Bimodal spatial distribution of macular pigment: evidence of a gender relationship

Retinal and choroidal structure and vascularity in Chinese emmetropic and myopic children

PURPOSE

This study evaluated the structural features of the retinal and choroidal regions and their correlations with ocular biometric and vascular parameters in Chinese children using optical coherence tomography angiography (OCTA).

METHODS

A total of 159 children, 6-13 years of age, were included in this prospective study. The sample consisted of 55 emmetropes (spherical equivalent ≤ +0.75 and > -0.50 D), 53 low-moderate myopes (≤ -0.50 to > -6.00 D) and 51 high myopes without pathological changes (≤ -6.00 D). Optical coherence biometry was used to measure axial length (AL) and anterior segment parameters. Swept-source optical coherence tomography/OCTA was used to assess the macular structures and vascular characteristics in a 6 × 6 mm region centred on the macula.

RESULTS

In a comprehensive analysis adjusting for age, sex, AL, macular blood perfusion, intraocular pressure and anterior segment parameters, retinal thickness (RT) showed a significant positive association with deep retinal vascular density and superficial retinal vascular density in the foveal area, but not with AL. Moreover, RT exhibited a significant negative association with AL in the parafoveal and perifoveal regions. Further, a significant positive correlation was observed between choroidal thickness and both choroidal vascular volume and choriocapillaris perfusion area, along with a negative correlation with AL across the entire macular region.

CONCLUSIONS

This study showed that the thickness of retina and choroid in Chinese children was not only associated with AL but also showed dynamic properties such as the blood perfusion of the retina and choroid, particularly in the foveal area.

When Sex Matters: Differences in the Central Nervous System as Imaged by OCT through the Retina

BACKGROUND

Retinal texture has gained momentum as a source of biomarkers of neurodegeneration, as it is sensitive to subtle differences in the central nervous system from texture analysis of the neuroretina. Sex differences in the retina structure, as detected by layer thickness measurements from optical coherence tomography (OCT) data, have been discussed in the literature. However, the effect of sex on retinal interocular differences in healthy adults has been overlooked and remains largely unreported.

METHODS

We computed mean value fundus images for the neuroretina layers as imaged by OCT of healthy individuals. Texture metrics were obtained from these images to assess whether women and men have the same retina texture characteristics in both eyes. Texture features were tested for group mean differences between the right and left eye.

RESULTS

Corrected texture differences exist only in the female group.

CONCLUSIONS

This work illustrates that the differences between the right and left eyes manifest differently in females and males. This further supports the need for tight control and minute analysis in studies where interocular asymmetry may be used as a disease biomarker, and the potential of texture analysis applied to OCT imaging to spot differences in the retina.

Macular Pigment Optical Density in First Degree Relatives of Age-Related Macular Degeneration Patients

PURPOSE

To measure the macular pigment optical density in first-degree relatives of patients with age-related macular degeneration and compare it with a healthy control group.

METHODS

One hundred and twenty-eight healthy subjects who were first-degree relatives of age-related macular degeneration patients were included in the study (Group 1). As the control group, 74 healthy subjects were included in the study (Group 2). The right eyes of all cases were included in the study. Macular pigment optical density was measured with a commercially available device (MPSII®, Elektron Technology, Switzerland) using technology based on heterochromatic flicker photometry. Central foveal thickness and subfoveal choroidal thickness were measured with spectral-domain optical coherence tomography. Values were compared between the two groups.

RESULTS

There were 54 males and 74 females in Group 1 and 32 males and 42 females in Group 2. The mean ± SD ages of Group 1 and Group 2 were 49.0 ± 7.6 and 41.8 ± 8.6, respectively. Mean ± SD macular pigment optical density values of Group 1 and Group 2 were 0.43 ± 0.09 and 0.47 ± 0.12 (p = 0.048), mean ± SD central foveal thickness were 208 ± 19 and 216 ± 8 µm (p = 0.014), and mean ± SD subfoveal choroidal thickness were 232 ± 29 and 250 ± 21 µm (p = 0.002), respectively.

CONCLUSION

The macular pigment optical density values were significantly lower in the first-degree relatives of patients with age-related macular degeneration than in the control group. Macular pigment optical density may be a marker for the development of age-related macular degeneration in the future in the first-degree relatives of age-related macular degeneration patients. Further prospective studies with a larger number of participants will be needed to confirm our results moreover, to clarify its benefit as an early diagnostic biomarker.

Macular and Plasma Xanthophylls Are Higher in Age-related Macular Degeneration than in Normal Aging: Alabama Study on Early Age-related Macular Degeneration 2 Baseline

Purpose

Quantification of retinal xanthophyll carotenoids in eyes with and without age-related macular degeneration (AMD) via macular pigment optical volume (MPOV), a metric for xanthophyll abundance from dual wavelength autofluorescence, plus correlations to plasma levels, could clarify the role of lutein (L) and zeaxanthin (Z) in health, AMD progression, and supplementation strategies.

Design

Cross-sectional observational study (NCT04112667).

Participants

Adults ≥ 60 years from a comprehensive ophthalmology clinic, with healthy maculas or maculas meeting fundus criteria for early or intermediate AMD.

Methods

Macular health and supplement use was assessed by the Age-related Eye Disease Study (AREDS) 9-step scale and self-report, respectively. Macular pigment optical volume was measured from dual wavelength autofluorescence emissions (Spectralis, Heidelberg Engineering). Non-fasting blood draws were assayed for L and Z using high-performance liquid chromatography. Associations among plasma xanthophylls and MPOV were assessed adjusting for age.

Main Outcome Measures

Age-related macular degeneration presence and severity, MPOV in fovea-centered regions of radius 2.0° and 9.0°; plasma L and Z (μM/ml).

Results

Of 809 eyes from 434 persons (89% aged 60-79, 61% female), 53.3% eyes were normal, 28.2% early AMD, and 18.5% intermediate AMD. Macular pigment optical volume 2° and 9° were similar in phakic and pseudophakic eyes, which were combined for analysis. Macular pigment optical volume 2° and 9° and plasma L and Z were higher in early AMD than normal and higher still in intermediate AMD (P < 0.0001). For all participants, higher plasma L was correlated with higher MPOV 2° (Spearman correlation coefficient [Rs] = 0.49; P < 0.0001). These correlations were significant (P < 0.0001) but lower in normal (Rs = 0.37) than early and intermediate AMD (Rs = 0.52 and 0.51, respectively). Results were similar for MPOV 9°. Plasma Z, MPOV 2°, and MPOV 9° followed this same pattern of associations. Associations were not affected by supplement use or smoking status.

Conclusions

A moderate positive correlation of MPOV with plasma L and Z comports with regulated xanthophyll bioavailability and a hypothesized role for xanthophyll transfer in soft drusen biology. An assumption that xanthophylls are low in AMD retina underlies supplementation strategies to reduce progression risk, which our data do not support. Whether higher xanthophyll levels in AMD are due to supplement use cannot be determined in this study.

