Normal and defective colour vision in large field.
Colour vision is spatially organized. A light stimulus has to strike spectrally different photoreceptors, covering the center and surround of the receptive field of a colour opponent retinal ganglion cell. Otherwise, no colour opponent processing of signals will occur. Vice versa, spatial summation provided by a large field may compensate for weak opponency. This happens not only in congenital, but also in acquired colour vision defects, when opponency is weakened secondary to a reduced receptoral input. Large field colour vision in Daltonians. Large field red-green opponency is a common phenomenon in patients fitting into the criteria of protanopia and deuteranopia. The difference between small and large field colour vision can be demonstrated by the "projection anomaloscope". At a 30 degrees test field, many anopes behave like the respective anomalous observers. The majority of anopes appear to have some "forbidden cones" at their retinal disposal. So, anomaly and anopia share a common photochemical basis, i.e., the anomalous pigment. However, in anopes, the number of those anomalous cones is extremely small. Therefore, anopic observers usually need a very large amount of spatial summation to arrive at a well defined match of the projection anomaloscope. In protanopes the large field match in our experiments was always a protanomalous one, with the exception of one large field protanope. In deuteranopes, however, there was no such constant behaviour in large field matching. We found deuteranomalous matches as well as matches in the vicinity of the normal mid-match point. Contrary to this behaviour of anopes anomalous observers do not significantly alter their matching pattern irrespectively of whether small (1 degree) or large (30 degrees) test fields are used. So-called peripheral colour blindness of normal observer. Results of classical colour perimetry reveal a dichromatism of the intermediate and a monochromatism of the extreme retinal periphery of the normal observer. These results appear to contradict the common everyday experience of colour constancy throughout the visual field. But a threshold correlation of colour constancy at different retinal exentricities can be demonstrated by recording spectral increment thresholds with test field diameters increasing towards the retinal periphery. So, the colour blindness of the retinal periphery is merely an area phenomenon. It can be overcome by large field observation, rendering spatial summation. Congenital achromatopsia. Remnants of colour vision can be demonstrated in many achromats.(ABSTRACT TRUNCATED AT 400 WORDS)
D003118:Color Perception; D003117:Color Vision Defects / Q000151:congenital / Q000175:diagnosis / Q000503:physiopathology*; D006801:Humans; D009885:Ophthalmology / Q000295:instrumentation; D014787:Vision Tests; D014794:Visual Fields