The case against protan drivers holding professional driving licenses.
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Biomedical subjects
Algis J Vingrys
Publications and source records attributed to Algis J Vingrys.
Development of efficient threshold strategies for frequency doubling technology perimetry using computer simulation.
PURPOSE: To develop new test procedures for frequency-doubling technology (FDT) perimetry that improve performance beyond those currently used. METHODS: Two novel threshold estimation procedures were evaluated: a rapid, efficient binary search technique (REBS) and a maximum-likelihood estimation (ZEST) procedure. A computerized visual field simulation model was developed to determine the accuracy and efficiency of these procedures. This model was constructed using previously derived characteristics of FDT perimetry from both normal observers (n = 506) and those with glaucomatous visual field loss (n = 352). The computer simulation program was used to determine the best parameters for the two new procedures and the effect of variability and response errors on algorithm performance. Comparisons were made to the performance of the modified binary search (MOBS) procedure used in the current commercial implementation of the FDT perimeter. RESULTS: Both the optimized REBS and ZEST procedures approximately halved the time required for FDT threshold testing without loss of accuracy or reproducibility. CONCLUSIONS: With suitable parameter choices, comparable performance was achieved using either ZEST or REBS. Simulation results indicate that accurate thresholds can be measured with an optimized ZEST or REBS procedure in approximately half the time required by traditional estimation methods.
Aged↗
Performance of efficient test procedures for frequency-doubling technology perimetry in normal and glaucomatous eyes.
PURPOSE: To validate the clinical performance of two new efficient threshold-estimation procedures for frequency-doubling technology (FDT) perimetry in both visually normal individuals and patients with glaucomatous visual field loss. METHODS: Forty-one normal subjects (mean age, 48.3 +/- 11.6 years) and 50 patients with glaucomatous visual field loss (mean age, 72.7 +/- 10.0 years) were tested. Some of these participants were retested within a 3-month period. FDT perimetry was performed on a color monitor driven by a visual-stimulus-generating video board, with stimulus parameters designed to closely mimic those of the commercial FDT test. Visual field sensitivity was measured using three procedures: a modified binary search (MOBS) identical with the one used in the commercial FDT device, a rapid efficient binary search (REBS), and a procedure the uses Bayesian methods (zippy estimation of sequential testing; ZEST). The selection of optimum parameters for REBS and ZEST were based on results from previous simulations. RESULTS: Both ZEST and REBS were 40% to 50% faster than MOBS. All three methods produced similar visual field sensitivity measures, with 95% of the differences occurring between +/-2 dB for normal subjects and +/-3 dB for glaucoma patients. Test-retest performance was similar for all three procedures. CONCLUSIONS: The test time for full-threshold FDT perimetry can be approximately halved, by using either the ZEST or REBS procedure, without affecting the accuracy or reliability of the measurements. These findings in normal subjects and patients with glaucoma provide clinical confirmation of our previous investigations of these test strategies that use computer simulation.
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Altered retinal function and structure after chronic placental insufficiency.
PURPOSE: To consider whether growth restriction secondary to chronic placental insufficiency results in postnatal deficits in retinal structure and function. METHODS: Chronic placental insufficiency was induced just before midgestation in guinea pigs through unilateral ligation of the uterine artery. Eight weeks after birth, electroretinograms were recorded from prenatally compromised (PC, n = 6) and control (n = 15) animals. Data were collected for b-wave amplitude and implicit time, also the modeled receptoral (P3) response and oscillatory potentials were extracted. After electroretinography, retinas were prepared for structural analysis (PC, n = 6; control, n = 7). A separate cohort of PC (n = 8) and control (n = 9) animals underwent tyrosine hydroxylase immunoreactivity (TH-IR, dopaminergic neurons) and nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) histochemistry (neuronal nitric oxide synthase, nNOS)--these being markers of amacrine cell subpopulations. RESULTS: Electroretinography revealed two PC guinea pigs with marked changes to saturated receptoral amplitude (Rm(P3)), sensitivity (log S) and postreceptoral waveforms. Grouped PC data revealed significantly reduced Rm(P3), whereas log S was not affected. The b-wave amplitudes were normal, but b-wave implicit times were delayed (P < 0.05) in PC animals. Amplitudes and peak times of oscillatory potentials were also significantly reduced and delayed (P < 0.05). Morphologic analysis revealed significant reductions in all cellular and plexiform (synaptic) layers in both the central (P < 0.05) and peripheral (P < 0.05) retina in PC animals. The outer retina, which contains the photoreceptors and the outer plexiform layer was particularly affected. The reduced growth of plexiform layers suggests a reduction in the growth of the neuropile in PC animals compared with control animals. The total number (P < 0.03) and density (P < 0.05) of TH-IR neurons was reduced, whereas the total number and density of nNOS-positive amacrine cells was not significantly different between PC and control animals. CONCLUSIONS: Chronic placental insufficiency results in morphologic and functional alterations to the retina. Electroretinogram deficits in PC animals indicated both inner and outer retinal anomalies. Such affects could contribute to the visual impairments reported in very-low-birth-weight children, some of whom are growth restricted.
