A double-blind, placebo-controlled study on the effects of lutein and zeaxanthin on photostress recovery, glare disability, and chromatic contrast.

PURPOSE: Past studies have shown that higher macular pigment optical density (MPOD) and lutein (L) and zeaxanthin (Z) supplementation are related to improvements in glare disability, photostress recovery, and chromatic contrast. This study assessed those links using a randomized, double-blind, placebo-controlled design. METHODS: The visual effects of 1 year of supplementing L (10 mg/d) and Z (2 mg/d) were investigated. One hundred fifteen young, healthy subjects were recruited and randomized into the study (58 received placebo, 57 L+Z). Several dependent measures were collected at baseline and then once every 3 months: serum L and Z measured by HPLC chromatography; MPOD measured using customized heterochromatic flicker photometry; photostress recovery assessed by measuring the time needed to recover visual acquisition of a grating target after 30 seconds of an intense xenon white flash exposure; glare disability evaluated as the energy in a surrounding annulus necessary to veil a central grating target; and chromatic contrast assessed by measuring thresholds for a yellow grating target superposed on a 460-nm background. RESULTS: Macular pigment optical density increased significantly versus placebo at all eccentricities (10, 30, 60, and 105 minutes from the center of the macula). Serum L and Z also increased significantly by the first follow-up visit (at 3 months), and remained elevated throughout the intervention period of 1 year. Chromatic contrast and photostress recovery time improved significantly versus placebo. Glare disability was correlated with macular pigment density throughout the study period but did not increase significantly in the treated group. CONCLUSIONS: Daily supplementation with L+Z resulted in significant increase in serum levels and MPOD and improvements in chromatic contrast and recovery from photostress. These results are consistent with past studies showing that increasing MPOD leads to improved visual performance. (ClinicalTrials.gov number, NCT00909090.).

What is meso-zeaxanthin, and where does it come from?

The carotenoids lutein (L), zeaxanthin (Z), and meso-zeaxanthin (MZ) accumulate in the central retina, where they are collectively known as macular pigment (MP). Each of these three compounds exhibit a regional dominance, with MZ, Z, and L being the dominant carotenoids at the epicentre, mid-periphery, and periphery of the macula, respectively. There is a growing and evidence-based consensus that MP is important for optimal visual performance, because of its blue light-filtering properties and consequential attenuation of chromatic aberration, veiling luminance, and blue haze. It has also been hypothesised that MP may protect against age-related macular degeneration because of the same optical properties and also because of the antioxidant capacity of the three macular carotenoids. Challenges inherent in the separation and quantification of MZ have resulted in a paucity of data on the content of this carotenoid in foodstuffs, and have rendered the study of tissue concentrations of this compound problematic. As a consequence, the few studies that have investigated MZ have, perhaps, been disproportionately influential in the ongoing debate about the origins of this macular carotenoid. Certainly, the narrative that retinal MZ is derived wholly and solely from retinal L needs to be revisited.

The impact of macular pigment augmentation on visual performance in normal subjects: COMPASS.

This study was conducted to investigate whether augmentation of macular pigment (MP) enhances visual performance (VP). 121 normal subjects were recruited. The active (A) group consumed 12 mg of lutein (L) and 1mg of zeaxanthin (Z) daily. MP optical density (MPOD) was assessed by customized heterochromatic flicker photometry. VP was assessed as best corrected visual acuity (BCVA), mesopic and photopic contrast sensitivity (CS), glare disability, photostress, and subjective visual function. Subjects were assessed at baseline; 3; 6; 12 months (V1, V2, V3 and V4, respectively). Central MPOD increased significantly in the A group (p < 0.05) but not in the placebo group (p > 0.05). This statistically significant increase in MPOD in the A group was not, in general, associated with a corresponding improvement in VP (p>0.05, for all variables), with the exception of a statistically significant time/treatment effect in "daily tasks comparative analysis" (p = 0.03). At V4, we report statistically significant differences in mesopic CS at 20.7 cpd, mesopic CS at 1.5 cpd under high glare conditions, and light/dark adaptation comparative analysis between the lower and the upper MP tertile groups (p < 0.05) Further study into the relationship between MP and VP is warranted, with particular attention directed towards individuals with low MP and suboptimal VP.

Macular pigment and visual performance under glare conditions.

