What's the deal with UV light absorption through the eyes? I read a few years back that it is essential to let some sunlight into our eyes, especially during the winter months, yet having spoken to people about this, most of them are adamant that their opticians have told them that any strong sunlight whatsoever into the eyes is very damaging.
Paleolithic man did not wear sunglasses or baseball caps of course, but even though he probably avoided the midday sun, at other times he would have not been able to avoid sunlight in his eyes.
Last year I did not wear sunglasses and my eyes became accustomed (mostly to reflected sun) after a few weeks and my intolerance of bright lights really improved, but do the benefits of not wearing sunglasses outweigh the dangers?
On the flip side of this, is there any evidence to suggest that wearing sunglasses all year round (as some people do nowadays) is detrimental to our health?
And lastly, do people with blue eyes need more sun eye-exposure than brown-eyed people?
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The main concern with unprotected eyes and UV exposure is cataract development. It is thought that long term exposure to UV in the range 380 to 400nm is what causes catarct development. Sunglass manufacturers in most developed countries have to make sure that their products will absorb UV up to 400nm to be compliant with regulations. I am not aware of any pathway that vitamin D could be absorbed through the eyes, so I think that you can pretty much can the idea that there are health benefits to allowing your eyes to have direct exposure to UV. Please do not get light and UV mixed up. UV is invisible so exposure to UV would make no difference to the stimulation of the hypothalamus. If you want to protect your eyes from UV but still want the full illumination of the sun then just wear glasses with clear lenses and a UV absorption coating. The question I have is what the incidence of cataract formation in older members of hunter gatherer tribes is and whether there is a nutritional link to cataract formation. On the subject of macular degeneration there appears to be a strong nutritional link with some ophthalmologists now recommending high dose anti oxidants to their patients with macular degeneration which in some cases halts the progression of the disease and in some cases reverses it slightly.
Light that reaches your eyes stimulates the hypothalamus in your brain, which is connected to the pineal gland. The pineal gland regulates sleep/wake cycles via the secretion of the hormone melatonin ( http://www.wayfinding.net/pineal.htm ). The natural variation of light during the day and night helps to assure a healthy sleep/wake cycle. Conversely, this can be disrupted either by light deprivation or by over-stimulation with artificial light. The downside to too much light reaching the eyes is that it may contribute to macular degeneration (an age-related eye disease), but this remains unproven ( http://www.mayoclinic.com/health/macular-degeneration/DS00284/DSECTION=risk-factors ). Those with lighter-colored eyes are more prone to macular degeneration, so those with blue eyes may actually need LESS light than those with brown eyes. I don't know if wearing sunglasses is enough to disrupt your day/night cycles. Personally, I've found that my worst corneal sunburns have occurred when I was wearing sunglasses. I think that I keep my eyes open more with sunglasses, whereas without them I adapt by squinting.
I also think you may be confusing the benefits of the natural VISIBLE daylight spectrum in terms of circadian hormone regulation with the benefits of UV light on the skin and synthesis of "vitamin" D (inverted commas, since this is a misnomer - it's really a pre-hormone). It bas been demonstrated that daylight lamps really help with SAD, but also that Vit D supplementation is useful.
Having said that, you don't mention vitamin D.
As others have said, UV light - especially the UV light that stimulates the synthesis of Vit D, is actually harmful to the eyes. So it's good to expose the skin, but protect the eyes, roughly 2hrs either side of midday. Interestingly, from the perspective of sub 400nm wavelength UV, "sunrise" is around 11am, and "sunset" is around 3pm in the Summer (daylight saving assumed, so that midday is 1pm). In short, this means that there's little point in sunbathing outside those hours, since you won't generate any Vit D. On the other hand, you can also put your sunglasses away.
I don't think the "I tried it it worked for me" concept is a good arguement in this particular instance. This is literally playing with fire. If there is solid proof and evidence that the sun can, at the very least, cause even temporary blindness then we should leave it at that. Don't be stupid and burn your retinas or something else very permanent upon speculation.
Seasonal Affective Disorder (another SAD) is what it is called. But it is not sunlight on the eyes...it is lack of sunshine on the skin...and therefore a lack of Vit D.
I do remember a sitcom based in Alaska called Northern Exposure where some of the citizens of the town wore rediculous hats with small battery powered lights aimed back towards the eyes to counteract the effects of winter with little or no sunlight. The characters were portrayed as being a little maniac.
Have never seen any references..good or bad..to any eyes needing or not needing sunlight. Grok did not have Solar Rays but we don't need to re-enact paleolithic times...just enjoy life....and if sunglasses work for you, go for it. I wear them all the time.
Nutrition plays a huge role in the way our eyes weather UV exposure, just like it does in that way our skin ages. If someone is living on white bread bologna sandwiches, canned soup, and koolaid, they are going to need to wear UV protection for their eyes or risk earlier cataract formation. A nutrient dense diet full of antioxidants is going to likely buy you more time because you'll have the components on hand to rebuild your eyes.
Sleep/wake cycles are regulated by light exposure to the eyes even more than the skin. With age (usually starting in the '50's) it is common for the cornea to start to yellow, and not allow as much blue spectrum light into the eyes. As a result sleep goes to hell in a handbasket, and the risk of depression rises dramatically even if there is good sun exposure. I worry that people, particularly wearing sunglasses with a brown tint might be doing the same thing to themselves.
"Paleolithic man did not wear sunglasses"
Paleolithic man did not have a life expectancy such that cataracts and eye damage in old age were a concern. We do many things these days in diet and lifestyle that our ancient ancestors did not do. We have the realistic objective of being healthy and independent into our 80s. I studied history. One interesting anecdote is that the ship navigators in pre-modern times would routinely be blind by their 40s due to taking positions against the sun (without sunglasses).
For the reasons others have stated in their responses, sunlight can definitely damage your eyes. Look what sunlight does to skin (long-term exposure). Wearing sunglasses is important, especially during summer. Key: don't accept "full spectrum protection" claims on face value. Look for this protection factor; "UV400." if you're buying drugstore sunglasses for $8 that "must be" highly protective because they're "really really really dark," you are not protecting your eyes.