The Differential Contribution of Macular Pigments and Foveal Anatomy to the Perception of Maxwell's Spot and Haidinger's Brushes

The relationship of macular pigments and foveal anatomy to the perception of Maxwell's spot (MS) and Haidinger's brushes (HB) entoptic phenomena were investigated. Dual-wavelength-autofluorescence and OCT were used to define macular pigment density and foveal anatomy in 52 eyes. MS was generated by alternating unpolarized red/blue and red/green uniform field illumination. HB was generated by alternating the linear polarization axis of a uniform blue field. In Experiment 1, horizontal widths of MS and HB were measured using a micrometer system and compared with macular pigment densities and OCT-defined morphometry. MS radius (mean 1.4°) was significantly less than HB radius (mean 1.6°), with the spatial extent of both phenomena falling between the boundaries of the foveola and foveal pit. Multiple regression showed MS and HB radii to be significantly associated with the macular pigment spatial profile radius. HB radius, but not MS radius, was also significantly associated with foveolar morphometry. Experiment 2 compared perceptual profiles of MS with macular pigment distribution patterns and demonstrated close agreement. The size and appearance of MS is a direct indicator of macular pigment density and distribution. Measures of HB radii are less specific, with dependence on both macular pigment density and foveal structure.

FLUORESCENCE LIFETIME IMAGING OPHTHALMOSCOPY AS PREDICTOR OF LONG-TERM FUNCTIONAL OUTCOME IN MACULA-OFF RHEGMATOGENOUS RETINAL DETACHMENT

PURPOSE

To assess whether macular fluorescence lifetimes may serve as a predictor for long-term outcomes in macula-off rhegmatogenous retinal detachment.

METHODS

A single-center observational study was conducted. Patients with pseudophakic macula-off rhegmatogenous retinal detachment were included and evaluated 1 and 6 months after successful reattachment surgery. Fluorescence lifetime imaging ophthalmoscopy lifetimes in the central Early Treatment Diabetic Retinopathy Study grid subfield, in two distinct channels (short spectral channel and long spectral channel) were analyzed. Best-corrected visual acuity optical coherence tomography of the macula and fluorescence lifetimes were measured at month 1 and month 6.

RESULTS

Nineteen patients were analyzed. Lifetimes of the previously detached retinas were prolonged compared with the healthy fellow eyes. Short lifetimes at month 1 were associated with better best-corrected visual acuity improvement (short spectral channel: r2 = 0.27, P < 0.05, long spectral channel: r2 = 0.23, P < 0.05) and with good final best-corrected visual acuity (short spectral channel: r2 = 0.43, P < 0.01, long spectral channel: r2 = 0.25, P < 0.05). Lifetimes were prolonged in some cases of outer retinal damage in optical coherence tomography scans.

CONCLUSION

Fluorescence lifetime imaging ophthalmoscopy might serve as a prediction tool for functional recovery in pseudophakic macula-off rhegmatogenous retinal detachment. Retinal fluorescence lifetimes could give insight in molecular processes after rhegmatogenous retinal detachment.

The influence of the macular carotenoids on women's eye and brain health

Introduction: The mortality-morbidity paradox refers to the inconsistency in survival and disease between males and females: females live longer but tend to suffer greater age-related disease and disability. Many aspects of the latter can be targeted by lifestyle interventions, such as changes in dietary behavior.Methods: The relevant literature is reviewed.Conclusion: Dietary intake of the pigmented carotenoids appears to be particularly important for issues such as visual and cognitive loss. This may be due to the highly selective presence of a fraction of carotenoids, namely lutein (L) and zeaxanthin (Z), in specific tissues of the eye and brain. At those sites, L and Z have been shown to directly improve function and prevent central nervous system degeneration. On the palliative side, retinal LZ reduce glare disability, discomfort and photostress, improve chromatic contrast and visual range (e.g., the ability to see through blue atmospheric haze). These effects on input reflect changes in neural output such as improved visual processing speed, problem solving, memory and executive function (presumably due, also, to local effects in areas such as the hippocampus and frontal cortex). These effects on function throughout the central nervous system are mirrored by effects on disease progression. As potent antioxidants/anti-inflammatory agents, and "blue-blockers" within the retina, the pigments prevent loss that precedes neurodegenerative diseases such as age-related macular degeneration and some forms of dementia.

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.

Identification of Sex and Age from Macular Optical Coherence Tomography and Feature Analysis Using Deep Learning

PURPOSE

To develop deep learning models for identification of sex and age from macular optical coherence tomography (OCT) and to analyze the features for differentiation of sex and age.

DESIGN

Algorithm development using database of macular OCT.

METHODS

We reviewed 6147 sets of macular OCT images from the healthy eyes of 3134 individuals from a single eye center in Taiwan. Deep learning-based algorithms were used to develop models for the identification of sex and age, and 10-fold cross-validation was applied. Gradient-weighted class activation mapping was used for feature analysis.

RESULTS

The accuracy for sex prediction using deep learning from macular OCT was 85.6% ± 2.1% compared with accuracy of 61.9% using macular thickness and 61.4% ± 4.0% using deep learning from infrared fundus photography (P < .001 for both). The mean absolute error for age prediction using deep learning from macular OCT was 5.78 ± 0.29 years. A thorough analysis of the prediction accuracy and the gradient-weighted class activation mapping showed that the cross-sectional foveal contour lead to a better sex distinction than macular thickness or fundus photography, and the age-related characteristics of macula were on the whole layers of retina rather than the choroid.

CONCLUSIONS

Sex and age could be identified from macular OCT using deep learning with good accuracy. The main sexual difference of macula lies in the foveal contour, and the whole layers of retina differ with aging. These novel findings provide useful information for further investigation in the pathogenesis of sex- and age-related macular structural diseases.

Foveal morphology of normal fellow eyes of patients with unilateral macular hole

PURPOSE

To determine the morphology of the fovea in the ophthalmoscopically and tomographically normal fellow eyes of patients with unilateral idiopathic macular hole (MH) and to determine the association between the foveal morphological parameters and the foveal outer nuclear layer (ONL) thickness.

DESIGN

Retrospective observational study.

PARTICIPANTS

Two hundred three normal fellow eyes of patients with unilateral MH and 216 normal eyes of 216 healthy subjects.

METHODS

All eyes were examined by swept source optical coherence tomography (OCT). The built-in software measured the average retinal and choroidal thickness in the center and in the inner four subfields defined in the Early Treatment Diabetic Retinopathy Study. The total retinal thickness and the three retinal layers at the fovea and parafovea (0.25- and 0.5-mm nasal and temporal from fovea) and foveal floor width (FFW) were measured in the image of a horizontal scan passing through the center of the fovea. We defined the thickness between the internal limiting membrane and outer plexiform layer as the inner retinal thickness, and the thickness between the external limiting membrane and retinal pigment epithelium as the outer retinal thickness. Multiple regression analyses were performed with the age, sex, axial length, and the presence of a posterior vitreous detachment as the dependent variables.

MAIN OUTCOME MEASURES

OCT measurements and correlations between the foveal parameters and foveal ONL thickness.

