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Biomedical subjects

R W Massof

Publications and source records attributed to R W Massof.

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

Properties of electroretinographic intensity-response functions in retinitis pigmentosa.

Dark-adapted electroretinogram (ERG) b-wave amplitudes and implicit times were recorded as a function of stimulus luminance for 15 retinitis pigmentosa (RP) patients and 15 normal subjects. B-wave amplitude as a function of log stimulus luminance was fit by non-linear regression with the Naka-Rushton equation, which has 3 independent parameters: The maximum response (Rmax), slope (n) and half-saturation constant (K). B-wave implicit-time as a function of log stimulus luminance was fit by linear regression. Compared to normal, the RP Rmax values were markedly reduced, suggesting response compression; the RP K values were elevated by an average of 0.76 log unit, suggesting relatively small losses in retinal sensitivity. There was no correspondence between Rmax and visual field area for the RP patients (coefficient of correlation = -0.02). All but 2 of the 15 RP patients had normal or shallower-than-normal implicit-time intensity-response functions, indicating that over most of the dynamic range of the ERG, the implicit-times were either normal or faster-than-normal. These results are discussed in terms of possible RP disease mechanisms.

Adolescent↗
PubMed1983

Morphologic changes in the lamina cribrosa correlated with neural loss in open-angle glaucoma.

We divided 25 glaucomatous human eyes into three groups representing mild (Group 1, seven eyes), moderate (Group 2, 11 eyes), and severe (Group 3, six eyes) optic nerve damage, based on visual field testing or remaining number of optic nerve fibers. The optic nerve head of each eye was examined by scanning electron microscopy. Compression of the successive lamina cribrosa sheets was the earliest detected abnormality, occurring in some eyes before the detection of visual field loss. Backward bowing of the entire lamina cribrosa was a later change and involved its upper and lower poles more than the mid-nerve head. The diameter of the scleral opening at the level of Bruch's membrane did not enlarge in these adult glaucomatous eyes. Mechanical compression of the nerve head occurred early enough to be considered a primary pathogenetic event in glaucomatous damage.

Adult↗
PubMed1982

The photomyoclonic reflex: an artefact in the clinical electroretinogram.

An artefact may appear in the clinical electroretinogram (ERG) that can interfere with the recording and interpretation of the ERG b wave. This artefact, the photomyoclonic reflex (PMR), was studied by covering the eye containing the recording electrode and stimulating the fellow eye. Records obtained by this technique before and after administration of a modified Van Lint lid block demonstrated that most of the PMR is due to a reflex contraction of the orbicularis muscle. The remaining part of the PMR was ascertained by eye movement recordings to be a 1.5 degrees to 3.5 degrees downward and medial eye movement. In most persons the PMR occurs with a latency that is fast enough (59 ms +2- 7 ms) to interfere with interpretation of the b wave under most conditions. The PMR can be minimised in some cases by habituation or conditioned suppression. However, these methods generally do not extinguish the PMR but reduce it enough so that it would not readily be rejected as artefact. In such cases the PMR may produce a wave form that mimics a normal amplitude ERG but with delayed implicit time.

Blinking↗
PubMed1981

Two forms of autosomal dominant primary retinitis pigmentosa.

Two types of autosomal dominant retinitis pigmentosa (RP) are identified on the basis of perimetric measures of rod sensitivity relative to cone sensitivity. Type 1 dominant RP patients are characterized by an early diffuse loss of rod sensitivity with a later loss of cone sensitivity and by childhood onset of night blindness. Type 2 dominant RP patients are characterized by a regionalized and combined loss of rod and cone sensitivity with adulthood onset of nightblindness. Comparisons of losses in the photopic and scotopic electroretinogram amplitudes corroborate the psychophysical results. Clinical findings are similar for the two dominant RP subtypes, however, there are differences in natural history.

Adult↗
PubMed1981

Peripheral absolute threshold spectral sensitivity in retinitis pigmentosa.

Dark-adapted spectral sensitivities were measured in the peripheral retinas of 38 patients diagnosed as having typical retinitis pigmentosa (RP) and in 3 normal volunteers. The patients included those having autosomal dominant and autosomal recessive inheritance patterns. Results were analysed by comparisons with the CIE standard scotopic spectral visibility function and with Judd's modification of the photopic spectral visibility function, with consideration of contributions from changes in spectral transmission of preretinal media. The data show 3 general patterns. One group of patients had absolute threshold spectral sensitivities that were fit by Judd's photopic visibility curve. Absolute threshold spectral sensitivities for a second group of patients were fit by a normal scotopic spectral visibility curve. The third group of patients had absolute threshold spectral sensitivities that were fit by a combination of scotopic and photopic spectral visibility curves. The autosomal dominant and autosomal recessive modes of inheritance were represented in each group of patients. These data indicate that RP patients have normal rod and/or cone spectral sensitivities, and support the subclassification of patients described previously by Massof and Finkelstein.

Adolescent↗
PubMed1980

Vector model for normal and dichromatic color vision.

The inclusion of cone mechanisms in a slightly revised version of an earlier model allows accounts of phenomena that involve receptor effects as well as dichromatic color vision. Intensity-dependent parameters that stimulate the adaptation of receptors and opponent and nonopponent mechanisms are varied to predict a wide range of data for both normals and dichromats, including: (i) color matching; (ii) the approximate apparent hue and saturation of the spectrum; (iii) foveal spectral sensitivities obtained by flicker photometry and by detection in the dark and under conditions of achromatic or chromatic adaptation; (iv) heterochromatic additivity failures in the dark-adapted and chromatically adapted eye; (v) approximate differences between brightness and luminance; and, (vi) color and wavelength discrimination under varying adaptation conditions.

