20th March, 2013

Nutrition & Visual Excellence

Nutrition & Visual Excellence

By Dr. Mark Kirby Ph.D

‘Vision includes the capacity to detect objects against a contrasting background, to detect gaps between objects, to perceive colour, to detect movement, and to perceive depth’ – Dr. James Loughman, Dublin School of Optometry

Visual performance is a relatively new term which describes how well one visually perceives their surrounding environment, and, as alluded to in the quote above, it cannot be quantified by a simple visual acuity test (i.e. black letters of decreasing size set on a white background).  Up until now, and in the absence of pathology, optimum vision was achieved with the correct pair of lenses.  However, with the emergence of new scientific data, it is now possible to take an individual with good, corrected vision, and make it better, i.e., the achievement of visual excellence.

The task which a pilot must perform demands visual excellence.  Pilots, more than most other professions, operate in a high glare environment.  Glare (glare from the clouds, the ground, the runaway lights) seriously compromises a pilot’s ability to perceive contrast.  Contrast sensitivity [CS] refers to the ability to distinguish an object from its background, and the measurement of which better represents ‘how well we see’ (as opposed to visual acuity).  New research conclusively demonstrates a 30% improvement in CS by simply enriching the nutritional requirements of the retina.1

Macular pigment (MP) is a conspicuous accumulation of three, dietary-derived nutrients (meso-zeaxanthin, zeaxanthin and lutein– known as carotenoids) at the back of the eye.  MP is an antioxidant and a selective filter of short wavelength blue light, with the latter function directly influencing visual performance.2  Specifically, short wavelength blue light is not required for sharp, central vision (there are no ‘blue-sensitive’ photoreceptors at the very centre of the retina).  In fact, blue light actually reduces the quality of the image which we are viewing, the reason for which is as follows.

Blue light is subject to light scatter and chromatic distortion (more than any other wavelength of light), which results in veiling luminance (commonly referred to as ‘blue haze’) and a reduction in focus, respectively.  Blue light in varying amounts is directly responsible for glare discomfort and glare disability.  The rationale, therefore, suggests that by supplementing the MP (i.e., enrich the yellow filter which absorbs blue light) will attenuate a large percentage of this blue light before it reaches the light-sensitive part of the photoreceptors, thereby enhancing CS, reducing glare, and improving overall visual performance.3

These findings are unsurprising from a nutritional perspective.  As a society, we have long since digressed from a diet of freshly sourced and freshly prepared fruits and vegetables.  Given that MP is entirely of dietary origin (i.e. if you never ate any fruits and vegetables, you would have zero MP), it comes as no surprise that the average Western individual has poor MP status.  Importantly, chronic issues such as obesity and smoking are also associated with low MP.  In fact, it is widely accepted that the 2-3 mg/day of lutein/zeaxanthin which we typically consume is insufficient to maintain adequate MP.

The new research, published in November 2012 from one of the leading research laboratories in the world, concludes that ‘supplementation with all three macular carotenoids resulted in significant improvements in CS (with and without glare) and in corrected distance visual acuity’.  This was achieved in a period of 6 months using a MP supplement containing all three macular nutrients (some supplements contain only one, or possibly two, of the required nutrients, which is proven to dilute the retinal response and also the potential improvements in vision).

In conclusion, this research represents concrete scientific evidence that dietary supplementation of all three macular nutrients can potentially double retinal levels of this important visual pigment, in virtually all subjects.  In light of this, and given the proven consequential enhancements in visual performance with supplementation, MP enrichment should be considered as a necessary lifestyle intervention for individuals where optimization of visual function is paramount.

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1. The impact of macular pigment augmentation on visual performance using different carotenoid formulations. Loughman J, Nolan JM, Howard AN, Connolly E, Meagher K, Beatty S. Invest Ophthalmol Vis Sci. 2012 Nov 29;53(12):7871-80.

2. Glare disability, photostress recovery, and chromatic contrast: relation to macular pigment and serum lutein and zeaxanthin. Hammond BR Jr, Fletcher LM, Elliott JG. Invest Ophthalmol Vis Sci. 2012 Dec 4.

3. The influence of filtering by the macular carotenoids on contrast sensitivity measured under simulated blue haze conditions. Hammond BR Jr, Wooten BR, Engles M, Wong JC. Vision Res. 2012 Jun 15;63:58-62.