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Biomedical subjects

M A Sandberg

Publications and source records attributed to M A Sandberg.

68 records · Page 4Linked to original sources
PubMed1983

Color plates to help identify patients with blue cone monochromatism.

A new color vision test distinguishes patients with X-chromosome-linked blue cone monochromatism from those with autosomal recessive rod monochromatism. The test consists of two instructional and four test plates. Each test plate has three identical blue-green arrows and one purple-blue arrow; test plates differ from one another only with respect to the chroma of the purple-blue arrow. All five patients with blue cone monochromatism, aged 5 to 31 years, easily distinguished the purple-blue arrow on all four test plates, whereas none of the seven patients with rod monochromatism, aged 6 to 60 years, could distinguish the purple-blue arrow on all four plates. If a boy has a reduced visual acuity, normal rod electroretinograms, and 30-Hz cone electroretinograms reduced more than 97% below normal, this test can be used to determine whether his condition is an X-chromosome-linked one or an autosomal recessive one.

Adolescent↗
PubMed1983

Visual acuity and cone spatial density in retinitis pigmentosa.

Cone increment thresholds were measured psychophysically in 42 patients (ages 10 to 59) with retinitis pigmentosa and visual acuities of 20/20 to 20/70. A 6-min arc diameter stimulus was flashed to the foveola at a background retinal illuminance for which Weber's law was in effect; under these test conditions, cone increment thresholds depended on the number of remaining functioning cones (cone spatial density) but not on their outer segment length (cone optical density). Log threshold and log visual acuity were correlated inversely (P less than 0.001). The slope of the regression line relating these two measures was compatible with the idea that reduced cone spatial density is a major determinant of reduced visual acuity in retinitis pigmentosa. In a subset of these patients with visual acuities of 20/25 or better, results of cone increment threshold testing suggested that cone spatial density was reduced significantly less in the foveola than in the parafovea.

Adolescent↗
PubMed1982

Psychophysical studies of cone optical bandwidth in patients with retinitis pigmentosa.

Estimates of variation in the alignment of cones with the pupil were obtained from the fovea and parafovea in normal subjects and in patients with retinitis pigmentosa known to have reduced directional sensitivity. The degree of cone disarray was inferred from differences in sensitivity between Stiles-Crawford functions obtained with a stimulus alone and with the stimulus superimposed on a background entering the pupil at a point corresponding to the peak of the Stiles-Crawford function. The magnitude of the selective effect of the background in normals was consistent with previous estimates of variations in photoreceptor alignment in the macula. In contrast, the selective adaptation effect was not present in patients with retinitis pigmentosa. These results exclude increased disarray among cones with normal optical bandwidths, but rather, suggest that morphological abnormalities increasing the optical bandwidths of individual cones underlie reduced directional sensitivity in these patients.

Adaptation, Ocular↗
PubMed1982

The Stiles-Crawford effect in retinitis pigmentosa.

Stiles-Crawford functions were obtained from the maculas of 22 patients with different genetic types of retinitis pigmentosa and visual acuity of 20/40 or better. Reduced cone directional sensitivity was seen in the fovea with both focal cone electroretinographic testing and psychophysical testing. Functions from the parafovea determined with psychophysical testing showed either significant flattening or displaced peak locations. Results are discussed in terms of factors know to affect photoreceptor orientation and histologic findings in retinitis pigmentosa.

Adult↗
PubMed1981

Rod-cone interaction in the distal human retina.

During the rod-isolated phase of dark adaption, b-wave implicit time of the human cone electroretinogram increased exponentially with a time constant corresponding to that for the regeneration of rhodopsin. In the presence of different photopically equated short-wave backgrounds, cone b-wave implicit time varied inversely with the scotopic brightness of the background. Taking into account the origin of the b wave, these measurements support the idea of a rod effect on cone function in the distal human retina.

Electroretinography↗
PubMed1981

Temporal aspects of the dark-adapted cone a-wave in retinitis pigmentosa.

Cone electroretinograms were elicited with a full-field red flash after-45 min of dark adaptation from 16 patients with retinitis pigmentosa and from 17 normal subjects. The average latency and implicit time of the cone a-waves recorded from the patients were each significantly delayed (p less than 0.005) compared with the average normal values. In addition, the patient's waveforms typically showed a loss of two oscillations on the rising slope of the come b-wave. These delays and waveform changes could be simulated in normal subjects by reducing the luminance, but not the diameter, of the stimulus. These studies in normal subjects suggest that shortening of outer segments of remaining cones and not simply loss of cones account for the waveforms observed in patients with retinitis pigmentosa. The results also suggest that remaining cones generate an a-wave in the dark that is normal for a reduced cone visual pigment density.

Adult↗
PubMed1979

Foveal cone electroretinograms in retinitis pigmentosa and juvenile maular degeneration.

