Visual pigment concentration and photoreceptor outer segment length in the human retina.

PURPOSE: The Beer-Lambert law suggests that visual pigment optical density (OD) should be linearly related to the length of photoreceptor outer segments (POSs). Mammalian studies indicate that visual pigment concentration increases with POS length, but the nature of this relationship may vary due to factors such as visual pigment packing density or retinal eccentricity, and may not necessarily be linearly related. The purpose of this study was to establish the relationship between OD and POS length in humans. METHODS: Spectral domain optical coherence tomography (OCT) was used to image POS, and imaging retinal densitometry (IRD) was used to measure OD at corresponding locations in 19 healthy participants (age range 25-82 years). POS length and OD measurements were extracted from OCT and IRD images at 23 discrete locations spanning the central 9° of the retina. The averaged data from all participants were fitted with models based on the Beer-Lambert law to establish the relationship between OD and POS length. RESULTS: Visual pigment OD increased monotonically with POS length, but the relationship was non-linear, and a straight-line fit, based on a simple interpretation of the Beer-Lambert law, provided a poor description. A model allowing for different rod and cone visual pigment concentrations provided a superior fit. Specifically, the data were well described by a model where the molar concentration of visual pigment in cones and rods were 3.8 × 10-3 mol/L and 1.8 × 10-3mol/L, respectively. CONCLUSIONS: In accordance with the Beer-Lambert law, the results indicate that OD increases monotonically with POS length in humans, but the precise relationship is dependent on photoreceptor type. These results suggest that visual pigment concentration in rods is only about 48% of that found in cones. This may be due to the ubiquitous nature of artificial light that works to reduce the concentration of rhodopsin in rod photoreceptors.

An Investigation into Retigabine (Ezogabine) Associated Dyspigmentation in Rat Eyes by MALDI Imaging Mass Spectrometry.

Retigabine (RTG) is an antiepileptic drug approved as an adjunctive treatment for refractory partial-onset seizures in adults. In April 2013, the Food and Drug Administration issued a warning that RTG could cause changes in retinal pigmentation and discoloration of skin, resulting in a blue appearance. As part of a larger preclinical effort to gain a mechanistic understanding as to the origins of retinal pigment changes associated with RTG, we conducted a long-term repeat dosing study in rats. Matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI IMS) was used to determine the distribution of RTG and its metabolites in the rat eye following 13 and 39 weeks of dosing. IMS revealed the presence of RTG, a previously characterized N-acetyl metabolite of RTG (NAMR), and several species structurally related through the dimerization of RTG and NAMR. These species were highly localized to the melanin-containing layers of the uveal tract of the rat eye including the choroid, ciliary body, and iris, suggesting that the formation of these dimers occurs from melanin bound RTG and NAMR. Furthermore, several of the RTG-related dimers have UV absorbance which give them a purple color in solution. We propose that the melanin binding of RTG and NAMR effectively concentrates the two compounds to enable mixed condensation reactions to occur when the binding provides the proper geometry in the redox environment of the uveal tissues. High lateral resolution images illustrate that the blood-retinal barrier effectively restricts retinal access to RTG-related compounds. The spatial information provided by MALDI IMS was critical in contextualizing the homogenate concentrations of key RTG-related compounds and helped provide a basis for the mechanism of dimer formation.

Controlled drainage of subretinal fluid during scleral buckling surgery for rhegmatogenous retinal detachment: the pigment stream sign.

PURPOSE: To describe the macroscopic characteristics of the subretinal fluid (SRF) and its spilling modality during evacuative puncture in scleral buckling (SB) surgery for rhegmatogenous retinal detachment. METHODS: We retrospective reviewed all the SB surgeries performed over a period of 26 months at the University Eye Clinic of Trieste, Italy. We selected a cohort of 102 patients in which SRF drainage by means of evacuative puncture was performed. A high-definition video was recorded during the whole duration of the procedures, and the macroscopic characteristics of the SRF leakage were assessed. RESULTS: Pigmented dark-brownish deposits spilling in the fluid outcoming from the evacuative puncture was observed during the surgeries. In all cases, this macroscopic feature was detected during the late phases of the drainage. Moreover, indirect ophthalmoscopic evaluation showed the almost complete SRF drainage and a flattened retina at that moment. CONCLUSIONS: The pigment stream sign, easily detectable by the surgeon, allows to understand, during the evacuative puncture, when the SRF has been drained almost completely and that the drainage procedure is therefore close to the end.

