Biomedical subjects

A J Vingrys

Publications and source records attributed to A J Vingrys.

At least 19 recordsLinked to original sources

PubMed1997

The effect of an interrupted daily period of normal visual stimulation on form deprivation myopia in chicks.

The aim of this study was to determine whether an integrator of neural activity influences the amount of myopia and axial elongation resulting from deprivation of form vision. The effects on ocular parameters of a continuous period of 30 min per day of normal vision was compared to two exposures of 15 min duration each, or three exposures of 10 min each. For the remaining time, chicks had monocular translucent occlusion in a 12 hr light/12 hr dark diurnal cycle, for either 2 or 3 weeks. Fellow eyes and the eyes of bilaterally unoccluded chicks were used as controls. We found that several short periods of normal visual stimulation per day were more effective in preventing the development of form deprivation myopia and axial elongation than was one single period of the same total duration, after both 2 and 3 weeks of treatment. This study suggests that the level of neural activity in the retina may have a cumulative effect in influencing ocular growth.

Animals↗

PubMed1996

The effect of docosahexaenoic acid on the electroretinogram of the guinea pig.

Docosahexaenoic acid (DHA), an n-3 polyunsaturated fatty acid, is found in consistently high concentrations in the retinae of mammals, yet its role in vision remains unclear. In this study, a mammalian model of variable retinal DHA concentration has been developed, such that the retinal phospholipids of guinea pigs contained between 2.5 and 30.8% DHA. Visual function was assessed using full-field flash electroretinography, over a range of exposure levels spanning six log units. Trend analysis indicated that retinal function was altered by the tissue DHA level, and was described by a second-order polynomial "inverted U-shaped" function. The results suggested that although some amount of DHA is essential for normal retinal function, increases in the DHA level past an optimal amount, found to be 19%, provided diminishing returns. In this study, manipulation of the retinal DHA level accounted for 21-35% of the electroretinographic variability.

Animals↗

PubMed1996

Normal saturation processing provides a model for understanding the effects of disease on color perception.

Saturation discrimination has been reported to be affected early in the course of a disease. Our empirical data show a compressive curvi-linear relationship between opponent/nonopponent channel activity and saturation thresholds in normal trichromatic observers. This relationship can be explained by a model based on the Hurvich and Jameson saturation coefficient (1957), Psychology Reviews, 64, 384-404. The model considers effects of both selective and nonselective channel losses on saturation processing based on the assumption that disease produces elevated thresholds while maintaining normal psychometric response functions. Both the model and data support clinical observations of saturation losses occurring early in disease. However, the results also indicate that saturation may not be the best modality for monitoring long-term progression of such conditions. We suggest that the different processing characteristics for blue-yellow thresholds may yield added information for saturation testing under some circumstances and that saturation processing occurs at a higher cortical level.

Adult↗

PubMed1996

Effect of dietary n-3 deficiency on the electroretinogram in the guinea pig.

Despite the abundance of n-3 polyunsaturated fatty acids, particularly docosahexaenoic acid (DHA), in the retina of all mammals, their role in vision remains unclear. However, the widely accepted notion that DHA is universally important in the retinal function was questioned in an earlier study (see text) involving guinea pigs, completely depleted of retinal DHA. The purpose of this study was to replicate this mammalian model of such deficiency and to determine any abnormalities in the electroretinogram. Guinea pigs were raised through three generations on 1 of 2 semipurified diets, containing different amounts of n-3 fatty acids, as determined by the supplementary oil which was the sole source of lipid in each diet. The added oils were safflower oil (n-6/n-3 = 72.0) or canola oil (n-6/n-3 = 2.5). Comprehensive electroretinographic assessment was conducted on guinea pigs, aged 6-9 weeks (safflower n = 13, canola n = 12), and retinae were extracted and the phospholipid fatty acid profile analyzed. Phospholipid fatty acid analysis revealed significant DHA deficiency (p < 0.001) in guinea pigs reared on the safflower oil diet (retinal DHA 2.5%) as compared with the canola oil group (retinal DHA 21.0%). Analysis of the electroretinogram showed significant reductions (p < 0.003) in both peak-to-peak and a-waves of safflower oil fed animals.

