo-High-Pass Filtered Letters

PURPOSE: The Moorfields Acuity Chart (MAC)—comprising pseudo-high-pass filtered “vanishing optotype” (VO) letters—is more sensitive to functional visual loss in age-related macular degeneration (AMD) compared to conventional letter charts. It is currently unknown the degree to which MAC acuity is affected by optical factors such as cataract. This is important to know when determining whether an individual's vision loss owes more to neural or optical factors. Here we estimate recognition acuity for VOs and conventional letters with simulated lens aging, achieved using different levels of induced intraocular light scatter. METHODS: Recognition thresholds were determined for two experienced and one naive participant with conventional and VO letters. Stimuli were presented either foveally or at 10 degrees in the horizontal temporal retina, under varying degrees of intraocular light scatter induced by white resin opacity-containing filters (WOFs grades 1 to 5). RESULTS: Foveal acuity only became significantly different from baseline (no filter) for WOF grade 5 with conventional letters and WOF grades 4 and 5 with VOs. In the periphery, no statistical difference was found for any stray-light level for both conventional and VOs. CONCLUSIONS: Recognition acuity measured with conventional and VOs is robust to the effects of simulated lens opacification, and thus its higher sensitivity to neural damage should not simultaneously be confounded by such optical factors. TRANSLATIONAL RELEVANCE: The MAC may be better able to differentiate between neural and optical deficits of visual performance, making it more suitable for the assessment of patients with AMD, who may display both types of functional visual loss

Vanishing Optotype acuity: repeatability and effect of the number of alternatives

Purpose:  Vanishing Optotype letters have a pseudo high-pass design so that the mean luminance of the target is the same as the background and the letters thus ‘vanish’ soon after the resolution threshold is reached. We wished to determine the variability of acuity measurements using these letters compared to conventional letters, and in particular how acuity is affected by the number of alternatives available to the subject. Methods:  Acuity was measured using high contrast letters of both conventional and Vanishing Optotype design for three experienced normal subjects. Thresholds were determined for central vision in a forced choice paradigm for two alternatives (2AFC; AU and OQ), 4AFC (AQUO), 6AFC (QUANGO) and 26AFC (whole alphabet) using a QUEST procedure. Three measurements were made for each condition. Results:  Threshold letter size was always larger for the Vanishing Optotypes than conventional letters, although the size of this difference (0.11–0.34 logMAR) depended on the number of alternatives and what they were. The effect of the number of AFC, and the individual letters employed, was smaller for the Vanishing Optotypes, implying that they are more equally legible than conventional optotypes. Variability was also lower for the Vanishing Optotype sets (0.01–0.03 logMAR) than the conventional letter sets (0.03–0.06). Conclusions:  The smaller effect of the number of letter alternatives, combined with more equal discriminability and lower threshold variability, implies that Vanishing Optotypes may be appropriate targets from which to design letter charts to measure small clinical changes in acuity

Relationship between psychophysical measures of retinal ganglion cell density and in vivo measures of cone density in glaucoma

Purpose: Considerable between-individual variation in retinal ganglion cell (RGC) density exists in healthy individuals, making identification of change from normal to glaucoma difficult. In ascertaining local cone-to-RGC density ratios in healthy individuals, we wished to investigate the usefulness of objective cone density estimates as a surrogate of baseline RGC density in glaucoma patients, and thus a more efficient way of identifying early changes. Design: Exploratory cohort study. Participants: Twenty glaucoma patients (60% women) with a median age of 54 years and mean deviation (MD) in the visual field of –5 dB and 20 healthy controls (70% women) with a median age of 57 years and a mean MD of 0 dB were included. Methods: Glaucoma patients and healthy participants underwent in vivo cone imaging at 4 locations of 8.8° eccentricity with a modified Heidelberg Retina Angiograph HRA2 (scan angle, 3°). Cones were counted using an automated program. Retinal ganglion cell density was estimated at the same test locations from peripheral grating resolution acuity thresholds. Main Outcome Measures: Retinal cone density, estimated RGC density, and cone-to-RGC ratios in glaucoma patients and healthy controls. Results: Median cone-to-RGC density was 3.51:1 (interquartile range [IQR], 2.59:1–6.81:1) in glaucoma patients compared with 2.35:1 (IQR, 1.83:1–2.82:1) in healthy participants. Retinal ganglion cell density was 33% lower in glaucoma patients than in healthy participants; however, cone density was very similar in glaucoma patients (7248 cells/mm2) and healthy controls (7242 cells/mm2). The area under the receiver operator characteristic curve was 0.79 (95% confidence interval [CI], 0.71–0.86) for both RGC density and cone-to-RGC ratio and 0.49 (95% CI, 0.39–0.58) for cone density. Conclusions: Local measurements of cone density do not differ significantly from normal in glaucoma patients despite large differences in RGC density. There was no statistically significant association between RGC density and cone density in the normal participants, and the range of cone-to-RGC density ratios was relatively large in healthy controls. These findings suggest that estimates of baseline RGC density from cone density are unlikely to be precise and offer little advantage over determination of RGC alone in the identification of early glaucomatous change