Evaluation of the anterior chamber angle in pseudoexfoliation syndrome.

BACKGROUND: Pseudoexfoliation syndrome (PEX) is the most frequently identifiable cause of secondary open-angle glaucoma, known as pseudoexfoliation glaucoma. The exact pathophysiology and etiology of PEX and associated glaucoma remains obscure. OBJECTIVES: The purpose of this study was to determine the differences in the morphology of the anterior chamber angle in people with pseudoexfoliation syndrome and pseudoexfoliation glaucoma compared to a control group. We also evaluated the correlation between intraocular pressure (IOP) and pigmentation of the angle with the amount of exfoliated material in the anterior segment. MATERIAL AND METHODS: The study group was composed of 155 eyes from 103 patients aged between 43 and 86 years. Each patient underwent a complete ophthalmological examination. RESULTS: Some difference was found in intraocular pressure between the PEX group and the control group and between the pseudoexfoliation glaucoma group and the control group, but no significant difference was found between the 2 study groups. There was a significant difference in the incidence of some degree of pigmentation in the anterior chamber angle and no difference in the widths of the angle between each group. A significant positive relationship was observed between intraocular pressure and the degree of pigmentation of the anterior chamber angle in both the PEX group and the pseudoexfoliation glaucoma group. CONCLUSIONS: The results of this study indicate that the amount of pigmentation and exfoliation material in the anterior segment significantly correlates with the level of IOP and possibly with the degree of trabecular dysfunction. It seems that for clear identification of PEX and pseudoexfoliation glaucoma factors, clinical assessment appears to be insufficient.

Two eyes for two purposes: in situ evidence for asymmetric vision in the cockeyed squids Histioteuthis heteropsis and Stigmatoteuthis dofleini.

The light environment of the mesopelagic realm of the ocean changes with both depth and viewer orientation, and this has probably driven the high diversity of visual adaptations found among its inhabitants. The mesopelagic 'cockeyed' squids of family Histioteuthidae have unusual eyes, as the left and right eyes are dimorphic in size, shape and sometimes lens pigmentation. This dimorphism may be an adaptation to the two different sources of light in the mesopelagic realm, with the large eye oriented upward to view objects silhouetted against the dim, downwelling sunlight and the small eye oriented slightly downward to view bioluminescent point sources. We used in situ video footage from remotely operated vehicles in the Monterey Submarine Canyon to observe the orientation behaviour of 152 Histioteuthis heteropsis and nine Stigmatoteuthis dofleini We found evidence for upward orientation in the large eye and slightly downward orientation in the small eye, which was facilitated by a tail-up oblique body orientation. We also found that 65% of adult H. heteropsis (n = 69) had yellow pigmentation in the lens of the larger left eye, which may be used to break the counterillumination camouflage of their prey. Finally, we used visual modelling to show that the visual returns provided by increasing eye size are much higher for an upward-oriented eye than for a downward-oriented eye, which may explain the development of this unique visual strategy.This article is part of the themed issue 'Vision in dim light'.

An Unexpected Diversity of Photoreceptor Classes in the Longfin Squid, Doryteuthis pealeii.

Cephalopods are famous for their ability to change color and pattern rapidly for signaling and camouflage. They have keen eyes and remarkable vision, made possible by photoreceptors in their retinas. External to the eyes, photoreceptors also exist in parolfactory vesicles and some light organs, where they function using a rhodopsin protein that is identical to that expressed in the retina. Furthermore, dermal chromatophore organs contain rhodopsin and other components of phototransduction (including retinochrome, a photoisomerase first found in the retina), suggesting that they are photoreceptive. In this study, we used a modified whole-mount immunohistochemical technique to explore rhodopsin and retinochrome expression in a number of tissues and organs in the longfin squid, Doryteuthis pealeii. We found that fin central muscles, hair cells (epithelial primary sensory neurons), arm axial ganglia, and sucker peduncle nerves all express rhodopsin and retinochrome proteins. Our findings indicate that these animals possess an unexpected diversity of extraocular photoreceptors and suggest that extraocular photoreception using visual opsins and visual phototransduction machinery is far more widespread throughout cephalopod tissues than previously recognized.