RESULTS

The fellow eyes had a thinner central retinal subfield, thinner fovea, thinner ONL at all points except 0.5 mm nasal, significantly thicker outer retina at all points, and a wider FFW (P=.040 to P<.0001). The foveal ONL thickness was significantly and positively correlated with the central subfield retinal thickness and foveal thickness and negatively with the FFW (all P< .0001).

CONCLUSIONS

The thinner and deeper fovea and the thinner ONL of the fellow eyes of patients with a unilateral MH makes these eyes more susceptible to forming MH.

Bardet-Biedl syndrome-7 (BBS7) shows treatment potential and a cone-rod dystrophy phenotype that recapitulates the non-human primate model

Purpose: To provide a detailed ophthalmic phenotype of two male patients with Bardet-Biedl Syndrome (BBS) due to mutations in the BBS7 geneMethods: Two brothers ages 26 (Patient 1, P1) and 23 (P2) underwent comprehensive ophthalmic evaluations over three years. Visual function was assessed with full-field electroretinograms (ffERGs), kinetic and chromatic perimetry, multimodal imaging with spectral domain optical coherence tomography (SD-OCT), fundus autofluorescence (FAF) with short- (SW) and near-infrared (NIR) excitation lights and adaptive optics scanning light ophthalmoscopy (AOSLO).Results: Both siblings had a history of obesity and postaxial polydactyly; P2 had diagnoses of type 1 Diabetes Mellitus, Addison's disease, high-functioning autism-spectrum disorder and -12D myopia. Visual acuities were better than 20/30. Kinetic fields were moderately constricted. Cone-mediated ffERGs were undetectable, rod ERGs were ~80% of normal mean. Static perimetry showed severe central cone and rod dysfunction. Foveal to parafoveal hypoautofluorescence, most obvious on NIR-FAF, co-localized with outer segment shortening/loss and outer nuclear layer thinning by SD-OCT, and with reduced photoreceptors densities by AOSLO. A structural-functional dissociation was confirmed for cone- and rod-mediated parameters. Worsening of the above abnormalities was documented by SD-OCT and FAF in P2 at 3 years. Gene screening identified compound heterozygous mutations in BBS7 (p.Val266Glu: c.797 T > A of maternal origin; c.1781_1783delCAT, paternal) in both patients.Conclusions: BBS7-associated retinal degeneration may present as a progressive cone-rod dystrophy pattern, reminiscent of both the murine and non-human primate models of the disease. Predominantly central retinal abnormalities in both cone and rod photoreceptors showed a structural-functional dissociation, an ideal scenario for gene augmentation treatments.

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.

Evaluation of Macular Pigment Optical Density in Healthy Eyes Based on Dual-Wavelength Autofluorescence Imaging in South Indian Population

Purpose

To estimate macular pigment optical density (MPOD) values across different age groups in the South Indian population across various spatial profiles using dual-wavelength autofluorescence.

Methods

Sixty eyes of 31 healthy subjects underwent MPOD measurement with Spectralis HRA+OCT. The average MPOD and macular pigment optical volume (MPOV) at 1°, 2°, and 6° radii, the mean MPOD in the classical Early Treatment Diabetic Retinopathy Study (ETDRS) grid, and the spatial profiles of two different age groups across 12 plots covering the radial sectors were recorded.

Results

The mean age was 39.1 ± 12.7 years. The mean MPOD and MPOV values were 0.38 ± 0.11 and 787.95 ± 225.13 at 1° eccentricity, 0.23 ± 0.08 and 2000 ± 708.24 at 2° eccentricity, and 0.05 ± 0.02 and 4335 ± 2007.71 at 6° eccentricity, respectively. In the ETDRS grid, the mean MPOD was found to be highest in the central sector and lowest in the inferior peripheral ring. We also found that along the radial sectors the lower quadrants tended to have low MPOD as compared to the upper quadrants. Subjects 40 years of age or older had significantly higher averaged MPOD in certain areas (–15° to 15° and 75° to 105°) along the radial sectors than subjects less than 40 years of age.

Conclusions

This study establishes a reference value for future studies of diseased eyes in the South Indian population.

Translational Relevance

Our study is unique in that it reports MPOD among the South Indian population across different age groups, as well as the distribution of MPOD in all nine zones of the classical ETDRS grid and various spatial profiles covering the 30° radial sectors centered on the fovea.

Why is Zeaxanthin the Most Concentrated Xanthophyll in the Central Fovea?

Diet-based xanthophylls (zeaxanthin and lutein) are conditionally essential polar carotenoids preferentially accreted in high concentrations (1 mM) to the central retina, where they have the capacity to impart unique physiologically significant biophysical biochemical properties implicated in cell function, rescue, and survival. Macular xanthophylls interact with membrane-bound proteins and lipids to absorb/attenuate light energy, modulate oxidative stress and redox balance, and influence signal transduction cascades implicated in the pathophysiology of age-related macular degeneration. There is exclusive transport, sequestration, and appreciable bioamplification of macular xanthophylls from the circulating carotenoid pool to the retina and within the retina to regions required for high-resolution sensory processing. The distribution of diet-based macular xanthophylls and the lutein metabolite meso-zeaxanthin varies considerably by retinal eccentricity. Zeaxanthin concentrations are 2.5-fold higher than lutein in the cone-dense central fovea. This is an ~20-fold increase in the molar ratio relative to eccentric retinal regions with biochemically detectable macular xanthophylls. In this review, we discuss how the differences in the specific properties of lutein and zeaxanthin could help explain the preferential accumulation of zeaxanthin in the most vulnerable region of the macula.

Computer-aided fixation detection using retinal birefringence in multi-modal ophthalmic systems: Computer, electronics, algorithms

Many diagnostic and some therapeutic ophthalmic devices require a reliable complementing method to track the direction of gaze or just to validate fixation of the eye on a presented target. This would allow acquisition of artefact-free robust images of the fovea and the surrounding macula. So far, there have been only few attempts to provide fast and dependable fixation information to an optical imaging system in real time, to guide image acquisition. The author's lab has developed several instruments that detect the location of the fovea using retinal birefringence scanning (RBS), proven to be very effective. Here, an RBS-based fixation detection subsystem is proposed, designed to operate conjointly with a number of ophthalmic imaging technologies. Combining RBS with such technologies is not trivial, because RBS uses polarized light and polarization-sensitive optics, while most other modalities don't. The polarization optics was optimized by means of enhanced computer modeling. Both the electronic hardware and the software were designed for fast and reliable performance. Because many retinal imaging systems are used in pediatric settings, extensive audio-visual circuitry was employed for efficient attention/fixation attraction. The optomechanics has been optimized for robust data acquisition. This computer-aided conjoint system employs true anatomical information from the back of the eye and needs no calibration. The prototype instrument uses a decision-making logic based on four frequencies generated during scanning. The results reveal the applicability of RBS as an adjunct fixation monitoring modality, showing promise to remove the limitation imposed by eye movements upon advanced ophthalmic imaging technologies.

Spatial distribution of macular pigment estimated by autofluorescence imaging in elderly Japanese individuals

PURPOSE

To determine the spatial distribution types of macular pigment (MP) in elderly Japanese individuals and to consider their origin.

STUDY DESIGN

Observational case series.