Amacrine Cells↗
Fast psychophysical procedures for clinical testing.
INTRODUCTION: Psychophysical methods are used in clinical settings to obtain estimates of visual performance. Such methods should be fast and accurate, yet robust to the corrupting effects of false responses. METHODS: In this paper, we develop these concepts and investigate the efficiency of two maximum likelihood methods (bestPEST and ZEST) for use in clinical applications. The performance of both methods will depend on whether a criterion-free paradigm (alternate forced choice) is adopted. RESULTS: Our data show that the number of trials needed to obtain reliable thresholds with a yes/no paradigm can be as few as six to eight, provided no false responses are given within the first few trials. In addition, we show that the reliability and short-term variability of the endpoint of the methods is compatible with clinical applications. CONCLUSION: We show that a yes/no maximum likelihood method using a small number of presentations will yield reliable and accurate estimates of threshold in a clinical setting.
Journal Article↗
Postnatal development of flicker sensitivity in guinea pigs.
BACKGROUND: The retinal response to flickering stimuli (steady state ERG) recruits many retinal elements and is a sensitive indicator of early retinal dysfunction. This study reports the post-natal maturation of the steady state ERG response in guinea pigs. METHODS: The steady state ERG response to flickering stimuli (0.6 to 20 Hz) was recorded from dark adapted (more than 12 hrs) English Shorthair guinea pigs (n = 7) using flashes that produced rod and cone dominated responses. Temporal sensitivity functions and critical fusion frequencies (CFF) were derived over a range of ages from postnatal day (PND) 1 to 45. RESULTS: Guinea pig rod and cone temporal sensitivity functions show shape characteristics and CFF similar to humans. Furthermore, the post-natal development of the guinea pig temporal characteristics is also similar to that of humans - they are present at birth and mature rapidly post-natally. The time-course of CFF maturation is similar for rod and cone mediated responses. CONCLUSIONS: These data show that the temporal response and its maturation in the guinea pig retina is similar to that in humans. Therefore, we propose that the guinea pig is a particularly useful animal model to study retinal disease in early childhood.
Journal Article↗
Clinical testing of contrast thresholds using a commercial television monitor system.
Background: The Medmont AT-20 has incorporated a contrast threshold test using a predetermined letter size that can be applied in clinical settings. This paper describes a pilot study that evaluates this technology and the effects of certain parameters on test outcomes. Methods: A photometric calibration of the test was performed to define the relationship between the AT-20 scale and Weber contrast (W%). We determined the effects of repeated measures (precision), target size (6/6 to 6/96), viewing duration (50 to 1,000 msec), defocus (+0.50 to +1.50 DS) and a macula scotoma on thresholds. The accuracy of the staircase (PEST) procedure was evaluated with and without false-negative responses. Results: The AT-20 scale has an almost linear relationship to a logarithmic transformation of W% and provides a suitable measure of contrast threshold. In the absence of monitor calibration, threshold uncertainty could be as great as 0.22 log units (W%) compared with published norms. We found that threshold variability averaged +/- 7.1 AT-20 scale units (95 per cent limits of agreement) and was proportional to threshold magnitude. One dioptre of defocus decreased thresholds by about one log unit (W%) for a 6/24 target. We propose that a 6/24 letter shown for 500 msec should provide a useful target for most clinical settings. The PEST procedure can yield endpoints in 47 (+/-12) seconds, is robust to false negative (FN) responses and gives abnormal thresholds in the presence of a macula scotoma. Conclusions: The Medmont AT-20 contrast test provides a useful clinical measure of contrast threshold. With calibration, the test could also be applied to research projects.