Comparison of two methods to measure macular pigment optical density in healthy subjects.

PURPOSE: To evaluate and compare macular pigment optical density (MPOD) measurements obtained using the modified Heidelberg Retina Angiograph (HRA) and the Visucam 200. METHODS: Healthy young subjects were included in this prospective study. MPOD was measured with the modified HRA at 0° and 0.5°, 1°, 2°, and 6° eccentricities from the fovea. The parameters obtained with the Visucam 200 (maximum, mean, area, and volume) were recorded the same day on the same subjects. Intraclass correlation coefficients (ICCs) and correlation coefficients were used to evaluate the agreement between the two devices. The repeatability and the reproducibility of each method were also assessed. RESULTS: Sixty-seven subjects were included whose median (interquartile ratio) age was 25 years (range, 23-30 years). The MPODs as measured with the modified HRA were higher than those measured with the Visucam 200 (P < 0.0001). The ICCs were low, ranging from 0.020 to 0.188. The correlation coefficients between the two methods were very low and ranged from 0.05 to 0.22. Repeatability and reproducibility were good with both methods, with ICCs ranging from 0.697 to 0.923. CONCLUSIONS: Agreement between the modified HRA and the Visucam in measuring MPOD was rather low. These results suggest that the two methods are not interchangeable. Before using the Visucam 200 in clinical and research setting, further evaluation seems mandatory (http://ansm.sante.fr/ number, 2009-A00448-49).

Macular pigment levels do not influence C-Quant retinal straylight estimates in young Caucasians.

BACKGROUND: Individuals with higher than normal levels of macular pigment optical density (MPOD) are less affected by disability glare, when using glare source lights with a strong short-wavelength component. The aim of this study was to investigate whether estimates of retinal straylight from the Oculus Cataract Quantifier (C-Quant), which corresponds to disability glare, are associated with estimates of macular pigment levels in young Caucasian eyes. METHODS: Thirty-seven Caucasian individuals (aged 19 to 40 years) with good visual acuity, free from ocular disease and with clear ocular media participated. Macular pigment optical density was measured at 0.5 degrees eccentricity from the foveal centre using a heterochromatic flicker photometry-based densitometer instrument from MacularMetrics. Retinal straylight was estimated using the C-Quant, a commercially available device, which uses a psychophysical compensation comparison method. RESULTS: Mean MPOD was 0.39 ± 0.18 log units (range zero to 0.80) and was not significantly related to age (r = -0.07, p = 0.66). Mean straylight parameter (s) was 1.01 ± 0.09 log units (range 0.86 to 1.21) and was not significantly related to age (r = -0.03, p = 0.86). Although there was a small tendency for straylight measurements to be reduced in individuals with higher levels of MPOD, there was no statistically significant relationship between retinal straylight and MPOD (r = -0.17, p = 0.30). CONCLUSION: Ocular straylight, estimated by the Oculus C-Quant, is little influenced by macular pigment optical density. As the C-Quant uses balanced (white) lights, it is suggested that the previous findings on the effect of macular pigment critically depend on the use of blue-dominant glare sources.

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.

Interrelationships between maternal carotenoid status and newborn infant macular pigment optical density and carotenoid status.

