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G Haegerstrom-Portnoy

Publications and source records attributed to G Haegerstrom-Portnoy.

At least 37 records · Page 2Linked to original sources
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↗
PubMed1984

Predicting visual resolution from detection thresholds.

Visual acuity is one of the most frequent health measures and is central to vision assessment in schools, industry, aviation, drivers' licensing, and ocular health examinations. There is a need for a rapid, simple, and interpretation-free measure of visual acuity which is amenable to automated and objective assessment. This study shows that a rapid (15 s) and simple contrast threshold measure for a 5 min arc spot correlates highly (r = 0.75) with letter acuity in 360 clinic patients. Assessments by optometrist and technician correlated highly (r = 0.88) as did repeated measures by the same examiner (r = 0.85). The instrumentation appears to be well suited for rapid, automated, and interpretation-free assessment of visual acuity and for visual acuity screening.

Humans↗
PubMed1983

Dyslexic children have normal vestibular responses to rotation.

We examined the rotational vestibular responses of carefully screened dyslexic and control populations (34 dyslexics and 33 controls). The subject groups had equivalent performance IQs but differed significantly on verbal IQ and on silent and oral reading. Children with significant neurologic, visual, or hearing deficits were excluded. We measured eye movements provoked by sinusoidal rotation of the subjects (in total darkness) at low frequencies (0.01 to 0.16 Hz). Gain, phase, and preponderance (asymmetry) of the responses were calculated from the eye velocity and stimulus velocity waveforms. There were no differences between the groups in any of these measures. We conclude that there are no clinically measurable differences in this aspect of vestibular function in our carefully selected populations of dyslexic and control children.

Child↗
PubMed1983

Predictive eye movements do not discriminate between dyslexic and control children.

Pavlidis has suggested that predictive saccadic tracking eye movements distinguish between reading disabled and normal children. We have examined saccadic eye movement tracking in 34 dyslexic and 33 control subjects, between 10 and 12 yr old. The subjects were equivalent in performance IQ (WISC-R), with differences between verbal and performance IQ of less than 30 points. Children with neurological, visual or auditory deficits or histories of emotional problems and hyperactivity were excluded. There were no differences between the groups on the eye movement tracking task when scored objectively by computerized analysis of the eye movement records, or by ranking of the records by an experienced observer. Our results (and those of other recent studies) fail to support Pavlidis' contention that eye movements hold the key to dyslexia.

Child↗
PubMed1983

Tracking eye movements are normal in dyslexic children.

We measured saccadic and smooth eye tracking movements in 34 dyslexic and 35 control subjects and were unable to show differences in any of the tasks or parameters measured. Subjects were carefully screened for neurological, optometric, audiological, and behavioral problems before admission to the study. We suggest that differences between our results and those of previous investigators are based on sampling differences. We conclude that while there may be children with reading disorders secondary to visual or oculomotor deficits, dyslexia can and does exist independent of such deficits. Because, in this and other studies, we have ruled out peripheral involvement, we feel that dyslexia is primarily a deficit of central information processing of written or spoken material.

Child↗
PubMed1982

Effects of benactyzine hydrochloride on dynamic vision functions.

We have investigated the effects of an anticholinergic drug, benactyzine HCl on vision and vision function. Our experiments assess the time course and severity of benactyzine effects on visual acuity for static and moving targets, amplitude and dynamics of accommodation, pupil response to light and the spatial contrast sensitivity function. A single dose of the drug (4.14 mg/70 kg body weight, which is within the therapeutic range) and placebo were administered intramuscularly to 12 subjects. Large and significant decrements in visual function were demonstrated after the administration of benactyzine, particularly for those functions performed at near focus. The drug effect was rapid in onset, beginning 7-10 min after injection, peaked at approximately 30-40 min, and declined to baseline values over the next 2 h. The drug increased pulse rate and blood pressure, and induced an intoxicated state involving loss of concentration, attention, and short-term memory.

Accommodation, Ocular↗
PubMed1982

Effects of an anticholinergic drug, benactyzine hyrochloride, on vision and vision performance.

Benactyzine is an anticholinergic agent which has been used in past years in psychiatry, but is little used today. It has central and peripheral anticholinergic effects, and when administered intramuscularly, it has a rapid onset of action. This may make it useful as an antidote for organophosphate poisoning, in spite of side-effects such as deficits of short term memory, concentration, and attention. As an anticholinergic drug it could also be expected to produce vision changes by its action on the intraocular musculature controlling the pupil and lens accommodation. We tested the drug on six volunteer subjects to establish the visual side-effects of intramuscular administration. We found that it reduced static and dynamic visual acuity, increased pupil size, reduced amplitude of accommodation and contrast sensitivity, while having little or no effect on glare recovery, color vision, intraocular pressure, stereoacuity, oculomotor tracking, and distance heterophoria. Benactyzine produced reductions in visual performance for up to 3 h and had the greatest effects on functions which have significant cognitive components. The present results suggest that the drug is unsuitable for treatment for oganophosphate poisoning when continuous performance is required, although a definitive test of ths suggestion would require that performance should be tested when benactyzine and the organophosphate of interest were combined.

Adult↗