METHODS

Local MP optical density (MPOD) at some eccentricities and MP volume were measured using the MPOD module of a MultiColor Spectralis in 96 pseudophakic eyes of 96 participants (age range, 52-86 years; mean age, 72.8 ± 8.3 years). The MP distribution types were determined from the MP spatial profiles. The retinal thickness (RT) at the foveal center, at both 0.5° and 0.9° eccentricities, and the foveal width were measured using optical coherence tomography.

RESULTS

The mean local MPOD at the foveal center was 0.79. Spatial distribution was classified into four types: central peak (24.0%), ring-like (40.6%), intermediate (22.9%), and central dip (12.5%). The ring-like type was the most frequent in these Japanese participants. The central-peak type showed lower MPOD than did the other types in the area outside 0.9°. The ring-like type occurred frequently in eyes with small RT at 0.5° and wider foveal width. A rough contour of the Müller cell cone was found more frequently in the central-dip type than in the other types.

CONCLUSIONS

The present characteristics of the different distribution patterns could be explained by the hypothesis that MP presents mainly in the Müller cell cone within 0.5° and in Müller cells in the outer and inner plexiform layers in the area outside 0.5°. The anatomic characteristics of Müller cells at the fovea and parafovea likely affect the MP distribution.

Adaptive optics imaging of the human retina

Adaptive Optics (AO) retinal imaging has provided revolutionary tools to scientists and clinicians for studying retinal structure and function in the living eye. From animal models to clinical patients, AO imaging is changing the way scientists are approaching the study of the retina. By providing cellular and subcellular details without the need for histology, it is now possible to perform large scale studies as well as to understand how an individual retina changes over time. Because AO retinal imaging is non-invasive and when performed with near-IR wavelengths both safe and easily tolerated by patients, it holds promise for being incorporated into clinical trials providing cell specific approaches to monitoring diseases and therapeutic interventions. AO is being used to enhance the ability of OCT, fluorescence imaging, and reflectance imaging. By incorporating imaging that is sensitive to differences in the scattering properties of retinal tissue, it is especially sensitive to disease, which can drastically impact retinal tissue properties. This review examines human AO retinal imaging with a concentration on the use of the Adaptive Optics Scanning Laser Ophthalmoscope (AOSLO). It first covers the background and the overall approaches to human AO retinal imaging, and the technology involved, and then concentrates on using AO retinal imaging to study the structure and function of the retina.

Antecedents of Soft Drusen, the Specific Deposits of Age-Related Macular Degeneration, in the Biology of Human Macula

AMD pathobiology was irreversibly changed by the recent discovery of extracellular cholesterol-containing deposits in the subretinal space, between the photoreceptors and retinal pigment epithelium (RPE), called subretinal drusenoid deposits (SDDs). SDDs strikingly mirror the topography of rod photoreceptors in human macula, raising the question of whether an equivalent process results in a deposition related to foveal cones. Herein we propose that AMD's pathognomonic lesion-soft drusen and basal linear deposit (BLinD, same material, diffusely distributed)-is the leading candidate. Epidemiologic, clinical, and histologic data suggest that these deposits are most abundant in the central macula, under the fovea. Strong evidence presented in a companion article supports the idea that the dominant ultrastructural component is large apolipoprotein B,E-containing lipoproteins, constitutively secreted by RPE. Lipoprotein fatty acids are dominated by linoleate (implicating diet) rather than docosahexaenoate (implicating photoreceptors); we seek within the retina cellular relationships and dietary drivers to explain soft druse topography. The delivery of xanthophyll pigments to highly evolved and numerous Müller cells in the human fovea, through RPE, is one strong candidate, because Müller cells are the main reservoir of these pigments, which replenish from diet. We propose that the evolution of neuroglial relations and xanthophyll delivery that underlie exquisite human foveal vision came with a price, that is, soft drusen and sequela, long after our reproductive years.

Repeatability of the macular pigment spatial profile: A comparison of objective versus subjective classification

PURPOSE

Classification of macular pigment (MP) spatial profile phenotypes varies and is often based on subjective visualisation. We investigated repeatability of MP optical density (MPOD) comparing an objective versus subjective profiling system.

METHODS

The coefficient of repeatability (CoR) was calculated for point MPOD values (0-3.8°) obtained by dual-wavelength fundus autofluorescence (FAF) from two scans obtained in a single visit of 40 healthy individuals (39 ± 9 years). For each individual's dataset, the MP profile was classified as exponential, ring-like or central dip using an objective method (based on deviations away from an exponential fit), as well as by subjective visual profiling. Existing FAF images of 88 monozygotic (MZ) and 69 dizygotic (DZ) twin pairs were reanalysed using the objective profiling method and concordance and heritability of ring-like profiles determined.

RESULTS

The CoR was 0.23 at 0° and 0.06 at 0.8°. Agreement of objective profiling between scans was excellent (κ = 0.85, 95% CI 0.69 to 1.00; p < 0.0005). Subjective profiling showed moderate agreement between scans (κ = 0.48, 95% CI 0.23 to 0.73; p < 0.0005). Agreement between objective and subjective classification was low (κ = 0.23, 95% CI 0.04 to 0.42; p = 0.02). Concordance for the ring-like profile using objective profiling was 0.74 for MZ compared to 0.36 for DZ twins. Heritability was calculated as 81.5% (95% confidence interval 61.1-93.1%).

CONCLUSION

Compared to visual assessment, objective MP profiling is a more reliable method and should be considered in future observational and interventional studies. In addition, MP profile phenotypes showed high heritability.

The clinical relevance of visualising the peripheral retina

Recent developments in imaging technologies now allow the documentation, qualitative and quantitative evaluation of peripheral retinal lesions. As wide field retinal imaging, capturing both the central and peripheral retina up to 200° eccentricity, is becoming readily available the question is: what is it that we gain by imaging the periphery? Based on accumulating evidence it is clear that findings in the periphery do not always associate to those observed in the posterior pole. However, the newly acquired information may provide useful clues to previously unrecognised disease features and may facilitate more accurate disease prognostication. In this review, we explore the anatomy and physiology of the peripheral retina, focusing on how it differs from the posterior pole, recount the history of peripheral retinal imaging, describe various peripheral retinal lesions and evaluate the overall relevance of peripheral retinal findings to different diseases.

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.

Changes in macular pigment optical density after membrane peeling

Introduction

To highlight the differences in macular pigment optical density (MPOD) between eyes with vitreoretinal interface syndrome and healthy control eyes, to assess the changes in MPOD in eyes treated with macular peeling, to investigate the relationships between MPOD changes and measures of retinal sensitivity such as best corrected visual acuity (BCVA) and microperimetry.

Methods

In this cross-sectional comparative study, 30 eyes affected by idiopathic epiretinal membrane (iERM, 15eyes) or full-thickness macular hole (FTMH, 15eyes) were compared with 60 eyes from 30 healthy age-matched patients. MPOD values (mean MPOD, maximum MPOD, MPOD area, and MPOD volume) were measured in a range of 4°–7° of eccentricity around the fovea, using the one-wavelength reflectometry method (Visucam 200, Carl-Zeiss Meditec). Patients affected by iERM and FTMH were treated with vitrectomy and epiretinal membrane-inner limiting membrane (ERM-ILM) peeling, with follow-up examinations performed preoperatively and 6 months postoperatively. The main outcome measures were the differences in MPOD between eyes with vitreoretinal interface syndrome and healthy eyes, changes in MPOD after ERM-ILM peeling, and relationships between MPOD and functional changes.

