Objective determination of the macular pigment optical density using fundus reflectance spectroscopy

Macular Pigment Optical Density as a Measurable Modifiable Clinical Biomarker

BACKGROUND

Carotenoids are present throughout retina and body its dense deposition leads to an identifiable yellow spot in the macula. Macular pigment optical density (MPOD) measured in the macula is vital to macular well-being and high-resolution visual acuity. MPOD has also been associated with various health and disease states. We sought to review the literature on this topic and summarize MPODs role as a measurable modifiable clinical biomarker, particularly as a measure of the eye's antioxidant capacity in the context of oxidative damage and retinal ischemia.

METHODS

A literature review collated the articles relevant to MPOD, carotenoid intake or supplementation, and their influence on various health and disease states.

RESULTS

Literature reveals that MPOD can serve as a reliable biomarker for assessing the retinal defense mechanisms against oxidative stress and the deleterious effects of excessive light exposure. Elevated MPOD levels offer robust protection against the onset and progression of age-related macular degeneration (AMD), a prevalent cause of vision impairment among the elderly population. MPOD's implications in diverse ocular conditions, including diabetic retinopathy and glaucoma, have been explored, underscoring the real need for clinical measurement of MPOD. The integration of MPOD measurement into routine eye examinations presents an unparalleled opportunity for early disease detection, precise treatment planning, and longitudinal disease monitoring.

CONCLUSIONS

Longitudinal investigations underscore the significance of MPOD in the context of age-related ocular diseases. These studies show promise and elucidate the dynamic nuances of MPOD's status and importance as a measurable, modifiable clinical biomarker.

The Macular Pigment Optical Density (MPOD) Decrease in Chinese Primary Angle Closure Glaucoma Using the One-Wavelength Reflectometry Method

PURPOSE

The objective of this study was to observe the macular pigment optical density (MPOD) and the relationship between MPOD and retinal thickness in Chinese primary angle-closure glaucoma (PACG) patients by the one-wavelength reflectometry method.

METHODS

This study was a prospective comparative observational study, including 39 eyes from 39 PACG patients (15 men and 24 women, mean age 61.89 ± 12.30) and 41 eyes from 41 controls (20 men and 21 women, mean age 63.24 ± 14.02). We measured the MPOD 7-degree area by the one-wavelength reflectometry method and analyzed both the max and mean optical density (OD). The central retinal thickness (CRT) and the total thickness of the macular ganglion cell layer (GCL), and inner plexiform layer (IPL)were measured by spectral-domain-optical coherence tomography (SD-OCT). Statistical methods such as Shapiro-Wilk test, Fisher's exact test, chi-square test, two independent samples test and Spearman's correlation coefficient were used to observe the differences in the MPOD between normal subjects and PACG patients and the correlation between the MPOD and retinal thickness.

RESULTS

The max optical density (Max OD) (PACG group: 0.302 ± 0.067d.u, control group: 0.372 ± 0.059d.u., p < .001) and mean optical density (Mean OD) (PACG group: 0.124 ± 0.035d.u., control group: 0.141 ± 0.028d.u., p < 0.05) were significantly reduced in PACG patients compared with control subjects. Significant decreases in GCL + IPL thickness (PACG group: 74.71 ± 39.56 μm, control group:113.61 ± 8.14 μm, p < 0.001) and CRT (PACG group: 254.49 ± 41.47 μm, control group:329.10 ± 18.57 μm, p < 0.001) were also observed in PACG eyes. There was no statistically significant correlation between the MPOD and GCL + IPL thickness (p = .639, p = .828).

CONCLUSIONS

MPOD was significantly lower in Chinese PACG patients than in the control group, potentially due to thinning of the GCL + IPL thickness. This study provides insights for the pathophysiology, assessment of PACG and potential guidance for lifestyle modifications.

Macular Pigment Assessment in Indian Population Using Degree of Polarization Threshold: Impact of Diet on Macular Pigment Density

Purpose

To determine macular pigment (MP) density scores in healthy Indians and examine correlations with demographic and lifestyle variables.

Methods

We observed 484 Indians without an ocular pathology. Body mass index (BMI) and self-reported lifestyle factors (sunglasses usage, physical activity, and smoking) were noted. MP density was assessed as the threshold of perception of the shadow of their macular pigments on their retina using a new MP assessment tool (MP-eye). Lutein and zeaxanthin intake was assessed using a prevalidated questionnaire regionally designed for the Indian diet. Clusters of participants were created for statistical analysis based on MP-eye scores secondarily to detect any relevant effects in very low, low, medium, and high ranges of MPs.

Results

Data analyzed included 235 males and 249 females with mean age of 36.1 ± 12.9 years (range, 14-72). The median MP-eye score was 6 (range, 0-10, with 10 being high). Most were non-smokers (413, 85.3%) and did not use sunglasses (438, 90.5%), and 314 (64.9%) had low physical activity. Diabetes was present in 62 participants (12.8%) and hypertension in 53 (10.9%). Advancing age (r = -0.209; P < 0.000) and BMI (r = -0.094; P = 0.038) had weak negative correlation with MP-eye scores. Hypertension was less prevalent (7/88) in the cluster with the highest median MP-eye score (P = 0.033). Dietary intake of MPs and other lifestyle factors did not correlate significantly with MP-eye score overall or when analyzed in clusters.

Conclusions

MP-eye scores of an Indian population were normally distributed. Higher age, high BMI, and presence of hypertension were weakly associated with lower MP-eye scores. The impact of diet on MPs requires further evaluation.

Translational Relevance

This normative regional database enables risk stratification of macular degeneration.

Measuring macular pigment optical density using reflective images of confocal scanning laser system

PURPOSE

To develop a method to measure the macular pigment optical density (MPOD) using scanning laser ophthalmoscopic images in young adults and children.

STUDY DESIGN

Cross-sectional study.

METHODS

Blue light reflectance fundus images of 32 healthy subjects were used. A profile of the linear reflectance changes across the center of the fovea on a grayscale fundus image was generated. The ratio of the macula-to-periphery reflection was designated as the peak value of the MPOD (MPOD[FR]) based on established fundamentals. In the MPOD profile, the basal width of the pixels at MPOD < 0 (wMP) and width at one-half value of the MPOD[FR] (wMP0.5) were determined. The MOPD at eccentricity of 0.5° was measured by heterochromatic flicker photometry (MPOD[HFP]), and the correlation between the MPOD[FR] and MPOD[HFP] was evaluated.

RESULTS

The MPOD[FR] ranged from 0.17 to 0.73 with a mean of 0.40 ± 0.13. The wMP ranged from 88 to 173 pixels with a mean of 121.7 ± 24.2 pixels, and the wMP0.5 ranged from 38 to 83 pixels with a mean of 54.1 ± 10.3 pixels. A significant correlation was found between the MPOD[FR] and MPOD[HFP] (r = 0.41, P = 0.02).

CONCLUSIONS

This simplified method can provide accurate and reliable values of the MPOD comparable to heterochromatic flicker photometry. Obtaining the fundus images in this fast and easy way should be suitable for children thus enabling clinicians to determine the MPODs for children.

Fluorescence lifetime imaging ophthalmoscopy and the influence of oral lutein/zeaxanthin supplementation on macular pigment (FLOS) - A pilot study

BACKGROUND & AIMS

Oral lutein (L) and zeaxanthin (Z) supplementation enhances macular pigment optical density (MPOD) and plays a protective role in the development of age-related macular degeneration (AMD). Fluorescence lifetime imaging ophthalmoscopy (FLIO) is a novel in vivo retinal imaging method that has been shown to correlate to classical MPOD measurements and might contribute to a metabolic mapping of the retina in the future. Our aim was to show that oral supplementation of L and Z affects the FLIO signal in a positive way in patients with AMD.

METHODS

This was a prospective, single center, open label cohort study. Patients with early and intermediate AMD received oral L and Z supplementation during three months, and were observed for another three months after therapy termination. All visits included measurements of clinical parameters, serum L and Z concentration, MPOD measurements using heterochromatic flicker photometry, dual wavelength autofluorescence imaging, and FLIO. Correlation analysis between FLIO and MPOD were performed.

