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Biomedical subjects

A J Adams

Publications and source records attributed to A J Adams.

At least 55 records · Page 3Linked 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↗
PubMed1990

Visual acuity and contrast sensitivity of the S cone pathway: preliminary measures with letter charts.

Letter charts were used to measure visual acuity and peak contrast sensitivity of the short wavelength sensitive (S cone)-pathway. The accommodative response was monitored retinoscopically. The mean visual acuity (0.92 logMAR) and spatial contrast threshold (8.7%) were comparable to values reported elsewhere, and variability was relatively low. Both S-pathway acuity and contrast sensitivity were selectively reduced in one patient with central serous retinopathy and in another with retinitis pigmentosa. These simple spatial tests offer an additional index of S-pathway integrity which will be useful for detection and evaluation of ocular disease.

Accommodation, Ocular↗
PubMed1990

Comparison of the standard and Adams desaturated D-15 tests with congenital colour vision deficiencies.

The Adams desaturated D-15 was designed to be administered to patients with acquired colour vision defects by simply reducing the chroma of the Munsell colours by 2 for each cap in the test. In this study, the performance of the Adams desat D-15 in the assessment of congenital colour vision deficiencies is evaluated. The standard D-15 and Adams desat D-15 tests were administered to 75 congenital red-green colour deficient subjects who had been diagnosed on the basis of their performance on the Nagel anomaloscope Mark 1. The results were analysed in terms of the directions, extent and specificity of errors and compared with the diagnosis on the Nagel anomaloscope. Of the 13 colour-deficient subjects who made no errors on the standard D-15, 1 failed the Adams desat D-15 and 2 made single crossings. No colour-deficient subject who failed the standard D-15 made anything less than a simple inversion of adjacent caps on the Adams desat D-15. The Adams desat D-15 did not perform as well as the standard D-15 in identification of the type of defect in dichromats. On the basis of these data, it is predicted that about 5% of dichromats will be mis-classified by the Adams desat D-15 whilst under 0.1% will be mis-classified by the standard D-15. However, with the anomalous trichomats, more crossings were made on the Adams desat D-15, particularly by the milder anomals, and a diagnosis was possible in more cases. Where a diagnosis was possible, it was also correct more often with the Adams desat D-15.(ABSTRACT TRUNCATED AT 250 WORDS)

Color Vision Defects↗
PubMed1989

Evidence for a neural basis of age-related visual field loss in normal observers.

Many studies have reported a decrease in visual field sensitivity as a function of increasing age in normal individuals. This age-related sensitivity loss has mainly been attributed to reductions in pupil size and transmission losses of the ocular media (particularly the lens), although neural losses in the retina, optic nerve and visual cortex have also been suggested. We evaluated the role of preretinal factors on normal visual field changes associated with aging. The central visual field of both eyes of 62 normal subjects (ages 20 to 72) were evaluated with Program 30-2 of a modified Humphrey Field Analyzer. Three test procedures were employed: (1) a standard visual field evaluation; (2) a yellow target on a yellow background condition (530 nm cutoff filter) to minimize the influence of lens transmission losses with age; and (3) a large target/high background luminance "yellow on yellow" test condition (530 nm cutoff filter, 635 asb background, Size V target) to minimize both pupil size and lens effects on central visual field sensitivity. In addition, relative lens absorption estimates were obtained for each subject. All three test conditions revealed a loss in visual field sensitivity with increasing age (approximately 0.8 dB per decade) but no meaningful differences were found among the three test procedures. Relative lens density increased with age but was not related to visual field sensitivity for any of the three test conditions. These data suggest that normal age-related visual field sensitivity changes are primarily due to neural losses rather than preretinal factors.

Adult↗
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

Visual acuity changes with age: some new perspectives.