Animals↗

PubMed1995

Dietary manipulation of long-chain polyunsaturated fatty acids in the retina and brain of guinea pigs.

High levels of n-6 docosapentaenoic acid (22:5n-6) have been reported in the retina of guinea pigs fed commercially-prepared gain-based rations (commercial diet). In rats and monkeys, high levels of 22:5n-6 are an indicator of n-3 polyunsaturated fatty acid (PUFA) deficiency. We have examined the fatty acid composition of the retina and brain in guinea pigs fed a commercial diet or one of three semi-purified diets containing three different levels of n-3 PUFA. The diets comprised a diet deficient in n-3 PUFA (semi-purified diet containing safflower oil), two diets containing alpha-linolenic acid (standard commercial laboratory diet and semi-purified diet containing canola oil), and a diet containing alpha-linolenic acid, eicosapentaenoic acid, and docosahexaenoic acid (DHA) (semi-purified diet containing canola oil, safflower oil, and fish oil). Two groups of guinea pigs were given the diets from day 1 to 4 wk or day 1 to 8 wk, when they were sacrificed and the retinal tissues were extracted and analyzed for PUFA content by gas-liquid chromatography. Fatty acid analyses of the retinal phospholipids of the four-week-old animals revealed that the group fed DHA (from the fish oil) had the highest level of DHA (32%), compared with values of 19 and 13% for the groups fed canola oil diet and commercial diet, respectively, and 2% for the group fed the diet deficient in n-3 PUFA.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1995

The duration of normal visual exposure necessary to prevent form deprivation myopia in chicks.

The aim of this study was to determine the minimum daily period of exposure to normal visual stimulation required to prevent occlusion induced myopia in chicks. Chicks were treated with monocular translucent occlusion in a 12 hr light/12 hr dark cycle. Occluders were removed for 0 (constant occlusion), 15, 20, 30, 40, 60, 75, 90, 120, 150, 240 or 720 (no occlusion) minutes each day for either 2 or 3 weeks. Fellow eyes and the eyes of normal chicks (bilaterally unoccluded) were used as controls. Occlusion-induced myopia and axial elongation were found to decrease significantly (P < 0.01) with increasing daily exposure to normal visual stimulation. Application of a time series equation to the data estimates that 30 and 130 min of normal visual exposure per day reduces myopia by 50 and 95% respectively. This study demonstrated that the regulation of ocular growth is affected strongly by short periods of normal visual stimulation in the presence of long periods of abnormal stimulation.

Animals↗

PubMed1995

Scoring the Farnsworth-Munsell 100-hue for vocational guidance.

BACKGROUND: We considered whether the color discrimination of mild color defectives scoring < or = 100 is the same as that of normals. METHODS: We analyzed the FM 100-hue results of 126 normals and 94 congenital color defectives retrospectively by considering the Total Error Score (TES) and individual cap errors (error profiles). RESULTS: A TES of 100 passes 95% of normals and 24% of congenital color defectives. The error profiles of some of the mild defectives who pass show abnormal peaks along a red-green axis. An error > or = 5 in these regions is a good indicator of abnormal color discrimination. CONCLUSIONS: Some 30% of mild defectives (TES < or = 100) have limited hue discrimination in the red-green domain, so both the TES and error profiles need to be considered when providing vocational guidance.

Adult↗

PubMed1995

Using computers to test visual acuity.