RESULTS

Twenty-one patients completed the follow up period. Serum L and Z concentrations significantly increased during supplementation (mean difference 244.8 ng/ml; 95% CI: 81.26-419.9, and 77.1 ng/ml; 95% CI: 5.3-52.0, respectively). Mean MPOD units significantly increased (mean difference 0.06; 95% CI: 0.02-0.09; at 0.5°, 202; 95% CI: 58-345; at 2°, 1033; 95% CI: 288-1668; at 9° of eccentricity, respectively) after three months of supplementation with macular xanthophylls, which included L and Z. Median FLIO lifetimes in the foveal center significantly decreased from 277.3 ps (interquartile range 230.2-339.1) to 261.0 ps (interquartile range 231.4-334.4, p = 0.027). All parameters returned to near-normal values after termination of the nutritional supplementation. A significant negative correlation was found between FLIO and MPOD (r² = 0.57, p < 0.0001).

CONCLUSIONS

FLIO is able to detect subtle changes in MPOD after L and Z supplementation in patients with early and intermediate AMD. Our findings confirm the previous described negative correlation between FLIO and MPOD. Macular xanthophylls seem to contribute to short foveal lifetimes. This study is registered at ClinicalTrials.gov (identifier number NCT04761341).

Analysis of macular carotenoids in the developing macaque retina: The timeline of macular pigment development

In the mature retina, the components of the macular pigment, lutein (L), R,R-zeaxanthin (RRZ), R,S-zeaxanthin (RSZ, meso-zeaxanthin) are most concentrated in the central macula. L and RRZ are of dietary origin but RSZ is produced in situ from L. The relative proportions of L and Z isomers vary across the retina with eccentricity in the adult retina. Early reports have shown that during development, the proportions of L and Z isomers undergo changes as the total pigment levels increase. The methods described here demonstrate the unique utility of chiral phase HPLC to measure the amounts of L, RRZ, and RSZ, discriminating between the two zeaxanthin stereoisomers. In three concentric retinal sections of macaque retinas chiral phase HPLC has been employed to document the developmental changes in the distribution of each L, RSZ, and RRZ during the period just prior to full term gestation through 19 months after birth. The net rate of accumulation of carotenoids within the central retina during the first 20 months is quasi-linear and fit by a linear regression. During development, the rate of transport of L (0.12 (±0.033)ngmm^-2mo^-1 (SE)) into the central 2mm of the retina is double that of RRZ (0.062 (±0.02)ngmm^-2mo^-1 (SE)). The rate of accumulation of RSZ (0.06 (±0.01)ngmm^-2mo^-1 (SE)) is comparable to that of RRZ. In the peripheral retina, the rates of accumulation of L and RRZ are not correlated with increasing age, whereas accumulation of RSZ does correlate with age. The changing proportions of L to Z isomers in the central retina during development are explained by the rates for carotenoid accumulation within the central retina. At birth, the macular pigment in the central retina is dominated by L and RRZ, 0.35±0.11 and 0.21±0.054ngmm^-2. In the central retina, RSZ was rarely detected in the youngest tissues analyzed. It can be estimated to represent 6% of the total macular pigment (0.033±0.11ngmm^-2) at birth based on extrapolation from measurements in the peripheral retina and the ratio of L/(RRZ+RSZ) is ≈1.5. At maturity, the concentrations for L, RRZ, and RSZ in the central macaque retina are estimated to be 1.7, 1.8 and 1.08ngmm^-2, with L/(RRZ+RSZ) being 0.6.

Macular Pigment and Open-Angle Glaucoma in the Elderly: The Montrachet Population-Based Study

(1) Background: To compare macular pigment optical density (MPOD) and its spatial distribution between eyes with primary open-angle glaucoma (POAG) and control eyes in an elderly population. (2) Methods: The Montrachet study (Maculopathy Optic Nerve and nutrition neurovAsCular and HEarT) is a population-based study including participants aged 75 years and over. All participants had a slit lamp examination, fundus photographs, and a questionnaire about their medical past history and smoking status. Optic disc spectral domain optical coherence tomography was also performed. All glaucoma-suspected patients were convocated to have a new full examination. We only retained one eye with POAG for analysis in the glaucoma group and one eye without optic neuropathy in the control participants group. MPOD measurements were performed with the two-wavelength autofluorescence method (488 and 514 nm). (3) Results: Overall, 601 eyes had MPOD measurements among 1153 participants. Among the 601 eyes, 48 had POAG. The mean age for the glaucoma and control participants was 84.01 ± 4.22 years and 81.94 ± 3.61 years, respectively (p < 0.001). In the multivariable analysis, we could not find any association between POAG and MPOD at 0.5° (p = 0.336). We found no significant difference regarding MP spatial distribution between the two groups (p = 0.408). (4) Conclusion: In this elderly population-based study, eyes with POAG and control eyes without optic neuropathy did not differ in terms of MPOD and MP spatial distribution.

A Systematic Review of Carotenoids in the Management of Age-Related Macular Degeneration

Age-related macular degeneration (AMD) remains a leading cause of modifiable vision loss in older adults. Chronic oxidative injury and compromised antioxidant defenses represent essential drivers in the development of retinal neurodegeneration. Overwhelming free radical species formation results in mitochondrial dysfunction, as well as cellular and metabolic imbalance, which becomes exacerbated with increasing age. Thus, the depletion of systemic antioxidant capacity further proliferates oxidative stress in AMD-affected eyes, resulting in loss of photoreceptors, neuroinflammation, and ultimately atrophy within the retinal tissue. The aim of this systematic review is to examine the neuroprotective potential of the xanthophyll carotenoids lutein, zeaxanthin, and meso-zeaxanthin on retinal neurodegeneration for the purpose of adjunctive nutraceutical strategy in the management of AMD. A comprehensive literature review was performed to retrieve 55 eligible publications, using four database searches from PubMed, Embase, Cochrane Library, and the Web of Science. Epidemiology studies indicated an enhanced risk reduction against late AMD with greater dietary consumption of carotenoids, meanwhile greater concentrations in macular pigment demonstrated significant improvements in visual function among AMD patients. Collectively, evidence strongly suggests that carotenoid vitamin therapies offer remarkable synergic protection in the neurosensory retina, with the potential to serve as adjunctive nutraceutical therapy in the management of established AMD, albeit these benefits may vary among different stages of disease.

Macular Pigment Reflectometry: Developing Clinical Protocols, Comparison with Heterochromatic Flicker Photometry and Individual Carotenoid Levels

The study was designed to: (1) Analyze and create protocols of obtaining measurements using the Macular Pigment Reflectometry (MPR). (2) To assess the agreement of MPOD measurements obtained using the heterochromatic flicker photometry (MPS II) and MPR. (3) To obtain the lutein and zeaxanthin optical density obtained using the MPR in the central one-degree of the macula. The measurements were performed using the MPR and heterochromatic flicker photometry. The MPR measurements were performed twice without pupillary dilation and twice following pupillary dilation. The MPR measurements were performed for a 40-s period and the spectrometer signal was parsed at different time points: 10–20, 10–30, 10–40, 20–30, 20–40, and 30–40 s. The MPR analyzes the high-resolution spectrometer signal and calculates MPOD, lutein optical density and zeaxanthin optical density automatically. The MPR-MPOD data was compared with MPPS II-MPOD results. The MPR-MPOD values are highly correlated and in good agreement with the MPS II-MPOD. Of the various parsing of the data, the data 10–30 interval was the best at obtaining the MPOD, lutein, and zeaxanthin values (8–12% coefficient of repeatability). The lutein to zeaxanthin ratio in the central one-degree of the macula was 1:2.40. Dilation was not needed to obtain the MPOD values but provided better repeatability of lutein and zeaxanthin optical density. MPR generates MPOD measurements that is in good agreement with MPS II. The device can produce lutein and zeaxanthin optical density which is not available from other clinical devices.

A Systematic Review of Carotenoids in the Management of Diabetic Retinopathy

Diabetic retinopathy, which was primarily regarded as a microvascular disease, is the leading cause of irreversible blindness worldwide. With obesity at epidemic proportions, diabetes-related ocular problems are exponentially increasing in the developed world. Oxidative stress due to hyperglycemic states and its associated inflammation is one of the pathological mechanisms which leads to depletion of endogenous antioxidants in retina in a diabetic patient. This contributes to a cascade of events that finally leads to retinal neurodegeneration and irreversible vision loss. The xanthophylls lutein and zeaxanthin are known to promote retinal health, improve visual function in retinal diseases such as age-related macular degeneration that has oxidative damage central in its etiopathogenesis. Thus, it can be hypothesized that dietary supplements with xanthophylls that are potent antioxidants may regenerate the compromised antioxidant capacity as a consequence of the diabetic state, therefore ultimately promoting retinal health and visual improvement. We performed a comprehensive literature review of the National Library of Medicine and Web of Science databases, resulting in 341 publications meeting search criteria, of which, 18 were found eligible for inclusion in this review. Lutein and zeaxanthin demonstrated significant protection against capillary cell degeneration and hyperglycemia-induced changes in retinal vasculature. Observational studies indicate that depletion of xanthophyll carotenoids in the macula may represent a novel feature of DR, specifically in patients with type 2 or poorly managed type 1 diabetes. Meanwhile, early interventional trials with dietary carotenoid supplementation show promise in improving their levels in serum and macular pigments concomitant with benefits in visual performance. These findings provide a strong molecular basis and a line of evidence that suggests carotenoid vitamin therapy may offer enhanced neuroprotective effects with therapeutic potential to function as an adjunct nutraceutical strategy for management of diabetic retinopathy.