Results

Mean MPOD differed significantly between control eyes and those with iERM (P = .0001) or FTMH (P = .0006). The max MPOD and MPOD area increased, but not significantly. After peeling, the only significant change in MPOD was in MPOD volume (P = .01). In the ERM group, postoperative mean MPOD correlated significantly with best-corrected visual acuity (r = .739, P = .002).

Conclusions

MPOD was reduced in patients with iERM or FTMH compared with healthy eyes. We found a significant correlation between the mean postoperative MPOD and postoperative BCVA, hypothesizing that the postoperative increase in mean MPOD could be due to a change in distribution for unfolding and expansion of the fovea after the peeling. MOPD may be considered as a prognostic factor associated with a good visual prognosis in patients with iERM.

Rod-Mediated Dark Adaptation and Macular Pigment Optical Density in Older Adults with Normal Maculas

PURPOSE

To examine the association between macular pigment optical density (MPOD) and rod-mediated dark adaptation (RMDA) in persons ≥60 years old with normal maculas as determined by an accepted color fundus photography grading system.

METHODS

This cross-sectional analysis used baseline data from eyes in the Alabama Study on Early Age-Related Macular Degeneration. Eyes at step 1 in the AREDS 9-step grading system were considered normal. Eyes were additionally assessed by spectral domain optical coherence tomography (SD-OCT). Foveal MPOD was estimated via heterochromatic flicker photometry, and RMDA was assessed with a computerized dark adaptometer. The association between RMDA and MPOD was examined via Spearman correlation coefficients adjusted for age.

RESULTS

In 306 eyes from 306 persons (mean age 68.2 years) in normal macular health, MPOD was not associated with RMDA (age-adjusted rank correlation = 0.043, p = 0.45). After 81 eyes with incidental macular findings by SD-OCT evaluation were excluded, the association between MPOD and RMDA remained null (N = 225, age-adjusted r = 0.015, p = 0.82).

CONCLUSION

In a large sample of normal aged eyes, RMDA, a visual function that is rate limited by retinoid availability to photoreceptors across the complex of retinal pigment epithelium, Bruch's membrane, and choriocapillaris, is not related to MPOD in the neurosensory retina.

Sex-Dependent Choroidal Thickness Differences in Healthy Adults: A Study Based on Original and Synthesized Data

PURPOSE

The purpose of this study is to determine the influence of sex on choroidal thickness (CT) in healthy adults.

METHODS

Healthy Chinese adults were recruited and complete ophthalmic examinations were performed. The choroid was imaged by swept-source optical coherence tomography and the macular CT in Early Treatment Diabetic Retinopathy Study grids was obtained by the intrinsic automated segmentation software. CT in males and females was compared after controlling other factors. All of the published studies in PubMed were systemically tracked, and a syntheses analysis of the combined data of the present study and previous studies was performed to address this issue further.

RESULTS

A total of 104 healthy adults were included, of whom 38 (37%) were male and 66 (63%) were female. Older age and longer axial length (AL) each were significantly associated with thinner CT. After controlling for age and AL, the foveal CT and average macular CT were 25.5 μm (95% CI: 0.5-50.4 μm) and 22.1 μm (95% CI: 2.7-41.4 μm) thicker in men than in women, respectively. Significant differences in CT between males and females were also observed in inner and outer rings after controlling for age and AL (P < 0.05). After strict screening, 15 previously reported studies were determined to be eligible for inclusion. The combination of data collected from 2821 males and 3389 females provided further evidence that the choroid is thicker in males, with a pooled mean difference of 19.5 μm (95% CI: 11.4 to 27.6) for foveal CT and 14.7 μm (95% CI: 6.8 to 22.6) for average CT.

CONCLUSION

Our study of Chinese subjects, along with the syntheses analysis, strengthens the evidence that CT is greater in males than in females, based on OCT measurements. This observation may be pertinent for the sex disparities in some clinical conditions related to CT.

Quantifying Fundus Autofluorescence in Patients With Retinitis Pigmentosa

Purpose

Using quantitative fundus autofluorescence (qAF), we analyzed short-wavelength autofluorescent (SW-AF) rings in RP.

Methods

Short-wavelength autofluorescent images (486 nm excitation) of 40 patients with RP (69 eyes) were acquired with a confocal scanning laser ophthalmoscope equipped with an internal fluorescent reference. Mean qAF was measured in eight preset segments (qAF₈) and in region of interest (ROI)-qAF (200–700 μm) within and external to the borders of the rings at superior, temporal, and inferior sites relative to the ring. For both groups, qAF in patients with RP was compared to age-similar and race/ethnicity-matched healthy eyes at equivalent retinal locations.

Results

In 71% of eyes of RP patients, qAF₈ acquired internal to the inner border of the ring, was within the 95% confidence interval (CI) for healthy eyes, while in the remaining RP eyes qAF₈ was either higher or lower than the CI. Measured external to the ring, qAF₈ values were within the CI in 47% of RP eyes with the other eyes being higher or lower. In 28% of sites measured by ROI-qAF within the SW-AF ring, values were above the 95% CI of healthy controls. Region of interest-qAF measured just external to the ring was within the CI of healthy eyes in 74% of locations. The average local elevation in qAF within the ring was approximately 15%. In SD-OCT scans, photoreceptor-attributable reflectivity bands were thinned within and external to the ring.

Conclusions

Increased fluorophore production may be a factor in the formation of the SW-AF rings in RP.

The Association between Foveal Morphology and Macular Pigment Spatial Distribution: An Ethnicity Study

Purpose

Macular pigment (MP) spatial distribution varies considerably among individuals. We investigated ethnic variations in MP spatial distribution in relation to foveal architecture.

Methods

We measured MP optical density (MPOD) using heterochromatic flicker photometry (MAP test, City, University of London) in 76 white, 80 South Asian and 70 black volunteers (18 to 39 years). MPOD spatial profiles were classified objectively as exponential, ring-like or central dip, based on deviations away from an exponential fit. Measurements including total retinal thickness (RT), inner retinal layer (IRL), inner and outer plexiform layer (IPL and OPL) thickness, foveal width and foveal pit slope were taken from Spectralis SD-OCT (Heidelberg, Germany) scans.

Results

Integrated MPOD up to 1.8° (MPODint) was higher in South Asian (0.84±0.26) and black (0.84±0.31) than whites (0.63±0.24, P<0.0005). Ethnicity explained around 10% of the variance while gender played no significant role. MPOD profile phenotypes were associated with ethnicity: 58% with ring profiles were South Asian and 43% with dip profiles were black (χ²(4,226) = 13.4, P = 0.009). MPODint was lower in exponential (0.66±0.21) compared to ring-like (0.96±0.26) and central dip (1.00±0.32, P<0.0005) groups. White subjects had thicker IRL at 0° (130±21μm) than South Asian (123±16μm) and blacks (116±14μm; F(2) = 12.4, P<0.0005), with comparable results for IPL (P<0.0005) and OPL (P = 0.03). There was no significant difference in IRL, IPL or OPL (from 0 to 3.8° retinal eccentricity) or foveal width between MP profile groups (P>0.05).

