Clinical imaging of macular pigment optical density and spatial distribution

Raman Spectroscopy of Carotenoid Compounds for Clinical Applications-A Review

Carotenoid compounds are ubiquitous in nature, providing the characteristic colouring of many algae, bacteria, fruits and vegetables. They are a critical component of the human diet and play a key role in human nutrition, health and disease. Therefore, the clinical importance of qualitative and quantitative carotene content analysis is increasingly recognised. In this review, the structural and optical properties of carotenoid compounds are reviewed, differentiating between those of carotenes and xanthophylls. The strong non-resonant and resonant Raman spectroscopic signatures of carotenoids are described, and advances in the use of Raman spectroscopy to identify carotenoids in biological environments are reviewed. Focus is drawn to applications in nutritional analysis, optometry and serology, based on in vitro and ex vivo measurements in skin, retina and blood, and progress towards establishing the technique in a clinical environment, as well as challenges and future perspectives, are explored.

Ocular biometric parameters of mild hyperopia to mild myopia children aged 6-14 years from Wenzhou optometry center: A cross-sectional study

Introduction

Myopia is the most common visual disorder in school-aged children and adolescents worldwide. This study aimed to explore the ocular biometric characteristics of children aged 6–14 years from the Wenzhou optometry center and to determine the relationship between spherical equivalent refraction (SER) and macular pigment optical density (MPOD).

Subjects and methods

Participants underwent a full-scale ophthalmic examination anteriorly and posteriorly. Relevant parameters were documented, such as axial length (AL), anterior chamber depth (ACD), SER and lens thickness (LT), corneal curvature radius (CCR), and MPOD. Lens power (LP) was calculated using Bennett’s formula. Shapiro–Wilk tests and histograms were used to check the normality of the distribution of refractive and ocular biometric parameters. Scatter diagrams were adopted to analyze the relationships between refraction and parameters of ocular biometry. Multiple linear regression models were employed to fit the associated factors of AL, AL/CCR, and LP.

Results

A total of 902 mild hyperopia to mild myopia (+3.00 D ≤ SE ≤ −3.00 D) children aged 6–14 years were included. The mean age of participants was 10.03 ± 2.47 years, and the prevalence of mild hyperopia, emmetropia, and myopia was 5.65, 27.05, and 67.30%, respectively. The prevalence of mild myopia increased from 30.53% at 6 years of age to 93.62% at 14 years of age. Overall, AL, ACD, and AL/CCR increased, but LP declined from 6 to 14 years of age, whereas CCR and MPOD remained stable. An increase of 1 mm in AL was associated with −0.69 D of myopic change. A unit increase in AL/CCR was associated with −7.87 D in SER. As for the SER variance, AL explained 30.5% and AL/CCR explained 51.1%, whereas AL/CCR and LP accounted for 59.2%.

Discussion

In this work, we have studied the distributions of ocular biometric characteristics of mild hyperopia to mild myopia children from the perspective of an optometry center rather than a sampling survey. In addition, we found that children from the optometry center had a slower progression toward myopia than those from previous sampling surveys, which was an informative finding for future myopia prevention. In addition, we have made a correlation analysis between the macular pigment optical density and spherical equivalent refraction. Though, no correlation was found.

An appraisal of trials investigating the effects on macular pigment optical density of lutein and zeaxanthin dietary interventions: a narrative review

Lutein and zeaxanthin (L/Z), xanthophylls obtained from the diet, are deposited in the macula of the eye. The macular concentration of L/Z is quantifiable as macular pigment optical density (MPOD). The aim of this review was to critically appraise the effect on MPOD of increasing L/Z intake by dietary intervention in adults. Pubmed, Cochrane Library, Web of Science, and Cinahl were searched up to April 2020. Ten studies investigating populations with and without age-related macular degeneration were included. MPOD increased significantly in 2 of the 8 controlled studies. Studies varied largely in the prescribed dietary L/Z dosage, duration, and participant characteristics. No relationships between types of dietary L/Z interventions and MPOD response could be determined. Limited monitoring of habitual dietary L/Z intake was identified as a major limitation of all 10 studies. Habitual dietary L/Z intake should be closely monitored in future studies to account for their effects on MPOD response to dietary L/Z interventions.