Carotenoids in the Management of Glaucoma: A Systematic Review of the Evidence

Primary open-angle glaucoma (POAG) remains a leading cause of irreversible blindness globally. Recent evidence further substantiates sustained oxidative stress, and compromised antioxidant defenses are key drivers in the onset of glaucomatous neurodegeneration. Overwhelming oxidative injury is likely attributed to compounding mitochondrial dysfunction that worsens with age-related processes, causing aberrant formation of free radical species. Thus, a compromised systemic antioxidant capacity exacerbates further oxidative insult in glaucoma, leading to apoptosis, neuroinflammation, and subsequent tissue injury. The purpose of this systematic review is to investigate the neuroprotective benefits of the macular carotenoids lutein, zeaxanthin, and meso-zeaxanthin on glaucomatous neurodegeneration for the purpose of adjunctive nutraceutical treatment in glaucoma. A comprehensive literature search was conducted in three databases (PubMed, Cochrane Library, and Web of Science) and 20 records were identified for screening. Lutein demonstrated enhanced neuroprotection on retinal ganglion cell survival and preserved synaptic activity. In clinical studies, a protective trend was seen with greater dietary consumption of carotenoids and risk of glaucoma, while greater carotenoid levels in macular pigment were largely associated with improved visual performance in glaucomatous eyes. The data suggest that carotenoid vitamin therapy exerts synergic neuroprotective benefits and has the capacity to serve adjunctive therapy in the management of glaucoma.

Foveal macular pigment dip in offspring of age-related macular degeneration patients is inversely associated with omega-3 index

Background

Offspring of parent(s) with age-related macular degeneration (AMD) have a 45% lifetime risk of developing the disease. High foveal macular pigment optical density (MPOD) is protective, whereas individuals with a “foveal macular pigment dip” (FMPD) are at increased risk. Shortage of the dietary carotenoids lutein, zeaxanthin as well as fish consumption are reported AMD risk factors. This Early Biomarkers of AMD (EBAMD) study evaluates serum factors that protect foveal MPOD architecture in Caucasian offspring of parent(s) with AMD.

Methods

N = 130 subjects [mean (SD) age 62.8 (8.6) years; 36/94 male/female] were recruited from Scripps Health/ Scripps Memorial Hospital/ Scripps Mericos Eye Institute between 2012 and 2017. Macula pigment 3D topography was evaluated using specular reflectance. Buccal genetic cheek swab, circulating serum dietary carotenoids and long-term RBC omega-3 fatty acid status, as well as common secondary clinical structural and vision function parameters were obtained.

Results

41 % of offspring of AMD parent(s) presented with FMPD. These offspring were about 4 years younger than those without FMPD (controls; P = 0.012) and had thinner foveas (P = 0.010). There were no differences in gender, BMI, % body fat, visual acuity or contrast sensitivity between those with and without FMPD. % RBC membrane docosahexaenoic acid (DHA) was reduced in FMPD offspring vs. control offspring (P = 0.04). The Omega-3 Index was significantly decreased in the FMPD group (P = 0.03).

Conclusions

The percentage of FMPD in AMD offspring is nearly twice that reported for the general population in the scientific literature. Offspring presenting FMPD had similar AMD genetic risk, but significantly reduced % RBC membrane omega-3 fatty acids and thinner foveas compared with those without FMPD. Our data supports the importance of ‘essential fatty’ acids as an independent AMD risk factor.

The Light and the Dark of Early and Intermediate AMD: Cone- and Rod-Mediated Changes Are Linked to Fundus Photograph and FAF Abnormalities

Purpose

The purpose of this paper is to describe the extent to which scotopic and photopic measures of visual function predict color fundus photograph (CFP) and fundus autofluorescence (FAF) changes in early and intermediate nonexudative AMD.

Methods

Sixty-nine observers were recruited: 56 AMD patients (mean age, 73 ± 12.98 years) and 13 controls (mean age, 67.77 ± 9.72 years). A nonmydriatic retinal camera was used to obtain stereo fundus photographs and FAF images were recorded with a cSLO Heidelberg Spectralis HRA+OCT. Visual acuity (VA) was measured using an Early Treatment of Diabetic Retinopathy Study chart. Contrast sensitivity (CS) was assessed with a Pelli-Robson chart. Dark adaptation (DA) curves were recorded at 3° eccentricity using a PC-based technique. Analysis of these curves yielded five parameters: cone threshold (CT), cone time constant (CC), cone-rod break (α), slope of the second rod component (S2), and rod-rod break (β).

Results

Both cone and rod sensitivity recovery were grossly abnormal in the patients. The rod recovery slope (S2) most accurately predicted the fundus photograph-based grade and the FAF classification (ρ = 0.61 and ρ = 0.60, respectively; both P < 0.0001). CS showed a strong association with FAF (ρ = 0.50, P < 0.0001) and with fundus photograph-based grade (ρ = 0.38, P < 0.002). There was no correlation between VA and either imaging method.

Conclusions

Dynamic, rod-based measures most accurately reflect the severity of early AMD. Although less specific to AMD than DA changes, static photopic abnormalities such as CS also correspond with morphologic changes. Assessment of function in early AMD should include dynamic rod- and cone-mediated measurements of sensitivity recovery.

Objective method for measuring the macular pigment optical density in the eye

Macular pigment is a yellowish pigment of purely dietary origin, which is thought to have a protective role in the retina. Recently, it was linked to age-related macular degeneration and improved visual function. In this work, we present a method and a corresponding optical instrument for the rapid measurement of its optical density. The method is based on fundus reflectometry and features a photodetector for the measurement of reflectance at different wavelengths and retinal locations. The method has been tested against a commercially available instrument on a group of healthy volunteers and has shown good correlation. The proposed instrument can serve as a rapid, non-midriatic, low-cost tool for the measurement of macular pigment optical density.

Investigating the potential of Zernike polynomials to characterise spatial distribution of macular pigment

It has been postulated that particular patterns of macular pigment (MP) distribution may be associated with the risk for eye diseases such as age-related macular degeneration (AMD). This work investigates the potential of Zernike polynomials (ZP) to characterise the level and distribution of MP, and their suitability as a representation for analysis of the effects of age and AMD on MP patterns. As the case study, MP distribution maps computed using an experimental method based on fundus reflectance (MRIA) were obtained for ninety volunteers representing three groups: under-fifty without AMD, fifty and over without AMD, and fifty and over with AMD. ZP with 105 coefficients were fitted to the maps using least-squares optimisation and found to represent MP maps accurately (RMSE<10⁻¹). One-way MANOVA analysis carried out on ZP representations showed that the three subject groups have significantly different means (Wilk’s Lambda 0.125, p<0.0001). Linear discriminant analysis with leave-one-out scheme resulted in accuracy, sensitivity and specificity of classification according to, respectively, disease status regardless of age (81% all); disease status in the age-matched groups (87%, 88%, 86%); age irrespective of disease status (81%, 83%, 73%); and age for subjects without AMD (83%, 88%, 80%). Mean MP distributions computed from ZP coefficients for the three groups showed more elevated and more peaked MP for the healthy under-fifty group; more irregular and more elevated peripheral levels in over-fifty AMD group than in over-fifty non-AMD group; and moderate radial asymmetry in non-AMD over-50 group. The results suggest that ZP coefficients are capable of accurately representing MP in a way that captures certain spatial patterns of its distribution. Using the ZP representation MP maps could be classified according to both age and disease status with accuracy significantly greater than chance, with peak elevation, pattern irregularity and radial asymmetry identified as important features.

Macular Pigment and Visual Function in Patients With Glaucoma: The San Diego Macular Pigment Study

Purpose

Although recent studies have shown that macular pigment (MP) is significantly lower in glaucoma patients, this relationship merits further investigation.

