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Biomedical subjects

H J Dartnall

Publications and source records attributed to H J Dartnall.

At least 19 recordsLinked to original sources
PubMed1983

Human visual pigments: microspectrophotometric results from the eyes of seven persons.

The material for this work was obtained from seven eyes removed because of malignant growths. Foveal and parafoveal samples of the retinas were taken and transverse measurements were made of the absorbance spectra of the outer segments of the rods and cones, using a Liebman microspectrophotometer. Four kinds of spectra were obtained with absorbance peaks at the following wavelengths: rods, 496.3 +/- 2.3 nm (n = 39); red cones, 558.4 +/- 5.2 nm (n = 58); green cones, 530.8 +/- 3.5 nm (n = 45); blue cones, 419.0 +/- 3.6 nm (n = 5). The distribution of the peaks was unimodal for the rods. For the red and green cones, however, there was evidence for bimodal distributions, with sub-population maxima at 563.2 +/- 3.1 nm (n = 27) and 554.2 +/- 2.3 nm (n = 31) for the reds and at 533.7 +/- 2.1 nm (n = 23) and 527.8 +/- 1.8 nm (n = 22) for the greens. A substantial difference in mean spectral location of the red cones was observed between patient 1 (561 nm) and patient 4 (553 nm). Both patients were classified as normal trichromats by all clinical tests of colour vision but there was a clear difference in their relative sensitivities to long-wave fields. In both direction and magnitude, this difference proved to be that required by the microspectrophotometric results.

Humans↗
PubMed1980

Microspectrophotometric demonstration of four classes of photoreceptor in an old world primate, Macaca fascicularis.

1. Microspectrophotometric measurements reveal four classes of photoreceptor in the retina of the cynomolgus monkey, Macaca fascicularis, which is known to possess colour vision similar to that of a normal human trichromat. 2. Although the eyes were removed in bright illumination, the densities of pigment were comparable to those we have measured in dark-adapted rhesus retinae. 3. The mean wave-lengths of peak sensitivity (lambda max) for the four classes of photoreceptor were 415, 500, 535 and 567 nm. 4. The band widths of the absorbance spectra decreased linearly as the wave-number of peak sensitivity decreased. 5. If, by assuming a reasonable value for the axial density of the rod outer segment and correcting for lens absorption, a spectral sensitivity for human vision is reconstructed from the P500 pigment, it is found to be systematically broader than the CIE scotopic sensitivity function. 6. Given explicit assumptions, it is possible from the P535 and P567 pigments to reconstruct human psychophysical sensitivities that resemble the pi 4 and pi 5 mechanisms of W. S. Stiles. 7. Although the P415 pigment has a lambda max much shorter than that of the psychophysically measured blue mechanisms, the two spectral-sensitivity functions are brought into proximity when the microspectrophotometric data are corrected for absorption by the optic media.

Animals↗
PubMed1980

Visual pigments of rods and cones in a human retina.

1. Microspectrophotometric measurements have been made of the photopigments of individual rods and cones from the retina of a man. The measuring beam was passed transversely through the isolated outer segments. 2. The mean absorbance spectrum for rods (n = 11) had a peak at 497.6 +/- 3.3 nm and the mean transverse absorbance was 0.035 +/- 0.007. 3. Three classes of cones were identified. The long-wave cones ('red' cones) had a lambda max of 562.8 +/- 4.7 nm (n = 19) with a mean transverse absorbance of 0.027 +/- 0.005. The middle-wave cones ('green' cones) had a lambda max of 533.8 +/- 3.7 nm (n = 11) with a mean transverse absorbance of 0.032 +/- 0.007. The short-wave cones ('blue' cones) had a lambda max of 420.3 +/- 4.7 nm (n = 3) with a mean transverse absorbance of 0.037 +/- 0.011. 4. If assumptions are made about the length of cones and about pre-receptoral absorption, it is possible to derive psychophysical sensitivities for the cones that closely resemble the appropriate pi mechanisms of W. S. Stiles. 5. If assumptions are made about the length of rods and about pre-receptoral absorption, however, the psychophysical sensitivity derived for the rods is considerably broader than the C.I.E. scotopic sensitivity function.

Humans↗
PubMed1978

The visual pigments of rods and cones in the rhesus monkey, Macaca mulatta.

1. New microspectrophotometric measurements have been made of the photo-pigments of individual rods and cones from the retina of the rhesus monkey (Macaca mulatta). The measuring beam was passed transversely through isolated outer segments. 2. The transverse absorbance for rods ranged from 0.02 to 0.04 and that for cones from 0.01 to 0.03. 3. The mean absorbance spectrum for rods (n = 25) had a peak of 502 +/- 2.7 nm. A digitonin extract from the same group of eyes gave a lambda-max. of 499 +/- 1 nm. 4. Of a sample of 82 cones, 40 were 'red' (P565 nm) and 42 were 'green' (P536 nm). The mean absorbance spectrum for the green cones is very similar to the Dartnall nomogram, but that for the red cones is narrower. 5. No bleachable, blue-sensitive outer segments were recorded, although structures were found that absorbed at short wave-lengths and were neither photosensitive nor dichroic. 6. If the long wave-length and middle wave-length cone pigments of the rhesus monkey are assumed to be identical to those of man and if additional assumptions are made about the lengths of human outer segments and about prereceptoral absorption, it is possible to derive psychophysical sensitivities that closely resemble the pi5 and pi4 mechanisms of W. S. Stiles.

Animals↗
PubMed1977

The gecko visual pigments: a microspectrophotometric study.

1. A dual system of visual pigments having absorbance maxima in the green and blue respectively has been found in the retinas of geckos both by single cell microspectrophotometry and by the method of extraction. Microspectrophotometry has shown the system to be present in four species of geckos representing four genera. Along with previous work with extracts (Crescitelli, 1972) this indicates a fundamental property in this family of lizards. No other photopigments have been detected.2. For Gekko gekko, the species most intensively studied, the two pigments have absorbance maxima at 521 and 467 nm respectively. Both are based on vitamin A(1) and both are characterized by absorbance spectra that nearly conform to the Dartnall nomogram.3. In situ, the 521-pigment is not temperature-sensitive, and has virtually the same absorbance spectrum at 23 degrees C as at 5 degrees C. On extraction into digitonin solution, however, the absorbance spectrum of the pigment becomes temperature-dependent and, though identical when measured at low temperature (2-5 degrees C) with the constant in situ curve, is displaced to shorter wave-lengths at higher temperatures (10-25 degrees C). Thus the extract spectrum is relevant to the in situ spectrum only at low temperature (and in the presence of chloride ions).4. Unlike the rhodopsins of several vertebrates, the gecko 521-pigment displays no evidence of a meta-III stage in the sequence of products following photic bleaching, even at low temperatures. This is true for the pigment in situ as well as in the extracted condition.

Animals↗