PURPOSE: Deposition of the macular pigment carotenoids lutein and zeaxanthin in the human retina occurs early in life. In this study, we examined the interrelationships of maternal carotenoid status and newborn infant macular pigment levels and systemic carotenoid status. As a secondary measure, we also evaluated the effects of intrauterine growth restriction (IUGR) on carotenoid status in term newborn infants. METHODS: We measured mother and infant skin carotenoids using resonance Raman spectroscopy (RRS), serum carotenoids by HPLC, and mother breast milk carotenoids by HPLC. We measured infant macular pigment levels using noninvasive blue light reflectometry. RESULTS: We enrolled 30 healthy term infants, their mothers, and 10 IUGR infants and their mothers. A subset of 16 infants was imaged for macular pigment optical density (MPOD). Infant serum zeaxanthin levels correlated with MPOD (r = 0.68, P = 0.007). Mother serum zeaxanthin levels correlated with infant MPOD (r = 0.59, P = 0.032). Infant and mother serum lutein did not correlate with MPOD. Mother-infant correlations were found for total serum carotenoids (r = 0.42, P = 0.020) and skin carotenoids (r = 0.48, P = 0.001). No difference was seen between IUGR infants and controls in total serum or skin carotenoids. Mothers of IUGR infants had lower total serum carotenoids (P = 0.019) and breast milk carotenoids than controls (P = 0.006). CONCLUSIONS: Our findings suggest that maternal zeaxanthin status may play a more important role than lutein status in macular pigment deposition in utero. Controlled trials are needed to determine whether maternal zeaxanthin prenatal supplementation can raise infant macular pigment levels and/or improve ocular function.

Macular pigment optical density in a Central European population.

BACKGROUND AND OBJECTIVE: The purpose of this study is to measure the macular pigment optical density and study its spatial profile as well as identify its determinant factors in a Central European population. PATIENTS AND METHODS: The macular pigment optical density (MPOD) and its distribution were assessed in 228 eyes of 129 subjects using fundus reflectometry with the Visucam 500 (Carl Zeiss Meditec, Jena, Germany). RESULTS: A statistically significant positive association between a diet rich in xanthophylls and all MPOD values was found. A positive monotonic relationship was demonstrated between an increasing degree in pigment distribution eccentricity and age, as well as all MPOD values except for area. CONCLUSION: Assuming that macular pigment is protective against age-related macular degeneration, our study highlights the role of nutritional counseling and intervention in preventing this disease. Furthermore, MPOD appears to increase with age, and the distribution of macular pigment appears to form more eccentric profiles.

The microstructural and functional changes in the macula of heavy habitual smokers.

To investigate whether heavy habitual smoking affects microstructures and functions of the macula, 45 age- (20-39 years old) and sex-matched adult smokers (≥1 box/day for ≥5 years) and 45 nonsmokers (controls) were enrolled in this case-control study. Central macular thickness (CMT), macular autofluorescent pigment density (MAPD), macular electroretinogram (ERG), and photostress recovery time (PRT) measurements were performed. The mean age of smokers and nonsmokers was 32.9 ± 3.9 and 33.1 ± 4.1 years, respectively (p = 0.43), and smoking duration was 11 ± 5.6 years. CMT in smokers (220 ± 28 µm) and nonsmokers (217.2 ± 31 µm; p = 0.57) was similar. Smokers had lower MAPD values (124.6) than nonsmokers (138.2) (p = 0.010). Multifocal ERG parameters in the central (6°) hexagon were similar in both groups (p > 0.05 for latency and amplitudes of P1 and N1). PRT in smokers and nonsmokers was similar (7.2 ± 1.2 and 7.4 ± 1.9 min, respectively; p = 0.33); however, foveal threshold value (FTV) at the first minute after photostress was statistically higher in smokers (36.1 ± 1.04 dB) than nonsmokers (34.8 ± 1.05 dB) (p = 0.011). We conclude that decreased MAPD and altered response to photostress may be indicative of early nicotine toxicity in microstructurally sound macula of adult chronic smokers.

Evaluation of blotchy pigments in the anterior chamber angle as a sign of angle closure.