BACKGROUND: This paper describes a computer-generated acuity test that can be produced on IBM compatible equipment in the Windows 3.1 environment. METHODS: The acuity test was applied to 14 observers using two psychophysical methods (staircase and method of constant stimuli [MOCS]) to determine the validity and reliability of the outcomes. Comparisons were made between test methods and a hard copy LogMAR chart using statistics suited to intra-class comparisons. The effect that screen luminance has on outcomes and hardware warm-up requirements were also considered. RESULTS: The computer staircase was found to provide a reliable estimate of acuity. The hard copy chart and computer staircase have an Intraclass Correlation Coefficient (ICC) of 0.98. The threshold derived from the different psychophysical methods is also highly correlated (ICC = 0.98). The monitor provides a stable luminance 30 minutes after a cold start, and a 1 logunit (10 times) change in screen luminance has little effect on outcomes. CONCLUSIONS: A computer-driven acuity staircase provides a good estimate of threshold if a 30-minute warm-up period is allowed to stabilize monitor luminance. It also gives a measure of variability. A staircase is adequate for clinical applications as it provides a reasonable compromise between test time and accuracy. An extra 30 seconds is needed to obtain a staircase result (compared with hard copy), which is offset by the provision of this error term.

Adult↗

PubMed1994

Efficient and unbiased modifications of the QUEST threshold method: theory, simulations, experimental evaluation and practical implementation.

QUEST [Watson and Pelli, Perception and Psychophysics, 13, 113-120 (1983)] is an efficient method of measuring thresholds which is based on three steps: (1) Specification of prior knowledge and assumptions, including an initial probability density function (p.d.f.) of threshold (i.e. relative probability of different thresholds in the population). (2) A method for choosing the stimulus intensity of any trial. (3) A method for choosing the final threshold estimate. QUEST introduced a Bayesian framework for combining prior knowledge with the results of previous trials to calculate a current p.d.f.; this is then used to implement Steps 2 and 3. While maintaining this Bayesian approach, this paper evaluates whether modifications of the QUEST method (particularly Step 2, but also Steps 1 and 3) can lead to greater precision and reduced bias. Four variations of the QUEST method (differing in Step 2) were evaluated by computer simulations. In addition to the standard method of setting the stimulus intensity to the mode of the current p.d.f. of threshold, the alternatives of using the mean and the median were evaluated. In the fourth variation--the Minimum Variance Method--the next stimulus intensity is chosen to minimize the expected variance at the end of the next trial. An exact enumeration technique with up to 20 trials was used for both yes-no and two-alternative forced-choice (2AFC) experiments. In all cases, using the mean (here called ZEST) provided better precision than using the median which in turn was better than using the mode. The Minimum Variance Method provided slightly better precision than ZEST. The usual threshold criterion--based on the "ideal sweat factor"--may not provide optimum precision; efficiency can generally be improved by optimizing the threshold criterion. We therefore recommend either using ZEST with the optimum threshold criterion or the more complex Minimum Variance Method. A distinction is made between "measurement bias", which is derived from the mean of repeated threshold estimates for a single real threshold, and "interpretation bias", which is derived from the mean of real thresholds yielding a single threshold estimate. If their assumptions are correct, the current methods have no interpretation bias, but they do have measurement bias. Interpretation bias caused by errors in the assumptions used by ZEST is evaluated. The precisions and merits of yes-no and 2AFC techniques are compared.(ABSTRACT TRUNCATED AT 400 WORDS)

Adaptation, Ocular↗

PubMed1994

The role that binocular vision and stereopsis have in evaluating fundus features.

PURPOSE: We report two experiments that address the role of stereopsis in viewing the fundus. METHODS: Thirteen observers viewed stereo slides obtained by lateral displacement of a fundus camera. We quantified the capacity of seven clinicians (normal stereopsis) to resolve depth in a model eye viewed monocularly and binocularly. We also compared the ability of the same seven and six additional clinicians (with reduced stereopsis) to determine the relative position of the cup shown in normal and reverse disparity as well as answering a questionnaire. We determined optimal performance based on a schematic eye. RESULTS: Monocular viewing gives better than expected results with binocularity being of greatest benefit for small disparities. Clinicians perform much worse in stereoscopic judgments than predicted by calculation. Few clinicians report making stereo depth judgments in practice. All amblyopic observers report using hyperacuity cues. CONCLUSION: This study shows that binocularity and stereopsis are beneficial for judging small disparities under limited circumstances. The level of stereopsis achieved in practice fails to approach the expected limit. We believe that this constriction arises from a known limit to stereo acuity associated with extended fields.

Adult↗

PubMed1994

Detection and discrimination of moving stimuli: the effects of color, luminance, and eccentricity.

