- Edited
Continuing on that same article
We already know about AMD prevention, so lets look at its optical properties.
...Beyond its “protective” hypothesis, MP's optical and anatomic properties have prompted the “optical” hypotheses of this pigment... include MP's ability to enhance visual function and comfort by attenuation of the effects of chromatic aberration (Figure 12) and light scatter (Figure 13), via its light-filtering properties... MP could improve acuity by reducing the deleterious effects associated with the aberration of short-wave light
Wait a second though
However, in 2007 Engles et al modelled and evaluated the hypothesis and found that MPOD did not correlate significantly with either gap or hyperacuity measured in the yellow or white conditions, and therefore, their data did not support the predictions of the acuity hypothesis
Since a reduction in luminance isn't really harmful for us (frankly, I can't make my monitor any darker, and it still seems too bright), I'll take the reduction in luminance in exchange for a cleaner visual field with less aberrations
It appears that any acuity advantage gained by higher levels of MP is offset by a commensurate reduction in luminance (which correlates positively with acuity). It has also been suggested that MP could enhance the contrast of objects on a background via color filtering... This hypothesis was recently tested and found to be tenable, which has important implications for visual function in the non-diseased eye
Sounds good to me
For example, under natural conditions (e.g. walking outside), objects are often presented on short-wavelength backgrounds, such as a blue sky or green leaves, meaning that the filtering properties of MP is likely to impact positively on real-life vision. MP's pre-receptoral filtration of short-wavelength (blue) light is believed to reduce the adverse impact of glare disability, light scatter and chromatic aberration, thereby optimizing contrast sensitivity... It follows, therefore, that augmentation of MP would result in enhanced contrast sensitivity and improved glare disability
Here are their illustrations of chromatic aberration and light scatter
Next there is a diagram on the visual benefits of xanthophyll supplementation in healthy subjects. It's been studied since 1948 and most of trials found benefits in healthy people. However trial design has come a long way since then.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4698241/table/T1/
Patience, young grasshoper
Of note, however, this modest augmentation in MP using a lutein-based formulation was observed only at the 12-month study visit
Next up, in this trial the group taking all 3 xanthophylls had the most improvement
Tthe second group was given 10 mg lutein, 10 mg meso-zeaxanthin and 2 mg zeaxanthin... every day for six months. A statistically significant increase in MP was observed (determined at three months following commencement of supplementation) only among subjects supplemented with a formulation containing all three macular carotenoids, including meso-zeaxanthin (Group 2). Statistically significant improvements in visual acuity were observed at six months, but only for subjects in Group 2
In conclusion, there is a biologically plausible rationale, supported by MP's light-filtering properties, which suggests that augmentation of MP will enhance visual function and comfort by attenuation of the effects of chromatic aberration and light scatter. Indeed, clinical trials have repeatedly shown that supplementation with the macular carotenoids lutein, zeaxanthin, and meso-zeaxanthin results in augmentation of MP, and consequential benefits in visual performance such as improved contrast sensitivity and reduced glare diability.
Next in the article is a bunch of stuff on AMD.
Good questions
The macula lutea contains lutein, zeaxanthin, and meso-zeaxanthin at a 1:1:1 ratio, yet the typical American consumes these carotenoids from the diet in a ratio of 5:1:0. AREDS2 teaches us that xanthophyll carotenoid supplementation has health benefits, but is the current 10 mg lutein and 2 mg zeaxanthin dose optimal? Would higher levels of supplementation and/or altered ratios of these three carotenoids increase MP more efficiently and promote better vision and lessen risk of AMD progression? Now that meso-zeaxanthin is readily available from commercial sources, is it beneficial to bypass the postulated ocular enzymatic metabolism of lutein to meso-zeaxanthin by supplying it pre-formed in a supplement? Are there any long-term consequences to consuming high concentrations of all three macular carotenoids, given that a typical diet contains circa 1.5 mg per day of lutein and zeaxanthin, and little or no meso-zeaxanthin? In light of our current knowledge that known binding proteins cannot discriminate between zeaxanthin and meso-zeaxanthin, should both be administered in equal amounts, or is one preferred over the other?