1/12. An acquired color defect of the opponent-color system.An acquired unilateral color defect in a 22-year-old man has been investigated with standard clinical tests and by using techniques which, it is thought, test specifically for the sensitivity of the luminance and opponent-color systems. The spectral sensitivity of the defective left eye, using 1 degree 200 ms. test flashes on a white background, has a single broad peak at about 550 nm. and resembles the photopic luminosity curve; in contrast, the normal curve, measured in the same conditions, has three peaks at about 440, 520, and 600 nm. However, the subject's spectral sensitivity curve for detecting 20 Hz. flicker is quite normal and is similar to his curve for 200 ms. flashes. It has recently been proposed that the three peaks of the normal curve for 200 ms. flashes reflect the activity of the opponent-color system, whereas the single peak for flicker detection is related to the luminance system. The preceding observations may thus be interpreted in terms of a specific loss of the subject's opponent-color system and this would explain his poor color discrimination. His luminance system appears to be normal, and evidence is presented for the maintained function of red- and green-sensitive (but not blue-sensitive) cones. The spectral sensitivity of the subject's right eye is nearly normal, suggesting a precortical origin of the defect; however, there seems to be some abnormality in this eye, indicating a less developed form of the same defect.- - - - - - - - - - ranking = 1keywords = near (Clic here for more details about this article) |
2/12. Macular dystrophy with protan genotype and phenotype studied with cone type specific ERGs.PURPOSE: To determine the L- and M-cone driven ERG responses in a male patient with macular dystrophy and a protan phenotype. methods: We measured large field ERG thresholds to stimuli which modulated exclusively the L- or the M-cones or the two in various combinations (both in-phase and in counterphase). In none of the stimuli, the S-cones were modulated. Additionally, standard and multifocal ERGs were measured. Analysis of the L- and M-cone pigment genes was performed by means of PCR, RFLP analysis and dna sequencing techniques. RESULTS: Macular dystrophy was revealed by the markedly abnormal multifocal ERGs in presence of near normal standard ERGs. The large field ERG responses were exclusively driven by the M-cones with enlarged thresholds when compared with otherwise normal protanopes. In addition, the M-cone driven ERG response phases were abnormal. Pigment gene analysis confirmed a protan genotype with the presence of a single 5'red/3'green hybrid pigment gene. CONCLUSIONS: Our novel stimulus technique allows a reliable analysis of the separate cone pathways even in cases with macular dysfunction. The increased thresholds and the abnormal phase behavior of the M-cone driven ERGs reflect altered mechanisms of the retinal physiology in this patient. The data strongly suggest that the macular dystrophy and the protanopia have independent origins.- - - - - - - - - - ranking = 1keywords = near (Clic here for more details about this article) |
3/12. Japanese family with blue cone monochromatism.The diagnosis of blue cone monochromatism (BCM) is based on severely affected color vision with preserved blue function, nearly nonrecordable photopic ERG, and a family pedigree compatible with X-linked inheritance. We have studied the color vision and ocular function of three members of a family with BCM and a female carrier in the same family. Two of the three affected family members, 9- and 7-year-old brothers, showed the unique features of BCM in their color vision and ERG. The third affected family member, a 43-year-old uncle, showed achromatic vision. He had diabetic retinopathy and moderate cataract which were thought to disturb his blue cone function, causing apparent rod monochromatism. The female carrier, the mother of the brothers, showed normal visual functions except for a slight reduction in photopic ERG amplitude. We believe that this is the first description of BCM in a Japanese family.- - - - - - - - - - ranking = 1keywords = near (Clic here for more details about this article) |
4/12. Luminance-dependent hue shift in protanopes.For normal trichromats, the hue of a light can change as its luminance varies. This Bezold-Brucke (B-B) hue shift is commonly attributed to nonlinearity in the blue-yellow opponent system. In the present study, we questioned whether protanopes experience analogous changes. Two protanopes (Ps) viewed spectral lights at six luminance levels across three log steps. Two normal trichromats (NTs) were tested for comparison. A variant of the color-naming method was used, with an additional "white" term. To overcome the difficulty of Ps' idiosyncratic color naming, we converted color-naming functions into individual color spaces, by way of interstimulus similarities and multidimensional scaling (MDS). The color spaces describe each stimulus in terms of spatial coordinates, so that hue shifts are measured geometrically, as displacements along specific dimensions. For the NTs, a B-B shift derived through MDS agreed well with values obtained directly by matching color-naming functions. A change in color appearance was also observed for the Ps, distinct from that in perceived brightness. This change was about twice as large as the B-B shift for NTs and combined what the latter would distinguish as hue and saturation shifts. The protanopic analogue of the B-B shift indicates that the blue-yellow nonlinearity persists in the absence of a red-green signal. In addition, at mesopic levels (< or = 38 td), the Ps' MDS solution was two dimensional at longer wavelengths, suggesting rod input. Conversely, at higher luminance levels (76 td-760 td) the MDS solution was essentially one dimensional, placing a lower limit on S-cone input at longer wavelengths.- - - - - - - - - - ranking = 2keywords = near (Clic here for more details about this article) |
5/12. Bull's-eye maculopathy and negative electroretinogram.The authors studied four patients with a bull's-eye maculopathy and otherwise normal fundus. A single-flash electroretinogram (ERG) with an intense white light stimulus in the dark showed a normal a-wave but reduced b-wave amplitude (negative ERG). Other findings common to all four patients were initially normal visual acuity, subsequent progressive decrease in visual acuity, mild to moderate deficiency of color vision, normal peripheral visual field, relatively well preserved cone ERG, normal 30-Hz flicker ERG, normal EOG, near emmetropia and selective involvement in males. Cone dystrophy, retinitis pigmentosa, congenital retinoschisis, congenital stationary night blindness, and Batten's disease were excluded. The correlation between this disease and benign concentric annular macular dystrophy is discussed.- - - - - - - - - - ranking = 1keywords = near (Clic here for more details about this article) |