Snellen chart visual acuity is thought to change very little up to age 60 years. However, any changes in contrast in the retinal and/or neural image with age may only be detected in low contrast and low luminance testing conditions. Only under these conditions does contrast significantly influence visual acuity measurements. In this pilot experiment we show that low contrast visual acuity is considerably worse (two lines of Snellen acuity) for an older group (N = 8, mean age 57) than for a younger group (N = 9, mean age 24.6) in spite of the fact that each subject was referred to the study with 6/6 (20/20) or better acuity. At conventional contrast and luminance levels there is no significant difference between the two groups. The results also suggest that a simple measurement of contrast sensitivity for a small spot of light may allow a contrast correction factor to account for both age and luminance level differences in the contrast vs. acuity function.

Adult↗
PubMed1988

Age-related changes in the central visual field for short-wavelength-sensitive pathways.

The sensitivity of short-wavelength-sensitive (SWS) cone pathways throughout the central 30-deg visual field was determined in both eyes of 62 normal volunteers between the ages of 20 and 72 years. We found an average SWS cone pathway sensitivity decrease with age of approximately 0.15 log unit per decade. The sensitivity reduction was approximately linear, with a slightly larger decrease beyond the age of 50 years. The age-related SWS cone pathway sensitivity reductions also became larger as a function of increasing stimulus eccentricity. Measurements of ocular-media absorption characteristics in each eye revealed that 30-40% of the age-related sensitivity loss could be attributed to reductions in transmission of short-wavelength light by the ocular media. After corrections for preretinal media transmission loss, the decrease in the sensitivity of SWS cone pathways with age was approximately 0.09 log unit per decade. This age-related loss is greater than age-related sensitivity decreases in the middle-wavelength-sensitive and/or long-wavelength-sensitive cones (approximately 0.06 to 0.07 log unit per decade). In the age group older than 60 years, there was an inverse relationship between media-corrected SWS cone pathway sensitivity and media absorption characteristics (i.e., media-corrected SWS cone pathway sensitivity was higher in eyes with lower media transmission of short wavelengths). This relationship was not so evident for younger subjects. A similar inverse relationship between transmission loss in the ocular media and SWS cone pathway sensitivity was found between left and right eyes of the same individual.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Central visual fields for short wavelength sensitive pathways in glaucoma and ocular hypertension.

While conventional clinical visual acuity and kinetic visual fields may be essentially normal in ocular hypertension and early stages of glaucoma, other foveal aspects of vision (eg color, spatial and temporal contrast sensitivity) may be quite abnormal. Specifically, a selective vulnerability of the short wavelength sensitive (SWS) visual pathways in these conditions has previously been noted. Here we studied the central visual fields of 33 primary open angle glaucoma (POAG) patients, 32 ocular hypertensives (OHT), and 24 age-matched normal controls using blue and yellow test flashes on bright yellow backgrounds. SWS cone and MWS and/or LWS cone pathway sensitivities were measured at the fovea and at 2.5 degrees, 5 degrees, 10 degrees and 15 degrees eccentricities, in either the inferior temporal (for OHT) or horizontal nasal retina (for POAG). As expected, all groups had normal sensitivity to yellow flashes--detected by LWS and/or MWS cones--in these meridians. By comparison, for the blue flashes--detected by the SWS cones--the POAG and OHT groups had sensitivity deficits, uniformly across the central visual field, of about 6X and 1.8X, respectively, compared to normals. While six of 31 (19%) OHT subjects had localized glaucomatous field defects (greater than 0.4 log units) in the non-foveal inferior temporal retina, none of the 12 OHT subjects who were also tested in the horizontal nasal retina showed loss in this meridian. Finally, while no POAG subjects had localized sensitivity loss for yellow flashes in the horizontal nasal retina, four did show local field defects with blue test flashes.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1987

Clinical measures of central vision function in glaucoma and ocular hypertension.

