Biomedical subjects

R I Land

Publications and source records attributed to R I Land.

3 recordsLinked to original sources

PubMed1999

A practical method for measuring macular pigment optical density.

PURPOSE: Increasing evidence indicates that the macular pigments (MP) protect the central retina and may retard macular disease. For that reason, a practical method for measuring MP that does not require elaborate optics and can be applied to diverse populations by operators with a modest amount of experience was developed and validated. METHODS: A small tabletop device based on light-emitting diodes (LEDs) as the light source with electronic controls was constructed. Macular pigment was measured with the tabletop device with a 1 degrees test stimulus at 460 nm using heterochromatic flicker photometry, and the results were compared with measurements using a traditional three-channel Maxwellian view system with a xenon-arc source. RESULTS: Macular pigment density of 30 subjects (age range, 16-60 years) was measured with both stimulus systems. Macular pigment measured with the LED tabletop device in free view was highly correlated with MP measured in Maxwellian view (y = -0.03 + 1.06x, r = +0.95). The average absolute difference between the two techniques was 0.04 (SD, 0.03). The new technique was not significantly affected by variations in lens optical density, pupil size, or small head movements. CONCLUSIONS: Psychophysical measurement of MP provides a unique opportunity to make repeated noninvasive assessment of the concentration of a protective nutrient in the retina. The availability of this new device should make this measurement technology accessible to a wide variety of investigators for application to diverse populations.

Adolescent↗

PubMed1997

Dietary manipulation of plasma carotenoid concentrations of squirrel monkeys (Saimiri sciureus).

Primate retinas accumulate the dihydroxy xanthophylls, lutein and zeaxanthin, from the diet via the plasma. Control of plasma concentrations of these carotenoids may be useful for prevention of retinal disease by manipulating carotenoid content of the retina. We have measured the plasma response of male squirrel monkeys to changes in the carotenoid content of a nonpurified diet. We have also supplemented the diet with zeaxanthin and beta-carotene. Plasma responses to dietary changes were rapid. Within one week, most of the change in plasma concentrations had already occurred. Within two weeks of increasing zeaxanthin intake, plasma zeaxanthin concentrations were at a new, relatively stable level. beta-carotene concentrations in the plasma were low while the monkeys were consuming a standard laboratory diet, and were only slightly increased by supplementation. Plasma lutein concentrations were unaffected by zeaxanthin supplementation. Our results suggest that it should be possible to manipulate plasma concentrations of each of the retinal carotenoids with little impact on the plasma concentrations of the other. This will facilitate exploration of the rates of accumulation of lutein and zeaxanthin in the retina, as well as exploration of the possibility of bioconversion from one xanthophyll to another.

Animals↗

PubMed1990

Plasma carotenoids of monkeys (Macaca fascicularis and Saimiri sciureus) fed a nonpurified diet.

The major carotenoid pigments in the plasma and in a common, nonpurified diet of two species of monkeys (Macaca fascicularis and Saimiri sciureus) were measured. The xanthophylls, lutein, zeaxanthin, alpha-cryptoxanthin, and beta-cryptoxanthin, were the principal carotenoids in both the diet and the plasma. Lutein and zeaxanthin were abundant in the all-trans, the 9-cis, and the 13-cis geometrical isomers in the diet, but the 9-cis form was rarely measurable in plasma. However, the 13-cis isomers of lutein and zeaxanthin were found in higher proportions in plasma than in the diet. For both the monohydroxy-xanthophylls, alpha-cryptoxanthin and beta-cryptoxanthin, and the dihydroxy-xanthophylls, lutein and zeaxanthin, the beta, beta structural isomer (beta-cryptoxanthin or zeaxanthin) is less abundant than the beta, epsilon isomer in plasma than in the diet. These results indicate substantial specificity in the absorption or retention of closely related carotenoid isomers in primates. The proportions of different geometrical isomers of lutein and zeaxanthin in the plasma of both species of monkeys were nearly identical and were similar to human values. The hydrocarbon carotenoids, alpha-carotene, beta-carotene and lycopene were usually undetectable in monkey plasma. The monkeys appear to be like humans in their utilization of lutein and zeaxanthin but distinctly different in some other aspects of carotenoid utilization.

Animal Feed↗