27.02.2018

American Study Changes How Eye Doctors Think Of Melanopsin Cells

A new study out of the University of Pennsylvania challenges the conventional understanding of how the eyes process visual stimuli. Specifically, doctors looked into how the protein cells called melanopsin reacted to light waves.

Melanopsin is extremely sensitive to blue-light and is crucial for establishing a healthy Circadian rhythm. The melanopsin proteins naturally tighten the pupils to protect our eyes from bright lights.
Researchers involved in this study were curious what happens in the brain when they send a melanopsin-specific light wave into the eyes. For this experiment, researchers created a light pulse that only melanopsin cells could detect.

Interestingly, scientists noticed that there was activity in patients' brains as they flashed the light into their eyes. Even more surprising, study participants said they could see the light as it was pulsing through their eyes.

The functional MRI scans in this study show that the light pulses increased activity in the brain's occipital cortex. Study authors believe these brain scans prove that we do experience visual sensations from melanopsin stimulation alone.

In total, 20 people participated in this experiment. When doctors asked participants to describe what they saw when the light flashed, most described the experience as an annoying "blurry brightness."

Since there are less melanopsin cells in the eyes, doctors aren't surprised that patients saw blurry images. The network of connections between melanopsin cells isn't as strong as it is for cones.

Although eye doctors had a hunch that melanopsin might play a role in vision, they were never able to isolate these cells in a study before. Whenever light passes into the eye it not only effects melanopsin but also numerous cone cells. For years, doctors assumed that the cone cells did most of the work processing visual data.

University of Penn researchers had to use highly advanced software to choose the correct color scheme that would target melanopsin cells. This light pulse causes melanopsin cells to constrict the pupil very slowly, but cones cannot detect it.

Study authors suggest that this research could help eye doctors better understand the eye condition photophobia. People with photophobia experience discomfort and/or pain whenever blue light passes into their eyes. A few professors believe photophobia patients may have more (or more sensitive) melanopsin cells than people with healthy vision.

About 80 percent of people with photophobia also suffer from frequent migraine headaches. Also, about 30 percent of photophobia patients suffer from blepharospasm.

When most people see the word "photophobia" they instantly think it must be related to a fear of light. In case you were wondering, the irrational fear of light is known as heliophobia.

All of this research was conducted at the University of Penn's Perelman School of Medicine and School of Arts and Sciences. Dr. Geoffrey K. Aguirre, who teaches in the university's Department of Neurology, was the lead author.

Anyone who wants to learn more about this fascinating topic can read the full study in the latest edition of Proceedings of the National Academy of Sciences. This article was entitled, "The human visual cortex response to melanopsin-directed stimulation is accompanied by a distinct perceptual experience."


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