Search PubMed⌕ Search

Biomedical subjects

A J Adams

Publications and source records attributed to A J Adams.

At least 73 records · Page 4Linked to original sources
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

Adaptation of a color-opponent mechanism increases parafoveal sensitivity to luminance flicker.

Sensitivity to 25 Hz luminance flicker is enhanced as the intensity of a background is increased. This effect is due, in part, to light adaptation of cones. Preliminary studies suggested that, in the parafovea, the enhancement of flicker sensitivity is due to the adaptation of a color-opponent mechanism rather than a single cone mechanism or achromatic mechanism. In the present study, action spectra and field additivity experiments demonstrated that the enhancing effect was opponent in nature. The field sensitivity function had a notch at 570 nm; fields on either side of the notch acted subadditively. This suggests that, in the parafovea, the sensitivity of an achromatic flicker mechanism is influenced by the adaptation of a chromatic mechanism.

Adaptation, Ocular↗
PubMed1986

Spatial extent of rod-cone and cone-cone interactions for flicker detection.

Over a large range of light adaptation levels, sensitivity to 25 Hz flicker improves as the light level of the background increases. Using small background discs and annular surrounds, this effect was shown to be mediated by the surround and not the average luminance of the test region, in agreement with recent reports. The effect is due to two types of lateral interaction: at mesopic light levels (from 0.1 to 1.0 td), cone-mediated flicker resolution is enhanced by the stimulation of surrounding rods; at photopic light levels (above 10 td), flicker sensitivity improves with light stimulation of adjacent cones. The spatial zone, or extent, over which the surround contributes to the flicker threshold was measured. The spatial area over which rods influence the cone 25 Hz flicker threshold is larger than the analogous spatial area of cone influence. In the parafovea, at 5 deg eccentricity, cone flicker sensitivity for a 20' spot is influenced by cones in a 1 deg diameter area centered on the spot; the corresponding area of rod influence is about 3 deg. In the fovea, flicker sensitivity for a 10' spot is influenced by cone stimulation in an area of about 20' diameter. Rods which affect foveal flicker sensitivity appear to occupy an annular zone with about a 2 deg outer diameter and 1 deg inner diameter, centered on the fovea.

Adaptation, Ocular↗
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↗
PubMed1986

Total occlusion does not disrupt photoreceptor alignment.

Previous measurements of the photopic Stiles-Crawford function (SCF) in human observers prior to, during, and after (1) total occlusion, and (2) displacement of the eye's pupil, indicate by inference the presence of a phototropic mechanism which actively maintains photoreceptor alignment. In an attempt to replicate and expand the conclusions of these experiments, full SCFs were measured on three normal eyes and one abnormal eye prior to and after at least 6 days total occlusion. Counter to previous reports, total occlusion induced few if any alterations in the SCF rho value in both the normal and abnormal eyes.

Darkness↗
PubMed1985

Toward the design of an optimal filter for enhancement of dichromat monocular chromatic discrimination.

Based on Farnsworth's theories of color confusion and discrimination, "rose-colored" or "pink" filters such as the X-Chrom material of 0.16 mm in thickness or the Kodak Wratten no. 30 filter act as monocular chromatic enhancers for red/green color deficients by virtue of colorimetrically lengthening color space in a direction perpendicular to the dichromatic axis of color confusion. Using derived formulas for dichromat colorimetry, a set of representative isoluminant-isochroma spectral hues, and interactive computer graphic colorimetric tools, it is possible to determine an optimum spectrophotometric filter curve. Such a filter has minimal middle wavelength transmission and is optimal in terms of providing maximal monocular chromatic clues for discriminative tasks involving confused colors.

Color Perception↗
PubMed1985

Performance of air traffic control tasks by protanopic color defectives.

Air traffic controllers perform a number of tasks which involve color identification, color discrimination, and color naming. Normal color vision is required for air traffic controllers, although the requirement is currently under review. The most critical task involving color is the distinction of red and black on flight strips; the distinction must be made reliably, quickly, and routinely for flight safety. In this study of four protanopes and three normals, all the protanopes were unable to make this distinction reliably under the lighting levels encountered at air traffic control (ATC) centers, whereas none of the normals had any difficulty. Protanopes also made numerous errors with other ATC tasks involving color. The use of a red filter, often recommended to aid color defectives, actually made performance worse and additionally compounded the usual protanopic loss of brightness for red light. When Snellen visual acuity was tested using the red filters, protanopes needed up to four times larger letters than the color normals. It is concluded that protanopes have inadequate vision for safe performance of some current ATC tasks.

Aviation↗
PubMed1984

The use of the plasma epinephrine response in the diagnosis of idiopathic postprandial syndrome.

Patients with idiopathic postprandial syndrome (IPS) report recurrent postprandial episodes that resemble the clinical manifestations of hypoglycemia. In an effort to find objective criteria for diagnosis of IPS, we studied a group of patients with IPS and controls during an oral glucose tolerance test. Patients with IPS had a significantly lower mean glucose nadir and higher hypoglycemic index than controls. Although 74% of patients with IPS had glucose nadirs higher than 50 mg/dL, their responses of epinephrine, cortisol, growth hormone, glucagon, and norepinephrine were significantly higher than the respective changes in the controls. Of the five hormones, only the epinephrine response separated the patients from the controls without overlap. The epinephrine response may represent a valuable diagnostic criterion for this disorder.

Adolescent↗
PubMed1984

Rod-cone interaction in flicker detection.