Psychophysical detection and direction discrimination thresholds for 1c/o, 1-Hz Gabors are plotted in a Weberian long-middle-wavelength-sensitive cone contrast plane. The shape of these threshold contours suggests linear cone contributions to additive (delta L/Lb + delta M/Mb) and opponent (delta L/Lb - delta M/Mb) postreceptoral mechanisms. The opponent mechanism dominates thresholds at the fovea, but sensitivity decreases rapidly with eccentricity in comparison with the additive mechanism. Cone contributions to the mechanisms vary in a small and nonsystematic manner across the retina. The experiments show that the additive mechanism is directionally sensitive at detection threshold. At all eccentricities studied (0-24 degrees), 0.3-log-unit suprathreshold contrasts are necessary for the opponent mechanism to signal direction of motion.

Adult↗

PubMed1993

Visual losses in early age-related maculopathy.

Age-related maculopathy (ARM) can be considered a transition from normal retinal changes to pathological processes. It is important to recognize patients who have progressed beyond a normal state in order to provide appropriate clinical management. This pilot study considers the clinical dilemma of diagnosing and monitoring early ARM. We carried out a controlled study and tested the visual functions of 11 pre-ARM (PARM) and 11 early ARM subjects. Apart from compromised visual acuity, losses in central visual field, color vision, and visual adaptation were also recorded in our ARM subjects. We found a low contrast (LC) Amsler grid to be most sensitive to central field defects and that the desaturated panel D-15 gave too many false positives among normal elderly subjects. Our results indicate foveal sparing in early ARM and question the capacity of acuity assessment to reflect early functional changes adequately. A clinical battery is recommended to detect and monitor ARM.

Adaptation, Ocular↗

PubMed1992

The use of colour difference vectors in diagnosing congenital colour vision deficiencies with the Farnsworth-Munsell 100-hue test.

Colour difference vector analysis provides useful and meaningful information in scoring the Farnsworth-Munsell (FM) 100-hue test. However, the FM 100-hue test is limited in its ability to diagnose type and severity of congenital colour vision defect. Type classification for all subjects is incorrect in 21% of cases, and for deuteranomals the misclassification rate is 38%. Visual inspection of the plots yields a similar misclassification rate and classification of plots with few errors (under 180) is generally less reliable. The FM 100-hue test has a limited ability to separate dichromats from anomalous trichromats. A test protocol based on joint D15 and FM 100-hue tests should pass 36% of anomalous trichromats and 26% of all colour defectives yet fail all dichromatic observers. We conclude that administering the FM 100-hue test is of less value than a combination of D15 panels (Standard D15 and L'Anthony's desaturated D15) in the clinical diagnosis of congenital colour defective observers. Our results for the FM 100-hue panel are similar to those reported previously by other investigators.

Adult↗

PubMed1991

Quantitative scoring methods for D15 panel tests in the diagnosis of congenital color vision deficiencies.

Farnsworth's standard D15 and L'Anthony's desaturated D15 panel tests were administered to 99 congenital red-green color defective subjects. The results were analyzed in three ways: (1) by summing the color differences between adjacent caps according to Bowman, (2) by averaging color difference vectors (CDV) according to Vingrys and King-Smith, and (3) by visually inspecting and counting the crossings. The Bowman measure was highly correlated with one of the CDV measures but provides less information regarding a cap arrangement. The desaturated D15 test can be expected to misclassify 5% of dichromats by type (protan/deutan) compared to a type misclassification rate of less than 0.1% for the D15 panel test. The correct diagnostic rates for type were 45% for the standard D15 test and 58% for the desaturated D15 test. However, the improvement in correct diagnostic rate for the latter test was accompanied by an increase in the misdiagnostic rate from 2 to 10%. The main value of the desaturated D15 test in congenital color vision diagnosis would seem to be in providing classification of those subjects who pass the standard D15 test. Quantitative scoring of the tests provides a good estimate of severity of defect. Visual inspection provides a similar diagnostic rate to CDV analysis, but has a lower type misdiagnostic rate at the desaturated D15 test and is more likely to be correct when the two methods disagree. We suggest that quantitative scoring techniques are of limited benefit for the clinical diagnosis of congenital color vision defects but that they are of use in clinical trials or for the monitoring of changes in color vision over time.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1991

Correlation of chromatic, spatial, and temporal sensitivity in optic nerve disease.