BACKGROUND: Blotchy pigments in the anterior chamber (AC) angle are considered diagnostic of primary angle closure (PAC). But there are no reports either on the prevalence of blotchy pigments in AC angles or the validity of this sign. AIMS: To determine the prevalence of blotchy pigments in AC angles and to evaluate their relationship with glaucomatous optic neuropathy (GON) in eyes with occludable angles. SETTING AND DESIGN: Cross-sectional, comparative study. MATERIALS AND METHODS: Gonioscopy was performed in 1001 eyes of 526 subjects (245 eyes of 148 consecutive, occludable angle subjects and 756 eyes of 378 non-consecutive, open angle subjects), above 35 years of age. Quadrant-wise location of blotchy pigments was documented. STATISTICAL ANALYSIS: Odds of blotchy pigments in occludable angles against that in open angles were evaluated. Relationship of GON with blotchy pigments in occludable angle eyes was evaluated using a multivariate model. RESULTS: Prevalence of blotchy pigments in occludable angles was 28.6% (95% CI, 22.9-34.3) and in open angles was 4.7% (95% CI, 3.2-6.3). Blotchy pigments were more frequently seen in inferior (16%) and superior quadrants (15%) of occludable angles, and inferior quadrant of open angles (4%). Odds of superior quadrant blotchy pigments in occludable angles were 33 times that in open angles. GON was seen in 107 occludable angle eyes. Blotchy pigments were not significantly associated with GON (odds ratio = 0.5; P = 0.1). CONCLUSIONS: Blotchy pigments were seen in 28.6% of occludable angle eyes and 4.7% of open angles eyes. Presence of blotchy pigments in the superior quadrant is more common in occludable angles. Presence of GON in occludable angle eyes was not associated with blotchy pigments.

The heritability of macular response to supplemental lutein and zeaxanthin: a classic twin study.

PURPOSE: Antioxidant supplements may reduce age-related macular degeneration (AMD) progression. The macular carotenoids are of particular interest because of their biochemical, optical, and anatomic properties. This classic twin study was designed to determine the heritability of macular pigment (MP) augmentation in response to supplemental lutein (L) and zeaxanthin (Z). METHODS: A total of 322 healthy female twin volunteers, aged 16-50 years (mean 40 ± 8.7) was enrolled in a prospective, nonrandomized supplement study. Macular pigment optical density (MPOD) measurements using two techniques (2-wavelength fundus autofluorescence [AF] and heterochromatic flicker photometry [HFP]), and serum concentrations of L and Z, were recorded at baseline, and at 3 and 6 months following daily supplementation with 18 mg L and 2.4 mg Z for a study period of 6 months. RESULTS: At baseline, mean MPOD was 0.44 density units (SD 0.21, range 0.04-1.25) using HFP, and 0.41 density units (SD 0.15) using AF. Serum L and Z levels were raised significantly from baseline following 3 months' supplementation (mean increase 223% and 633%, respectively, P < 0.0001 for both), with no MPOD increase. After 6 months' supplementation, a small increase in MPOD was seen (mean increase 0.025 ± 0.16, P = 0.02, using HFP). Subdivision of baseline MPOD into quartiles revealed that baseline levels made no difference to the treatment effect. Genetic factors explained 27% (95% confidence interval [CI] 7-45) of the variation in MPOD response. Distribution profiles of macular pigment did not change in response to supplementation. CONCLUSIONS: MPOD response to supplemental L and Z for a period of 6 months was small (an increase over baseline of 5.7% and 3.7%, measured using HFP and AF, respectively), and was moderately heritable. Further study is indicated to investigate the functional and clinical impact of supplementation with the macular carotenoids.

Association of macular pigment optical density with risk factors for wet age-related macular degeneration in the Indian population.

PURPOSE: To investigate macular pigment optical density (MPOD) in patients with and without wet age-related macular degeneration (AMD) and to elucidate the association between MPOD and the risk factors for AMD in an Indian population. METHODS: Thirty-three subjects with wet AMD and 29 controls above 50 years old underwent MPOD measurement with the 'Macular Densitometer'. The subjects were also tested for their smoking history, lifetime ultraviolet (UV) exposure, dietary intake of carotenoids, and body mass index (BMI). RESULTS: Smokers had a higher risk for AMD than the non-smokers (P=0.032) and a lower MPOD level than non-smokers (mean (95% CI)) (0.16 (0.09-0.23) vs 0.28 (0.22-0.34), adjusted P=0.026). Subjects with lowest UV exposure had higher MPOD than those with the highest (0.46 (0.38-0.54) vs 0.17 (0.01-0.33), P=0.01). MPOD was significantly lower among those with the lowest quartile of dietary intake of carotenoids (0.14 (0.08-0.21) vs 0.25 (0.13-0.36), P=0.012). Smoking, obesity, and UV index showed an inverse association with the MPOD. Low MPOD, smoking, and UV exposure had 5.11 (1.73-15.08), 3.54 (1.08-11.57), and 5.24 (1.06-25.96) odds for AMD, respectively, whereas higher dietary intake of carotenoids showed a protective effect for AMD. CONCLUSION: We found an inverse association between wet AMD and MPOD. Among the established risk factors of wet AMD, we found an inverse association of smoking, UV index, and obesity with MPOD, whereas a positive association was found between dietary intake of carotenoids and MPOD.

