Biomedical subjects

A J Vingrys

Publications and source records attributed to A J Vingrys.

At least 37 records · Page 2Linked to original sources

PubMed1999

Localized scotomata detected with temporal modulation perimetry in central serous chorioretinopathy.

AIM: Flicker deficits have been reported in various maculopathies, including age-related macular degeneration. We test whether flicker losses exist in patients with central serous chorioretinopathy (CSC) and whether the size and flicker frequency of the target is important in detecting such losses. METHODS: We examined four CSC patients with temporal modulation (flicker perception) perimetry using the Medmont auto-flicker module (Medmont Pty Ltd, Melbourne, Vic. Australia), as well as static perimetry and colour vision. One case was examined using sophisticated laboratory equipment to precisely measure their temporal contrast sensitivity function (temporal CSF or de Lange curve) using larger targets to consider the effect of target frequency and size. Two patients were followed longitudinally and tested after resolution of the maculopathy. We compared our patients with an age-matched control group of 11 people. RESULTS: Temporal modulation perimetry detected larger and more localized defects in all cases of active CSC compared with static perimetry. There appeared to be size and frequency tuning to the deficit, with greatest loss being found at 16 Hz with small (0.5 degree) targets. The losses resolved in one case where the retina recovered in 4 weeks, but remained to a lesser degree in another case who suffered a 2 year long fluctuating course before the CSC subsided. CONCLUSIONS: Temporal modulation perimetry detects a loss of flicker sensitivity in patients with CSC. Deeper and more clearly defined scotomata are found with a flickering stimulus compared with a steady state one. The greatest losses of flicker sensitivity are found with 16 Hz modulation and with small targets located directly over the lesion. The duration of the disease may be important for recovery of flicker sensitivity. Temporal modulation perimetry appears to be a valuable tool for the confirmation of functional loss due to CSC.

Adult↗

PubMed1999

A new look at threshold estimation algorithms for automated static perimetry.

Automated perimetry is often associated with lengthy test times when a staircase algorithm is applied. This arises because the fixed step sizes used during threshold estimation (e.g.,4/2 dB) yield reduced test efficiency, with test times being dependent on the relative positioning of the start and endpoints, as well as the step size. Neighborhood logic may speed up the process, although several presentations are still required for normal threshold values and many more presentations are required for abnormal values. We consider whether there is any justification for using a fixed step size during the threshold procedure. We show how empirical data can be applied, within a Bayesian framework, to reduce test time with little or no loss of accuracy. Finally, we demonstrate the effect that the starting probability density function can have on test efficiency by implementing an empirically determined and bimodal probability density function that provides fast outcomes.

Algorithms↗

PubMed1999

Effects of dietary n-3 fatty acid deficiency and repletion in the guinea pig retina.

PURPOSE: To investigate the nature and reversibility of biochemical and functional changes in the retina encountered over a single generation of dietary n-3 polyunsaturated fatty acid deficiency in guinea pigs. METHODS: Dunkin-Hartley guinea pigs were fed for 16 weeks after weaning with diets supplemented with safflower seed oil (n-3 deficient) or canola oil (n-3 sufficient, control). A number of deficient animals were repleted at 6 weeks with canola oil for 5 or 10 weeks, or at 11 weeks for 5 weeks. Electroretinograms (0.8 and 4.3 log scot td x sec) were collected at 6, 11, and 16 weeks after weaning. Conventional waveforms (a- and b-waves), oscillatory potentials, and receptoral and postreceptoral subcomponents (PIII and PII, respectively) were evaluated. Cone pathway function was assessed with 30-Hz flicker at the brighter intensity. Retinal phospholipid fatty acids were measured by capillary gas-liquid chromatography. RESULTS: Electroretinographic amplitudes showed statistically significant losses in b- and a-waves after 6 and 16 weeks of dietary n-3 deficiency, respectively. The response amplitude to 30-Hz flicker was reduced 42% after 16 weeks. Retinal docosahexaenoic acid (DHA) levels of animals maintained on the safflower oil diet for 16 weeks were 42% of levels in age-matched control subjects. There were significant losses in maximum response amplitudes (R(mPIII) and R(mPII)), although the major effect was a reduction in sensitivity of the receptoral response. Complete functional recovery was observed only in animals repleted for 10 weeks. CONCLUSIONS: Functional deficits in PIII and PII of the electroretinogram were apparent in first-generation guinea pigs fed an n-3 deficient diet. These losses showed a correlation with age and retinal DHA level, although varying degrees of dependence on the DHA level were found. All functional deficits were reversed after 10 weeks of dietary n-3 repletion. The results suggest that DHA may serve several functional and structural roles in the retina and further emphasize the requirement for DHA in the normal development of vision.