Methods

This cross-sectional study included 85 glaucoma patients and 22 controls. All subjects had standard automated perimetry (SAP) and retinal nerve fiber layer (RNFL) thickness measurements. Intake of lutein (L) and zeaxanthin (Z) was estimated using a novel dietary screener. The Heidelberg Spectralis dual-wavelength autofluorescence (AF) technology was employed to study the relationship between MP and glaucoma. The association between MP volume and glaucoma was investigated using linear regression models accounting for potential confounding factors.

Results

Glaucoma patients had significantly worse SAP mean deviation (MD) and lower RNFL thickness in the study eye compared to control subjects (P < 0.001 for both). MP (volume) was comparable between groups (P = 0.436). In the univariable model, diagnosis of glaucoma was not associated with MP volume (R² = 1.22%; P = 0.257). Dietary intake of L and Z was positively and significantly related to MP in the univariable (P = 0.022) and multivariable (P = 0.020) models.

Conclusions

These results challenge previous studies that reported that glaucoma is associated with low MP. Dietary habits were found to be the main predictor of MP in this sample. Further research is merited to better understand the relationship between glaucoma, MP, and visual performance in these patients.

Assessment of Macular Pigment Optical Density Using Fundus Reflectometry in Diabetic Patients

PURPOSE:

Diabetic retinopathy (DR) is a major cause of visual disability and may be associated with reduction in macular pigment (MP) density and insufficient data are available. We present MP optical density (MPOD) measured by fundus reflectometry in eyes with and without early and moderate DR.

SUBJECTS AND METHODS:

This was a cross-sectional study conducted in the year 2014–2015. Participants were divided into three groups: the normal individuals without diabetes constituted Group I, while diabetic patients without DR and the patients with mild-to-moderate DR constituted Group II and Group III, respectively. MPOD and maximum optical density (Max OD) were measured using a Visucam 500 fundus camera (Carl Zeiss Meditec AG, Jena, Germany).

RESULTS:

Fifty diabetic patients without DR, 50 with mild and moderate DR, and 50 healthy individuals underwent MPOD and Max OD measurements. The mean pigment density was the same in all the three groups (0.12). HbA1c levels were inversely correlated with MPOD (P = 0.01) and Max OD (P = 0.002). There was no relationship between MP density and age (P = 0.66), gender (P = 0.24), or duration of diabetes (P = 0.85). The duration of diabetes was compared between the two groups of diabetic patients with and without DR.

CONCLUSIONS:

The mean pigment density assessed by fundus reflectometry was 0.12 in each of the three groups studied. Higher HbA1c levels in diabetic patients correlated with decreased MPOD and Max OD. Better glycemic control may influence macular health in diabetic patients.

Optical Detection of Macular Pigment Formation in Premature Infants

Purpose

To demonstrate the presence of macular pigment in the retina of premature infants, and to examine its changes with age.

Methods

The participants included 40 premature infants. Infants who had received laser photocoagulation for retinopathy of prematurity were excluded. Macular pigment optical density (MPOD) was measured by fundus reflectometry using RetCam3, a digital fundus camera. The reflection imaging was performed for ROP screening. The imaging time points were from a post menstrual age (PMA) of 29 weeks 0 days to 46 weeks 5 days.

Results

The MPOD levels could be obtained from 39 premature infants. The levels at the first measurement ranged from 0 to 0.18 (mean 0.076, SD 0.044). The earliest time, when a nonvanishing MPOD level was obtained, was at a PMA of 33 weeks and 2 days, and that level was 0.05. The initial examination MPOD levels showed a moderate correlation with age (R² = 0.32, P < 0.00017). The mean MPOD levels measured each week during the follow-up period showed a very strong correlation with age (R² = 0.91, P < 0.0001). A regression line of MPOD = 0.0069 × age − 0.1783 was derived, where age is counted in PMA days.

Conclusions

The MPOD levels of premature infants were for the first time measured in living eyes. Macular pigment increased linearly with age.

Translational Relevance

Macular pigment increased with the development of macular morphology. This result suggested the importance of nutritional management of infants and mothers during perinatal period.

Effect of intraocular scattering in macular pigment optical density measurements

Fundus reflectometry is a common in-vivo, noninvasive method to estimate the macular pigment optical density (MPOD). The measured density, however, can be affected by the individual's intraocular scattering. Scattering causes a reduction in the contrast of the fundus image, which in turn leads to an underestimation of the measured density. Intraocular scattering was measured optically in a group of seven young, healthy subjects using the method of optical integration and was subsequently used to correctly estimate the MPOD from fundus images. It was shown that when scattering is not considered, the measured optical density using fundus reflectometry can be underestimated by as high as 16% for our group of subjects.

Bayer Filter Snapshot Hyperspectral Fundus Camera for Human Retinal Imaging

PURPOSE

To demonstrate the versatility and performance of a compact Bayer filter snapshot hyperspectral fundus camera for in-vivo clinical applications including retinal oximetry and macular pigment optical density measurements.

METHODS

12 healthy volunteers were recruited under an Institutional Review Board (IRB) approved protocol. Fundus images were taken with a custom hyperspectral camera with a spectral range of 460-630 nm. We determined retinal vascular oxygen saturation (sO₂) for the healthy population using the captured spectra by least squares curve fitting. Additionally, macular pigment optical density was localized and visualized using multispectral reflectometry from selected wavelengths.

RESULTS

We successfully determined the mean sO₂ of arteries and veins of each subject (ages 21-80) with excellent intrasubject repeatability (1.4% standard deviation). The mean arterial sO₂ for all subjects was 90.9% ± 2.5%, whereas the mean venous sO₂ for all subjects was 64.5% ± 3.5%. The mean artery-vein (A-V) difference in sO₂ varied between 20.5% and 31.9%. In addition, we were able to reveal and quantify macular pigment optical density.

CONCLUSIONS

We demonstrated a single imaging tool capable of oxygen saturation and macular pigment density measurements in vivo. The unique combination of broad spectral range, high spectral-spatial resolution, rapid and robust imaging capability, and compact design make this system a valuable tool for multifunction spectral imaging that can be easily performed in a clinic setting.

Intraocular scattering compensation in retinal imaging

Intraocular scattering affects fundus imaging in a similar way that affects vision; it causes a decrease in contrast which depends on both the intrinsic scattering of the eye but also on the dynamic range of the image. Consequently, in cases where the absolute intensity in the fundus image is important, scattering can lead to a wrong estimation. In this paper, a setup capable of acquiring fundus images and estimating objectively intraocular scattering was built, and the acquired images were then used for scattering compensation in fundus imaging. The method consists of two parts: first, reconstruct the individual's wide-angle Point Spread Function (PSF) at a specific wavelength to be used within an enhancement algorithm on an acquired fundus image to compensate for scattering. As a proof of concept, a single pass measurement with a scatter filter was carried out first and the complete algorithm of the PSF reconstruction and the scattering compensation was applied. The advantage of the single pass test is that one can compare the reconstructed image with the original one and see the validity, thus testing the efficiency of the method. Following the test, the algorithm was applied in actual fundus images in human eyes and the effect on the contrast of the image before and after the compensation was compared. The comparison showed that depending on the wavelength, contrast can be reduced by 8.6% under certain conditions.

Macular pigment optical density: repeatability, intereye correlation, and effect of ocular dominance

Purpose

To evaluate short-term repeatability, intereye correlation, and effect of ocular dominance on macular pigment optical density (MPOD) measurements obtained using the QuantifEye Heterochromatic Flicker Photometer.

Patients and methods

A total of 72 study participants were enrolled in this prospective, cross-sectional study. Participants underwent a comprehensive ocular evaluation, including visual acuity, evaluation of ocular dominance, slit lamp examination, intraocular pressure measurement, and optic nerve head and macula analysis using optical coherence tomography and fundus photography. All study participants after initial training underwent MPOD measurement twice in both eyes in a randomized sequence. The repeatability was tested using Altman and Bland plots for first measurements with the second measurements for right eye and left eye and additionally by grouping eyes as a function of ocular dominance. The Pearson correlation coefficient was performed to assess the intereye correlation of MPOD values.

Results

The mean age of study participants was 35.5 years (range 22–68 years). The mean MPOD measurements for OD (right eye) and OS (left eye) were 0.47 and 0.48, respectively, which followed a normal distribution (Shapiro–Wilk test, P=0.6 and 0.2). The 95% limits of agreement of Altman and Bland plots for the first and second measurements were −0.12 to +0.11 and −0.13 to +0.12 for OD and OS, respectively. The correlation coefficient of mean MPOD measurements of OD and OS was r statistic =0.94 (Pearson correlation coefficient P<0.0001; r² 0.89). The 95% limits of agreement of Altman and Bland plots when evaluated by laterality of eye or by ocular dominance were narrow, with limits of agreement ranging from −0.13 to +0.12.