A generalized loss of visual sensitivity, even for foveal targets, has been reported as an early sign of glaucoma. In the present study of central vision, we used relatively simple and rapid clinical tests of color thresholds, color discrimination, and spatial contrast sensitivity to compare the vision of three age-matched groups of patients who had primary open angle glaucoma (n = 33) or ocular hypertension (n = 32) as well as normal subjects (n = 24). The largest sensitivity losses for both glaucoma and ocular hypertensive groups were disclosed by a color threshold test with blue lights designed to isolate the blue-sensitive pathways of the visual system. The loss of sensitivity for both the glaucoma group and the ocular hypertensive group is consistent with recent reports (from postmortem studies of human eyes) of extensive axon death even in the absence of glaucomatous field defects.

Aged↗
PubMed1987

Optical density of human macular pigment.

Foveal and parafoveal spectral sensitivities of the G cone mechanism were used to derive the difference spectrum for the macular pigment for 12 observers. Measurements of the peak density of the macular pigment were obtained with a shortened version of the same procedure for an additional 15 observers. The mean density for all 27 observers at 460 nm was 0.77 +/- 0.06 with a range of 0.21-1.22. The mean density is higher than that previously reported and, compared to the standard absorbance curve (Wyszecki and Stiles, 1967), the results indicate higher density values for wavelengths on the long wavelength side of the absorption maximum.

Adult↗
PubMed1987

New clinical color threshold test for eye disease.

Selective loss of sensitivity to blue light, when it is detected by the short wavelength-sensitive cones (B cones), is a common early sign of many retinal and visual pathway disorders. A reliable clinical test is needed to allow detection of this defect. We describe a new, simple forced-choice clinical test of B cone function which is brief, reliable, and free of patient criteria for seeing. Test results are relatively unaltered by up to 2 D of uncorrected refractive error and the usual small fixation changes the patient makes during the test. A comparison of three different test results, all obtained within 5 min, allows measurement of R and/or G cone function free of age and individual differences caused by yellowing of the ocular media in the B cone test result. The test has been used to demonstrate B cone sensitivity losses related to the severity of retinopathy in 60 diabetics, as well as selective B cone loss in glaucoma and ocular hypertension.

Color Perception Tests↗
PubMed1987

Axial length elongation, not corneal curvature, as a basis of adult onset myopia.

Adult-onset myopia is most often reported in college age individuals. Its prevalence and the refractive component(s) responsible are essentially unknown; some recent studies implicate corneal curvature. Here I present a single case of adult-onset myopia over a period of 23 years in which axial elongation, and not steepening corneal curvature, is suggested as the most likely basis for the 4.50 D increase in refractive error.

Adult↗
PubMed1987

Short-wavelength-sensitive cones do not contribute to mesopic luminosity.

It has been suggested that the short-wavelength-sensitive cones (S cones) play a significant role in the transition from scotopic to photopic vision (the Purkinje shift). We address this issue directly over a 5-log10-unit range of light levels covering scotopic, mesopic, and photopic vision. At each light level we make flicker matches to two reference stimuli by 2-Hz flicker photometry. The two reference lights (441 and 481 nm) differ only in their stimulation of S This novel technique utilizes the different magnitudes of the rod and cone Stiles--Crawford effects. Despite the large difference in S-cone stimulation by the two reference lights (more than 1 log10 unit), the pairs of luminosity functions are indistinguishable at each light level tested. The results indicate that S cones do not contribute to either photopic or mesopic luminosity.

Humans↗
PubMed1987

Foveal and non-foveal measures of short wavelength sensitive pathways in glaucoma and ocular hypertension.

Blue-sensitive cone thresholds (the ability to detect blue test lights presented on a bright yellow background) were measured to examine foveal and central vision field sensitivity in groups of 33 glaucoma, 31 ocular hypertension (OHT) and 24 age matched normal subjects. Results showed these thresholds were substantially reduced (in all areas tested) for the glaucoma group (approximately 0.8 log units) and less reduced for the OHT group (approximately 0.2 log units), when compared to the normal group threshold. Measures of red-sensitive and green-sensitive cone thresholds showed no difference for all three groups. Furthermore, 16% of the OHT group showed visual field abnormalities for the blue-sensitive cone threshold measure. We conclude that efforts to detect early function loss in glaucoma and OHT could be improved using these measures in clinical practice.

Color Perception↗