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Results for “Color Vision Defects”

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At least 109 records · Page 6Linked to original sources
PubMedDate not supplied

Vision screening in a national sample of 11-year-old children.

This report describes the results of vision screening carried out by local health authorities on a national sample of 11-year-old schoolchildren using a standard Snellen chart. Of the 12 772 children tested, 78% had an unaided distant visual acuity of 6/6 or better in both eyes (optimal vision), 10% had a distant visual acuity of 6/9 in the worse or both eyes (near-optimal vision) and 12% had a visual acuity of 6/12 or worse in one or both eyes eyes (definite visual defect). In addition, near visual acuity was tested for 12 737 children and 5% were found to have defective near vision. Glasses had been prescribed for current use in 12% of children but a quarter of those prescribed glasses did not have them available at the time of the test. Testing revealed that 22% of children whose glasses were available had optimal or near-optimal unaided distant vision, the number increasing to 98% when retested wearing glasses. In contrast, 43% of the children who were without their glasses had optimal or near-optimal vision; 27% had a bilateral defect. Amongst the children for whom glasses had not been prescribed 4-6% had a visual defect. A higher proportion of children from non-manual family background than from manual family background had visual impairment and had been prescribed glasses, but there was no significant social class difference amongst the children with visual defects for whom no glasses had been prescribed. A defect of red/green colour vision was recorded in 6% of boys and 1% of girls. The proportion of children with poor visual acuity was similar in the group of children with defective colour vision and the group with normal colour vision.

Child↗
PubMed1978

Blue cone function in a family with an inherited tritan defect, tested with electroretinography and psychophysics.

The sensitivity of the blue cone system to low frequency flicker was tested with a psychophysical and an electroretinographical method. With the psychophysical method the subjects, members of a family with an inherited tritan defect, showed no sign of the presence of the blue cone system. With the electroretinogram the sensitivity was also significantly lower than in normal subjects, thus indicating a retinal origin of the tritan defect.

Adolescent↗
PubMed1976

New data on the vision of South American Indians.

A total of 466 males and 437 females from four Brazilian Indian tribes were tested for color blindness with Ishihara's plates. Defective persons were found in three of the four tribes, but when these and other groups are considered the evidence suggests that the frequency of this trait is lower among Amerindians than among Caucasian populations. Visual acuity tests were performed on 296 Yanomama Indians. Their visual acuity was apparently not as sharp as that of the Cayapo or Xavante. But the scarcity among the Yanomama of persons with serious visual impairment of subcutaneous nodules suggests that the focus of onchocerciasis discovered among them is of recent origin.

Adolescent↗
PubMed1976

Unilateral colour vision defect resembling tritanopia.

A case of unilateral tritan defect is described. Colour-naming experiments showed that the tritanopic eye could perceive multiple colour hues. Although the defect resembled congenital tritanopia, it was considered to be acquired secondary to retinal pathology.

Adult↗
PubMed1989

Effects of viewing conditions on standard measures of acquired and congenital color defects.

We examined the effect of variations in viewing distance and viewing duration on the performance of color-normal observers with four standard tests of color vision. Significant effects of the experimental manipulations were obtained: both increasing viewing distance and decreasing viewing duration significantly increased the number of errors made by observers. Moreover, the four tests differed widely in their sensitivity to the variations in viewing conditions. Practical implications of the findings for the administration and selection of plate tests are discussed, and possible mechanisms underlying the results are suggested.

Color Perception↗
PubMed1990

Cone dystrophy and supernormal dark-adapted b-waves in the electroretinogram.

A male patient suffering from cone dystrophy was followed over 9 years. In addition to the typical clinical and electrophysiologic signs, supernormal b-waves were found in the dark-adapted electroretinogram. Our case is compared with 12 similar patients described in the literature. Our patient differed from the other patients in the following aspects: he was male and had a congenital stationary disease with a small pigment epithelial scar in the left eye only and no other fundus changes up to the age of 22 years. He did not complain of night blindness. The dark-adapted electroretinogram of our patient showed a normal b-wave threshold with increased b-wave amplitudes and markedly prolonged b-wave latencies and implicit times. This combination of signs has not been reported to date in any other patient and points towards a postreceptoral defect of the interneuronal connection.

Adolescent↗
PubMed1976

Examination of colour vision by use of induced contrast colours. Design of a new series of tissue paper contrast tests.

The ability to induce contrast colours is evident in normal persons by the tissue paper contrast principle. However, tests of good quality are not easily available. The design of a new series of charts follows two principles: 1) Selection of background hues in accordance with the maximally desaturated regions of the spectrum as seen by the colour defectives. 2) Exact adjustment of the neutral test field (constituted by the chart figures) in order to eliminate any false clue due to brightness contrasts. By introducing chart figures of alternative grey values appropriate tests can be attained for each type of colour vision defect. 37 persons with congenital colour defect and 15 persons with acquired defects were examined. The charts, according to the criteria for selection, proved to be selective in their screening efficiency.

Adolescent↗
PubMedDate not supplied

Color vision testing.

1. Color deficiency occurs in about 8% of the population, due to alterations in the chemistry of one of the three receptive pigments for colored light, or the substitution of one pigment for another in the photoreceptor cones. 2. Subjects with pigment alteration can see a broad range of color; those with substitution of one pigment for another have broad areas of color perception defect. 3. The most common tests are pseudoisochromatic (color confusion) plates, designed with patterns hidden to the color deficient. Other tests use colored caps, tracing patterns, or an anomaloscope.

Color Vision Defects↗
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↗
PubMed1976

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.

Adult↗
PubMed1976

A family with congenital deutan and tritan defects.

A family has been found with deuteranopia and a tritan defect which is not sex-linked. It is proposed that there is also an autosomal dominant gene for tritan defects showing variable expressivity.

Adolescent↗