ISSN:
1573-2622
Keywords:
Achromatopsia
;
rod monochromatism
;
nystagmus
;
photophobia
;
color vision tests
;
ERG recovery during dark adaptation
;
ERG photopic components
;
scotopic components
;
photopic activity in purely scotopic ERGs
;
ERG as function of intensity
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract 39 patients suffering from congenital achromatopsia were investigated by various methods, including electroretinography, during both light and dark adaptation. This condition was typically expressed by the presence of photophobia, low visual acuity, nystagmus and various degrees of ametropia. The fundus was normal in 9 cases. Most of the other cases showed various macular or foveal abnormalities. 24 patients showed complete absence of color vision, and practically all displayed the ‘scotopic line’ in the Farnsworth Panel D-15 test. The electroretinogram (ERG) was almost always extinct in light. In the dark, in most patients the ERG displayed the scotopic mechanism solely, but some ERGs indicated subnormal photopic components either at the beginning or during all dark adaptation. This presence of photopic activity in the ERG of achromats was verified by 2 additional experiments. In one, the recovery of the positive wave of four achromats was compared on a percentage scale with that of four normal subjects and found to be similar, although the slightly faster course in achromats indicates less photopic activity than in normals. In the second, the positive amplitudes of the ERGs of 12 achromats with purely scotopic ERGs were recorded at completed dark adaptation as function of increasing stimulus intensities, all above the photopic threshold, and compared with those of 16 normal subjects. The amplitudes increased linearly with the 1.2 log intensity range in both groups, though the slope of the curve of the achromats was 1/4 that of the normals. In another experiment, the positive wave of the ERG, as elicited by light over 5 log units in the scotopic range, was found in an achromat to be of very similar shape as that of a normal, indicating scotopic acitivity to be similar in both subjects. The fact that, nevertheless, photopic components were not demonstrable in most ERGs, despite present photopic activity, can be explained by the relatively insensitive electrical method coupled with the subnormality of the retinal photopic mechanism in every achromat.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00149675
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