Conclusion

The MPOD measurements obtained using the QuantifEye show good short-term repeatability. There is excellent intereye correlation, indicating that the MPOD values of one eye data can predict the fellow eye value with 89% accuracy. The ocular dominance had no bearing on the outcome of this psychophysical test in ocular healthy eyes.

Individual Colorimetric Observer Model

This study proposes a vision model for individual colorimetric observers. The proposed model can be beneficial in many color-critical applications such as color grading and soft proofing to assess ranges of color matches instead of a single average match. We extended the CIE 2006 physiological observer by adding eight additional physiological parameters to model individual color-normal observers. These eight parameters control lens pigment density, macular pigment density, optical densities of L-, M-, and S-cone photopigments, and λmax shifts of L-, M-, and S-cone photopigments. By identifying the variability of each physiological parameter, the model can simulate color matching functions among color-normal populations using Monte Carlo simulation. The variabilities of the eight parameters were identified through two steps. In the first step, extensive reviews of past studies were performed for each of the eight physiological parameters. In the second step, the obtained variabilities were scaled to fit a color matching dataset. The model was validated using three different datasets: traditional color matching, applied color matching, and Rayleigh matches.

Lutein, zeaxanthin, and meso-zeaxanthin: The basic and clinical science underlying carotenoid-based nutritional interventions against ocular disease

The human macula uniquely concentrates three carotenoids: lutein, zeaxanthin, and meso-zeaxanthin. Lutein and zeaxanthin must be obtained from dietary sources such as green leafy vegetables and orange and yellow fruits and vegetables, while meso-zeaxanthin is rarely found in diet and is believed to be formed at the macula by metabolic transformations of ingested carotenoids. Epidemiological studies and large-scale clinical trials such as AREDS2 have brought attention to the potential ocular health and functional benefits of these three xanthophyll carotenoids consumed through the diet or supplements, but the basic science and clinical research underlying recommendations for nutritional interventions against age-related macular degeneration and other eye diseases are underappreciated by clinicians and vision researchers alike. In this review article, we first examine the chemistry, biochemistry, biophysics, and physiology of these yellow pigments that are specifically concentrated in the macula lutea through the means of high-affinity binding proteins and specialized transport and metabolic proteins where they play important roles as short-wavelength (blue) light-absorbers and localized, efficient antioxidants in a region at high risk for light-induced oxidative stress. Next, we turn to clinical evidence supporting functional benefits of these carotenoids in normal eyes and for their potential protective actions against ocular disease from infancy to old age.

Autofluorescence imaging of macular pigment: influence and correction of ocular media opacities

The healthy adult human retina contains in its macular region a high concentration of blue-light absorbing carotenoid compounds, known as macular pigment (MP). Consisting of the carotenoids lutein, zeaxanthin, and meso-zeaxanthin, the MP is thought to shield the vulnerable tissue layers in the retina from lightinduced damage through its function as an optical attenuator and to protect the tissue cells within its immediate vicinity through its function as a potent antioxidant. Autofluorescence imaging (AFI) is emerging as a viable optical method for MP screening of large subject populations, for tracking of MP changes over time, and for monitoring MP uptake in response to dietary supplementation. To investigate the influence of ocular media opacities on AFI-based MP measurements, in particular, the influence of lens cataracts, we conducted a clinical trial with a large subject population (93 subjects) measured before and after cataract surgery. General AFI image contrast, retinal blood vessel contrast, and presurgery lens opacity scores [Lens Opacities Classification System III (LOCS III)] were investigated as potential predictors for image degradation. These clinical results show that lens cataracts can severely degrade the achievable pixel contrasts in the AFI images, which results in nominal MP optical density levels that are artifactually reduced. While LOCS III scores and blood vessel contrast are found to be only a weak predictor for this effect, a strong correlation exists between the reduction factor and the image contrast, which can be quantified via pixel intensity histogram parameters. Choosing the base width of the histogram, the presence or absence of ocular media opacities can be determined and, if needed, the nominal MP levels can be corrected with factors depending on the strength of the opacity.

Macular pigment optical density measurements by one-wavelength reflection photometry--influence of cataract surgery on the measurement results

PURPOSE

The main objective of the present study was the investigation of possible influence of lens opacification on macular pigment optical density (MPOD) measurements.

METHODS

Eighty-six eyes of 64 patients (mean age 73.4 ± 8.3 years) were included in the study. MPOD was prospectively measured using the one-wavelength reflection method (Visucam500, Carl Zeiss Meditec AG) before and after cataract extraction, with implantation of a blue-light filtering intraocular lens (AlconSN60WF). The median of the maximum optical density (MaxOD) and the median of the mean optical density (MeanOD) measurements of macular pigment across the subject group were evaluated.

RESULTS

Statistically significant differences were noticed between pre-operative and post-operative measurements, the absolute values were generally lower after cataract extraction. The following median (lower/upper quartile) differences across the group were determined: MaxOD -33.8 % (-46.2 to -19.1 %), MeanOD -44.0 % (-54.6 to -26.6 %). Larger changes were observed in elderly patients [<70 years of age (n = 25 eyes): MaxOD -13.4 % (-20.5 to 3.6 %), MeanOD -23.6 % (-30.5 to -15.3 %) versus patients ≥70 years (n = 61 eyes) MaxOD -40.5 % (-53.2 to -30.1 %), MeanOD -47.2 % (-57.8 to -40.1 %)] and in patients with progressed stage of cataract. MaxOD for lens opacification grade 1 (n = 9 eyes): -27.4 % (-42.1 to -19.6 %), grade 2 (n = 26 eyes): -35.0 % (-44.2 to -25.3 %), grade 3 (n = 21 eyes): -34.4 % (-45.4 to -11.4 %), grade 4 (n = 25 eyes): -32.6 % (-53.2 to -6.4 %), and grade 5 (n = 5 eyes): -53.5 % (-61.7 to -38.7 %) and MeanOD for cataract stage 1 (n = 9 eyes): -42.6 % (-46.0 to -26.0 %), stage 2 (n = 26 eyes): -44.1 % (-51.8 to -26.2 %), stage 3 (n = 21 eyes): -45.7 % (-54.7 to -24.7 %), stage 4 (n = 25 eyes): -39.5 % (-59.4 to -26.1 %), and stage 5 (n = 5 eyes): -57.0 % (-66.1 to -51.4 %).

CONCLUSIONS

As established by comparison of pre- to post-operative measurements, cataract presented a strong effect on MPOD measured by one-wavelength reflection method. Particular care should therefore be taken when evaluating MPOD using this method in elderly patients with progressed stage of cataract. Future optimization of correcting parameters of scattered light and consideration of cataract influence may allow more precise evaluation of MPOD.

Changes in spatial extent and peak double optical density of human macular pigment with age

The purpose of the present work was to estimate the changes in spatial distribution and optical density of macular pigment (MP) with age. A fundus imaging system with high spatial and spectral resolution was adapted to form an indirect ophthalmoscope. The double optical density at 490 nm of the MP as a function of the location in the retina was obtained for 33 healthy subjects (ages: 21-60 years). There was an increase in spatial extent and decrease in double optical density with age. Furthermore, the spatial distribution of MP showed central areas with irregular shapes and a tendency toward asymmetry.

Reflection-based imaging of macular pigment distributions in infants and children

We have developed a reflection-based capability of the RetCam(®) platform, an FDA-cleared pediatric retinal-imaging instrument, for the purpose of measuring macular pigment levels as well as their spatial distributions in infants and children. Our modifications include narrow-band blue-wavelength excitation of the macular pigment absorption in combination with spectrally selective blue-wavelength readout of the reflection signals received by the instrument's CCD detector array. Furthermore, an algorithm is developed that allows the computation of optical density maps for the macular pigment relative to peripheral retinal areas. This made it possible for the first time to directly measure macular pigment levels and their spatial features in the developing human retina. In contrast to adults, infants with measurable pigment levels had almost exclusively a narrow, circularly symmetric, pigment distribution. The described methodology holds promise for future investigations into the role of macular pigment in the developing human retina and the effect of dietary interventions in diseases resulting from a lack of normal carotenoid levels.