PURPOSE: Many parameters of visual performance (e.g., contrast sensitivity) are compromised under glaring light conditions. Recent data indicate that macular pigment (MP) is strongly related to improvements in glare disability and photostress recovery based on a filtering mechanism. In this study, we assessed the causality of this relation by supplementing lutein and zeaxanthin for 6 months while measuring MP, glare disability, and photostress recovery. METHODS: Forty healthy subjects (mean age = 23.9) participated in the study. Subjects were followed for 6 months and assessed at baseline, 1, 2, 4, and 6 months. Spatial density profiles of MP were measured using heterochromatic flicker photometry. Disability glare was measured using a 1 degree-diameter circular grating surrounded by a broadband glare source (a xenon-white annulus). The intensity of the annulus (11 degree inner and 12 degree outer diameters) was adjusted by the subject until the grating target was no longer seen. For the photostress recovery experiment, the time required to detect a 1 degree-diameter grating stimulus after a 5-s exposure to a 2.5 muW/cm2, 5 degree-diameter disk was recorded. Subjects were tested under central viewing and eccentric viewing (10 degree temporal retina) conditions. RESULTS: At the baseline time point, MP optical density (OD) at 30' eccentricity ranged from 0.08 to 1.04, and was strongly correlated with improved visual performance in the two glare tasks. After 6 months of lutein (L) and zeaxanthin (Z) supplementation, average MPOD (at 30' eccentricity) had increased from 0.41 to 0.57, and was shown to significantly reduce the deleterious effects of glare for both the visual performance tasks assessed. CONCLUSIONS: MP is strongly related to improvements in glare disability and photostress recovery in a manner strongly consistent with its spectral absorption and spatial profile. Four to 6 months of 12 mg daily L + Z supplementation significantly increases MPOD and improves visual performance in glare for most subjects.

Simulating human cones from mid-mesopic up to high-photopic luminances.

A computational model of human cones for intensities ranging from 1 td up to full bleaching levels is presented. The model conforms well with measurements made in primate horizontal cells, follows Weber's law at high intensities, and performs range compression consistent with what is known of cones in other vertebrates. The model consists entirely of processes with a clear physiological interpretation: pigment bleaching, saturation of cGMP hydrolysis, calcium feedback on cGMP synthesis, and a nonlinear membrane. The model is implemented according to a very fast computational scheme useful for simulations, and sample programs in Matlab and Fortran are provided as supplementary material.

Macular pigment optical density and photophobia light threshold.

Light absorption by macular pigment may attenuate visual discomfort, or photophobia, for targets composed of short-wavelength light. Macular pigment optical density (MPOD) and photophobia light thresholds were measured psychophysically in 10 subjects. The energy necessary to induce photophobia for a short-wavelength target relative to a long-wavelength target was linearly related to MPOD, as well as estimates of peak MPOD and integrated macular pigment. In four subjects who consumed lutein supplements, increases in MPOD corresponded to increases in photophobia light thresholds. Light absorption by macular pigment appears to influence the amount of short-wavelength light necessary to elicit photophobia.

The macular xanthophylls.

The macular pigments are predominantly composed of three carotenoids: lutein, zeaxanthin, and meso-zeaxanthin. These carotenoids are concentrated and distributed in a selective manner. The properties of these pigments are further explored along with their methods of uptake, stabilization, and storage. The dual nature of these pigments as filters and antioxidants are elaborated upon in relation to their protective effects upon the macula, specifically in age-related macular degeneration. Evidence suggests that increased levels of macular pigment are correlated with a decreased risk of age-related macular degeneration. Many have sought to exploit this therapeutic relation. Studies reveal that oral supplementation with lutein and zeaxanthin can increase the levels of macular pigments in the retina and plasma. The effects of such supplementation on actual ocular function have yet to be fully addressed. New and standardized methods of assessing macular pigment density are discussed and future areas of research to further our understanding of macular xanthophylls as they pertain to age-related macular degeneration are highlighted.

Biologic mechanisms of the protective role of lutein and zeaxanthin in the eye.

The macular region of the primate retina is yellow in color due to the presence of the macular pigment, composed of two dietary xanthophylls, lutein and zeaxanthin, and another xanthophyll, meso-zeaxanthin. The latter is presumably formed from either lutein or zeaxanthin in the retina. By absorbing blue-light, the macular pigment protects the underlying photoreceptor cell layer from light damage, possibly initiated by the formation of reactive oxygen species during a photosensitized reaction. There is ample epidemiological evidence that the amount of macular pigment is inversely associated with the incidence of age-related macular degeneration, an irreversible process that is the major cause of blindness in the elderly. The macular pigment can be increased in primates by either increasing the intake of foods that are rich in lutein and zeaxanthin, such as dark-green leafy vegetables, or by supplementation with lutein or zeaxanthin. Although increasing the intake of lutein or zeaxanthin might prove to be protective against the development of age-related macular degeneration, a causative relationship has yet to be experimentally demonstrated.

The molecular mechanism for the spectral shifts between vertebrate ultraviolet- and violet-sensitive cone visual pigments.