Macular pigment optical density and visual quality of life

PURPOSE

There is robust evidence that higher macular pigment concentrations help reduce both veiling and discomfort glare in patients with or without ocular disease. We investigated whether there was also a relationship between macular pigment optical density (MPOD) and patient surveys about glare or ocular discomfort.

METHODS

We measured MPOD psychophysically in 23 healthy subjects and administered the National Eye Institute Visual Functioning Questionnaire (VFQ-25). Responses for each survey question were sorted from low (no limitation) to high (very severe limitation). The median response for each question was determined, and independent t-tests were performed on the mean MPOD values for survey responses above and below the median. We also performed a non-parametric correlation analysis between MPOD and survey responses.

RESULTS

While the median response was "no limitation" for most (22 of 25) survey questions, responses were slightly higher for two questions concerning ocular discomfort and one question related to driving at night. MPOD levels were significantly higher in subjects that reported no discomfort in or around their eyes than in those that reported mild discomfort. There was also a trend toward higher MPOD levels in subjects who reported that pain in or around their eyes never limited their activity as well as in subjects who reported no difficulty driving at night.

CONCLUSION

These preliminary findings are consistent with the well-established discomfort and glare hypotheses for MPOD. The current findings on subjective ocular discomfort in the absence of glare deserve further study.

Macular pigment optical density after panretinal photocoagulation

CLINICAL RELEVANCE

Panretinal photocoagulation, an important treatment method in diabetic retinopathy, can affect macular pigment optical density, which has protective and antioxidant properties. As a result of this effect, the retina may become more sensitive to high-energy visible light.

BACKGROUND

The current study assesses the effect of panretinal photocoagulation treatment on macular pigment optical density, which has essential functions for the retina.

METHODS

In this prospective clinical study, the colour perimetry method was used to measure macular pigment optical density. Thirty-six eyes of 36 participants with severe non-proliferative diabetic retinopathy without macular involvement were included in the study. Conventional panretinal photocoagulation treatments were applied at baseline, one month, two months, and at three months to the participants who clinically required this treatment. Macular pigment optical density and retinal thickness measurements were performed at baseline, months one, two, three and six.

RESULTS

The mean macular pigment optical density reduction in the fovea over the six-months was 0.02 ± 0.02 logarithmic units (p < 0.001). Similarly, the pericentral areas declined by 0.04 ± 0.03 logarithmic units (p < 0.001). Mean central macular thickness and foveal thickness increased by 5.03 ± 5.02 μm and 2.78 (interquartile range 2-4) μm, respectively. In this study, correlation analysis shows that the laser energy applied was significantly and strongly correlated with reductions in macular pigment optical density (for the fovea and pericentral area respectively: r = -0.855, p < 0.001; r = -0.895, p < 0.001). Further, there were significant and strong correlations between the applied laser energy, and central macular thickness and fovea thickness (r = 0.751, p < 0.001; ρ = 0.718, p < 0.001, respectively).

CONCLUSION

Panretinal photocoagulation may potentially cause a decrease in macular pigment density in proportion to the laser energy applied.

Effects of lutein supplementation in age-related macular degeneration

The purpose of this meta-analysis was to evaluate the effects of lutein supplementation on macular pigment optical density (MPOD) in randomized controlled trials involving patients with age-related macular degeneration (AMD). A comprehensive search of the literature was performed in PubMed, Cochrane Library, Web of Science, China National Knowledge Infrastructure, Chinese Biomedical Literature Database, and Wan Fang database through December 2018. Nine randomized controlled trials involving 920 eyes (855 with AMD) were included. Meta-analysis suggested that lutein supplementation (10 or 20 mg per day) was associated with an increase in MPOD (mean difference (MD) 0.07; 95% confidence interval (CI) 0.03 to 0.10), visual acuity (MD 0.28; 95%CI 0.06 to 0.50) and contrast sensitivity (MD 0.26; 95%CI 0.22 to 0.30). Stratified analyses showed the increase in MPOD to be faster and greater with higher dose and longer treatment. The available evidence suggests that dietary lutein may be beneficial to AMD patients and the higher dose could make MPOD increase in a shorter time.

