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Biomedical subjects

G Haegerstrom-Portnoy

Publications and source records attributed to G Haegerstrom-Portnoy.

16 recordsLinked to original sources
PubMed1990

LWS cone effects on rod threshold and saturation in achromats with residual cone function.

Rod saturation on flashed and steady red backgrounds was investigated in normals and three achromats, two of whom were found to have some residual cone function. LWS cones selectively reduce the background level at which rod saturation occurs and elevate rod thresholds at flashed background levels well below saturation. Both of these LWS cone actions are also present in eyes with greatly reduced LWS cone function. In normal eyes LWS cones also elevate rod thresholds on steady backgrounds. We thus conclude that LWS cones influence rods through different mechanisms under transient (flashed) and steady-state background stimulation and that the increase in rod visual sensitivity observed during prolonged presentation of a background is due to a time-dependent reduction of LWS cone influence on rods. Finally, the finding that rod-cone interactions of the same magnitude found in normals can be seen in individuals where the cones' ability to mediate vision is severely reduced suggests the rod saturation paradigm as a sensitive technique for revealing residual LWS cone function.

Adaptation, Ocular↗
PubMed1990

Spatial sensitization in the short wavelength sensitive pathways under dichoptic viewing conditions.

Spatial sensitization (Westheimer) functions were measured under conditions that isolated the short wavelength sensitive pathways. The variable diameter pedestal and the test probe were either presented to the same eye (monoptic presentation) or to different eyes (dichoptic presentation). The most significant new finding was that a dichoptically presented, small, blue pedestal caused threshold elevations of about 1-2 long units for an S cone detected probe. However, a large pedestal caused little or no change in threshold. This result contrasts with previous results using white light stimuli, which showed that steadily presented dichoptic pedestals caused little or no threshold change. Furthermore, we show there is little masking when the probe is detected by the isolated M or L cone pathways. These data thus demonstrate a binocular, size dependent interaction revealed only when S cones detect the probe.

Contrast Sensitivity↗
PubMed1990

Predicting visual acuity from detection thresholds.

Visual performance based exclusively on high luminance and high contrast letter acuity measures often fails to predict individual performance at low contrast and low luminance. Here we measured visual acuity over a wide range of contrasts and luminances (low mesopic to photopic) for 17 young normal observers. Acuity vs. contrast functions appear to fit a single template which can be displaced laterally along the log contrast axis. The magnitude of this lateral displacement for different luminances was well predicted by the contrast threshold difference for a 4 min arc spot. The acuity vs. contrast template, taken from the mean of all 17 subjects, was used in conjunction with individual spot contrast threshold measures to predict an individual's visual acuity over a wide range of luminance and contrast levels. The accuracy of the visual acuity predictions from this simple procedure closely approximates test-retest accuracy for both positive (projected Landolt rings) and negative contrast (Bailey-Lovie charts).

Adult↗
PubMed1989

Visual assessment of the multiply handicapped patient.

The visual capabilities of the multiply handicapped and/or developmentally delayed patient are difficult to assess with methods that depend on the patient's subjective responses. Fifty-nine patients with multiple neurological handicaps and unknown visual capabilities were examined using a modified ophthalmic examination which included visual acuity measures using visual evoked potential (VEP) and preferential looking (PL) techniques. Patients ranged in age from 3 to 33 years; median age 9 years. Significant refractive error (in 73%) and strabismus (in 71%) were the most common ocular disorders. Of the 43 patients with a significant refractive error, only 16 (37%) were wearing their proper correction (ranging from -21 to +20 D). In 27 patients the uncorrected refractive error ranged from -10 to +20 D. Binocular acuities (with refractive correction) could be obtained from 56 patients (95%) using a spatial frequency sweep VEP technique, and in 41 patients (70%) using PL grating acuity cards. The VEP and PL grating acuity measures agreed to within 1 octave (a factor of 2 in minimum angle of resolution) in 27 of 41 patients. VEP acuity was 1.1 to 2.7 octaves higher in 12 patients. Grating acuity of at least 6/12 (20/40) was estimated in 12 patients. Residual vision can be measured in "difficult to examine" multiply handicapped patients with VEP and PL techniques.

Adolescent↗
PubMed1988

Spatial sensitization of the B cone pathways.