There is considerable evidence in the literature that rod-cone interaction occurs when both rods and cones simultaneously detect a test target. More recent evidence, however, has shown a parafoveal rod-cone interaction during dark adaptation for a purely cone-detected flickering test stimulus; this influence on cone threshold appears to be mediated by surrounding rods. In this study, we demonstrate a similar rod-mediated influence on parafoveal cone-detected flicker threshold. More surprisingly, foveal cone-detected thresholds are also influenced by rods. This effect occurs over at least a 2 log unit intensity range of mesopic background level; cone-detected 25 Hz flicker sensitivity is enhanced by increasing the radiance of the background. The action spectrum of this effect fits the scotopic spectral sensitivity curve. At higher background levels, this rod-cone interaction disappears and surrounding cone activity then influences the cone flicker threshold. The results suggest that, as rods recover sensitivity, they reduce cone-detected flicker sensitivity, even at the fovea. The rod influence on cone flicker is most apparent for long wavelength test stimuli. Our results, in agreement with recent reports, suggest that the rod-cone interaction is laterally-mediated and may be specific for the long wavelength-sensitive cone type.

Adaptation, Ocular↗
PubMed1984

Development of quantitative tools for filter-aided dichromats.

Historically, there has been little quantitative rationale for the prescription of colored filters for color deficients . A formal prediction of the effects of any filter on dichromat luminance and chromatic discrimination is presented; these predictions were generated by using colorimetric concepts and related derived formulas to create four interactive computer-graphic tools. In addition to predicting performance of presently available commercial filters, such tools can be used to describe, classify, and even design new filters.

Color↗
PubMed1984

An experimental test of filter-aided dichromatic color discrimination.

Using derived formulas for dichromat colorimetry and related computer graphic colorimetric tools, predictions of color discrimination performance are made for a deuteranope and protanope standard observer for each of three commercial color deficiency "treatment" filters. Five deuteranopes and five protanopes then participated in two experiments. They were asked to order the caps of the D-15 test, and in a second experiment arrange color pairs (from the D-15 test) in order of difference. Predictions and subject performance reveal that although X-Chrom aided dichromats gain both luminous and chromatic information, all dichromats used predominantly chromaticity information in discrimination tasks. The colorimetric tools correctly predicted that protanopes would derive less useful luminous information from the X-Chrom filter compared with deuteranopes , and correctly predicted an increase in discrimination of blues and purples for both classes of red-green color deficients .

Adolescent↗
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↗
PubMed1984

Effect of ophthalmic filter thickness on predicted monocular dichromatic luminance and chromaticity discrimination.

The majority of ophthalmic filters, whether they be in the form of spectacles or contact lenses, are absorbance type filters. Although color vision researchers routinely provide spectrophotometric transmission profiles of filters, filter thickness is rarely specified. In this paper, colorimetric tools and volume color theory are used to show that the color of a filter as well as its physical properties are altered dramatically by changes in thickness. The effect of changes in X-Chrom filter thickness on predicted monocular dichromatic luminance and chromaticity discrimination is presented.

Color Perception↗
PubMed1984

Color vision screening: a comparison of the AO H-R-R and Farnsworth F-2 tests.

Vision screening tests should include a simple, reliable, and valid test of color vision defects. In this investigation the single plate Farnsworth F-2 test and the AO H-R-R pseudoisochromatic plates were compared as primary screening tests for red-green color defective vision. The tests were administered to 2827 children, kindergarten through high school grades. Both tests failed a higher percentage of children than expected in the lower grades (kindergarten through 3). In grades 4 through high school, however, 4.16% failed the F-2 test and 4.02% failed the AO H-R-R, compared to a predicted 4.2% of the general population with inherited red-green deficiencies. The failure rates of the F-2 test for 1171 high school boys and girls were 7.3 and 0.89%, respectively, very close to the expected incidence of red-green defects in males and females. Although the F-2 test passed a few pupils who failed the AO H-R-R test, their defects were categorized as mild or borderline on the AO H-R-R test and therefore not likely to be of practical significance. Less than 0.5% of the children in grades 4 through high school failed the F-2 test after passing the AO H-R-R. Some children with normal color vision, particularly very young children, may fail the F-2 test because of difficulty picking out the less obvious blue square. Nevertheless, for screening purposes the F-2 test is comparable to the AO H-R-R test and except for kindergarten and grade 1 pupils is an excellent single plate color vision screening test.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
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

Influence of glycogen on liver density: computed tomography from a metabolic perspective.

The liver is a metabolically active organ with a radiographic density that can be modified by its glycogen and fat content. In rhesus monkeys an increase in liver glycogen induced by glucose loading was accompanied by an increase in attenuation values on computed tomography and a decrease in total liver fat. Conversely, fasting depleted glycogen, increased fat, and decreased liver attenuation. Acute glycogen depletion without significant change in fat was induced by administration of glucagon and accompanied by a decrease in attenuation. These results along with in vitro measurements of glycogen solutions suggest that an increase of approximately 3 Hounsfield units can be expected for each percent increase in liver glycogen content.

Absorptiometry, Photon↗
PubMed1983

Macular pigment difference spectrum from sensitivity measures of a single cone mechanism.

We have obtained the difference spectrum for the macular pigment by comparing the spectral sensitivity of the "green-sensitive" or G cone mechanism in the foveal and parafoveal region. The method overcomes objections to previous attempts to obtain a difference spectrum from the spectral sensitivities by isolating a single receptor mechanism; it also provides a relatively easy approach for obtaining a reliable measure of the optical density of the macular pigment for individual subjects. Our results using this method suggest a higher optical density for the macular pigment than that obtained from data where more than one cone type influenced the difference spectrum.

Color↗