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Biomedical subjects

V C Smith

Publications and source records attributed to V C Smith.

At least 109 records · Page 6Linked to original sources
PubMed1981

Color matching in autosomal dominant tritan defect.

We evaluated color matching in 39 observers with an autosomal dominant tritan defect. Eleven tritans were dichromats with 1 degrees field, and only two were dichromats with an 8 degrees field. Twenty-one of the tritan observers ahd normal blue-green equations with an 8 degrees field, indicating that autosomal dominant tritans have short-wavelength-sensitive cones. Some of the tritan observers showed a shifted blue-green equation, which was ascribed to rod activity.

Adolescent↗
PubMed1980

Metastatic brain tumor from the prostate: two unusual cases.

Metastasis to the brain from prostatic cancer is very rare. Two cases are reported with additional unusual features, 1 with no other metastatic disease, and the other with repeated episodes of subarachnoid and intraventricular hemorrhage.

Adenocarcinoma↗
PubMed1979

Photoreceptor misalignment accompanying a fibrous scar.

A 9-year-old boy with dense fibrous scars at the macula had visual acuities of 6/12 and 6/9 and an abnormal color match (pseudoprotanomaly). The Stiles-Crawford effect functions were abnormal in both eyes, showing maximal sensitivity at the nasal edge of each pupil. The data suggest that the foveal photoreceptors, although spared destruction by an adjacent focus of healed chorioretinitis, have been distorted by fibrous traction arising from that defect.

Child↗
PubMed1979

Autosomal recessive incomplete achromatopsia with deutan luminosity.

Four patients in three different families had a form of autosomal recessive incomplete achromatopsia not previously described. The visual acuity was 6/18 to 6/60 (20/60 to 20/200) with minimal ophthalmoscopic abnormality and normal fluorescein angiogram. The photopic electroretinographic responses were present in all four patients; the fusion rate of 60 Hz was only slightly subnormal. The high-intensity scotopic response was subnormal. The patients failed color screening plates and accumulated over 400 errors with scotopic axis on the Farnsworth-Munsell 100-hue test. The Rayleigh match was abnormal, displaced toward the red primary, but with normal luminance. The photopic luminous efficiency function was similar to that of the deuteranope. Color matching revealed a trichromatic form of color vision mediated by long wavelength and short wavelength cones, and a rhodopsin receptor.

Adolescent↗
PubMed1979

A clinicopathologic study of autosomal dominant optic atrophy.

Of a family with 40 members, 12 had autosomal dominant optic atrophy. The affected members were aware of reduced vision from the first decade. Visual loss was moderate to severe, 6/12 (20/40) to 3/60 (10/200). The affected members showed similar centrocecal scotomata. Most affected patients had severe unclassified color defects. Electroretinography measurements were normal in all but one patient who had a small reduction in the scotopic response. The pathologic changes in a patient with autosomal dominant optic atrophy showed diffuse atrophy of the ganglion cell layer of the retina with a loss of myelin and nerve tissue within the optic nerves. We suggest that autosomal dominant atrophy is a primary degeneration of retinal ganglion cells.

Adult↗
PubMed1979

Chromatic information processing.

The investigation of visual processing mediated solely by chromatic information requires conditions preventing a subject's use of the luminance differences normally accompanying a chromatic change. In Experiment 1, which involved a discriminative reaction time (RT) task, chromatic and white stimuli of the same luminance were presented on a dimmer achromatic background. Subjects were instructed to respond only to the chromatic stimuli. RT was slowest at 570 nm and somewhat faster to short wavelengths than to long wavelengths. In Experiment 2, which compared two discriminative RT tasks, RT was faster when subjects responded to color than when they responded to white. Experiments 3 and 4 demonstrated that a brighter white surround decreased the perceived brightness of chromatic stimuli as well as their perceptual similarity to white, but did not affect RT. The results are discussed in terms of the response strength of the chromatic processing channel.

Color Perception↗
PubMed1979

Duration thresholds for chromatic stimuli.

The duration necessary to detect chromatic stimuli was measured for wavelengths between 463 and 620 nm. Stimuli were presented either in hue substitution (replacement of white by a chromatic stimulus of matched luminance) or as increments. Two observers viewed a 1 degrees 45' homogeneous white field. A trial consisted of replacement of the central 40' of the field by a chromatic stimulus. In substitution mode the white field was 2.4 cd/m2., the chromatic replacement was of matched luminance using heterochromatic flicker photometry (HFP). In increment mode, the white field was decreased to 1.2 cd/m2., the chromatic replacement remained at 2.4 cd/m2. In substitution mode, duration threshold varied from approximately 3--4 ms for the spectral extremes to 45--66 ms at 570 nm. Detected stimuli were always seen as a change in chromaticity. In increment mode, thresholds were in the 2--4 ms range with no dependence upon spectral composition. Detected stimuli were seen either as changes in chromaticity or brightness. A control experiment indicated that HFP did establish equivalent luminance for the hue substitution mode. We conclude that duration thresholds in substitution mode reveal chromatic processing channels; duration thresholds in increment mode are mediated by chromatic and/or achromatic processing channels.