Animals↗

PubMed1998

Color and luminance detection and discrimination asymmetries and interactions.

We investigated the nature of color and luminance processes under threshold and suprathreshold conditions in normal trichromatic observers. Detection and discrimination contours as well as threshold-vs-contrast (Tvc) functions were measured in the Derrington-Krauskopf-Lennie (DKL) color space using a masking paradigm. Such contours revealed substantial threshold asymmetries along the three cardinal axes for excursions of opposite polarity along a single axis (e.g. "red" vs "green"). The detection threshold asymmetry was significant for the "blue" and "yellow" (P < 0.05) and luminance increments and decrements (P < 0.01). For suprathreshold discrimination contours the polarity of these asymmetries reversed but remained significant for "blue" and "yellow" (P < 0.001) and luminance increments and decrements (P < 0.01). No significant differences were found between the "red" and "green" cardinal axes under either condition. The discrimination contours also indicated that suprathreshold performance had variable masking along the different axes. A characteristic Tvc curve was found in all cardinal directions except "yellow". The Tvc for "yellow" differed from the other cardinal directions by showing no masking after the initial facilitation and by giving a greater saturating response as a function of contrast. We considered whether the state of retinal adaptation had any role in producing the asymmetries.

Adaptation, Ocular↗

PubMed1998

Comparison of guinea pig electroretinograms measured with bipolar corneal and unipolar intravitreal electrodes.

This study considers the precision and accuracy of bipolar corneal electrodes compared with unipolar intravitreal methods in collecting electroretinographic (ERG) recordings from a small animal. Flash ERGs were obtained from 9 adult guinea pigs on three occasions. Corneal bipolar (Burian-Allen) electrodes were used to collect data on the first two occasions whereas unipolar intravitreal electrodes were used on the last. We identified the a-wave, b-wave, oscillatory potentials, PIII and PII responses. Intensity-response functions were fit using a Naka-Rushton relationship with a bootstrap estimating the 95% confidence limits. Discrepancy analysis was applied to determine the coefficient of agreement. We found significantly larger amplitudes with unipolar intravitreal electrodes (ANOVA; a-wave, p<0.002; b-wave, p<0.001; Oscillatory potentials (OPs), p<0.005) especially at high intensities. Implicit times showed little differences between electrodes for the a-wave, significantly faster (p<0.03) b-waves at some intensities, and significantly slower (p<0.005) OP implicit times across all intensities. The PIlI amplitude (log microV), sensitivity and timing were not significantly different (p>O.05) if expressed in logarithmic units but PII amplitude (log microV) was significantly smaller with corneal electrodes. We suggest that a conversion factor (x1.35) should be applied to data collected with bipolar corneal electrodes to estimate the amplitudes of the modelled parameters accurately. The corneal electrode gave a precision of +/-39 microV which yields a statistical power of 0.90 for a sample size of 7 subjects. We conclude that bipolar corneal electrodes provide smaller electroretinogram amplitudes due to their location and reduced span of the retinal generators.

Animals↗

PubMed1998

False-response monitoring during automated perimetry.

PURPOSE: To ascertain the accuracy and precision of the catch-trial monitor used to estimate the false-response rate in automated perimetry. METHODS: False responses were automatically injected at various rates by modified perimetric software while reliable perimetric subjects underwent visual field thresholding. Four repeat tests were conducted within a 1-hour period to quantify the variability and bias inherent in the catch-trial technique. RESULTS: The catch-trial method gave a very accurate estimate of the average false-response rate. Precision, however, was quite poor because of the small sample of catch trials. Outcomes were predicted using a binomial model, and we demonstrated good concordance between the model and empirical data. When the true false-response rate was 33%, estimates derived from catch trials ranged from 7 to 57%. CONCLUSIONS: Although the catch-trial method gave an accurate estimate of the false-response rate, confidence intervals were too wide to provide a high level of precision. Our data suggest that tests with reported false-response rates < 20% may be considered reliable.

Adult↗

PubMed1998

Developing a clinical probability density function for automated perimetry.

BACKGROUND: Automated perimetry is associated with lengthy test times, but Baysean predictions can be applied to speed up testing. A critical component of such methods is the starting probability density function (PDF). METHODS/RESULTS: In the present study we show that a unimodal PDF, suggested n the literature as adequate for clinical data, fails to describe the thresholds of diseased eyes and we develop a bi-modal PDF representative of a clinical population. CONCLUSION: We suggest that the implementation of a bi-modal PDF will save test time and retain test accuracy.