Spatial sensitization functions were determined under chromatic adaptation conditions designed to isolate the short-wavelength-sensitive pathways (B cone pathways). Spatial sensitization occurs over large retinal dimensions for B cone detected targets and can be produced both by signals from B cones and by signals from R and/or G cones. Field sensitivity measures demonstrate that the mechanism producing sensitization on short-wavelength backgrounds has the spectral sensitivity of B cones. The field sensitivity on long-wavelength backgrounds does not correspond to any receptor spectral sensitivity or any pi mechanism, but suggests that opponent interaction between medium and long-wavelength receptors produces sensitization of B cone detected targets.

Adaptation, Ocular↗
PubMed1988

Cone interaction occurs in the parafovea under pi 4 stimulus conditions.

This study shows that stimulus parameters that isolate Stiles' pi 4 mechanism at the fovea do not isolate pi 4 parafoveally. Instead, the parafoveal test sensitivity peaks at 520 nm and is relatively depressed at longer wavelengths. This narrowed spectral sensitivity is not due to rod intrusion or interaction but rather suggests cone interaction for a relatively wide range of spatial and temporal parameters. The anomalous shape of the parafoveal spectral sensitivity is not found in a protanope, further supporting the view that the effect seen in normal trichromats is the result of interaction between L and M cones. The study provides a unifying explanation for discrepant results by investigators studying the chromatic properties of spatial sensitization and the contrast after-flash effect. Foveal studies found independence of pi mechanisms while parafoveal studies found interaction. The present study emphasizes the importance of retinal eccentricity on color threshold experiments.

Color Perception↗
PubMed1988

Short-wavelength-sensitive-cone sensitivity loss with aging: a protective role for macular pigment?

The hypothesis was tested that the yellow macular pigment protects the human fovea from retinal neural damage caused by visible-light exposure over a lifetime. The sensitivities of the short-wavelength-sensitive-cone (S-cone) pathways and a long-wavelength-sensitive pathway were assessed across the central retina in a young group (average age, 23 years) and an older group (average age, 67 years) of normal healthy observers. No statistically significant difference was found at any retinal locations between the groups for the measures of long-wavelength sensitivity. However, the older group showed a significant differential loss of S-cone sensitivity across the retina compared with the younger group, with more loss of sensitivity at nonfoveal locations than at the fovea. This differential loss across the retina cannot be accounted for by yellowing of the crystalline lens, since lens effects are present equally at all retinal eccentricities. This result supports the hypothesis that the macular pigment protects the foveal area from light damage.

Aged↗
PubMed1988

Combined atropine and 2-PAM Cl effects on tracking performance and visual, physiological, and psychological functions.

Combinations of atropine (up to 4 mg.70 kg-1) and 2-PAM Cl (up to 1200 mg.70 kg-1) were studied for their effects on a pursuit tracking task, six visual functions, heart rate and blood pressure, and cognitive functions as measured by six psychological tests. Tracking performance in both bright light and dim light was significantly degraded up to 3.5 h after injection. High- and low-contrast near acuity was significantly altered up to 6 h after injection, whereas accommodation and pupil size remained altered for 24 h. Elevated pulse rates were observed for 4 h. Elevated systolic blood pressures were observed for 2 h while diastolic pressures remained elevated for 6 h. No drug effects were found for the psychological tests. Overall, the observed effects of these two drugs in combination are qualitatively similar to those of atropine alone although they are of greater magnitude. On two measures (accommodation and diastolic blood pressure), 2-PAM Cl was found to significantly potentiate the atropine effect.

Accommodation, Ocular↗
PubMed1987

Effects of atropine and 2-PAM chloride on vision and performance in humans.

These experiments assessed the time course and severity of effects of atropine and 2-PAM chloride on selected visual functions, physiological measures, and a tracking performance task. Atropine up to 4 mg X 70 kg-1 body weight and 2-PAM Cl in doses up to 1200 mg X 70 kg-1 body weight were administered intramuscularly in a double-blind Latin square design. A long lasting and dose-related increase in pupillary diameter and decrease in accommodative amplitude with accompanying loss of near visual acuity was found following atropine administration. These functions returned to baseline 2 d after injection. Distance acuity, contrast sensitivity, color vision, and intraocular pressure showed no changes after atropine. Tracking performance was significantly decreased by 4 mg of atropine. The changes in vision function cannot readily explain the tracking performance loss, since the tracking involved a distant visual target while the atropine produced degradation of near vision. Most of the physiological tests, tracking performance and all visual functions were unaffected by 2-PAM Cl.

