Color vision defects in retinal disease.
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Color vision testing was performed on a group of ten black tyrosinase-positive albino patients and a group of normal subjects. Testing was accomplished by means of a Farnsworth-Munsell (F-M) 100-hue test and Nagel anomaloscope. As a group, the albino patients showed an increase in number of errors scored on the FM-100 hue test, without any specific axis in the majority of cases. Results on the Nagel anomaloscope showed a 'widening' into the red end of the Rayleigh equation. A possible explanation for this apparent widening is discussed, which emphasizes anticipated results of matching ranges obtained on extrafoveal cones.
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The Ishihara plates are widely used as a test for colour vision. Originally designed for the purpose of detecting congenital red-green colour blindness, the test also has some value in demonstrating acquired colour vision defects. There are, however, several disadvantages in the present arrangement of the plates. A modification of the test, involving the rearrangement of the order of the plates, is presented which, together with a new recording chart, simplifies both the administration and the interpretation of the test.
The color vision of nine patients aged from 13 to 52 years with Stargardt's disease was studied with the following tests: Standard Pseudoisochromatic Plates part 2 (SSP2), Farnsworth-Munsell 100 hue test (FM100), Nagel (red-green) anomaloscope and Besançon (blue) anomalometer. At the beginning of the disease, a very slight defect in red-green color vision could be demonstrated. Later, a distinct acquired red (pseudo-protanomalous) defect in the Nagel anomaloscope and an abnormal error score in the FM100 test were observed. In advanced stages, the red defect became stronger (scotopization) and the FM100 test showed a red-green axis. In the course of the disease, a blue defect with the SPP2 plates and with the Besançon anomalometer could also be found. The visual acuities of the patients had a significant correlation with the matching ranges of the Rayleigh equation and the Moreland equation. The duration of the disease did not show any correlation with the color vision tests.
We studied color vision in 32 patients with autosomal recessive achromatopsia. Color matching revealed complete achromatopsia (rod monochromasy) in ten patients (Group I) and incomplete achromatopsia in the remaining twenty-two patients. Amongst the incomplete achromats, were three groups distinguishable by their color matching. Patients in Group II were dichromats; their color matches were mediated by rods and MWS (middle-wavelength sensitive) cones. Patients in Groups III and IV were trichromats. Color matches of patients in Group III were mediated by rods, LWS (long-wavelength sensitive) cones and MWS cones. Group III patients showed no evidence of SWS (short-wavelength sensitive) cones. Color matches of patients in Group IV were mediated by rods, LWS cones and SWS cones; color matching did not reveal MWS cones.
Sahlgren's Saturation Test (SST) is a simple sorting test designed for the detection and grading of acquired color vision defects. Like other pigment-based color vision tests, the SST color samples have medium lightness, i.e., they belong to the intermediate part of the gray scale. We tested normal controls and subjects with congenital or acquired dyschromatopsia with five SST versions that differed only in the amount of lightness. The sensitivity of the test increased considerably with increasing lightness. Therefore, the lightness level of SST has now been changed from 30 to 10 Natural Color System units.
A 31-year-old white male deutan produced reliably different profiles when examined binocularly and monocularly with a Farnsworth-Munsell 100-hue test. Discrimination in the long wavelengths improved under the binocular conditions. Intensive testing yielded no information to account for the phenomenon.
An influence of visual field disorders on sorting performance in the FM 100-hue test is reported. Patients with left-sided field disorders performed worse in the conventional testing direction, i.e. from left to right, compared with patients with right-sided defects. Reversing the direction of sorting led, however, to a similar impairment in patients with right-sided field defects. Observations in normals tested under different conditions of hue sorting support the view that the difference obtained cannot be accounted for by a hemisphere difference in colour processing but by the strategy adopted by subjects.
Recent research on classical red-green blind observers has shown that complete dichromacy may be present only under conditions where the viewing angle is small. For viewing angles greater than about 4 degrees, both rods and an anomalous cone have been shown to underlie a weak form of trichromacy. The conditions for rod or anomalous cone mediation of this trichromacy have also been shown to depend on the overall viewing luminance. These data taken together prompt a rethinking of the classical view of red-green dichromacy and lead to new considerations of the color discrimination performance of dichromatic candidates. In this paper we review the recent research on the presence of trichromatic abilities in classical dichromats and we relate these findings to the needs of the clinician, especially in the screening of young children.
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