Lasers not aimed at eye

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Hi there, a patient was asking if lasers have to be aimed directly at the eye to be harmful. As in, if they could see the laser pointer, and the laser pointer was on and was red, but the laser pointer was pointed perhaps 40 degrees away from their eyes, would this still be a danger to their eyes. I was not sure how to answer him. Please advise.

Most laser pointers are not instantly harmful to the eye even if aimed directly at the eye. The blink reflex automatically makes you avert your gaze to prevent damage. Some laser pointers that were bought online and have not gone through the safety regulation assessment might be more dangerous but in general 40 degrees away is harmless. Especially red, it is the wavelength of visible light that carries the least energy.

Originally Posted by Shnurek

Most laser pointers are not instantly harmful to the eye even if aimed directly at the eye. The blink reflex automatically makes you avert your gaze to prevent damage. Some laser pointers that were bought online and have not gone through the safety regulation assessment might be more dangerous but in general 40 degrees away is harmless. Especially red, it is the wavelength of visible light that carries the least energy.

Yes and no. Long wavelengths do have less potential for damage at the same energy level, but they are also less likely to be scattered than short wavelengths before getting to the posterior pole.

To the OPs question, the likelihood of injury from indirect exposure to laser energy is less, but will depend upon the laser in question. Low energy lasers, such as pointers, carry little risk. Laser we use in practice can potentially cause injury through indirect exposure.

Originally Posted by Visionary

Yes and no. Long wavelengths do have less potential for damage at the same energy level, but they are also less likely to be scattered than short wavelengths before getting to the posterior pole.

True, shorter wavelength light refracts more, scatters more and can be absorbed in a shorter medium so it would damage the anterior pole more than the red at the same energy level.

Originally Posted by Shnurek

True, shorter wavelength light refracts more, scatters more and can be absorbed in a shorter medium so it would damage the anterior pole more than the red at the same energy level.

Unlikely. The scattering will disperse the energy, thus reducing any damaging effects. Would have to be a pretty high energy laser.

Originally Posted by Visionary

Unlikely. The scattering will disperse the energy, thus reducing any damaging effects. Would have to be a pretty high energy laser.

Unlikely? So a red laser would damage the cornea/lens more than a ultraviolet laser of the same energy level? I find this hard to believe unless I am missing something here.

Excimer lasers are ultraviolet (short wavelength) and not red (long wavelength) for a reason. To target the corneal stroma.

Originally Posted by Shnurek

Unlikely? So a red laser would damage the cornea/lens more than a ultraviolet laser of the same energy level? I find this hard to believe unless I am missing something here.

Excimer lasers are ultraviolet (short wavelength) and not red (long wavelength) for a reason. To target the corneal stroma.

Didn't expect this to turn into a discussion of laser physics, but here goes.

Let me clarify. My response was in keeping with the OP. That is, what is the relative possibility of injury with direct or indirect exposure? A shorter wavelength laser has a greater likelihood of absorption/scatter through contact with objects before hitting the eye than a longer wavelength laser. At base, the destructive potential of a laser lies in the coherence of the light. If it's scattered, there's less coherence, and therefore, less destructive potential. That's the reason I can burn the RPE with as little as a 100 mW diode laser, yet survive turning on the 60 W incandescent in my living room. That was my point.

As for the cornea and lens, in their normal, youthful state, they are essentially transparent. How much do you think either will absorb?

As for the Excimer (or femtosecond Intralase, for that matter), you are incorrect, again. Yes, they are both short wavelength, but their destructive potential actually lies in the focusing of the energy at a particular plane. Think about it. If the wavelength itself were destructive to the cornea, how could you cut a flap with an Intralase? It would just obliterate the cornea.

Your response is circumlocutory and you are not answering my question.

Originally Posted by Shnurek

So a red laser would damage the cornea/lens more than a ultraviolet laser of the same energy level?

Originally Posted by Visionary

As for the Excimer (or femtosecond Intralase, for that matter), you are incorrect, again. Yes, they are both short wavelength, but their destructive potential actually lies in the focusing of the energy at a particular plane. Think about it. If the wavelength itself were destructive to the cornea, how could you cut a flap with an Intralase? It would just obliterate the cornea.

wtf?