Adult↗

PubMed1998

Effects of migraine on visual function.

BACKGROUND: Data is reported from an ongoing trial considering whether visual loss associated with migraine is consistent with a selective deficit in M- or P-cell functioning. METHODS: The psychophysical tests used include spatio-temporal contrast thresholds and luminance increment thresholds for a spot drifting across a spatially or temporally modulated background. A migraineur and 15 non-headache controls participated in the present study. Measurements were made foveally and at 10 degrees in the superior field. Static and flicker perimetry were conducted. RESULT/CONCLUSION: Regionalized losses occurred for stimuli with moderate temporal frequencies (16 Hz), which is consistent with M-cell dysfunction.

Adult↗

PubMed1998

Electroretinograms of albino and pigmented guinea-pigs (Cavia porcellus).

PURPOSE/METHODS: The present study compares the electroretinogram responses of albino and pigmented guinea-pigs (Cavia porcellus) with data published for the rat and mouse. RESULTS: We found that albino guinea-pigs gave significantly larger amplitudes and faster implicit times for a-wave and peak-to-peak responses than did pigmented animals. In contrast, pigmented and albino rats and mice do not show such differences between strains. CONCLUSION: We suggest that the guinea-pig may be a better model of the retinal response in human albinism as their response characteristics are consistent with those published for humans.

Albinism↗

PubMed1998

Effect of diet on the rate of depletion of n-3 fatty acids in the retina of the guinea pig.

This study has assessed the influence of maternal n-3 long chain polyunsaturated fatty acid supply and dietary manipulation after weaning on the retinal polyunsaturated fatty acid profile. Infant guinea pigs born of dams fed one of two commercial chow diets (differing in the amount of eicosapentaenoic, docosapentaenoic, and docosahexaenoic acids) were raised in two separate experiments, and subsequently partitioned into two diet groups, one supplied with a high level of alpha-linolenic acid (canola oil supplemented), the other with a very low level of alpha-linolenic acid (safflower oil supplemented). Guinea pigs born of dams supplied with the longer chain n-3 fatty acids in the commercial pellets (experiment 2) showed higher levels of retinal docosahexaenoic acid at weaning compared with those born to dams fed chow containing only alpha-linolenic acid (experiment 1). The rate of depletion of retinal docosahexaenoic acid after weaning onto the safflower oil diet was described by a two-stage exponential decay, possibly reflecting systemic and local conservation mechanisms, in conditions of dietary n-3 fatty acid deprivation. The rate of docosahexaenoic acid depletion in the group with the lower retinal docosahexaenoic acid at weaning was more than double the rate of depletion in the group with the higher weaning docosahexaenoic acid value. The endpoint retinal docosahexaenoic acid level at 16 weeks post-weaning after dietary n-3 fatty acid depletion on the safflower oil diet in the group, which started with the lower retinal docosahexaenoic acid level, was approximately half that compared with the group from the dams fed long chain n-3 fatty acids (experiment 1, 5% (interpolated), experiment 2, 9%). These results suggest that an adequately supplied mother is capable of providing an infant with enough n-3 fatty acids to withstand a longer period of dietary deprivation imposed after weaning.

Animals↗

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↗

PubMed1997

Comparison of red-green, blue-yellow and achromatic losses in glaucoma.

Achromatic losses in glaucoma would be expected to be greater than, or equal to, red-green chromatic losses if the following assumptions are made: (1) the function of the remaining axons is either unchanged or non-selectively reduced; (2) red-green chromatic information is signaled by the midget ganglion cell system; and (3) the function of the magnocellular system is reduced at least as much as that of the midget ganglion cells. This prediction was tested by measuring red-green (along with blue-yellow) mixture thresholds for 1 deg, 0.2 sec test spots presented on a color monitor on a white background of 50 cd/m2. Ellipses were fitted to plots of green contrast as a function of red contrast (or yellow as a function of blue), and major and minor axes of these ellipses were taken as measures of chromatic and achromatic thresholds, respectively. The study population consisted of 29 eyes in 29 patients with early glaucoma; control data were derived from a data bank of 83 normal eyes. Red-green losses were significantly (P < 0.05) greater than achromatic losses in 6 out of the 11 eyes which showed significant losses of either chromatic or achromatic sensitivity (or both). It is concluded that, for these eyes, at least one of the above three assumptions is incorrect.

Adult↗

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↗