Interindividual and topographical variation of L:M cone ratios in monkey retinas

Abstract

We analyzed the ratio of L:M cone photopigment mRNA in the retinas of Old World monkeys, using the method of rapid polymerase chain reaction-single-strand conformation polymorphism. The L:M cone pigment mRNA ratio in whole retina ranged from 0.6 to 7.0, with a mean of approximately 1.6 (standard deviation, +/- 0.56; n = 26). There was no change in this ratio with eccentricity up to 9 mm (approximately 45 degrees), though the ratio was approximately 30% greater in temporal than in nasal retina. The mRNA ratios are in good agreement with the L:M cone ratio in these same retinas, inferred from electrophysiological recordings of cone signal gain in horizontal cell interneurons. The correlation between mRNA ratios and physiological cone gain ratio supports the conclusion that both measures reflect the relative number of L and M cones.

Organization of the Human Trichromatic Cone Mosaic

“…The ERG estimates of L:M ratio reflect the cone ratio from an ϳ70°field, whereas the AO estimates are derived from relatively small (ϳ0.5°) patches of retina. The close agreement between the two techniques corroborates previous reports that the local ratio of L to M cones varies little within the central ϳ70° (Hagstrom et al, 1998;Deeb et al, 2000;Knau et al, 2001) (but see Albrecht et al, 2002). The histogram in Figure 7 shows that the range in L:M cone ratio for our seven male subjects reflects the overall range in the normal male population, based on the previously published ERG results .…”

“…We also observed a departure from random assignment of photopigment on a large spatial scale in subject AP whose L:M ratio was 1.24 (55.4% L) in nasal retina and 1.77:1 (63.9% L) in temporal retina. Deeb et al (2000) reported a similar nasal-temporal asymmetry in L:M cone ratio in the monkey retina. Conversely, Roorda and Williams (1999) found very similar L:M cone ratios at two foveal locations in one subject (subject JW).…”

“…Hagstrom et al (1998) and Bowmaker et al (2003) both found that L:M cone ratio increases greatly in the far periphery in human retina. Deeb et al (2000) showed a nasal-temporal asymmetry in L/M cone ratio in the macaque. Packer et al (1996), using photopigment transmittance imaging of excised patches of peripheral primate retina, reported a tendency for L and M cones to clump more than would be expected from random packing.…”

“…Over the past 60 years, a number of indirect techniques have suggested that there are more L than M cones with intersubject variability in the exact ratio (DeVries, 1946;Rushton and Baker, 1964;Dartnall et al, 1983;Pokorny et al, 1991;Jacobs and Neitz, 1993 techniques have begun to be validated directly in vivo [although Deeb et al (2000), using postmortem monkey retina, showed that mRNA-derived L:M cone ratios correlate with those inferred from electrophysiological recordings of cone signal gain in H1 horizontal cells]. For example, the relative contributions of the Land M-cone derived signals to the flicker photometric ERG have been used as an index of the variability in cone ratio among males with normal color vision (Jacobs and Neitz, 1993;Carroll et al, 2002).…”

“…Whereas the short-wavelength-sensitive-(S) cone submosaic has been relatively well characterized (Williams et al, 1981;de Monasterio et al, 1985;Ahnelt et al, 1987;Curcio et al, 1991), the organization of long-wavelength-sensitive (L) and middle-wavelength-sensitive (M) cones in the human retina has proven more elusive, because they exhibit no known morphological or histochemical differences and their pigments are 96% identical (Nathans et al, 1986). Several studies using indirect measurements have suggested that there are on average more L cones than M cones, with large intersubject variability (DeVries, 1946;Rushton and Baker, 1964;Cicerone and Nerger, 1989;Pokorny et al, 1991;Yamaguchi et al, 1997;Hagstrom et al, 1998;Brainard et al, 1999;Deeb et al, 2000;Kremers et al, 2000;Otake and Cicerone, 2000;Carroll et al, 2002). A limitation of these estimates is that they often involve the untested assumption that each M cone and each L cone contribute equally to the molecular, physiological, or psychophysical mechanisms being monitored to derive L:M ratio estimates.…”