Billy R. Wooten

Individual variations in the spatial profile of human macular pigment

Individual variations in the spatial profile of macular pigment (MP) density were measured for 32 subjects. Peak density of MP measured with a 460-nm, 12-arcmin stimulus averaged 0.58, standard deviation (SD) = 0.26, with a range of 0.175 to 1.39. To assess the symmetry of the MP distribution, MP density was measured on the horizontal and vertical meridians at +/-1 deg eccentricity. The density varied by no more than 16% at these four locations, indicating a basically symmetric distribution. Based on a linear interpolation between measured locations, the width of the spatial distribution of MP at half the maximal density averaged 1.03 deg, SD = 0.38, with a range of 0.25 to 1.9 deg. The average spatial profile of MP density across subjects was fitted with both an exponential and a Gaussian function. An exponential decay with eccentricity explained more variance in the data than did a Gaussian function. Assuming an exponential decay with eccentricity, once MP density has been measured in the center of the retina (denoted A), MP density at more eccentric locations (X, deg) can be predicted with a standardized equation (MP = A x 10(-0.42x)). For individual cases, small deviations from an exponential function suggest the existence of minor flanking peaks or shoulders for 40% of the subjects. We also examined the temporal stability of the MP profile of four subjects over a time span of 4-14 months and for a single spatial location for ten subjects over a time span of 1-16 years. These longitudinal data show that differences in MP density among subjects are maintained over time, if dietary patterns are stable.

Cigarette Smoking and Retinal Carotenoids: Implications for Age-related Macular Degeneration

The foveal region of the retina has a yellow pigmentation composed primarily of the carotenoids lutein and zeaxanthin. Past studies have shown that cigarette smoking depresses carotenoid concentrations in the blood. This is the first report on the effects of cigarette smoking on carotenoids in the retina. Macular pigment optical density (MP) was measured psychophysically by comparing foveal and parafoveal sensitivities to light of 460 and 550 nm. General dietary patterns, smoking frequency (cigaretts/day) and personal data were collected by questionnaire. Thirty-four smokers and 34 nonsmokers were compared. Subjects were matched with respect to age, sex, dietary patterns and overall pigmentation (i.e., eye, skin and hair color). The smoking group had a mean MP of 0.16 (SD = 0.12) compared to a mean MP of 0.34 (SD = 0.15) for nonsmokers (P < 0.0001). MP density and smoking frequency were inversely related (r = -0.498 P < 0.001) in a dose-response relationship. A variety of evidence suggests that MP protects the macula from actinic damage both passively (by screening potentially harmful short-wave light) and actively as an antioxidant (e.g., by quenching reactive oxygen species). If smoking causes a reduction in MP density, then smokers may be at risk. Epidemiologic data identifying smoking as a risk factor for the neovascular form of age-related macular degeneration are consistent with this hypothesis.

Sex Differences in Macular Pigment Optical Density:: Relation to Plasma Carotenoid Concentrations and Dietary Patterns

Sex differences in macular pigment (MP) optical density (measured psychophysically) were examined. Concentrations of lutein and zeaxanthin (L and Z) (non-separated) and beta-carotene (BC) in the blood were determined using reverse phase high-performance liquid chromatography. Dietary intake of L and Z, BC, fat, and iron were estimated by questionnaire. Males had 38% higher MP density than females (P < 0.001) despite similar plasma carotenoid concentrations and similar dietary intake (except for fat). Dietary intake of carotenoids, fat and iron, as well as plasma concentrations of L and Z were positively related to MP density in males. Conversely, only plasma L and Z was related to MP density for females, and dietary fat was negatively related to MP density. Sex differences in protection of the retina by MP and in the relationship between the retina, blood and diet could be a factor in the incidence of retinal diseases, especially age-related macular degeneration.

Macular pigment: influences on visual acuity and visibility.

There is increasing evidence that the macular pigment (MP) carotenoids lutein (L) and zeaxanthin (Z) protect the retina and lens from age-related loss. As a result, the use of L and Z supplements has increased dramatically in recent years. An increasing number of reports have suggested that L and Z supplementation (and increased MP density) are related to improved visual performance in normal subjects and patients with retinal and lenticular disease. These improvements in vision could be due either to changes in the underlying biology and/or optical changes. The optical mechanisms, i.e., preferential absorption of short-wave light, underlying these putative improvements in vision, however, have not been properly evaluated. Two major hypotheses are discussed. The acuity hypothesis posits that MP could improve visual function by reducing the effects of chromatic aberration. The visibility hypothesis is based on the idea that MP may improve vision through the atmosphere by preferentially absorbing blue haze (short-wave dominant air light that produces a veiling luminance when viewing objects at a distance).