The short-wave-sensitive (SWS) visual pigments of vertebrate cone photoreceptors are divided into two classes on the basis of molecular identity, SWS1 and SWS2. Only the SWS1 class are present in mammals. The SWS1 pigments can be further subdivided into violet-sensitive (VS), with lambda(max) (the peak of maximal absorbance) values generally between 400 and 430 nm, and ultraviolet-sensitive (UVS), with a lambda(max)<380 nm. Phylogenetic evidence indicates that the ancestral pigment was UVS and that VS pigments have evolved separately from UVS pigments in the different vertebrate lineages. In this study, we have examined the mechanism of evolution of VS pigments in the mammalian lineage leading to present day ungulates (cow and pig). Amino acid sequence comparisons of the UVS pigments of teleost fish, amphibia, reptiles and rodents show that site 86 is invariably occupied by Phe but is replaced in bovine and porcine VS pigments by Tyr. Using site-directed mutagenesis of goldfish UVS opsin, we have shown that a Phe-86-->Tyr substitution is sufficient by itself to shift the lambda(max) of the goldfish pigment from a wild-type value of 360 nm to around 420 nm, and the reverse substitution of Tyr-86-Phe into bovine VS opsin produces a similar shift in the opposite direction. The substitution of this single amino acid is sufficient to account therefore for the evolution of bovine and porcine VS pigments. The replacement of Phe with polar Tyr at site 86 is consistent with the stabilization of Schiff-base protonation in VS pigments and the absence of protonation in UVS pigments.

Cryptochrome: the second photoactive pigment in the eye and its role in circadian photoreception.

Circadian rhythms are oscillations in the biochemical, physiological, and behavioral functions of organisms that occur with a periodicity of approximately 24 h. They are generated by a molecular clock that is synchronized with the solar day by environmental photic input. The cryptochromes are the mammalian circadian photoreceptors. They absorb light and transmit the electromagnetic signal to the molecular clock using a pterin and flavin adenine dinucleotide (FAD) as chromophore/cofactors, and are evolutionarily conserved and structurally related to the DNA repair enzyme photolyase. Humans and mice have two cryptochrome genes, CRY1 and CRY2, that are differentially expressed in the retina relative to the opsin-based visual photoreceptors. CRY1 is highly expressed with circadian periodicity in the mammalian circadian pacemaker, the suprachiasmatic nucleus (SCN). Mutant mice lacking either Cry1 or Cry2 have impaired light induction of the clock gene mPer1 and have abnormally short or long intrinsic periods, respectively. The double mutant has normal vision but is defective in mPer1 induction by light and lacks molecular and behavioral rhythmicity in constant darkness. Thus, cryptochromes are photoreceptors and central components of the molecular clock. Genetic evidence also shows that cryptochromes are circadian photoreceptors in Drosophila and Arabidopsis, raising the possibility that they may be universal circadian photoreceptors. Research on cryptochromes may provide new understanding of human diseases such as seasonal affective disorder and delayed sleep phase syndrome.

Fourth module of Xenopus interphotoreceptor retinoid-binding protein: activity in retinoid transfer between the retinal pigment epithelium and rod photoreceptors.

PURPOSE: Interphotoreceptor retinoid-binding protein (IRBP), an extracellular protein believed to support the exchange of retinoids between the neural retina and retinal pigment epithelium (RPE) in the vertebrate eye, exhibits a modular, i.e., repeat, structure. The present study was undertaken to determine whether an individual module of IRBP has activity in retinoid transfer between the RPE and rod photoreceptors. METHODS: The retinoid transfer activity of a recombinant protein corresponding to the fourth module of Xenopus laevis IRBP (X4IRBP) was examined in two ways. First, X4IRBP was tested for its ability to support the regeneration of porphyropsin in detached/reattached Xenopus retina/RPE-eyecups. Following illumination and removal of native IRBP, Xenopus eyecups supplemented with 42 microM X4IRBP or (as a control) Ringer's solution were incubated in darkness and then analyzed for regenerated porphyropsin. Second, toad (Bufo marinus) RPE-eyecup preparations were used to evaluate X4IRBP's ability to promote the release of 11-cis retinal from the RPE. RESULTS: The regeneration of porphyropsin in X4IRBP-supplemented Xenopus retina/RPE-eyecups (0.45 +/- 0.04 nmol; mean +/- SEM, n = 11) exceeded that in controls (0.13 +/- 0.02 nmol, n = 11). For promoting the release of 11-cis retinal from the toad RPE, 42 microM X4IRBP was more effective than equimolar bovine serum albumin although considerably less than that of 26 microM native bovine IRBP. CONCLUSIONS: The results indicate a low but significant activity of IRBP's fourth module in reactions relevant to retinoid exchange.

Absorption spectra of human cone pigments.

