Biomedical subjects

A J Vingrys

Publications and source records attributed to A J Vingrys.

At least 55 records · Page 3Linked to original sources

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↗

PubMed1987

The effect of a moderate level of hypoxia on human color vision.

This study reports the effect of a moderate level of hypoxia on human color discimination. We found a generalized loss of color vision affecting both red-green and blue-yellow discrimination at an altitude of 12,000 feet. Although the residual color discrimination at this altitude was within age-matched, sea-level norms, a statistically significant increase over sea level error scores was measured on the Farnsworth-Munsell 100-Hue test and the Pickford-Nicolson anomaloscope. An analysis of psychophysical and electrophysiological studies indicates that hypoxia acts by depressing retinal ganglion cell activity and that it can affect photopic visual processes as well as scotopic vision. We conclude that studies evaluating man's visual performance at altitude must consider post-receptoral processes.

Adult↗

PubMed1986

Origins of colour vision standards within the transport industry.

Colour vision standards should reflect changes in our understanding of the nature of these defects as well as technological advances that place less importance upon the visual senses of the human operator. Therefore it is suggested that visual standards be subject to routine reviews in order to assess their suitability for modern work environments. This paper gives a chronological account of the introduction of colour vision standards by several national transport authorities and identifies historical reasons that led to their implementation. It is concluded that the same factors that gave rise to the adoption of early colour vision standards are still relevant for modern transport systems. However the recent deployment of automatic or semi-automatic control or navigational systems has substantially altered man's role from being the primary source of information input to one of a monitoring process. This has generated a good deal of debate and uncertainty regarding the level of responsibility that a human operator has for the control of modern transport vehicles. Nevertheless, it is argued that in the absence of complete automation some type of visual standard is needed whenever visual judgements must be made by human observers.

Aerospace Medicine↗

PubMed1983

Who fails lantern tests?

A battery of clinical colour vision tests was given to a group of 100 observers with abnormal colour vision who were also tested on the Farnsworth lantern and the Holmes-Wright lanterns types A and B. It was found that clinical colour vision tests are imperfect predictors of lantern test performance. However, observers classified as having a 'severe' colour vision defect were found to fail the lantern tests but only one half to two-thirds of those who fail the lantern tests can be identified in this way. It is not possible to identify with certainty any of the people likely to pass the lantern tests: about one-third to two-thirds of observers classified as being mildly affected fail the lantern tests. The Farnsworth D-15 and City University tests were found to be the best predictors of lantern test performance but other tests such as the Nagel anomaloscope, the H-16, L'Anthony's desaturated test can also be used. The lack of a strong correlation between clinical tests and the recognition of the small coloured stimuli presented by the lantern tests suggests that clinical tests do not test the same aspect of colour vision that is important to the recognition of signal lights. For this reason lantern tests should be retained for occupational testing of colour vision.

Adaptation, Ocular↗

PubMed1983

Validation of the Holmes - Wright lanterns for testing colour vision.

The recently introduced Holmes - Wright Type A and Type B lanterns and the Farnsworth lantern were administered to 100 observers with normal colour vision and 100 observers with defective colour vision. With the fail criteria adopted, all normals passed the Holmes - Wright Type A lantern and with one exception all normals passed the Farnsworth lantern. However, 8% of normals failed the more difficult Holmes - Wright Type B lantern. It is noted that the normals who fail this lantern test appear to do so not because of poor colour discrimination but because the coloured stimuli presented by the lantern have a point brilliance close to the average chromatic threshold. About one-third of the colour vision defective group passed the Farnsworth lantern and between 14 and 17% passed the Holmes - Wright Type A lantern depending on the test procedure used. Only two mild deuteranomals in the sample of 100 colour abnormal observers succeeded in passing the Holmes - Wright Type B lantern. Dichromats and severe anomalous trichromats fail all three lanterns so that those who pass are all mild anomalous trichromats. A significant proportion of protanomals pass the Farnsworth lantern and some protanomals pass the Holmes - Wright Type A lantern despite their reduced sensitivity to red light and correspondingly reduced signal range for red signals.