Density of the human crystalline lens is related to the macular pigment carotenoids, lutein and zeaxanthin

Purpose. Although oxidative stress may play an important role in the development of age-related cataract, the degree of protection reported for antioxidant vitamins and carotenoids has been inconsistent across studies. These varied results may be due in part to the lack of good biomarkers for measuring the long-term nutritional status of the eye. The present experiments investigated the relationship between retinal carotenoids (i.e., macular pigment), used as a long-term measure of tissue carotenoids, and lens optical density, used as an indicator of lens health. Methods. Macular pigment (460 nm) and lens (440, 500, and 550 nm) optical density were measured psychophysically in the same individuals. Groups of younger subjects—7 females (ages 24 to 36 years), and 5 males (ages 24 to 31 years)—were compared with older subjects—23 older females (ages 55 to 78 years), and 16 older males (ages 48 to 82 years). Results. Lens density (440 nm) increased as a function of age (r=0.65, p<0.001), as expected. For the oldest group, a significant inverse relationship (y=1.53−0.83x, r=−0.47, p<0.001) was found between macular pigment density (440 nm) and lens density (440 nm). No relationship was found for the youngest group (p<0.42). Conclusions. The main finding of this study was an age-dependent, inverse relationship between macular pigment density and lens density. Macular pigment is composed of lutein and zeaxanthin, the only two carotenoids that have been identified in the human lens. Thus, an inverse relationship between these two variables suggests that lutein and zeaxanthin, or other dietary factors with which they are correlated, may retard age-related increases in lens density.

The utility of using customized heterochromatic flicker photometry (cHFP) to measure macular pigment in patients with age-related macular degeneration

The purpose of this study was to assess the utility and validity of using customized heterochromatic flicker photometry (cHFP) to measure macular pigment optical density (MPOD) in patients with intermediate stages of age-related macular degeneration (AMD). The measurement procedure was optimized to accommodate individual differences in temporal vision related to age, disease, or other factors. The validity criteria were based on the similarity of the spectral absorption curves to ex vivo curves of lutein and zeaxanthin and the similarity of spatial density profiles to those measured in subjects without retinal disease. Macular pigment optical density (MPOD) spatial profiles were measured with an LED-based macular densitometer; spectral absorption curves were measured with a 3-channel Maxwellian view system including a monochromator. All patients were characterized via clinical exams and all but 2 subjects from whom data were obtained had masked grading of color fundus photographs using the Wisconsin Age-Related Maculopathy Grading System. Most of the patients were in AREDS category 2 (27%) or 3 (57%). Patients with visual acuity as poor as 20/80 were included, and could perform the task as long as they could see the stimulus. Eighty-one percent of the patients screened were able to perform the cHFP task, and data were obtained from 30 AMD patients. Spatial profiles of MPOD were measured in 19 subjects who could see the stimulus at all tested loci. These profiles were highly similar to those that have been measured with HFP in subjects without retinal disease. The average shape of the spectral absorption curves for the AMD subjects corresponded well to an ex vivo template. These data support both the utility and validity of the cHFP method for measuring MPOD in subjects with intermediate stages of AMD. The ability to measure the retinal response to nutritional intervention is of practical importance for monitoring patients being supplemented with lutein and zeaxanthin in hopes of retarding visual loss and/or disease progression.

CFF thresholds : Relation to macular pigment optical density

Purpose:  Only two small studies have evaluated the relation between individual differences in macular pigment (MP) levels and visual health prior to retinal disease. In this study, we assess the relation between MP and a general measure of visual health, the critical flicker fusion (CFF) threshold.

Spectral absorbance and spatial distribution of macular pigment using heterochromatic flicker photometry.

Purpose. The validity of the heterochromatic flicker photometric (HFP) technique for measuring macular pigment (MP) was assessed by evaluating the spatial density and spectral absorption curves of normal subjects. Methods. Standard Maxwellian view optics were used to measure MP spatial density and spectral absorption curves. Four subjects with normal color vision and one protanope were tested. All of the subjects were experienced psychophysical observers. Results. Spatial density profiles for all subjects were nearly symmetric. The width of the spatial distribution, at half maximal density, averaged 0.70° (standard deviation = 0.15). A first-order exponential decay with eccentricity described the distribution profile well (average r2 = 0.95). The shape of the spectral absorption curves matched an ex vivo template closely at wavelengths greater than approximately 430 nm. Stimulus size did not influence the derived spectral curves. Conclusion. Based on data from this study and others, the HFP method appears to be a valid method for measuring MP density in subjects without retinal disease.

Photopic and scotopic contributions to the human visually evoked cortical potential.

Abstract The spectral sensitivity of the human visually evoked cortical potential (VECP) was determined using implicit time as a criterion measure. The results obtained with relatively bright stimuli at a moderate level of light adaptation were in excellent agreement with psychophysically-determined photopic spectral sensitivity functions reported in the literature. The results obtained with stimuli of low intensity after dark adaptation corresponded well with the C.I.E. scotopic luminosity function except for a higher sensitivity in the wavelength region above 600 nm, where photopic contributions intruded. A completely scotopic VECP spectral sensitivity was achieved by utilizing the Stiles-Crawford effect to avoid stimulating the photopic system. Thus the VECP, like psychophysically-determined visual functions, is duplex: the photopic system is the major contributor when the stimuli are relatively bright; the scotopic system is the major contributor when the stimuli are relatively dim and the subject is dark adapted.

Electrical Measures and Psychophysical Data on Human Vision

This chapter compares psychophysical methods of studying human vision with more objective methods, especially that of recording electrical responses from the visual system. Two sites are available for obtaining these responses without undue discomfort or injury to the subject. These are (1) the cornea of the eye and (2) the scalp over the occipital cortex, as shown in Fig. 1. Accordingly, we give separate consideration to each of these sites, covering the topics of (a) the nature of the response recorded there, (b) techniques of eliciting and recording the response, and (c) resulting data, in comparison with psychophysical results under similar conditions.