Human colour vision is mediated by three light-sensitive pigments, each found in a different cone-cell type. The absorption spectra of the human cone pigments have been sought for over a century using techniques such as psychophysical colour matching, reflection densitometry, electroretinography, single-cell action spectra and, most directly, microspectrophotometry. We report here a direct determination of the human cone pigment photobleaching difference absorption spectra after the production of each cone pigment apoprotein in tissue culture cells transfected with the corresponding complementary DNA clones. The mean values for the wavelength of maximal absorption are 426 nm for the blue pigment, 530 nm for the green pigment, and 552 nm and 557 nm for two polymorphic variants of the red pigment.

Photoreceptor-specific efficiencies of beta-carotene, zeaxanthin and lutein for photopigment formation deduced from receptor mutant Drosophila melanogaster.

Drosophila rearing media had only beta-carotene, zeaxanthin or lutein as precursors for photopigment chromophores. Zeaxanthin and lutein are potentially optimum sources of the 3-hydroxylated retinoids of visual and accessory photopigments. Mutants made the electroretinogram in white (w) eyes selective for compound eye photoreceptors R1-6, R7 and R8: R1-6 dominates w's electroretinogram; R7/8 generates w;ora's (ora = outer rhabdomeres absent); R8 generates w sev;- ora's (sev = sevenless). Microspectrophotometry revealed R1-6's visual pigment. In w, all 3 carotenoids yielded monotonic dose-responses for sensitivity or visual pigment. An ultraviolet sensitivity peak from R1-6's sensitizing pigment was present at high but not low doses. In w;ora, all 3 carotenoids gave similar spectra dominated by R7's high ultraviolet sensitivity. For w sev;ora, all spectra were the shape expected for R8, peaking around 510 nm. The sensitivity dose-response was at its ceiling except for low doses in w;ora and zero supplementation in w sev;ora. Hence, without R1-6, most of our dose range mediated maximal visual pigment formation. In Drosophila, beta-carotene, zeaxanthin and lutein mediate the formation of all major photopigments in R1-6, R7 and R8.

Coupling of photoexcited rhodopsin to inositol phospholipid hydrolysis in fly photoreceptors.

Fly photoreceptor membranes were used to test the effect on defined biochemical reactions of light and of compounds causing photoreceptor excitation. Complementary electrophysiological studies examined whether putative second messengers excite the fly photoreceptor cells. This analysis revealed the following sequence of events: photoexcited rhodopsin activates a G protein by facilitating GTP binding. The G protein then activates a phospholipase C that generates inositol trisphosphate, which in turn acts as an internal messenger to bring about depolarization of the photoreceptor cell. Binding assays of GTP analogs and measurements of GTPase activity showed that there are 1.6 million copies of G protein per photoreceptor cell. The GTP binding component is a 41-kDa protein, and the light-activated GTPase is dependent on photoconversion of rhodopsin to metarhodopsin. Analysis of phospholipase C activity revealed that this enzyme is under stringent control of the G protein, that the major product formed is inositol trisphosphate, and that this product is rapidly hydrolyzed by a specific phosphomonoesterase. Introduction of inositol trisphosphate to the intact photoreceptor cell mimics the effect of light, and bisphosphoglycerate, which inhibits inositol trisphosphate hydrolysis, enhances the effects of inositol trisphosphate and of dim light. The interaction of photoexcited rhodopsin with a G protein is thus similar in both vertebrate and invertebrate photoreceptors. These G proteins, however, activate different photoreceptor enzymes: phospholipase C in invertebrates and cGMP phosphodiesterase in vertebrates.

Historic perspectives. Macular yellow pigment. The first 200 years.

Since 1782 there has been continuing controversy concerning the curious central coloration referred to as "macular yellow," but no cumulative source of information on the subject exists. This paper reviews the research efforts of two centuries to determine the existence, nature, location, and function of a specialized pigment in the foveal region. Using white-light illumination, it is difficult to see a macular yellow spot in the living eye; it is best observed and documented by red-free ophthalmoscopy and blue-light monochromatic photography. Histologic, biochemical, and spectral absorption data suggest that the yellow color is due to a xanthophyllic pigment, lutein, that is distributed in all retinal layers internal to the outer nuclear layer, with greatest concentration in the outer and inner plexiform layers. Clinically absent in newborns, the pigment gradually accumulates from dietary sources and appears to serve both as an optical filter, by absorbing blue light and reducing chromatic aberration, and in a protective capacity, preventing actinic damage. The absorption characteristics of the yellow pigment contribute to the central dark spot seen during fluorescein angiography and to the risk of photocoagulation near the fovea. Its apparent absence in albinos and the reported functional improvement in certain degenerative retinopathies following supplemental xanthophyll administration suggest a possible role in hereditary or acquired maculopathies.