Multiple processes mediate flicker sensitivity

AbstractBy systematically manipulating the luminance of a flickering spot and the area immediately surrounding it, we investigated why thresholds from flickering stimuli that cause a change in average luminance are elevated relative to those from stimuli with no luminance change. Threshold elevation resulted from local light adaptation and from temporal-frequency-specific interactions between the spot and its surround: at low frequencies, the contrast between the spot and the surround elevated thresholds, whereas at high frequencies, dark adaptation within the surround elevated thresholds. Our findings suggest that two common ways of determining temporal sensitivity may give markedly different outcomes

Effect of eccentricity on luminance-pedestal flicker thresholds

AbstractWe investigated the effect that spatially coincident luminance increments (luminance pedestals) have on flicker thresholds at several eccentricities and target sizes. Luminance pedestals elevated flicker amplitude-thresholds more when stimuli were presented eccentrically, both at low (4 Hz) and high (20 Hz) temporal frequencies. Altering the size of the eccentric stimulus failed to equate central and eccentric thresholds at all pedestal amplitudes. Comparisons with flicker thresholds at various background luminances suggests that the increase in luminance-pedestal flicker thresholds peripherally is due to increased suppressive rod–cone interactions, increased effectiveness of luminous contrast on edge-sensitive flicker mechanisms, as well as increased gain in the light adaptation response

An analysis of colour vision standards in the transport industry

© 1984 Dr. Algis Jonas VingrysColour vision standards were introduced by transport industries at the end of the nineteenth century. They have remained relatively unchanged since introduction, despite advances in transport technology and improved knowledge on the characteristics of human colour vision. No agreement exists on the precise level of rigour that standards should set, or if they are needed at all, which has led to an inconsistent diversity of standards used by many transport authorities. This thesis reports a critical analysis of the use of colour coding within the transport industry and concludes that colour still serves an important role in information transfer, despite an increasing reliance on electronic aids for navigation and communications. Disabilities suffered by colour defective observers identifying colour codes are also reviewed. Experimental studies reported in the literature show persons with abnormal colour vision are more likely to make colour confusions, have slower reaction times and reduced visual ranges to coloured signal lights. Accident statistics suggest certain colour defective groups may have a higher risk of accident than persons with normal colour vision. Thus it is concluded that standards of colour vision remain justified and should be retained, especially for operators of public transport vehicles. Experiments conducted and reported in this thesis consider problems specifically related to certain types of colour defective observer or the testing of colour vision. Protanomals and protanopes were found to have a similar reduction of visual range to deep red colours, even though protanomals possess a red-absorbing cone photopigment. Therefore protans should not be considered safe for employment where distant signals, especially red signals, must be recognized. The history of tests used for enforcement of colour vision standards is reviewed. Lantern tests, introduced in 1875, remain the principal test methods for the administration of colour vision standards. It is argued that lantern testing should continue because clinical tests poorly predict an observer's ability to recognize coloured signal lights. However, protanomals pass some lanterns and a clinical diagnosis should supplement these lantern tests to identify and reject protans. Ergonomic solutions, in the selection of colours, do not help colour defective observers reliably recognize a red-green-white colour code, even after allowing an extended practice trial at the recognition of these colours. Protanopes show least benefits from these engineering changes and give the worst performance. However, colour identification by other observer groups improves using a bluish-green or deeper red than the present orange limit recommended by the CIE. Finally, a rational approach is suggested for setting colour vision standards by transport authorities. This approach considers the variables of task demand, exposure, consequences of accident and community attitudes. It suggests international implementation of a set of equitable standards based upon these factors, rather than loosely or poorly defined standards that may be subject to various interpretations. Three classes of standard are recommended, namely, colour safe, colour normal and colour defective safe. These classes define the intent of the standard with each recommended fail criterion establishing the degree of difficulty set

Tear Interferon-Gamma as a Biomarker for Evaporative Dry Eye Disease

PURPOSE. To assess whether tear hyperosmolarity, being diagnostic of dry eye disease (DED), is associated with specific alterations to the cytokine content of human tears that may provide a biomarker for DED. METHODS. In this prospective, cross-sectional, clinical study, participants (n ¼ 77) were recruited from a single clinical site and categorized into groups based upon tear osmolarity status (n ¼ 62 hyperosmolar, n ¼ 15 normo-osmolar). Comprehensive anterior eye clinical assessments were undertaken. Concentrations of seven cytokines (IL-2, IL-4, IL-6, IL-10, IL-17A, IFN-c, and TNF-a) in basal tears were assayed using multiplex cytometric bead array. The main outcome measure was difference in cytokine concentration between groups. Group comparisons were undertaken using 2-tailed t-tests. Cohen's effect size was calculated for each finding. Spearman correlations between cytokine concentrations, clinical symptoms, and clinical parameters of DED were calculated. RESULTS. Tear hyperosmolarity was specifically associated with increased tear IFN-c levels (13.3 6 2.0 vs. 4.4 6 1.4 pg/mL, P ¼ 0.03). Cohen's effect size was large (0.8) for changes to tear IFN-c levels. Significant correlations were observed between IFN-c concentration and each of: tear osmolarity (r ¼ 0.34; P ¼ 0.007), total ocular surface staining (r ¼ 0.56, P < 0.0001), and Schirmer test score (r ¼ À0.33, P ¼ 0.003). CONCLUSIONS. Tear hyperosmolarity is specifically associated with higher levels of the proinflammatory cytokine IFN-c, which correlate with key clinical parameters of DED. The calculated effect size (0.8) suggests that this assay has diagnostic power as a biomarker for evaporative DED. Keywords: dry eye, diagnosis, cytokine, inflammation, osmolarity, tear, interferon-gamma T ear hyperosmolarity is a consequence of reduced lacrimal secretion and/or excessive tear evaporation, and is recognized to be a key pathogenic mechanism in dry eye disease (DED). 5 A diagnostic cut-off value of 316 mOsmol/L has been described to be highly specific for diagnosing clinically significant DED, yielding a sensitivity of 73% and a specificity of 90%. 8 In an animal model of ocular surface disease, tear hyperosmolarity resulted in conjunctival goblet cell death and tear film instability. 18-21 The aim of the study was to characterize tear composition in humans having hyperosmolar tears, to determine whether tear hyperosmolarity is associated with specific changes to tear cytokines that could be useful as a diagnostic clinical marker for DED