Foveal cone electroretinograms were elicited with a hand-held stimulator-ophthalmoscope from 16 patients with retinitis pigmentosa and 17 patients with juvenile macular degeneration. Among 11 patients with retinitis pigmentosa and visual acuities of 6/9 (20/30) or better, eight had foveal cone ERGs that were normal in amplitude and b-wave implicit time; all five patients tested with visual acuities of 6/12 (20/40) to 6/18 (20/60) had foveal cone ERGs that were reduced in amplitude and normal in implicit time. All patients with juvenile macular degeneration and visual acuities of 6/15 (20/50) or worse showed subnormal amplitudes with normal or delayed implicit times, or responses indistinguishable from noise. Amplitudes tended to be smaller and delays greater among patients with juvenile macular degeneration and visual acuities of 6/60 (20/200) or worse.

Adolescent↗
PubMed1979

Foveal cone electroretinograms in strabismic amblyopia: comparison with juvenile macular degeneration, macular scars, and optic atrophy.

A hand-held stimulator-ophthalmoscope was used to elicit foveal cone electroretinograms (ERGs) from fifteen patients with strabismic amblyopia. The ERGs were in response to a 4 degrees stimulus visualized on the fundus and centred on the fovea throughout testing. Foveal cone ERGs from amblyopic eyes were normal in amplitude and normal in b-wave implicit time. Interocular differences in ERGs in patients with amblyopia were no greater than those in normal subjects. Patients with comparable visual acuity loss due to macular scars or juvenile hereditary macular degeneration had abnormal foveal cone ERGs, while patients with optic atrophy had normal responses. These findings support the idea that the defect in strabismic amblyopia does not involve a functional abnormality in the fovea distal to the ganglion cell layer.

Adolescent↗
PubMed1977

Visually evoked response testing with a stimulator-ophthalmoscope. Macular scars, hereditary macular degenerations, and retinitis pigmentosa.

Visually evoked responses (VERs) were recorded from 47 patients under age 60 years with macular scars, hereditary macular degenerations, or retinitis pigmentosa. A hand-held, two-channel stimulator-ophthalmoscope was used to present to the central fovea a 1.5 degrees flickering stimulus centrally superimposed on a steady 10 degrees background. All 31 patients with visual acuity (VA) 20/50 or less had abnormal VERs; among patients with VA 20/25 to 20/40, all six with macular degenerations and five of ten with retinitis pigmentosa also showed abnormal VERs. Abnormal VERs were either out of phase or indistinguishable from noise. Sensitivity of the technique depended on a low ratio of stimulus to background retinal illuminance and the fact that the stimulus could be visualized by the examiner through the ophthalmoscope and maintained on the central fovea througout testing.

Adolescent↗
PubMed1977

A hand-held, two-channel stimulator-ophthalmoscope.

A hand-held optical system for presenting focused stimuli on known retinal areas by direct ophthalmoscopy is described. The optical system provides a time-modulated stimulus beam of variable dimension, retinal illuminance, wave-length, and polarization, and a steady background beam of variable retinal illuminance and wavelength. Both beams enter the patient's eye in maxwellian-view for precise control of the ratio of stimulus to background retinal illuminance. The stimulator-ophthalmoscope allows the examiner to compensate easily for variable fixation.

Child↗
PubMed1977

Blue and green cone mechanisms in retinitis pigmentosa.

Pronounced abnormalities in the increment threshold curves for the blue and green cone mechanisms only 10 degrees above the fovea, and in some cases in the fovea as well, have been found with a 2.5 degrees stimulus in different genetic types of retinitis pigmentosa. Whenever cone thresholds were abnormal, thresholds determined by the blue cone mechanism (pi1 and pi3) were more elevated than those determined by the green cone mechanism (pi4). Thresholds determined by the green cone mechanism were consistently more elevated at low background intensities than at intermediate and high background intensities. Threshold elevations for the blue and green cone mechanisms relative to each other in the perifovea in a given patient tested with the 2.5 degrees stimulus could be simulated in normal observers tested with a single small stimulus. These findings support the idea that the summation pools for blue and green cone mechanisms are proportionally reduced below normal in retinitis pigmentosa, at least in the perifovea, and are compatible with the idea that both mechanisms are comparably involved at the photoreceptor level.

Adolescent↗
PubMedDate not supplied

Submicrovolt full-field cone electroretinograms: artifacts and reproducibility.

The clinical utility of submicrovolt full-field 30-Hz (cone) electroretinograms was assessed by quantifying their contamination by electrical and photoelectric artifacts from xenon-flash stimulators and their test-retest variation in patients with retinitis pigmentosa. Artifacts obtained in saline with four commonly used electrodes varied with electrode type and consisted of an early, brief electrical component and a superimposed, extended photoelectric component. Techniques for minimizing these artifacts are described. Electroretinogram recordings from patients with advanced retinitis pigmentosa or congenital rod monochromatism indicate that these artifacts can be virtually eliminated with bipolar lenses. To assess test-retest variation, narrow-band-filtered responses were obtained twice during 6 weeks from patients with amplitudes less than 1 microV; threshold criteria for significant (p < 0.05) change in amplitude with this technique were approximately 0.25 log unit for each of two different systems.

Adolescent↗