Conclusion

We report a significant difference in the amount and distribution of MP between ethnicities that is not explained by variations in foveal morphology.

Analysis of foveal characteristics and their asymmetries in the normal population

The advance of optical coherence tomography (OCT) enables a detailed examination of the human retina in-vivo for clinical routine and experimental eye research. Only few investigations to date captured human foveal morphology in a large subject group on the basis of a detailed analysis employing mathematical models. However, even for important foveal characteristics unified terminology and clear definitions were not implemented so far. This might be a reason, why to this day the human fovea is considered to be a mostly symmetric and round structure. Therefore, the most important finding of this work is the detailed analysis of the asymmetric structure of the human fovea. We employed five clinically highly relevant foveal characteristics, which are derived from a previously published fovea model. For each, an accurate mathematical description is given. The presented properties include (1) mean retinal thickness inside a defined radius, (2) foveal bowl area, (3) a new, exact definition of foveal radius, (4) maximum foveal slope, and (5) the maximum height of the foveal rim. Furthermore, minimum retinal thickness was derived and analyzed. 220 strictly controlled healthy Caucasian subjects of European decent with an even distribution of age and gender were imaged with an Heidelberg Spectralis OCT. Detailed analysis demonstrated the following general results: (1) significant gender difference regarding the central foveal subfield thickness (CFST) but no significant differences for the minimum central retinal thickness, (2) a strong correlation between right and left eye of the same subject, and, as essential finding, (3) strong structural differences of the fovea form in the different anatomical directions (nasal, temporal, inferior and superior). In the analysis of the foveal asymmetry, it will be demonstrated that the foveal radius is larger in nasal and temporal direction compared to inferior and superior position. Furthermore, it will be shown that the circular fovea rather has an elliptic form with the larger axis along the nasal to temporal direction. Interestingly, the foveal slope shows a divergent behavior as the temporal direction has the smallest slope angle and both, inferior and superior angles are clearly larger than the others. The findings in this work can be used for an exact quantification of changes in early stages of various retinal diseases and as a marker for initial diagnosis.

Modeling Photo-Bleaching Kinetics to Create High Resolution Maps of Rod Rhodopsin in the Human Retina

We introduce and describe a novel non-invasive in-vivo method for mapping local rod rhodopsin distribution in the human retina over a 30-degree field. Our approach is based on analyzing the brightening of detected lipofuscin autofluorescence within small pixel clusters in registered imaging sequences taken with a commercial 488nm confocal scanning laser ophthalmoscope (cSLO) over a 1 minute period. We modeled the kinetics of rhodopsin bleaching by applying variational optimization techniques from applied mathematics. The physical model and the numerical analysis with its implementation are outlined in detail. This new technique enables the creation of spatial maps of the retinal rhodopsin and retinal pigment epithelium (RPE) bisretinoid distribution with an ≈ 50μm resolution.

The heritability of the ring-like distribution of macular pigment assessed in a twin study

PURPOSE

It has been suggested that ring-like patterns of macular pigment, as measured with dual wavelength autofluorescence, are observed less frequently in subjects with age-related maculopathy. We explored relative contributions of genetic and environmental factors in macular pigment optical density (MPOD) distributions using a classic twin study.

METHODS

As part of a previous nutritional study, 322 healthy Caucasian female twins, aged 16 to 50 (mean 40) years, underwent measurement of MPOD optical density by two-wavelength fundus autofluorescence. In the present study, the right eye MPOD profile was assessed for the presence of a ring-like pattern by two graders independently, using common criteria, with a third grader arbitrating in cases of disagreement. Concordance was calculated as 2C/(2C + D), where C is the number of twin pairs concordant, and D the number discordant, for the ring-like pattern. Also, heritability was calculated using maximum-likelihood structural equation modeling.

RESULTS

Images and zygosity data were available for 314 twins (88 monozygotic [MZ] and 69 dizygotic [DZ] pairs). The overall prevalence of the ring pattern was 25.8%. Respective concordances for MZ and DZ twins were 0.75 and 0.22. Additive genetic factors were estimated to contribute to 84.0% of the total variance (95% confidence intervals, 63.7%-94.6%).

CONCLUSIONS

Concordance for MZ twins was over three times that for DZ twins, with heritability estimated at 84%, indicating that genetic factors contribute to the development of the ring structure. Studies have suggested that ring-like patterns of macular pigment can affect risk for age-related maculopathy. In a classic twin study, we found that the presence of such a pattern was highly heritable.

Foveal slope measurements in subjects with high-risk of age-related macular degeneration

Background:

Recent reports indicated that the slope of the foveal depression influences the macular pigment (MP) spatial profile. MP has been shown to confer possible protection against age-related macular degeneration (ARMD) because of its antioxidant properties.

Aims:

To study the configuration of foveal slope and the foveal thickness in fellow eyes of subjects with unilateral neovascular ARMD.

Settings and design:

Case-control series.

Materials and Methods:

The study population consisted of 30 cases aged >50, who had unilateral choroidal neovascular membrane (CNVM) or disciform scar in the fellow eye and 29 controls aged >50, who had no sign of ARMD in the either eye. Using spectral-domain optical coherence tomography, foveal thickness at different locations including the central subfield foveal thickness (CSFT) was noted. The foveal slopes were calculated in the six radial scans (between 0.25° and 1° retinal eccentricity) as well as the 3D scan.

Results:

Cases had a significantly higher CSFT when compared to controls (215.1 ± 36.19 μ vs. 193.0 ± 17.38 μ, P = 0.004). On the 3D scan, the cases had shallower superior (cases 1.32 ± 0.32 vs. controls 1.45 ± 0.13, P = 0.04) and temporal slopes (cases 1.27 ± 0.21 vs. controls 1.39 ± 0.12, P = 0.01) in comparison to the controls.

Conclusions:

We noted a shallower superior and temporal foveal slope and a higher CSFT in the fellow eyes of subjects with a unilateral neovascular ARMD. Prospective studies observing the development of CNVM in subjects with altered foveal slope might provide more information on this optical coherence tomography finding.

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.

Association of age and macular pigment optical density using dual-wavelength autofluorescence imaging

Background

Several lines of evidence suggest that macular pigment may play a protective role against age-related macular degeneration, but the influence of age on macular pigment density levels remains unclear. This study was designed to investigate the relationship between age and the normal distribution of macular pigment optical density (MPOD) values surrounding the fovea.

Methods

Consecutive healthy subjects with no evidence of ocular disease were enrolled in this study. After inclusion, MPOD values were measured at specific eccentricities (0.5, 1, and 2 degrees) from the foveal center using a dual-wavelength autofluorescence method employing a modified confocal scanning laser ophthalmoscope. Whenever both eyes were eligible, one was randomly selected for analysis. The correlation between age and MPOD values was investigated using regression analysis.

