The Circadian Pathway

Understanding how circadian rhythms work is essential in controlling and preventing problems. Scientists have been able to show that when bright light enters the eye, it stimulates photoreceptors in the periphery of the retina. These photo-cells are connected to the body's master clock or suprachiasmatic nucleus via a nerve pathway called the retinohypothalamic tract. At the right time of day, light triggers the body clock into resetting its daily rhythms.

The circadian pathway breaks down when the photoreceptors in the eye can't perceive these light zeitgebers. Scientists have learned that very bright light can restore the circadian pathway, but they only recently discovered which photoreceptors are responsible. We now know what causes circadian related rhythm problems, and it's not what we thought.

Breakthrough Discovery

For over a hundred years, scientists believed that the rod and cone cells of the eye were responsible for our body's reaction to light. We now realize that a newly discovered photoreceptor, called melanopsin is responsible for activating the circadian pathway, and it does not respond to the same light as rod and cone cells. This discovery may hold the key to why we suffer from sleep and other body clock problems, and it's changing the way we treat circadian rhythm disorders.

What is Melanopsin?

Melanopsin is a light sensitive protein that lies in the periphery of the eye's retina. Unlike rod and cone cells, melanopsin detects intensity or changing levels of light, and when it gets brighter in the morning for example, melanopsin becomes very active and triggers the brain's suprachiasmatic nucleus, or body clock into shifting to an active day pattern.

Under normal light conditions, melanopsin doesn't respond, but in bright light, like sunshine, melanopsin cells become very active. The melanopsin cells are 'responsible for telling our bodies that it is daytime - daylight is always bright light,' according to Dr Rob Lucas at the Imperial College in London . Melanopsin cells help regulate a healthy body clock, and among other things, help keep us active and alert in bright sunshine.

Melanopsin deficiency

Those of us with fewer melanopsin cells don't recognize changing light signals, and so we don't 'wake up' like we're supposed to. That is why we struggle through the day, feeling down or gloomy, and why we may not sleep well at night. Melanopsin also causes our pupils to constrict and dilate, and pupils don't work as well in people with low melanopsin levels. Apparently, those with a melanopsin deficiency have pupils that are visibly different than normal subjects. Scientists haven't quite determined the relationship yet, but in the future, doctors may be able to tell if you're susceptible to circadian rhythm disorders by simply looking at your pupils' reaction to changes in light.

Why we get Circadian Rhythm Disorders

Apparently those of us who have body clock problems may have fewer melanopsin cells in our eyes. Those with few melanopsin cells don't react to brighter light and so their body clocks can't tell the difference between bright, daytime light and darkness. This may be the reason that very bright light and longer duration of bright light is necessary for sufferers to feel normal. Because they have fewer melanopsin cells, it takes more light for their body clocks to work properly.

We were wrong!

For decades researchers assumed that the rod and cone cells were responsible for mediating light, and so they created light boxes designed to stimulate rod and cone photoreceptors. But melanopsin doesn't respond to the same light that rod and cone cells do, and that discovery has dramatically changed the way we deliver light therapy.

Blue not white

While rod and cone cells respond best to white, full spectrum light, melanopsin cells do not. As a matter of fact, they only respond to a specific bandwidth of blue light, in the range of 446-477nm (nanometers). This discovery is critical for circadian rhythm disorder sufferers; because it means they will respond much stronger and quicker to this effective bandwidth of light than to full spectrum. Indeed, studies at Thomas Jefferson and Harvard suggest that this new wavelength of light is not only safer, but more effective as well.

"Our results imply that shorter wavelengths may be more effective and energy-efficient compared to higher energy polychromatic white light for phase-shifting the human circadian pacemaker...

Exposure to the optimum balance of light wavelengths may also reduce the undesirable side-effects associated with therapeutic use of light exposure such as glare, visual discomfort, headaches and nausea."

- Steven W. Lockely, MD
June 2003, J. of Endocrinology & Metabolism

Apollo has worked with researchers at TJU to develop this new light technology, called BLUEWAVE® . Because this technology is patented, only BLUEWAVE® products produce 100% of the effective bandwidth of light without the unnecessary full spectrum light.

Why white is wrong

Researchers used to think the response was through the visual spectrum, known as the photopic response curve, and light boxes were manufactured accordingly. Now we know that the photo-receptors responsible for circadian rhythm problems do not respond to the visual response curve, but rather to a very narrow slice or bandwidth of blue light, from 446-477 nm (nanometers). When stimulated by this bandwidth, melanopsin triggers the suprachiasmatic nucleus, or body clock to reset its circadian rhythms and produce the active energetic hormones.

The problem with 10,000 lux, full spectrum light

This new discovery may also give us some insight into why some people experience side effects with 10,000 lux, full spectrum light. In traditional light therapy, bright light at 10,000 lux intensity is used. This is because full spectrum is inefficient at producing enough blue light on its own. But by increasing full spectrum enough to stimulate the melanopsin photoreceptors, we may also be over stimulating the rod and cone cells and eye muscles, which result in headaches, eyestrain, excessive glare, nausea, etc. Although BLUEWAVE® is bright, it is only 1/25 th as bright as full spectrum light, and is much easier on the eyes.

Why We Have Circadian Rhythm Sleep Problems

Researchers now believe that circadian rhythm disorders are caused by a melanopsin deficiency. In addition to responding to blue light, melanopsin cells are responsible for detecting intensity changes. If the eye doesn't have enough melanopsin receptors, the body clock can't distinguish daylight signals and can't regulate circadian rhythms and energy, mood and sleep hormones. Those with sleep, SAD or similar circadian rhythm disorders have fewer melanopsin receptors and are more dependent on blue light.

Why Current technology falls short

The problem with current lighting technology is that it doesn't naturally produce the effective wavelength of light. Even at 10,000 lux, full spectrum and other white light is inefficient at treating sleep, SAD and related circadian rhythm disorders, because they don't produce the necessary bandwidth.

BLUEWAVE® is Changing Light therapy

In 2001 Apollo began working with researchers to create a new light source that could deliver the necessary blue light without the over-stimulation problems inherent with current technology. The resulting BLUEWAVE® technology was developed through a National Institutes of Health grant. Clinical testing and tens of thousands of products confirm the effectiveness and increased safety of BLUEWAVE® .

Next: How Circadian Rhythms Regulate Sleep and Activity »