6/12. Eight cases of congenital achromatopsia with amblyopia in two pedigrees from Northern sweden.Two families from northern sweden with a total of 8 patients with typical symptoms of congenital achromatopsia with amblyopia were studied. In one of the families 4 affected children (3 brothers and 1 sister) also showed pallor of the optic discs and marked astigmatism. The transmission of the disease was consistent with an autosomal recessive inheritance in both families. The study confirmed that complete and incomplete achromatopsia might be different expressions of the same gene. Six out or 13 near relatives of the achromatic patients showed minor colour vision defects, suggesting a tendency towards heterozygotic manifestation of the gene.- - - - - - - - - - ranking = 1keywords = near (Clic here for more details about this article) |
7/12. Colour vision tests and colour naming by thirteen incomplete achromats in Bishnupur.As an exploratory study six colour vision tests were given to nine male and two female achromats from the Shankhabanik community in Bishnupur, and to two additional similar males. All thirteen subjects had severe photophobia, fixation nystagmus, extreme weakness of vision (4/24 to 3/60) and the red end of the spectrum was much shortened. This research indicates that they had a form of incomplete achromatopsia, varying from an almost complete to a very severe partial loss of colour vision. The condition is inherited as an autosomal recessive. The most likely interpretation of these cases is that they are incomplete rod achromats. Their performance on the colour vision tests is tabulated, and shows complete inability to do the Ishihara test; nearly complete inability on the HRR test, with a possible slight tendency to do better in the yellow-blue than the red-green sub-tests; on Sloan's test they show approximate accordance with her results for achromats; they have severe difficulty with the dichotomous and 100-hue tests, with a possible slight tendency to make fewer errors on the G/B sections. The anomaloscope shows little abnormality of mid-matching points, but great increases in average matching ranges above the normal, although not absolute loss of colour sense, but with extreme darkening or shortening of the red end of the spectrum. Their colour naming was carefully recorded, and was fairly good occasionally, sometimes erroneous without being wildly at fault, and most often completely wrong. The records of colour naming were made, not, of course, as a form of colour vision test, but simply to illustrate the ways in which such defectives make an effort to use colour names in general use among their friends and relatives.- - - - - - - - - - ranking = 1keywords = near (Clic here for more details about this article) |
8/12. X-linked incomplete achromatopsia with more than one class of functional cones.Five affected males in the fifth generation of a large pedigree of X-chromosomal incomplete achromatopsia were tested. All had SWS cone function. A 19-year-old affected man was a classical blue cone monochromat on color matching and spectral sensitivity. A 16-year-old boy showed evidence of a long wavelength sensitive cone active in 8 degrees color matches. With a blue-green background, his cone spectral sensitivity function peaked near 550-560 nm. Three younger boys, aged 7-10 yrs were evaluated only with color matching. All showed evidence of long wavelength cone function with an 8 degree field and one showed long wavelength cones in 2 degree matches. An independent observation concerning the family was the finding that deuteranomaly was introduced in the third generation. The fourth generation women, all obligate carriers of X-linked achromatopsia, had a 0.5 chance to carry deuteranomaly. Neither carrier state per se is usually associated with expression of deuteranomaly. Three of the five tested expressed deuteranomaly. This finding of deuteranomaly in the carrier females might be a consequence of a double carrier state indicating association between the genes for deuteranomaly and X-linked achromatopsia.- - - - - - - - - - ranking = 1keywords = near (Clic here for more details about this article) |
9/12. Enhanced S cone syndrome: evidence for an abnormally large number of S cones.The cellular basis of the hypersensitivity of the S (blue) cone system in patients with enhanced S cone syndrome was examined by analyzing ERGs from three patients. The patients had large alpha-waves in response to the blue and white flashes. These alpha-waves were shown to be driven nearly entirely by the S cones. Although these S cone alpha-waves were 4-6 times the size of the normal L/M cone alpha-wave, they are of the same form, and could be quantitatively described with the same model previously shown to fit cone alpha-waves. We propose that the retina of these patients has many more S cones than the normal retina and that these cones replace some of the normal L/M cones and many of the rods.- - - - - - - - - - ranking = 1keywords = near (Clic here for more details about this article) |
10/12. Colour identification and colour constancy are impaired in a patient with incomplete achromatopsia associated with prestriate cortical lesions.We have examined visual functions, including colour vision, in a patient with bilateral cortical lesions involving mainly the fusiform and lingual gyri, areas known to be involved in the central processing of chromatic stimuli. The patient has near normal (6/9) acuity, and his responses to tests of binocular function and spatial vision are normal, as are his discrimination of changes in target speed and surface lightness. He does, however, exhibit minor losses in the upper visual field, mild prosopagnosia and topographical agnosia, all conditions commonly associated with cerebral achromatopsia. Colour matches and spectral response data establish that his cone photoreceptors have normal spectral characteristics and his spectral sensitivity measured against a white background reveals normal postreceptoral chromatic function. The patient's colour discrimination for differences in wavelength, hue or saturation is, however, impaired and his colour naming is significantly disturbed, particularly for blues and greens. We have determined the areas of the chromaticity chart that correspond to his naming categories for surface colours, and show that changes in illuminant cause him to alter the names of surface colours in a manner consistent with the changes in their chromaticities. Other subjects with normal or congenital red-green deficient colour vision make many fewer name changes under changes in illuminant. We conclude that the patient's colour constancy is impaired as a consequence of abnormal central processing of colour vision.- - - - - - - - - - ranking = 1keywords = near (Clic here for more details about this article) |
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