| MadSci Network: Anatomy |
When you say "sensitive", that is really hard to say. I am not certain that it is clear that light colored eyes are more sensitive to light than darker eyes. While someone with very dark brown eyes has more pigment in their iris tissues which will be a more effective shade as their pupils get smaller, we also can turn down our light sensitivity at the level of our retinas as well. The photoreceptor cells in our retinas allow us to see by converting photons of light into nerve impulses that will travel the optic nerves to our brains. The chemical reactions in the photoreceptor cells and the numerous interacting proteins and chemicals involved, are adjusted in their levels in different lighting conditions as well. In all humans, rod cells provide black and white (grey scale) information, while red green and blue cone cells detect the red, green and blue light ranges. All of these separate detectors give us the final color image that we see in our "minds eye". In bright sunlight, only our cone cells (color) are working, they work well in bright light, while our rod cells are "bleached" and are not providing information at all. In the dark, our very sensitive rod cells (B/ W) give us the picture, while our cone cells do not get enough light to be detecting at all.
One thing for certain, you can give your retina a break over your lifetime by wearing a ball hat and shading your eyes on bright days. You do not need dark dark sunglasses, as a matter of fact a person with only sunglasses may have more UV light entering their eye than someone with a ball cap, as much sunlite comes down over the glasses into our eyes. The dark glasses will make your pupils open wider, just letting in more light.
You may also like to know that you do not need to spend hundreds of dollars on designer glasses to "filter out UV light", because plastics are already good blockers of UV light, even clear plastics. Cheap sunglasses filter out UV light very effectively, and your cornea filters out anything left over.
Ken Mitton, Ph.D.
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