Accommodation, Ocular↗
PubMed1986

Contribution of vision variables to mobility in age-related maculopathy patients.

Can mobility performance be predicted from measures of vision function? This study addressed this question by measuring a series of vision variables including visual acuity, visual fields, and differential motion sensitivity in a group of patients with age-related maculopathy (ARM) and a group of age-matched normals. Mobility performance at three adaptation levels was determined objectively on an indoor course. The results indicate that for the patients with ARM, mobility variables can be predicted from measures of vision function, including differential velocity sensitivity, and that simple variables such as time taken to complete the course and average speed are those which relate best to vision.

Aging↗
PubMed1986

Dark adaptation in age-related maculopathy.

Dark adaptation was measured for patients with age-related maculopathy (ARM) and for age-matched controls; green and red test stimuli were flashed 15 degrees from the fovea to examine differential effects of ARM on rod and cone functions, respectively. The ARM patients showed decreases in sensitivity for both rods and cones (0.5-1.5 log units) and an increased time constant of recovery for rod function. After 20 min in the dark, sensitivity to both red and green stimuli was depressed at the fovea and at 5, 10, 15 and 25 degrees eccentric to the fovea. The greatest sensitivity loss was found in the macular area (fovea and 5 degrees eccentric). Our data suggest that the ARM patients have an abnormality in both rod- and cone-adaptation systems over a relatively large retinal area which extends beyond the zone of visual field abnormality.

Age Factors↗
PubMed1978

Marijuana, alcohol, and combined drug effects on the time course of glare recovery.

The time course of light adaptation after intense light exposure is significantly delayed by alcohol, marijuana, and a combined dose of alcohol and marijuana. These effects were found in a double blind experiment, using 10 subjects. The experimental treatments were placebo, 0.75 ml/kg of 95% ethanol, 8 and 15 mg of delta9 tetrahydrocannabinol (THC). and 0.75 ml/kg of 95% ethanol together with 15 mg of THC. The marijuana-induced delay in recovery is doserelated. Both drugs produce delayed recovery for at least 2 h after drug ingestion. The combined alcohol and marijuana treatment produces little more than the effect produced by either drug alone, suggesting some antagonism between the drugs--a suggestion supported by a significantly lower blood alcohol level for the alcohol dose when combined with marijuana than when taken alone.

Adaptation, Ocular↗
PubMed1977

Pupil size after use of marijuana and alcohol.

In an experiment using ten subjects, marijuana produced a dose-related constriction of the pupil at low photopic light levels; alcohol produced no effect on pupil size. The two drugs in combination produced no change in pupil size.

Adult↗
PubMedDate not supplied

Comparison of on- and off-axis photorefraction with cycloplegic retinoscopy in infants.

We have compared the performance of an off-axis (knife-edge) photorefractor with that of an on-axis (isotropic) system. Normal infants and children between the ages of 8 and 208 weeks were photographed with each camera both with and without cycloplegia. Refractive errors were estimated for each technique based on equations derived from ray-tracing. These refractions were compared to the results of retinoscopy under cycloplegia. Sensitivity and specificity of the two photorefraction systems were evaluated as a function of the magnitude of meridional hyperopia defined by retinoscopy. We also examined the effect of varying the photorefraction screening criterion. Thirteen percent of the infants in the screening sample presented with +3.50 diopters or more of meridional hyperopia. Using this level of ametropia as a referral criterion, the sensitivity and specificity of the off-axis system for infants without cycloplegia were 83% and 72%, respectively. For the on-axis system, sensitivity and specificity values were 85% and 53%. The use of cycloplegics did not significantly improve the performance of either system, but rather their use degraded the specificity of the on-axis system in the presence of moderate refractive errors. The results of the present study indicate that both on- and off-axis systems are effective in identifying highly ametropic infants, but that the off-axis system results in significantly fewer false positives. Moreover, the off-axis system has the advantages of an inherently greater dynamic range for a fixed camera design, and also more easily interpreted photographs.

Child, Preschool↗