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

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

Is macular pigment optical density really involved in fixation preference?

PURPOSE

To evaluate macular pigment optical density in healthy children and to compare the values with those of strabismic children with respect to fixation preference.

METHODS

The study recruited 54 healthy and 41 strabismic children. Two groups were matched in terms of gestational age, birth weight, and body mass index. All participants underwent complete ophthalmological evaluation and macular pigment optical density measurement and filled a self-reported food frequency questionnaire. Strabismic children were categorized according to fixation preference.

RESULTS

The mean age was 9.87 ± 2.39 years in healthy children and 9.07 ± 2.07 years in children with strabismus (p = 0.091). Mean macular pigment optical density was 0.23 ± 0.25 in healthy eyes and 0.25 ± 0.27 in non-preferred eyes of strabismic children (p = 0.964). Macular pigment optical density was significantly higher in preferred eyes of strabismic children (0.43 ± 0.34) compared to non-preferred eyes (p = 0.004) and healthy eyes (p = 0.001). There was a difference of macular pigment optical density between both eyes in patients with grades 1, 2, and 3 fixation preference, whereas patients with grade 4 preference had similar macular pigment optical density in both eyes (p = 0.008). There was a statistically significant positive correlation between macular pigment optical density in preferred eyes and body mass index (r = 0.354, p = 0.023).

CONCLUSION

Preferred eyes of children with strabismus seem to have higher macular pigment optical density readings. This difference may emerge from the higher tendency of recognizing the flicker stimulus while preferred eye is under testing. Similar macular pigment optical density in healthy and non-preferred eyes and the fact that both lower than preferred eyes remain unexplained. It should be kept in mind that macular pigment optical density results should be carefully interpreted and macular pigment optical density in cases with strabismus should be further investigated.

Macular pigment is associated with glare-affected visual function and central visual field loss in glaucoma

AIM

To evaluate the relationship between macular pigment optical density (MPOD) and glare disability in open-angle glaucoma.

METHODS

A cross-sectional analysis of baseline data (88 subjects; median age, 67 (range 36-84) years) collected during the Macular Pigment and Glaucoma Trial (ISRCTN registry number: 56985060). MPOD at 0.25°, 0.5° and 1° of retinal eccentricity was measured using customised heterochromatic flicker photometry. Mesopic contrast sensitivity with glare (mCSg), photostress recovery time (PRT) and self-reported glare symptoms were evaluated. Fourier-domain optical coherence tomography was used to analyse ganglion cell complex (GCC) and identify foveal involvement.

RESULTS

Low spatial frequency (f) mCSg was significantly correlated with MPOD at 0.25°(3 cycles per degree (cpd): r=0.25, p=0.04) and 0.5° (3 cpd: r=0.23, p=0.04) of retinal eccentricity. Those with foveal GCC loss exhibited lower MPOD, had worse low spatial fmCSg (1.5 cpd and 3 cpd, p=0.02 each) and prolonged PRT (p=0.02) in comparison with those without foveal involvement. The depth of central 10° field loss was related to MPOD at all eccentricities (p<0.01 for all). Those who reported glare symptoms had a significantly lower MPOD at all retinal eccentricities (0.25° and 1°: p=0.05 each; 0.5°: p=0.04), including those with foveal involvement (0.25°: p=0.05; 0.5°: p<0.01; 1°: p=0.01).

CONCLUSIONS

Macular pigment level may be an important consideration among those experiencing disability glare in glaucoma, including those with foveal involvement.

TRIAL REGISTRATION NUMBER

ISRCTN56985060, Post-results.