Color Perception Tests↗

PubMed1982

A survey and evaluation of lantern tests of color vision.

This paper reports a survey of the lantern tests that have been or are used to evaluate the color vision of people who wish to enter occupations that require the ability to recognize colored signal lights reliably. The origin of each lantern is traced and the principal features of each are described. The available data concerning failure rate of normals, the failure rate of people with defective color vision, and the extent to which scores on lantern tests correlate with field trials are summarized. Despite the fact that lantern tests have been used since the turn of the century and that some lanterns have been in use for more than 30 years and some for much longer periods, the available validation data are incomplete and sometimes conflicting. However, the data do indicate that some lanterns may fail a significant proportion of normals and that there is considerable variation between lanterns in the proportion of color vision defectives that will fail. It is noted that most lanterns will pass some protanomals despite their reduced sensitivity to red light and correspondingly short visual range for red signals. The view of Cameron is supported that a more rational approach would be to made a clinical diagnosis of the type of color vision defect, to reject protanopes, deuteranopes, and protanomals and to use a lantern test only to determine which deuteranomals should be accepted.

Aerospace Medicine↗

PubMedDate not supplied

Opponent-color detection threshold asymmetries may result from reduction of ganglion cell subpopulations.

Thresholds for psychophysically opposite stimuli--light and dark, or equiluminous red and green, or equiluminous blue and yellow--are usually nearly equal. This color threshold symmetry is sometimes violated in subjects who have optic nerve hypoplasia, a congenital loss of retinal ganglion cells. We describe a subject who has optic nerve hypoplasia, who exhibits large red-green and blue-yellow detection threshold asymmetries for equiluminous spots. Temporal and spatial integration for equiluminous red and green test spots also differed from normal; static perimetric thresholds for equiluminous green, blue, and yellow (but not red) spots lacked the normal "V" shaped minimum at the fovea. These asymmetries may relate to a developmental paucity of some ganglion cell subtypes. Optic nerve hypoplasia may allow the contributions to detection made by individual ganglion cell subtypes to be isolated psychophysically, in analogy to the study of cone spectral sensitivity in dichromats.

Adult↗

PubMedDate not supplied

Development of postreceptoral function in pigmented and albino guinea pigs.

Retinal neurons are generated in overlapping growth spurts with ganglion cell and cone populations peaking sooner than rod and bipolar cell numbers. As such the functional development of the inner and outer retinal components and elements within these strata (rods vs. cones) may differ. We considered the postnatal development of the postreceptoral components of the ERG (P2, oscillatory potentials) in the guinea pig. ERGs were also evaluated across albino and pigmented strains in order to consider the role that pigmentation has for functional development. Electroretinograms were collected on postnatal days PDI to PD60 (n = 4-7 per time point). The postreceptoral P2 amplitude and implicit time was extracted (digital subtraction of modelled P3 and filtering, 0.5-49 Hz). Intensity-response relationships were described using Naka-Rushton functions whose parameters were compared using a nonparametric bootstrap. Oscillatory potentials (OPs) were extracted following signal conditioning and filtering to remove the a- and b-waves and were described using a Gabor function. OP response parameters were compared using repeated measures ANOVA. Postreceptoral P2 amplitudes mature soon after birth (PD10-PD12). Oscillatory potentials show a similar postnatal amplitude development (PD10-PD12) but a later maturation in timing (PD20) compared with the postreceptoral waveform. All components (P3, P2, and OPs) declined at the same relative rate with age after PD12. Albino animals gave larger, faster, and more sensitive waveforms at all ages but showed the same age-related trends as did pigmented animals. Early development of inner retinal synapses in guinea pigs may underlie the rapid postnatal maturation of their postreceptoral response. These appear to be constrained by the development of receptoral responses. All components declined at the same rate suggesting either a change in the photoreceptoral response or changes to ocular impedance with age.

Aging↗