Colour vision in blue‐cone ‘monochromacy’

Abstract

SUMMARY1. Atypical (blue cone) monochromats show two action spectra when tested by the increment threshold method of Stiles with' central' fixation. One spectrum peaks near 450 nm and has the spectral characteristics of normal blue cones. The other resembles rhodopsin (r0) modified slightly by photostable macular pigment.2. Under some circumstances such observers are dichromats. There is a neutral point (matched to Illuminant 'C') in the neighbourhood of 460-470 nm.3. The spectral colour matching functions using two primaries have been measured on three such subjects. They can be fit reasonably well, although imperfectly, by linear combinations of oro and nr1. The chromaticity co-ordinates have been calculated according to the convention of W. D. Wright and compared to the results predicted from no and or1. The comparison suggests that part of the imperfections of the colour matching function fit is due to prereceptor differences (e.g. macular pigment) between the blue-cone monochromats and the hypothetical sTOp, iT observer.4. Colour matches made at high light levels continue to hold when the intensity of the field is reduced below the cone threshold.5. Therefore one of the visual pigments participating in the colour matches has an action spectrum which is not measurably different from that of the rod pigment rhodopsin.6. Increment threshold measurements show that the mechanism which has the rhodopsin action spectrum has the directional sensitivity of cones, not rods.7. Blue test threshold during dark adaptation after a full bleach follow a bipartite exponential recovery curve. The first exponential has a time constant of 1 min, the second 2 min. By comparing these curves to the increment thresholds it is possible to relate the first to the oTr, the second to the 7T0 cones.8. Using a broad band blue gelatin filter in the measuring light of the M. ALPERN AND OTHERS retinal densitometer and studying the same retinal region tested in 7 it is possible to follow the regeneration of a pigment after a full bleach which has an exponential recovery with a time constant of 10 min. With a yellow green filter in the measuring light the exponential recovery observed after a full bleach has a time constant of 2-0 min. 9. One of the two visual pigments participating in the colour matches resides in receptors which have the action spectrum, the directional sensitivity and probably the dark adaptation curve of normal blue cones.10. The other resides in receptors which have the action spectrum of normal rods but the directional sensitivity and the dark adaptation curve of normal red and green cones.

Chromosomal rearrangement segregating with adrenoleukodystrophy: associated changes in color vision.

“…His luminous efficiency curve (peak -510 nm) was characteristic of rhodopsin absorption modified by a modest amount of macular screening pigment xanthophyll (20). This is similar to the findings in both BCM (17) and RM (19).…”

“…The latter is a retinal dystrophy recessively inherited (16) at Xq28. It is actually a form of dichromacy, in which the limited color discrimination is mediated by light absorbed in two visual pigments, rhodopsin and the short-wave-sensitive cone pigment (17). For quantitative comparison, we fit the FM polar plot by a 2-cycle cosine function (18).…”

Visual acuity in the blue cone monochromat

“…There still remains at least one unexplained aspect of blue cone monochromacy. Alpern, Lee, Maaseidvaag & Miller (1971) convincingly show that these individuals have rudimentary colour vision. They are dichromats with colour matching functions which are consistent with colour vision mediated by receptors having the spectral sensitivity of rods and blue cones.…”

Rod and cone function in coneless mice

“…Examinations of human rod and cone monochromats are well-known examples of this strategy~Alpern et al., 1971;Hess et al, 1987! as are those experiments that exploit gene mutations in experimental animals; for example, a widely studied mouse mutant~rd0rd!…”