Color↗
PubMed1980

Vector magnitude operation in color vision models: derivation from signal detection theory.

Using the theory of signal detection, we have derived an expression for the detectability of a visual stimulus in terms of the general zone theory of color and brightness vision. This derived relationship elicidates the theoretical foundation of the Guth vector model for color vision by showing that the nonlinear vector magnitude operation used by Guth may arise from the observer decision-making process. Testable predictions of stimulus detectability are generated by the derived expression.

Color Perception↗
PubMed1979

Vision threshold profiles in sector retinitis pigmentosa.

Absolute vision thresholds were measured along the horizontal and vertical meridians in four patients from one pedigree and one patient from a second pedigree with dominantly inherited sector retinitis pigmentosa. From these studies we find that (1) visual function is decreased for all parts of the retina, including the fovea, (2) rod and cone systems are affected to the same degree, and (3) the disease progression is confined to the inferior portion of the retina.

Adolescent↗
PubMed1979

Bilateral symmetry of vision disorders in typical retinitis pigmentosa.

Bilateral symmetry of disorders of vision is examined in 60 typical patients with retinitis pigmentosa. We observed a very high degree of interocular congruence in the patterns of both kinetic visual field defects and threshold profiles and in abnormalities of foveal colour discrimination and visual acuity. Abnormalities of foveal colour vision are highly correlated with the extent of visual field loss.

Adolescent↗
PubMed1979

Vision threshold profiles in X-linked retinitis pigmentosa.

Absolute thresholds for blue-green and red stimuli were measured along the horizontal and vertical meridans in two patients with X-linked retinitis pigmentosa. From these data, we deduced that cones mediate detection of both stimuli in the central 10 degrees, there is a ring scotoma in the mid-periphery, and in the far periphery rods mediate detection of both stimuli. Conclusions drawn from the psychophysical measures about rod and cone function across the retina are in point-by-point agreement with the data of a recent electron microscopic study by Szamier et al. on the retina of a 24-year-old X-linked retinitis pigmentosa patient.

Adolescent↗
PubMed1979

Rod sensitivity relative to cone sensitivity in retinitis pigmentosa.

The present study evaluates rod sensitivity relative to cone sensitivity in retinitis pigmentosa patients. From perimetric measures of absolute thresholds to long- and short-wavelength stimuli, we find the results can be characterized in three different ways. For one group of patients it appears that only cone function is present in all parts of the visual field. For another group of patients, despite large losses in absolute sensitivity, rod sensitivity still exceeds cone sensitivity by at least the normal factor, suggesting concomitant rod and cone sensitivity losses. For a third group of patients it appears that central retinal thresholds are determined primarily by cones, midperipheral retinal thresholds determined by a composite of rod and cone function, and far- peripheral thresholds determined predominately by rods. The argument is put forward that the different groups of threshold results represent different disease mechanisms rather than different stages in the progression of a single disease process.

Adult↗
PubMed1978

A general zone theory of color and brightness vision. I. Basic formulation.

A general theory of color and brightness vision, developed from basic principles of the Helmholtz and Hering points-of-view on color vision is presented in a general mathematical form suitable for quantitative analysis. Visual sensation is described by a vector expressed in terms of Hering-like elements for color and brightness which underlie in their spatial-temporal variations the perceptions of form and change. The photic stimulus of vision is recognized to act first and only through photoabsorption producing a Helmholtz-like vector of quantum absorptions. The physiological transformation of the Helmholtz photochemical excitations into the Hering sensation responses is represented as a vector of general operators. The result is a mathematical framework encompassing traditional psychophysical and sensory scaling experiments. The theory is utilized to demonstrate that for many traditional (Class A) psychophysical observations, the physiological operator reduces to a linear (matrix) transformation. For static, uniform, focal stimulation, this reduction is seen to be the basis for earlier specific linear models of color vision. We also illustrate that static intensity-level effects (Bezold-Brücke hue shifts, unique hue invariance) can be modeled from the theory by power, but not logarithmic, intensity-level dependence for the sensation elements.

Color↗
PubMed1978

A general zone theory of color and brightness vision. II. The space-time field.

The elements of vision are brightness and color varying in time and space, constituting a vector space-time function: the visual sensation field. The sensory-field generated from the light-field variations on the retina is analyzed here in terms of elemental space-time responses (Green's functions). Both chromaticity and intensity variations in either time or space are included in a unified theory, to bridge the existing gap between color theory and analyses of spatial and temporal brightness. Sensory Green's functions are here related to standard color models and to familiar responses for special stimuli, and are shown to be advantageous for nonhomogeneous and/or nonstationary visual conditions. The theory is first applied for intensity space-time variations, to elucidate existing intensity-contrast analyses. Then the general theory including chromatic contrast is illustrated by deriving color vision generalizations of the Bloch and Ricco laws and a general space-time reciprocity law, by analyses of wavelength-pulse and color-flicker experiments, and by derivation of Abney's law of luminance additivity for heterochromoatic flicker and minimally distinct borders.

Color↗
PubMed1977

Flicker fusion thresholds in Best macular dystrophy.

Flicker fusion threshold intensities were measured as a function of flicker frequency for patients with Best macular dystrophy having normal or near-normal Snellen visual acuity. These data were found to differ from normal in ways that may be interpreted to be an abnormal elevation of the foveal cone threshold, a loss of cone temporal resolution, or both. The results led to the conclusion that Best macular dystrophy affects the neurosensory retina even when Snellen visual acuity is normal.

Flicker Fusion↗