Results

Thirty subjects (30 eyes) were included (mean age 48.6 ± 16.4 [range 23–77] years). Significant differences were found between MPOD values measured at 0.5, 1, and 2 degrees from the center of the fovea (0.49 ± 0.12 density units, 0.37 ± 0.11 density units, and 0.13 ± 0.05 density units, respectively, P < 0.05). Significant correlations between age and MPOD values at 0.5 and 1 degree were found (P ≤ 0.02). Values measured at 2 degrees did not correlate significantly with age (P = 0.06).

Conclusion

In healthy subjects, MPOD values were highest near the foveal center. These values appeared to increase during adulthood (peak at 45–50 years), followed by a gradual reduction after 60 years of age.

Adaptation of the central retina for high acuity vision: cones, the fovea and the avascular zone

Presence of a fovea centralis is directly linked to molecular specification of an avascular area in central retina, before the fovea (or 'pit') begins to form. Modelling suggests that mechanical forces, generated within the eye, initiate formation of a pit within the avascular area, and its later remodelling in the postnatal period. Within the avascular area the retina is dominated by 'midget' circuitry, in which signals are transferred from a single cone to a single bipolar cell, then a single ganglion cell. Thus in inner, central retina there are relatively few lateral connections between neurons. This renders the region adaptable to tangential forces, that translocate of ganglion cells laterally/centrifugally, to form the fovea. Optical coherence tomography enables live imaging of the retina, and shows that there is greater variation in the morphology of foveae in humans than previously thought. This variation is associated with differences in size of the avascular area and appears to be genetically based, but can be modified by environmental factors, including prematurity. Even when the fovea is absent (foveal hypoplasia), cones in central retina adopt an elongated and narrow morphology, enabling them to pack more densely to increase the sampling rate, and to act as more effective waveguides. Given these findings, what then is the adaptive advantage of a fovea? We suggest that the advantages of having a pit in central retina are relatively few, and minor, but together work to enhance acuity.

The putative role of lutein and zeaxanthin as protective agents against age-related macular degeneration: promise of molecular genetics for guiding mechanistic and translational research in the field

Age-related macular degeneration (AMD) is the primary cause of vision loss in elderly people of western European ancestry. Genetic, dietary, and environmental factors affect tissue concentrations of macular xanthophylls (MXs) within retinal cell types manifesting AMD pathology. In this article we review the history and state of science on the putative role of the MXs (lutein, zeaxanthin, and meso-zeaxanthin) in AMD and report findings on AMD-associated genes encoding enzymes, transporters, ligands, and receptors affecting or affected by MXs. We then use this context to discuss emerging research opportunities that offer promise for meaningful investigation and inference in the field.

Macular carotenoid supplementation in subjects with atypical spatial profiles of macular pigment

This study was designed to investigate the impact of macular carotenoid supplementation on the spatial profile of macular pigment (MP) in subjects where the profile does not exhibit the typical central peak (i.e. peaked MP at foveal epicentre). Thirty one healthy subjects with such atypical MP spatial profiles were assigned to one of three intervention groups: Group 1: (n = 10), 20 mg/day lutein (L), 2 mg/day zeaxanthin (Z); Group 2: (n = 10), 10 mg/day meso-zeaxanthin (MZ), 10 mg/day L, 2 mg/day Z; Group 3: (n = 10), 17 mg/day MZ, 3 mg/day L, 2 mg/day Z. Subjects were instructed to take one capsule daily over an 8-week period. MP at 0.25°, 0.5°, 1°, 1.75° and 3° was measured using customized-heterochromatic flicker photometry at baseline, four weeks and 8 weeks. Over the study period, we report no statistically significant increase in MP at any eccentricity in Group 1 (p > 0.05, for all eccentricities). There was a trend towards an increase in MP at all eccentricities in Group 2, with a significant increase found at 0.25° and 0.50° (p = 0.000 and p = 0.016, respectively). There was a statistically significant increase evident in MP at 0.25° in Group 3 (p = 0.005), but at no other eccentricity (p > 0.05, for all other). We report that the typical central peak of MP can be realised in subjects with atypical spatial profiles, following supplementation with a preparation containing all three macular carotenoids, but not with a supplement lacking MZ. The implications of our findings, in terms of visual performance and/or a (photo)-protective effect, warrant additional study.

Lutein: more than just a filter for blue light

Lutein is concentrated in the primate retina, where together with zeaxanthin it forms the macular pigment. Traditionally lutein is characterized by its blue light filtering and anti-oxidant properties. Eliminating lutein from the diet of experimental animals results in early degenerative signs in the retina while patients with an acquired condition of macular pigment loss (Macular Telangiectasia) show serious visual handicap indicating the importance of macular pigment. Whether lutein intake reduces the risk of age related macular degeneration (AMD) or cataract formation is currently a strong matter of debate and abundant research is carried out to unravel the biological properties of the lutein molecule. SR-B1 has recently been identified as a lutein binding protein in the retina and this same receptor plays a role in the selective uptake in the gut. In the blood lutein is transported via high-density lipoproteins (HDL). Genes controlling SR-B1 and HDL levels predispose to AMD which supports the involvement of cholesterol/lutein transport pathways. Apart from beneficial effects of lutein intake on various visual function tests, recent findings show that lutein can affect immune responses and inflammation. Lutein diminishes the expression of various ocular inflammation models including endotoxin induced uveitis, laser induced choroidal neovascularization, streptozotocin induced diabetes and experimental retinal ischemia and reperfusion. In vitro studies show that lutein suppresses NF kappa-B activation as well as the expression of iNOS and COX-2. Since AMD has features of a chronic low-grade systemic inflammatory response, attention to the exact role of lutein in this disease has shifted from a local effect in the eye towards a possible systemic anti-inflammatory function.

Quantal and non-quantal color matches: failure of Grassmann's laws at short wavelengths

Previous studies of color matching found that Grassmann's laws are not obeyed in the short-wavelength region when the method of maximum saturation matching is compared with Maxwell matching. The first experiment evaluated whether the discrepancy might be due to a discrimination matching range asymmetry around either the saturated or desaturated matches and concluded that asymmetry is not the dominant factor. The second and third experiments were designed to evaluate postreceptoral mechanisms. The results pointed to the conjunction of three factors as being the principal cause of the failures of Grassmann's laws: the spatial inhomogeneity of the macular pigment distribution, the spatially dissimilar L/M-and S-cone distributions, and a change in the weightings of postreceptoral mechanisms mediating S-cone chromatic and L/M-cone luminance discriminations.

Quantitative measurements of autofluorescence with the scanning laser ophthalmoscope

PURPOSE

To evaluate the feasibility and reliability of a standardized approach for quantitative measurements of fundus autofluorescence (AF) in images obtained with a confocal scanning laser ophthalmoscope (cSLO).