Concordance of macular pigment measurements obtained using customized heterochromatic flicker photometry, dual-wavelength autofluorescence, and single-wavelength reflectance

This study compares in vivo measurements of macular pigment (MP) obtained using customized heterochromatic flicker photometry (cHFP; Macular Metrics Densitometer(™)), dual-wavelength fundus autofluorescence (Heidelberg Spectralis(®) HRA + OCT MultiColor) and single-wavelength fundus reflectance (Zeiss Visucam(®) 200). MP was measured in one eye of 62 subjects on each device. Data from 49 subjects (79%) was suitable for analysis. Agreement between the Densitometer and Spectralis was investigated at various eccentricities using a variety of quantitative and graphical methods, including: Pearson correlation coefficient to measure degree of scatter (precision), accuracy coefficient, concordance correlation coefficient (ccc), paired t-test, scatter and Bland-Altman plots. The relationship between max MP from the Visucam and central MP from the Spectralis and Densitometer was investigated using regression methods. Agreement was strong between the Densitometer and Spectralis at all central eccentricities (e.g. at 0.25° eccentricity: accuracy = 0.97, precision = 0.90, ccc = 0.87). Regression analysis showed a very weak relationship between the Visucam and Densitometer (e.g. Visucam max on Densitometer central MP: R(2) = 0.008, p = 0.843). Regression analysis also demonstrated a weak relationship between MP measured by the Spectralis and Visucam (e.g. Visucam max on Spectralis central MP: R(2) = 0.047, p = 0.348). MP values obtained using the Heidelberg Spectralis are comparable to MP values obtained using the Densitometer. In contrast, MP values obtained using the Zeiss Visucam are not comparable with either the Densitometer or the Spectralis MP measuring devices. Taking cHFP as the current standard to which other MP measuring devices should be compared, the Spectralis is suitable for use in a clinical and research setting, whereas the Visucam is not.

Imaging system to assess objectively the optical density of the macular pigment in vivo

This paper presents an optical system called MacPI, which implements a two-color reflectance technique in combination with various hardware and software tools to assess objectively the macular pigment (MP) optical density in vivo. The system consists of a bespoke optical design, a control architecture, driver electronics, a collection of image-processing techniques, and a graphical user interface. The deficiencies of the technique employed and the solutions implemented in the MacPI system to confront those inherent frailties are presented. An overview of the effective interpretation of the acquired data and the techniques employed by MacPI in the acquisition of that data is discussed. The result of a comparison trial with an alternative device is also presented. We suggest that appropriate design of the hardware and an efficient interpretation of the acquired data should produce a system capable of consistent, accurate, and rapid measurements, while retaining the distinction of ease of use, portability, comfort for the subject, and a design that is economic to produce. Its versatility should allow both for a clinical screening application and for further investigation and establishment of the physiological role of the MP in a laboratory-based environment.

Blue-light reflectance imaging of macular pigment in infants and children

PURPOSE

While the role of the macular pigment carotenoids in the prevention of age-related macular degeneration has been extensively studied in adults, comparatively little is known about the physiology and function of lutein and zeaxanthin in the developing eye. We therefore developed a protocol using a digital video fundus camera (RetCam) to measure macular pigment optical density (MPOD) and distributions in premature infants and in children.

METHODS

We used blue light reflectance to image the macular pigment in premature babies at the time of retinopathy of prematurity (ROP) screening and in children aged under 7 years who were undergoing examinations under anesthesia for other reasons. We correlated the MPOD with skin carotenoid levels measured by resonance Raman spectroscopy, serum carotenoids measured by HPLC, and dietary carotenoid intake.

RESULTS

We enrolled 51 infants and children ranging from preterm to age 7 years. MPOD correlated significantly with age (r = 0.36; P = 0.0142), with serum lutein + zeaxanthin (r = 0.44; P = 0.0049) and with skin carotenoid levels (r = 0.42; P = 0.0106), but not with dietary lutein + zeaxanthin intake (r = 0.13; P = 0.50). All premature infants had undetectable macular pigment, and most had unusually low serum and skin carotenoid concentrations.

CONCLUSIONS

Our most remarkable finding is the undetectable MPOD in premature infants. This may be due in part to foveal immaturity, but the very low levels of serum and skin carotenoids suggest that these infants are carotenoid insufficient as a consequence of low dietary intake and/or severe oxidative stress. The potential value of carotenoid supplementation in the prevention of ROP and other disorders of prematurity should be a fruitful direction for further investigation.

Inverse relationship between macular pigment optical density and axial length in Chinese subjects with myopia

BACKGROUND

Macular pigment (MP) has been the focus of much attention in recent years, due to its protective effect against macular degenerations. In this study, we investigated the association between macular pigment optical density (MPOD) and axial length (AL) in Chinese subjects with myopia.

METHODS

In total, 173 myopes (mean spherical equivalent [MSE] ≤-1.00D) were recruited for this prospective observational study. MPOD was measured in both eyes of each subject using a macular metrics densitometer. AL was measured in eyes using an IOL-Master. A raw coefficient of correlation analysis and a partial correlation analysis were used to investigate the relationship between MPOD and AL.

RESULTS

The age of the subjects ranged from 18 to 67 years. The overall mean MPOD for the cohort was 0.412 ± 0.119 (range, 0.105-0.812). The mean AL was 25.18 ± 1.08 mm (range, 23.14-28.19 mm). Using a raw coefficient of correlation, a significant inverse correlation was found between MPOD and AL (r= -0.134, p=0.012). When using a partial correlation analysis to eliminate the impact of covariant, a significant inverse correlation was also found between MPOD and AL (r= -0.142, p=0.008). Furthermore, when AL was divided into two groups: AL>26 mm and AL ≤ 26 mm, a significant inverse correlation was observed between MPOD and AL in the former (r= -0.253, p=0.029), but no significant relationship was observed between these in the latter (r=0.104, p=0.067).

CONCLUSIONS

MPOD correlated inversely with AL in this sample of Chinese subjects with myopia.

Comparison of macular pigment in patients with age-related macular degeneration and healthy control subjects - a study using spectral fundus reflectance

PURPOSE

Previous studies have reported an age-dependent decline of macular pigment optical density (MPOD) as well as a relative lack of MPOD in age-related macular degeneration (AMD). Results are, however, strongly dependent on the technique used. In this study, we investigated the age dependence of MPOD using spectral fundus reflectance. In addition, we hypothesized that patients with AMD have a reduced MPOD as compared to healthy controls.

METHODS

A total of 85 healthy subjects and 96 patients with AMD were included in this study. The healthy control subjects showed a wide range of ages (mean, 51.6 years; range, 21-79years). Patients with AMD were significantly older (mean, 71.2 years; range, 50-89 years). Spectral fundus reflectance of the fovea was measured in a 2.3° detection field with a custom built fundus reflectometer. Calculation of MPOD was based on a previously published fundus reflectance model.

RESULTS

Patients with AMD showed a reduced MPOD (0.35 ± 0.12) as compared to the healthy control group (0.39 ± 0.12, p = 0.013 between groups). No age dependence of MPOD (r = -0.14, p = 0.19) was found in the healthy control group. In the AMD group, however, MPOD declined with age (r = -0.24, p = 0.019).

CONCLUSIONS

This study indicates that MPOD is reduced in patients with AMD. In addition, the data of this study indicate that MPOD is age dependent in AMD patients, but not in healthy controls. Taken together with data indicating that lutein supplementation increases MPOD, this provides a rationale for supplementation of the macular pigments in patients with AMD, although long-term clinical outcome data are lacking.

Macular lutein and zeaxanthin are related to brain lutein and zeaxanthin in primates

OBJECTIVES

Xanthophyll pigments lutein and zeaxanthin cross the blood-retina barrier to preferentially accumulate in the macular region of the neural retina. There they form macular pigment, protecting the retina from blue light damage and oxidative stress. Lutein and zeaxanthin also accumulate in brain tissue. The objective of the study was to evaluate the relationship between retinal and brain levels of these xanthophylls in non-human primates.

METHODS

Study animals included rhesus monkeys reared on diets devoid of xanthophylls that were subsequently fed pure lutein or pure zeaxanthin (both at 3.9 µmol/kg per day, n = 6/group) and normal rhesus monkeys fed a stock diet (0.26 µmol/kg per day lutein and 0.24 µmol/kg per day zeaxanthin, n = 5). Retina (4 mm macular punch, 4-8 mm annulus, and periphery) and brain tissue (cerebellum, frontal cortex, occipital cortex, and pons) from the same animals were analyzed by reverse-phase high-performance liquid chromatography.

