Antioxidant Nutrients, Early AMD, & Visual Function

What is Visual Function?

Vision is composed of many simultaneous functions. One function, called visual acuity, measures “sharpness” of vision, or how well we see details when they are presented with good contrast. This is measured by looking at a standard eye chart where you’re asked to read lines of black letters on a white background that get smaller from top to bottom. For example if you can see the smallest line that a person with normal acuity can read at a distance of 20 feet, you’re said to have 20/20 vision.

While visual acuity is the cornerstone of any eye exam, there are other important aspects of vision. Some of these include our ability to adapt to changing light conditions (light and dark adaptation), how well we deal with glare that can impair our vision (glare disability), and how well we see contrasting colors (chromatic contrast).

Macular Pigment and Visual Function

Macular pigment is the yellow spot found in the center of the eye’s retina known as the macula, and it acts like an internal pair of sunglasses. Made up of two antioxidant carotenoids that we get from our diet, lutein and zeaxanthin, the macular pigment plays a critical role in protecting the macula from harmful blue light,

The density of macular pigment is important. Low macular pigment density, for example, is considered a risk factor for age-related macular degeneration (AMD).  Results from a newly published study (1) suggest that macular pigment density can also have immediate effects on visual function.

Researchers from the University of Georgia measured blood levels of lutein and zeaxanthin as well as the density of macular pigment in 150 healthy young participants. They also performed tests to measure chromatic contrast, glare disability, and photo-stress recovery (the time it takes to recover vision after exposure to very intense light).

They found that blood levels of lutein and zeaxanthin were related to macular pigment density, and that participants with higher macular pigment density fared better on all three tests of visual function – functions that can impact everyday activities.

The research team will next explore whether giving the participants supplemental lutein and zeaxanthin (12 mg combined) or a placebo will improve macular pigment density and these measures of visual function over the course of a year.

Antioxidants and Early AMD

Nearly twelve years ago, The Age-related Eye Disease Study (AREDS) showed that high dose zinc with copper and antioxidants (vitamins C, E, beta-carotene) could slow the progression of AMD, but only in people with moderate to advanced stages of the disease.

Although the findings need to be confirmed in larger and longer clinical studies, a team of investigators from Ireland now reports that a combination of nutrients may also offer some benefit to people with early stage AMD (2).

Over 430 men and women aged 55 or older received either a placebo or a daily supplement containing lutein and zeaxanthin (12.6 mg), vitamin C (150 mg), vitamin E (15 IU), zinc (20 mg) and copper (.6 mg). 

While no significant difference in best-corrected visual acuity was seen between the two groups at the end of 1 year, some of the participants were followed for up to 3 years.

For participants followed for the 3-year period, those getting the supplement were found to read nearly 5 letters more on a standard eye chart than those in the placebo group. Also, those with higher blood levels of lutein had a slower disease progression as assessed by an AMD severity scale at years 1, 2 and 3.

References

1. Hammond BR et al. Glare disability, photostress recovery, and chromatic contrast: relation to macular pigment and serum lutein and zeaxathin. Invest Ophthalmol Vis Sci, ePub Dec. 4, 2012.
2. Beatty S et al. Secondary outcomes in a clinical trial of carotenoids with coantioxidants versus plaebo in early age-related macular degeneration. Ophthalmol, ePub Dec. 5, 2012.