ultraviolet

Ultraviolet radiation and myopia

Ultraviolet radiation and myopia 2

I feel like writing another article about the possible benefits of something we’ve all heard is bad for us. Ultraviolet radiation (UV) sounds bad. Maybe because of the word radiation (not a bad word though) and then maybe all the news warning us about UV exposure. I’ve had many sunburns and believe it’s contributed to a couple of skin problems I’ve had so I believe the redness and pain associated with sunburns is a pretty obvious sign of too much sun. As a kid in the 70’s I remember putting zinc oxide on my nose. It was a thick bright white cream that definitely was noticeable. I wish I had a picture of that when I was sitting on the lifeguard stand watching all the other kids get their UV (and chlorine) exposure at the pool.

You’ve got to wonder though how our species ever survived with that constant stream of the suns rays just bearing down on us all the time. Scientists have divided up that UV band of radiation into 3 forms….A, B and C. A is the least harmful and C is the worst but C doesn’t even reach us because the atmosphere’s ozone absorbs that band. Why did we even call it UV-C if it doesn’t reach us? We can create UV-C ourselves through welding however. See the chart at the end showing the UV ranges.

One huge benefit of UV exposure is our body uses it to produce vitamin D. We can also get vitamin D from other sources and you’ll find plenty of foods supplemented with vitamin D. That just makes me wonder why all the news about vitamin D deficiency. I have read that too much UV-B exposure can actually destroy vitamin D production but that article I read didn’t say if that was 1% destroyed or 100%. That’s what bothers me about some of the information we get unless you dig further in the research. And this is where I think some organizations have gone too far with their warnings. They make the sun sound like it’s horrible! Too much of anything isn’t good for you but articles talking about avoiding UV just seem wrong. Life wouldn’t exist without it. Too much vitamin D supplementation isn’t good either….that’s toxic. Do they talk about that? Rarely. Instead of warnings, we should talk about moderation.

Here’s another thing I’ve been interested in regarding UV radiation. Most of the contact lenses I prescribe have an FDA approved UV blocking agent in the lenses. I don’t know when that all started. Since I don’t wear contact lenses and neither do most other people, will those that wear these UV filtering contact lenses be better off than the rest of us? And then there are glasses that have UV protecting effects. Will people that wear glasses be better off when the results of UV accumulation over a lifetime are more obvious regarding diseases attributed to UV exposure? I do wear sunglasses outside….sometimes. Most sunglasses, even cheap ones, block practically all UV radiation and our car windshields block that as well. I’d like to know how I can measure my lifetime UV exposure. Have I exceeded it? How can I possibly know if I have a little left over so I can go play outside?

But there’s one more thing that is interesting about the possible benefits of UV exposure…in children. It’s thought that the outdoors might provide some protective effects against myopia development. That means some very credible studies are finding the sun is good for kids. There’s even at least one study that shows that UV exposure may provide a certain protective effect against myopia. Instead of “protective” can I say benefit?

I say get outside and enjoy whatever weather you’ve got. Put down the ipads and back off the consoles and let me put up a permanent basketball goal at my house! The kids need to be outside more!

Here’s a study about UV and myopia.

http://www.ncbi.nlm.nih.gov/pubmed/22669720

 

UV graphic

UV graphic

 

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Fluorescein in your eye

Fluorescein in your eye 0

If you’re an eye doctor you know about this stuff. If you’re not, it’s ok to get fluorescein “die” in your eye from the eye doctor. I’m referring to the topically applied orange colored little strips of paper that kinda looks like those pH test strips. But both of you hang on because I have a few interesting things to say about this commonly used diagnostic chemical. It sounds horrible…chemical….but it’s not at all horrible otherwise we wouldn’t use it.

What’s interesting about these strips with fluorescein is that they fluoresce. And pray tell what does that mean? This is where I get to talk about quantum mechanics again! If you didn’t read the last post, it all started there. This little piece of paper, the fluorescein strip when touched to your eye, will turn a different color when blue light is shined on it.

So here’s what I’m saying. The color of the fluorescein is orange on the strip. It goes in your eye orange. Blue light is turned on. The fluorescein in your eye no longer looks orange. It’s green! Turn the blue light off and the fluorescein in your eye is orange again.

Here’s where quantum mechanics comes in. Easy lesson here. The blue light has a certain wavelength, it’s shorter, and thus has more energy. It hits the orange fluorescein in your eye. The little electrons in the fluorescein absorb that energy but a cool property of something that fluoresces is those electrons return some of the energy. And the energy we see is less than the blue wavelength. The color looks green! Green has a longer wavelength than blue. And this is the case with most things that fluoresce. The higher energy of light causes the fluorescing material to “reflect” a lower energy wavelength. You might wonder what happened to the rest of the energy. It is also released by those electrons that sent out the green wavelengths. The remaining energy is heat. A pretty limited amount so there’s no heat you can feel. There’s a measurement of the ability of a material to fluoresce which is called quantum yield and fluorescein has a high yield which kinda means we see the green reflection very easily.

Let’s just take a made up example of fluorescence. Say you shine green light at a material that fluoresces. What are the likely wavelengths it would “reflect?” Right, maybe yellow or orange or red. Those have less energy than green.

But not all things fluoresce enough for us to see, obviously. If they did the world would be very psychedelic. But there are a lot of substances that when a certain wavelength of light hits them, they send back a different wavelength that we can see. Black lights (aka, ultraviolet lights) are very cool because there are a lot of things that fluoresce from that wavelength of energy. There are all kinds of things that fluoresce from UV light like some rocks. I read on a website that an apartment property manager was going to take an ultraviolet light to the carpet of a renter to see if there’s any urine from pets there. Yep, urine fluoresces under UV light. Better not try to hide your pets. Property managers have their “secret” ways to find out!

fluorescent eye

green (yellowish green) is where the fluorescein is

fluorescein strip

fluorescein strip