RESULTS

Lutein in the macula and annulus was significantly related to lutein levels in the cerebellum, occipital cortex, and pons, both in bivariate analysis and after adjusting for age, sex and n-3 fatty acid status. In the frontal cortex the relationship was marginally significant. Macular zeaxanthin was significantly related to zeaxanthin in the cerebellum and frontal cortex, while the relationship was marginally significant in the occipital cortex and pons in a bivariate model.

DISCUSSION

An integrated measure of total macular pigment optical density, which can be measured non-invasively, has the potential to be used as a biomarker to assess brain lutein and zeaxanthin status.

Short- and mid-term repeatability of macular pigment optical density measurements using spectral fundus reflectance

BACKGROUND

Several methods have been proposed for measuring macular pigment optical density (MPOD). To date, none of the realized techniques can be considered as "gold standard". A key issue for the clinical applicability of a method is its repeatability. In this study, we investigated short- and mid-term repeatability of MPOD measurements using reflectometry.

METHODS

A total of 12 healthy young subjects were measured 5 times on 5 consecutive days. Repeatability over 6 months was investigated in patients with AMD. The data in AMD patients were taken from a recently published placebo controlled study investigating the effect of lutein supplementation on MPOD (n = 37; [1]). Four measurements over 6 months were used to calculate repeatability. Spectral fundus reflectance of the fovea was measured in a 2.3° detection field with a custom-built fundus reflectometer. Calculation of MPOD was based on a previously published fundus reflectance model.

RESULTS

The coefficients of variation were 6.2 ± 2.4% and 8.0 ± 5.5% in the healthy and AMD group, respectively. Bland-Altman plots indicate that the difference between measurements at day 1 and day 5 in healthy subjects and day 1 and month 6 in AMD patients was small. The maximum deviation in MPOD in a healthy subject was 0.07 (22.6%), and 0.17 (51.5%) in a patient with AMD.

CONCLUSIONS

Reflectometry provides adequate short-term and mid-term repeatability for measuring MPOD. Accordingly, the technique makes it possible to monitor MPOD in patients with AMD and to study the influence of supplementation in these subjects. In addition, the variability of the technique is small enough to allow for clinical trials with reasonable sample size.

Assessment of macular pigment optical density (MPOD) in patients with unilateral wet age-related macular degeneration (AMD)

PURPOSE

To compare the macular pigment optical density (MPOD) of patients with unilateral wet age-related macular degeneration (AMD) with the MPOD of bilateral dry AMD patients and healthy elderly individuals.

METHODS

The MPOD of 34 patients with unilateral wet AMD was measured in their fellow eye that had the dry form of the disease (study group). The MPOD of the study group was compared with the MPOD of 33 patients with bilateral dry AMD (patients' control group) and 35 elderly subjects without any signs of retinal disease (control group). None of the subjects was under carotenoid supplementation. The MPOD was measured with Heterochromatic Flicker Photometry [QuantifEYE™- MPS 9000 (ZeaVision(©))]. The statistical package SPSS v 17.0 was used for the analysis.

RESULTS

The overall mean MPOD was 0.52 (SD 0.15). Patients with unilateral wet AMD have significantly higher levels of MPOD in their fellow eye compared with patients with bilateral dry AMD (0.58 versus 0.48, p = 0.026). Mean MPOD of patients with bilateral dry AMD does not differ significantly from that of healthy elderly subjects (0.48 versus 0.50, p = 0.865). In this population sample, no correlation with age was observed, while women have slightly but significantly higher levels of MPOD (0.55 versus 0.49, p = 0.029).

CONCLUSION

In the present study, the mean MPOD at the fellow eye of patients with unilateral wet AMD was found to be significantly higher than that of patients with bilateral dry AMD, while no other significant difference emerged between groups. Further investigation is demanded to clarify the role of macular pigment in AMD progression.

Recovery of macular pigment spectrum in vivo using hyperspectral image analysis

We investigated the feasibility of a novel method for hyperspectral mapping of macular pigment (MP) in vivo. Six healthy subjects were recruited for noninvasive imaging using a snapshot hyperspectral system. The three-dimensional full spatial-spectral data cube was analyzed using non-negative matrix factorization (NMF), wherein the data was decomposed to give spectral signatures and spatial distribution, in search for the MP absorbance spectrum. The NMF was initialized with the in vitro MP spectrum and rank 4 spectral signature decomposition was used to recover the MP spectrum and optical density in vivo. The recovered MP spectra showed two peaks in the blue spectrum, characteristic of MP, giving a detailed in vivo demonstration of these absorbance peaks. The peak MP optical densities ranged from 0.08 to 0.22 (mean 0.15+∕-0.05) and became spatially negligible at diameters 1100 to 1760 μm (4 to 6 deg) in the normal subjects. This objective method was able to exploit prior knowledge (the in vitro MP spectrum) in order to extract an accurate in vivo spectral analysis and full MP spatial profile, while separating the MP spectra from other ocular absorbers. Snapshot hyperspectral imaging in combination with advanced mathematical analysis provides a simple cost-effective approach for MP mapping in vivo.

Measuring macular pigment optical density in vivo: a review of techniques

BACKGROUND

Macular pigment has been the focus of much attention in recent years, as a potential modifiable risk factor for age-related macular degeneration. This interest has been heightened by the ability to measure macular pigment optical density (MPOD) in vivo.

METHOD

A systematic literature search was undertaken to identify all available papers that have used in vivo MPOD techniques. The papers were reviewed, and all relevant information was incorporated into this article.

RESULTS

Measurement of MPOD is achievable with a wide range of techniques, which are typically categorized into one of two groups: psychophysical (requiring a response from the subject) or objective (requiring minimal input from the subject). The psychophysical methods include heterochromatic flicker photometry and minimum motion photometry. The objective methods include fundus reflectometry, fundus autofluorescence, resonance Raman spectroscopy and visual evoked potentials. Even within the individual techniques, there is often much variation in how data is obtained and processed.

CONCLUSION

This review comprehensively details the procedure, instrumentation, assumptions, validity and reliability of each MPOD measurement technique currently available, along with their respective advantages and disadvantages. This leads us to conclude that development of a commercial instrument, based on fundus reflectometry or fundus autofluorescence, would be beneficial to macular pigment research and would support MPOD screening in a clinical setting.

Macular pigment optical density measurements: evaluation of a device using heterochromatic flicker photometry

PURPOSE

Accurate assessment of the amount of macular pigment (MPOD) is necessary to investigate the role of carotenoids and their assumed protective functions. High repeatability and reliability are important to monitor patients in studies investigating the influence of diet and supplements on MPOD. We evaluated the Macuscope (Macuvision Europe Ltd., Lapworth, Solihull, UK), a recently introduced device for measuring MPOD using the technique of heterochromatic flicker photometry (HFP). We determined agreement with another HFP device (QuantifEye; MPS 9000 series: Tinsley Precision Instruments Ltd., Croydon, Essex, UK) and a fundus reflectance method.

METHODS

The right eyes of 23 healthy subjects (mean age 33.9 ± 15.1 years) were measured. We determined agreement with QuantifEye and correlation with a fundus reflectance method. Repeatability of QuantifEye was assessed in 20 other healthy subjects (mean age 32.1 ± 7.3 years). Repeatability was also compared with measurements by a fundus reflectance method in 10 subjects.

RESULTS

We found low agreement between test and retest measurements with Macuscope. The average difference and the limits of agreement were -0.041 ± 0.32. We found high agreement between test and retest measurements of QuantifEye (-0.02 ± 0.18) and the fundus reflectance method (-0.04 ± 0.18). MPOD data obtained by Macuscope and QuantifEye showed poor agreement: -0.017 ± 0.44. For Macuscope and the fundus reflectance method, the correlation coefficient was r = 0.05 (P = 0.83). A significant correlation of r = 0.87 (P<0.001) was found between QuantifEye and the fundus reflectance method.

CONCLUSIONS

Because repeatability of Macuscope measurements was low (ie, wide limits of agreement) and MPOD values correlated poorly with the fundus reflectance method, and agreed poorly with QuantifEye, the tested Macuscope protocol seems less suitable for studying MPOD.

Repeated measures of macular pigment optical density to test reproducibility of heterochromatic flicker photometry

PURPOSE

To report the reproducibility of macular pigment optical density (MPOD) values assessed with heterochromatic flicker photometry (HFP) in healthy individuals.

METHODS

Twenty-four volunteers from our department underwent MPOD testing of both eyes by flicker photometry on three separate occasions. To test reproducibility of MPOD, the coefficient of variance was calculated separately for right and left eyes. In addition, we investigated MPOD averages of right and left eyes and interocular correlations (Pearson's r) at every visit.