Measurement of macular pigment optical density in a healthy Chinese population sample.

PURPOSE: Macular pigment may protect against age-related macular degeneration (AMD) by its capacity to absorb blue light and scavenge free radicals. Current information on human macular pigment density has been largely from studies on Caucasian populations. The purpose of this study was to assess macular pigment density and its determinant factors in a Chinese population sample. METHODS: Macular pigment optical density (MPOD) was measured in a healthy Chinese population using heterochromatic flicker photometry (HFP). Participants received a standard ophthalmic examination, and only subjects who were confirmed not to have any eye diseases except mild age-related cataract were included in the study. Demographic and lifestyle data and general health status were recorded by questionnaire. RESULTS: A total of 281 unrelated healthy Chinese individuals, including 96 males and 185 females, with ages ranging from 17 to 85 years, participated in the study. The mean and standard deviation of MPOD levels were 0.56 ± 0.19, 0.49 ± 0.18, 0.36 ± 0.15, and 0.19 ± 0.12, respectively, at 0.25°, 0.5°, 1.0°, and 1.75° eccentricity points. A significant age-related decline in MPOD was observed at 0.25° (P = 0.014). Females tended to have relatively lower levels of MPOD than males at 0.25° (P = 0.21), 0.5° (P = 0.025), and 1.0° (P = 0.16). No statistically significant association of MPOD was observed with body mass index or smoking status. CONCLUSIONS: Macular pigment density measured by HFP tended to decline with aging in this healthy Chinese population sample. Females may have lower levels of MPOD than males.

An evaluation of a novel instrument for measuring macular pigment optical density: the MPS 9000.

PURPOSE: Of the antioxidants found in the human retina, only the macular carotenoid quantities can be estimated noninvasively (albeit in a collective fashion), thus facilitating study of their role in that tissue. The aim of this study was to evaluate concordance between macular pigment optical density (MPOD) values recorded on a commercially available instrument, the MPS 9000, with those of an already validated heterochromatic flicker photometry instrument. Also, we assessed and compared test-retest variability for each instrument. METHODS: Macular pigment optical density at 0.5 retinal eccentricity was measured using two different heterochromatic flicker photometers, the MPS 9000 and the Macular Densitometer(TM), in 39 healthy subjects. Test-retest variability was evaluated separately for each instrument by taking three readings over a 1-week period in 25 subjects. RESULTS: There was a moderate positive correlation for MPOD at 0.5° of retinal eccentricity between the MPS 9000 and the Macular Densitometer described by the linear equation y = 0.763x + 0.172 (r = 0.68, p < 0.001, r(2) = 0.46); however, a paired-samples t-test showed a significant difference in terms of mean values, with a bias of lower MPOD values being yielded by the MPS 9000 (t = -4.103, p < 0.001). Bland-Altman analysis indicated only moderate agreement between the two instruments, reflected in 95% limits of agreement of 0.1 ± 0.27. Inter-sessional repeatability, expressed as a coefficient of repeatability, ranged from 0.18 to 0.21 [mean (±SD): 0.19 (0.02)] for the MPS 9000 and from 0.11 to 0.12 [mean (±SD): 0.12 (0.01)] for the Macular Densitometer. CONCLUSION: The results demonstrate that the MPS 9000 consistently yields MPOD readings, which are lower than that found with the Macular Densitometer, and exhibits substantial test-retest variability.