Journal Article↗
Management of patients with narrow angles and acute angle-closure glaucoma.
BACKGROUND: Acute closure of the anterior chamber angle can have catastrophic consequences for vision when it occurs in an unsupervised situation. Visual debilitation is much less likely to result when angle-closure occurs in a well-controlled environment that allows appropriate management. Therefore, it is desirable for optometrists to undertake a complete ocular health assessment, including mydriatic fundus examination, on patients who have narrow anterior chamber angles, provided that appropriate precautions and procedures are followed. CASE REPORT: We report on the case of a 59-year-old white female whose anterior chamber angles closed in response to mydriatic drops instilled during an optometric examination. Her optic discs and visual field results from before and four years after the angle-closure attack do not show any significant changes. CONCLUSION: We conclude that the optimal standard of care for patients presenting to an optometric practice, and who are subsequently found to have narrow anterior chamber angles, includes pupillary dilatation to allow stereoscopic visualisation of the optic nerve head. Precautions must be followed to ensure that, in the unlikely event of an ensuing angle-closure episode, the attack occurs under clinically supervised conditions.
Journal Article↗
Evidence for non-selective colour channel involvement in diabetic eyes especially after laser treatment.
PURPOSE: We consider the hypothesis that proliferative diabetes produces selective lossof colour channels. We also consider the possibility that laser treatment for this condition does not affect macula function. METHODS: We tested for the possibility of a selective colour channel involvement in 35 eyes of 33 cases of proliferative diabetes by considering the outcomes of saturation and hue testing before and after pan-retinal photocoagulation (PRP). Saturation testing was achieved with the Sahlgren Saturation Test (SST) and hue testing was via the Farnsworth-Munsell 100 (FM100) hue test. Our results were compared to a recent model1 that was developed to predict the saturation processing of diseased eyes. RESULTS: All diabetic eyes with normal hue (FM100) scores passed the saturation test (SST). Most pre-treatment eyes (29 of 35 or 83 per cent) failed the FM100 hue test but only 16 of 35 (46 per cent) failed the saturation test. Following laser treatment, 97 per cent of eyes were abnormal on the FM100 hue test but only seven per cent failed the saturation test. CONCLUSION: Untreated diabetic eyes with proliferative retinopathy show losses of both hue and saturation processing. The nature of this relationship is consistent with that modelled assuming moderate and asymmetric non-selective losses in both chromatic and luminance channels. Laser treatment (PRP) appears to produce a paradoxical normalisation in saturation percepts in the presence of deteriorating hue scores. We find that this outcome is consistent with a more severe generalised reduction of sensitivity in both the chromatic and luminance processes and conclude that pan-retinal photocoagulation results in these unexpected macula changes.
Journal Article↗
Recent Advances in the Management of Primary Open-angle Glaucoma: Reply to O'Shea et al.
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Letter↗
The many faces of glaucomatous optic neuropathy.
BACKGROUND: Glaucoma manifests mostly in the elderly, who frequently have otherocular changes that frustrate clear visualisation of the optic nerve head or nerve fibre layer. In the past, a large or asymmetric cup/disc ratio has been used to indicate the possibility of glaucoma. In this paper, I will argue that cup/disc ratios alone have poor sensitivity to glaucoma, and a more sophisticated approach is needed to make the earliest diagnosis. METHODS: This paper reviews the literature and describes the changes that occur at the optic nerve head and in the peripapillary region as a consequence of glaucomatous optic neuropathy (GON). RESULTS: The concept of 'risk factors' is developed to help screen for glaucoma. Glaucoma suspects require a full clinical investigation (visual field, IOP, assessment of anterior chamber, disc features and nerve fibres) and need to be monitored annually. For future reference, they should have their disc features recorded by instrumental methods or with photography at an early age. As no single sign provides the perfect diagnostic marker for the disease, clinicians need to examine for a group of signs before making the diagnosis. A clinical logic is developed in this paper to enhance the detection of glaucoma. CONCLUSION: Adoption of a protocol similar to that detailed in this paper will enhance the early and reliable detection of glaucoma.
Journal Article↗