Spearman rank-order correlations (R) were made between the color-mixture threshold, spatial contrast sensitivity, and flicker sensitivity measurements of 38 patients with a variety of optic nerve disorders. Patients had to satisfy the following criteria: greater than 0.5 log unit loss of chromatic or achromatic sensitivity (compared to age-matched normals), central fixation, no congenital color defects, and no ocular media abnormalities. The results of the analysis show a significant correlation between selective losses of high spatial frequency sensitivity (relative to low) and selective losses of red/green and blue/yellow sensitivities [R = -0.680 (P less than 0.001) and R = -0.439 (P less than 0.01), respectively]. A mild correlation was found between selective spatial and selective temporal losses [r = -0.399 (P less than 0.05)] (ie, low temporal frequency losses correlate with high spatial frequency losses and vice versa). A stronger correlation was found between selective red/green and selective blue/yellow sensitivity losses [R = 0.657 (P less than 0.001)]. No correlation was found between selective temporal losses and selective chromatic losses. These findings can be explained in terms of differential losses of three types of fibers: (1) fibers that are particularly sensitive to red/green color, high spatial and low temporal frequencies; (2) fibers signalling blue/yellow color; and (3) fibers that are relatively sensitive to high temporal frequencies and low spatial frequencies.

Adolescent↗

PubMed1991

Reduced contrast sensitivity when viewing through an aircraft windscreen.

The Contrast Sensitivity Function (CSF) of an experienced observer was measured under normal viewing conditions, when looking through an aircraft windscreen and when looking through the windscreen in the presence of a glare source. We found that contrast sensitivity was significantly reduced for frequencies above about 6 cycles/degree viewed through the windscreen and that the addition of a glare source further reduced contrast sensitivity for all spatial frequencies greater than 1 cycle/degree. These results demonstrate that the CSF is a sensitive metric of degraded visual performance when viewing through optical transparencies.

Aerospace Medicine↗

PubMed1988

A quantitative scoring technique for panel tests of color vision.

Panel tests of color vision (eg FM100-Hue test) lack a common quantitative method for the scoring of cap arrangements. We describe a scoring method applicable to all panel tests that makes use of a novel technique to analyze test cap data, namely the calculation of a moment of inertia from the Color Difference Vectors (CDVs) of any arrangement pattern. Using the Farnsworth D-15 panel, as an example, we specify how to determine CDVs and demonstrate the benefits of calculating a moment of inertia for the analysis of these vectors. Moment of inertia analysis yields three factors which quantify cap arrangements: the first is the confusion angle which identifies the type of color defect; the second is the Confusion index (C-index) which quantifies the degree of color loss relative to a perfect arrangement of caps; and the third is the Selectivity index (S-index) which quantifies the amount of polarity or lack of randomness in a cap arrangement. A retrospective study on the result of 53 normal and 66 congenitally color defective observers is reported and provides normative data. We show that the technique differentiates between different types of color defect and provides useful clinical information regarding a loss of color vision. Likewise, a similar observation is made on a smaller sample of FM100-Hue results. A BASIC computer program is provided for anyone wishing to use the technique.

Adolescent↗

PubMed1988

Are colour vision standards justified for the transport industry?

Colour vision standards are imposed in the road, rail, maritime and aviation industries and are often subject to vigorous opposition by those excluded by the standard. With greater emphasis in recent years on equality of opportunity, it is important that standards of personal fitness, such as colour vision standards, be subject to critical scrutiny. Such appraisal should be able to demonstrate that the community benefit arising from the application of the standard is sufficient to justify the personal and other costs of retaining the standard. This paper reviews the evidence relating to colour vision standards in the transport industries and concludes that a strong case can be made for their retention in public transport.

Accidents↗