RESULTS

The mean MPODs at the first visit were 0.61 +/- 0.24 and 0.72 +/- 0.27 in right and left eyes, respectively. Mean values of 0.58 +/- 0.29 and 0.60 +/- 0.21 (second visit) and 0.62 +/- 0.27 and 0.63 +/- 0.24 (third visit) were assessed for right and left eyes, respectively. Differences of the mean values between eyes were not significant. Correlations were weak at visits one and two (r = 0.49, p < 0.014 and r = 0.43, p < 0.038, respectively) and moderate at visit three (r = 0.58, p < 0.003). The coefficients of variance were 36.1% and 23% for right and left eyes, respectively.

CONCLUSION

Our mean MPODs are higher and the interocular correlations weaker compared to the literature. The coefficient of variance in both eyes is high and does not imply good reproducibility of obtained MPOD values.

Correspondence between retinal reflectometry and a flicker-based technique in the measurement of macular pigment spatial profiles

A comparison of macular pigment optical density (MPOD) spatial profiles determined by an optical and a psychophysical technique is presented. We measured the right eyes of 19 healthy individuals, using fundus reflectometry at 0, 1, 2, 4, 6, and 8 deg eccentricity; and heterochromatic flicker photometry (HFP) at 0, 0.5, 1, 2, 3, 4, 5, 6, and 7 deg, and a reference point at 8 deg eccentricity. We found a strong correlation between the two techniques. However, the absolute estimates obtained by fundus reflectometry data were higher than by HFP. These differences could partly be explained by the fact that at 8 deg eccentricity the MPOD is not zero, as assumed in HFP. Furthermore, when performing HFP for eccentricities of <1 deg, we had to assume that subjects set flicker thresholds at 0.4 deg horizontal translation when using a 1-deg stimulus. MPOD profiles are very similar for both techniques if, on average, 0.05 DU is added to the HFP data at all eccentricities. An additional correction factor, dependent on the steepness of the MPOD spatial distribution, is required for 0 deg.

A new desktop instrument for measuring macular pigment optical density based on a novel technique for setting flicker thresholds

A rapid portable technique for estimating macular pigment optical density (MPOD) in large populations is described. The new instrument utilises a novel method for setting flicker thresholds which is undemanding for naïve and elderly observers and easily operated by a non-technical person. The method has good repeatability (r = 0.97) and the data are comparable with an optical method based on retinal reflectometry (r = 0.78). MPOD spatial profiles are presented for seven normal observers and these are well described (r = 0.99) by a decaying exponential function consistent with previous reports. MPOD values are presented from 5581 (2435 females and 3146 males) individuals measured in 48 optometric practices. The mean MPOD of this population was 0.33 (S.D. +/- 0.187) which is similar to previous large scale studies of MP.

Long-term plant stanol and sterol ester-enriched functional food consumption, serum lutein/zeaxanthin concentration and macular pigment optical density

Observational epidemiological studies have shown that low carotenoid intake and/or low carotenoid blood levels increase the risk of degenerative diseases like age-related macular degeneration. Functional foods enriched with plant sterol or stanol esters may lower serum concentrations of fat-soluble carotenoids. Theoretically, as a result the macular pigment optical density (MPOD), a marker for eye health, may change. We carried out a double-blind placebo-controlled human intervention trial with a duration of 18 months to evaluate the possible effects of plant stanol and sterol esters on serum lutein/zeaxanthin concentration in relation to the MPOD. Forty-seven subjects were randomly assigned to one of the three treatment groups: margarine without added plant sterols or stanols, plant sterol-enriched margarine, or plant stanol-enriched margarine. Serum cholesterol and lutein/zeaxanthine concentrations and the MPOD were evaluated at baseline and at study end. Changes in lipid-adjusted serum lutein/zeaxanthine concentrations between baseline and study end differed significantly between the three groups (P = 0.001). We found no differences in the MPOD between the three treatment groups, despite the differences in both absolute and cholesterol-standardized serum lutein/zeaxanthine concentrations. This shows that the observed reduction in serum carotenoid concentrations during 18 months consumption of these functional foods does not affect MPOD.

Macular pigment: new clinical methods of detection and the role of carotenoids in age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of irreversible blindness in people over the age of 65. The Age-Related Eye Disease Study (AREDS) suggests antioxidants may delay the advance of age-related macular degeneration. The macular pigments zeaxanthin and lutein may serve as antioxidants as well as blue filter to protect the retina. In this review, the general characteristics of macular pigment are described. The nutritional value of zeaxanthin/lutein and methods to assess macular pigment are discussed. Several emerging instruments to assess macular pigment, including heterochromatic flickering photometer, motion detection photometer, fundus reflectance spectroscope, Raman spectrometer, and autofluorescence spectrometry, are introduced and reviewed. Optometrists should be aware that they may play a role to assess and monitor the risk of AMD. There is an opportunity to incorporate measurement of macular pigment in optometric practice.

Interocular agreement in melanin and macular pigment optical density

Macular pigment (MP) and melanin possibly protect the macular area by absorbing blue light and acting as antioxidants. Because little is known about the interocular correlation of melanin, we determined its optical density (MOD) in both eyes of healthy subjects using fundus reflectometry. The measuring method also provided optical densities of MP (MPOD). In addition to evaluating its interocular correspondence we checked its dependency on central retinal thickness as measured with optical coherence tomography (OCT). Spectral fundus reflectance was measured in 69 eyes of 37 healthy participants. Both eyes of 32 subjects (15 males and 17 females, aged 57.9+/-14.6 years) were used to evaluate interocular correspondences. MPOD data from 35 right eyes of 18 males and 17 females, aged 55.7+/-15.7 years, was used to evaluate the relation between central retinal thickness and MPOD. MOD was 0.99+/-0.30 (range: 0.57-2.07) for the left eyes and 1.02+/-0.28 (range: 0.62-2.07) for the right eyes. The intraclass correlation coefficient (ICC) was 0.89 (P<0.001). MPOD was 0.49+/-0.19 for the left eyes (range: 0.12-0.81) and 0.47+/-0.17 (range: 0.14-0.73) for the right eyes. The ICC was 0.91 (P<0.001). Macular retinal thickness (MRT), representing the average macular thickness in the central 1000 microm zone, was 210+/-28 microm. Foveal retinal thickness (FRT), representing the retinal thickness at the crossing of the 6 radial scan lines on OCT, was 175+/-34 microm. Pearson's correlation coefficient showed no significant linear association between MRT and MPOD (r=-0.04, P=0.82), and between FRT and MPOD (r=0.05, P=0.78). The optical density of melanin showed a high interocular correspondence in healthy white participants. Similar results were found for MPOD. Relative interocular differences of more than 32% in MOD, or more than 34% in MPOD, may point to pathology. No relation between central retinal thickness and MPOD was found.

Macular pigment optical density in the elderly: findings in a large biracial Midsouth population sample

PURPOSE

To report the macular pigment optical density (MPOD) findings at 0.5 degrees of eccentricity from the fovea in elderly subjects participating in ARMA, a study of aging and age-related maculopathy (ARM) ancillary to the Health, Aging, and Body Composition (Health ABC) Study.

METHODS

MPOD was estimated with a heterochromatic flicker photometry (HFP) method in a large biracial population sample of normal 79.1 +/- 3.2-year-old adults living in the Midsouth (n = 222; 52% female; 23% black, 34% users of lutein-containing supplements). Within a modified testing protocol, subjects identified the lowest and the highest target intensity at which the flicker sensation disappeared, and the exact middle of this "no-flicker zone" was interpolated by the examiner.

RESULTS

An MPOD estimate was obtained successfully in 82% of the participants. The mean MPOD in our sample was 0.34 +/- 0.21 (SD). The interocular correlation was high (Pearson's r = 0.82). Compared with lutein supplement users, mean MPOD was 21% lower in nonusers (P = 0.013). MPOD was also 41% lower in blacks than in whites (P = 0.0002), even after adjustment for lutein supplement use. There were no differences in MPOD by gender, iris color, or history of smoking.

CONCLUSIONS

Older adults in the Midsouth appear to have average MPOD and interocular correlation comparable to those in previous studies. Lutein supplement use and white race correlated with higher MPOD. No evidence of an age-related decline in MPOD was seen in the sample. The HFP method for the measurement of MPOD is feasible in epidemiologic investigations of the elderly, the group at highest risk of ARM.