METHODS

AF images (30°) were acquired in 34 normal subjects (age range, 20-55 years) with two different cSLOs (488-nm excitation) equipped with an internal fluorescent reference to account for variable laser power and detector sensitivity. The gray levels (GLs) of each image were calibrated to the reference, the zero GL, and the magnification, to give quantified autofluorescence (qAF). Images from subjects and fixed patterns were used to test detector linearity with respect to fluorescence intensity, the stability of qAF with change in detector gain, field uniformity, effect of refractive error, and repeatability.

RESULTS

qAF was independent of detector gain and laser power over clinically relevant ranges, provided that detector gain was adjusted to maintain exposures within the linear detection range (GL < 175). Field uniformity was better than 5% in a central 20°-diameter circle but decreased more peripherally. The theoretical inverse square magnification correction was experimentally verified. Photoreceptor bleaching for at least 20 seconds was performed. Repeatability (95% confidence interval) for same day and different-day retests of qAF was ±6% to ±14%. Agreement (95% confidence interval) between the two instruments was <11%.

CONCLUSIONS

Quantitative AF imaging appears feasible. It may enhance understanding of retinal degeneration, serve as a diagnostic aid and as a sensitive marker of disease progression, and provide a tool to monitor the effects of therapeutic interventions.

Foveal phase retardation changes associated with normal aging

This study quantified normal age-related changes to the photoreceptor axons in the central macula using the birefringent properties of the Henle fiber layer. A scanning laser polarimeter was used to acquire 15° × 15° macular images in 120 clinically normal subjects, ranging in age from the third decade to the eighth. Raw image data of the macular cross were used to compute phase retardation maps associated with Henle fiber layer. Annular regions of interest ranging from 0.25° to 3° eccentricity and centered on the fovea were used to generate intensity profiles from the phase retardation data, which were then analyzed using sine curve fitting and Fast Fourier Transform (FFT). The amplitude of a 2f sine curve was used as a measure of macular phase retardation magnitude. For FFT analysis, the 2f amplitude, as well as the 4f, were normalized by the remaining FFT components. The amplitude component of the 2f curve fit and the normalized 2f FFT component decreased as a function of age, while the eccentricity of the maximum value for the normalized 2f FFT component increased. The phase retardation changes in the central macula indicate structural alterations in the cone photoreceptor axons near the fovea as a function of age. These changes result in either fewer cone photoreceptors in the central macula, or a change in the orientation of their axons. This large sample size demonstrates systematic changes to the central cone photoreceptor morphology using scanning laser polarimetry.

Race- and sex-related differences in retinal thickness and foveal pit morphology

PURPOSE

To examine sex- and race-associated differences in macular thickness and foveal pit morphology by using spectral-domain optical coherence tomography (SD-OCT).

METHODS

One hundred eighty eyes of 90 healthy patients (43 women, 47 men) underwent retinal imaging with spectral-domain OCT. The lateral scale of each macular volume scan was corrected for individual differences in axial length by ocular biometry. From these corrected volumes, Early Treatment Diabetic Retinopathy Study (ETDRS) grids of retinal thickness were generated and compared between the groups. Foveal morphology was measured with previously described algorithms.

RESULTS

Compared with the Caucasians, the Africans and African Americans had reduced central subfield thickness. Central subfield thickness was also reduced in the women compared with the men, although the women also showed significant thinning in parafoveal regions. There was no difference between the sexes in foveal pit morphology; however, the Africans/African Americans had significantly deeper and broader foveal pits than the Caucasians.

CONCLUSIONS

Previous studies have reported race- and sex-associated differences in macular thickness, and the inference has been that these differences represent similar anatomic features. However, the data on pit morphology collected in the present study reveal an important and significant variation. Between the sexes, the differences are due to global variability in retinal thickness, whereas the variation in thickness observed between the races appears to be driven by differences in foveal pit morphology. These differences have important implications for the use of SD-OCT in detecting and diagnosing retinal disease.

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.

Augmentation of macular pigment following supplementation with all three macular carotenoids: an exploratory study

PURPOSE

At the macula, the carotenoids meso-zeaxanthin (MZ), lutein (L), and zeaxanthin (Z) are collectively referred to as macular pigment (MP). This study was designed to measure serum and macular responses to a macular carotenoid formulation.

MATERIALS AND METHODS

Ten subjects were recruited into this study (five normal and five with early age-related macular degeneration [AMD]). Subjects were instructed to consume a formulation containing 7.3 mg of MZ, 3.7 mg of L, and 0.8 mg of Z everyday over an eight-week period. The spatial profile of MP optical density (i.e., MPOD at 0.25 degrees , 0.5 degrees , 1 degrees , and 1.75 degrees ) was measured using customized heterochromatic flicker photometry, and a blood sample was collected at each study visit in order to analyze serum concentrations of MZ, L, and Z.

RESULTS

There was a significant increase in serum concentrations of MZ and L after two weeks of supplementation (p < 0.05). Baseline serum carotenoid analysis detected a small peak eluting at the same time as MZ in all subjects, with a mean +/- SD of 0.02 +/- 0.01 micromol/L. We report significant increases in MPOD at 0.25 degrees , 0.5 degrees , 1 degree , and average MPOD across its spatial profile after just two weeks of supplementation (p < 0.05, for all). Four subjects (one normal and three AMD) who had an atypical MPOD spatial profile (i.e., central dip) at baseline had the more typical MPOD spatial profile (i.e., highest MPOD at the center) after eight weeks of supplementation.

CONCLUSION

We report significant increases in serum concentrations of MZ and L following supplementation with MZ, L, and Z and a significant increase in MPOD, including its spatial profile, after two weeks of supplementation. Also, this study has detected the possible presence of MZ in human serum pre-supplementation and the ability of the study carotenoid formulation to rebuild central MPOD in subjects who have atypical profiles at baseline.

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.

The value of measurement of macular carotenoid pigment optical densities and distributions in age-related macular degeneration and other retinal disorders

There is increasing recognition that the optical and antioxidant properties of the xanthophyll carotenoids lutein and zeaxanthin play an important role in maintaining the health and function of the human macula. In this review article, we assess the value of non-invasive quantification of macular pigment levels and distributions to identify individuals potentially at risk for visual disability or catastrophic vision loss from age-related macular degeneration, and we consider the strengths and weaknesses of the diverse measurement methods currently available.

Macular pigment density assessed by directional fundus reflectance

Light radiated from foveal photoreceptors was analyzed in the eye's pupil at 470 nm and 532 nm. The reflectance of the inner limiting membrane was then measured at 6 deg from the fovea for the same wavelengths, allowing us to determine the macular pigment (MP) density D(dir) using the directional reflectance technique. In addition we measured the MP density D(nd) using the nondirectional reflectance technique (26 subjects). The mean values of D(dir) and D(nd) were 0.419+/-0.097 and 0.195+/-0.042 D.U., respectively (sample field of 2 deg). They were highly correlated (p<0.0001). Comparison of D(dir) and D(nd) implies that 57+/-12% of the light reflected from the fovea comes from layers anterior to MP at 470 nm. The mean directionality factors rho that we have measured at 470 nm and 532 nm were equal to 0.239+/-0.028 and 0.210+/-0.028 mm(-2), respectively. They were correlated (p<0.0001) and followed the spectral dependence suggested by Marcos.