"Excimer lasers use a 193 nm wavelength which is absorbed at the cornea's outer surface, immediately ablating tissue upon contact. The INTRALASE FS Laser uses a long wavelength (1053 nm) that is not absorbed but instead can pass through the cornea with absolutely no effect on tissue until it reaches the pre-programmed target."
(Source: http://www.clearvision.com.au/files/...0Intralase.pdf)

"Femtosecond lasers operate at the near-infrared wavelength of 1,053 nm."
(Source: http://bmctoday.net/crstodayeurope/2...osecond-lasers)

Dude you are getting owned by a kid with a bachelor's degree. Just give it up.

The Excimer laser is short wavelength to ablate any tissue it comes into contact with. Because a short wavelength laser causes more damage to the anterior pole than a long wavelength laser at the same energy level. Simple physics.

Originally Posted by Shnurek

Your response is circumlocutory and you are not answering my question.

Cool word.

Originally Posted by Shnurek

wtf?

"Excimer lasers use a 193 nm wavelength which is absorbed at the cornea's outer surface, immediately ablating tissue upon contact. The INTRALASE FS Laser uses a long wavelength (1053 nm) that is not absorbed but instead can pass through the cornea with absolutely no effect on tissue until it reaches the pre-programmed target."
(Source: http://www.clearvision.com.au/files/...0Intralase.pdf)

"Femtosecond lasers operate at the near-infrared wavelength of 1,053 nm."
(Source: http://bmctoday.net/crstodayeurope/2...osecond-lasers)

Dude you are getting owned by a kid with a bachelor's degree. Just give it up.

The Excimer laser is short wavelength to ablate any tissue it comes into contact with. Because a short wavelength laser causes more damage to the anterior pole than a long wavelength laser at the same energy level. Simple physics.

Ooops, got me. A refractive surgeon, I am not. Enjoy your e-cred.

The rest of my post is accurate.

If you make the wavelength short enough, yes, cell damage will occur, even in a transparent tissue. Most ultraviolet light is not of a sufficiently short wavelength to do so, and thus would pass through both the normal cornea and lens, just as longer wavelength light would. You will not find such short wavelengths in non-industrial lasers, such as the pointer in the OP's example.

My god, Shnurek, you're going to be an absolute nightmare, if and when you obtain clinic privileges. There's nothing quite like a shiny new 3rd year intern who knows virtually nothing about clinical optometry, but at the same time, believes they know more than their supervising ODs and MDs. I suspect your entry into clinic will be a very cold shower for you.

....and definitely use the word "circumlocutory" as often as possible when presenting to your attending, as that will convey understanding of complex topics very effectively.

Originally Posted by Visionary

Ooops, got me. A refractive surgeon, I am not. Enjoy your e-cred.

Thank you

Originally Posted by Visionary

The rest of my post is accurate.

Yes, it is. The retinal lasers you use work with the concept of focusing the beams on a single plane just as you stated but I just wanted to be right ^^

Originally Posted by Visionary

If you make the wavelength short enough, yes, cell damage will occur, even in a transparent tissue. Most ultraviolet light is not of a sufficiently short wavelength to do so, and thus would pass through both the normal cornea and lens, just as longer wavelength light would. You will not find such short wavelengths in non-industrial lasers, such as the pointer in the OP's example.

Yes, the tissue is transparent to visible light but not to UV-C light. UV-B penetrates a bit further but its still pretty opaque. Hmmm this is interesting. I will try to find a UV laser pointer lol.


(Source: http://www.photobiology.info/Rozanowska.html)

Dude its good for you to know this stuff even as a retina specialist. I'm sure you've gotten patients with electromagnetic radiation damage to their eyes and I'm sure you are a great Doctor.

Now that I think about it, I really should have known better. Gave a talk on femto, as it relates to SD-OCT, in fellowship. Same technology. Oh, well. Short circuit, I guess.