Color Perception↗
PubMed1978

Visual function in acute posterior multifocal placoid pigment epitheliopathy.

We examined a 19-year-old woman with acute posterior multifocal placoid pigment epitheliopathy one week after she noted blurring of central vision. Her corrected visual acuity was R.E.: 6/7.5 (20/25), and L.E.: 6/12 (20/40). The visual fields showed 10-degree pericentral scotomas. A color vision defect and an abnormal Stiles-Crawford effect were present. Dark adaptation showed a delayed time course, with normal final thresholds. The electro-oculogram was subnormal, suggesting widespread abnormality of the retinal pigment epithelium. Active lesions resolved within three weeks, but fluorescein angiography showed characteristic widespread residual changes. Within three weeks, she had normal visual acuity and a normal electro-oculogram. Other tests of visual function showed recovery with a slower time course. By one year, the visual fields, color matching, Stiles-Crawford effect, and dark adaptation were almost normal. Analysis of the color-matching data and Stiles-Crawford effect indicated that the abnormalities of macular function were caused by an underlying lesion of the pigment epithelium and photoreceptors. This caused a physical distortion of the photoreceptor layer and metabolic disfunction of the photoreceptors.

Adult↗
PubMed1978

Autosomal recessive incomplete achromatopsia with protan luminosity function.

A unique form of dichromatic color vision is described in a family with incomplete achromatopsia. In 1966, incomplete achromatopsia was diagnosed in 4 of 14 children of a consanguineous marriage. The 4 affected had best visual acuities of 6/60 or 6/180, pendular nystagmus, and aversion to bright lights. The ERG showed minimal photopic responses. No abnormality of rod function was present. There was a severe color vision defect. In 1976, one of the patients returned for further color testing. Color tests included measurement of the luminous efficiency function using heterochromatic flicker photometry and colorimetric evaluation. The luminous efficiency function resembled that of the protanope. From the colorimetric measurements, we conclude that the patient has a unique form of dichromatic color vision mediated by two visual photopigments: the normal MWS cone photopigment and a photopigment with the spectral characteristics of rhodopsin.

Adolescent↗
PubMed1978

Color matching and Stiles-Crawford effect in central serous choroidopathy.

Color matching and Stiles-Crawford effect measurement were performed in 3 patients with central serous choroidopathy, 2 normal and 1 deuteranomalous trichromats. The color matches in the affected eye of each patient were displaced to red and could be explained by the hypothesis that the visual photopigments are in reduced optical density due to receptor disorientation caused by serous elevation of the sensory retina. The Stiles-Crawford effects of the affected eyes was abnormal confirming the hypothesis of receptor disorientation. The type III color defect accompanied by pseudo-protanomaly ascribable to receptor disorientation as occurs in central serous choroidopathy may be differentiated from the type III defect without pseudo-protanomaly.

Absorption↗
PubMed1977

Large-field trichromacy in protanopes and deuteranopes.

Protanopes and deuteranopes do not accept the classical dichromatic matches when field size extends to 8 degrees visual angle. Their unique matches of spectral yellow to a mixture of red and green are then mediated by the photoreceptors of small-field dichromacy interacting with a photoreceptor with the spectral sensitivity of rhodopsin. Our data suggest that large-field trichromacy is a general feature of protanopia and deuteranopia.

Color Perception Tests↗
PubMed1977

Evaluation of single-pigment shift model of anomalous trichromacy.

The spectral sensitivity of the visual photopigments, the interobserver variability in color judgments, and the spectral locus of unique yellow provide three major problems for accounts of X-chromosomal-linked anomalous trichromacy. According to the single-pigment hypothesis, the primary defect in anomalous trichromacy is a wavelength shift in the peak sensitivity of one of the three visual photopigments. We show that this shift results in reduction of the anomalous trichromat's r-g opponent chromatic channel. The distribution of response variability in Rayleigh equation match widths due to factors other than the spectral characteristics of the photopigments is similar in normal and anomalous trichromats. When normal and anomalous trichromats make hue estimations of sets of stimuli designed to contain similar chromatic information, their judgments show similar variability. Calculation of the r-g opponent chromatic channel can provide correct predictions of the spectral loci for unique yellow for anomalous trichromats.

Animals↗