Sent from my Droid Incredible on SDN Mobile

Originally Posted by Visionary

Now that I think about it, I really should have known better. Gave a talk on femto, as it relates to SD-OCT, in fellowship. Same technology. Oh, well. Short circuit, I guess.

Ya, I was about to mention OCT imaging, how the near infra-red light penetrates deeper into tissue. The reason why I got you was because we had a lecture on clinical uses of lasers a week or two ago :P

Originally Posted by Shnurek

Because a short wavelength laser causes more damage to the anterior pole than a long wavelength laser at the same energy level. Simple physics.

Two lasers "at the same energy level" are also at the same wavelength. The word you are looking for is POWER. Unless you don't know the difference between energy and power? It sure seems like you don't since you've used the term "same energy level" when discussing lasers of two different wavelengths multiple times in this thread:

"True, shorter wavelength light refracts more, scatters more and can be absorbed in a shorter medium so it would damage the anterior pole more than the red at the same energy level."

"So a red laser would damage the cornea/lens more than a ultraviolet laser of the same energy level? "


I followed the link to this thread from a thread in allo (now deleted apparantly) where shnurek was bragging about how he "owned an md/phd opthamologist", so I just wanted him to have a taste of his own medicine. Anyone can make a simple error, no need to be a douchebag about it shnurek.

Originally Posted by Shnurek

Especially red, it is the wavelength of visible light that carries the least energy.

I used energy correctly in the beginning but later we both were not technical in our distinction between energy and power according to the Planck Constant.

Originally Posted by Visionary

Long wavelengths do have less potential for damage at the same energy level...

I was just going off of what Visionary was saying about wavelength distinction on the same energy level but you are correct I should have noticed the error myself and not repeated it.

See, Shnurek actually cares about these internet spats and e-cred. I, honestly, do not. I'm trying to help and educate others here. I'm not perfect, and I freely admit errors, when I make them. It probably is because I'm about twice Shnurek's age.

Sent from my Droid Incredible on SDN Mobile

Originally Posted by HopesandDreams

Two lasers "at the same energy level" are also at the same wavelength. The word you are looking for is POWER. Unless you don't know the difference between energy and power? It sure seems like you don't since you've used the term "same energy level" when discussing lasers of two different wavelengths multiple times in this thread:

"True, shorter wavelength light refracts more, scatters more and can be absorbed in a shorter medium so it would damage the anterior pole more than the red at the same energy level."

"So a red laser would damage the cornea/lens more than a ultraviolet laser of the same energy level? "


I followed the link to this thread from a thread in allo (now deleted apparantly) where shnurek was bragging about how he "owned an md/phd opthamologist", so I just wanted him to have a taste of his own medicine. Anyone can make a simple error, no need to be a douchebag about it shnurek.

Haha wow are you kidding me?

Shnurek, how pathetic can you be? I think you need to take care of some narcissistic issues that you have and grow the hell up.

Originally Posted by HopesandDreams

I followed the link to this thread from a thread in allo (now deleted apparantly) where shnurek was bragging about how he "owned an md/phd opthamologist", so I just wanted him to have a taste of his own medicine. Anyone can make a simple error, no need to be a douchebag about it shnurek.

If that thread did exist, that's absolutely pathetic.
I don't care how much you think you know, but with an attitude like that, you will always come off as a pompous tool to your patients. It will only get worse from here.

I can only assume that you're the student who comes to everybody's office hours, pontificating to every professor in how they made a typo on their lecture slides and/or arguing about every question on the test.

Originally Posted by Visionary

See, Shnurek actually cares about these internet spats and e-cred. I, honestly, do not. I'm trying to help and educate others here. I'm not perfect, and I freely admit errors, when I make them. It probably is because I'm about twice Shnurek's age.

Sent from my Droid Incredible on SDN Mobile

Fortunately, we all know at this point that Shnurek is troll of the highest order spending his days googling eye info to impress us all. So pathetic. But entertaining I suppose. Remember that beauty contestant a while back that babbled on with some crazy long answer "about, like, peace and ya know, stuff like that". Same thing.

http://www.youtube.com/watch?v=lj3iNxZ8Dww