Photons in your Eye!

[Ace82]

Ok, we all say to wear safety laser goggles, to protect our retinas so we can continue living a life of being able to see our lasers. And I agree, that staring at a dot bright enough to burn materials no matter the wavelength, that we should wear the proper eye gear. However, let me share a little event that took place with me last week:

I went to go see the Optometrist (eye doctor), because I was having a bad vision problem with my right eye. My central vision had become practically blinded, still had peripheral but no way could I even make out any letters no matter the size if I were to focus on them. And so they hooked me up with some gnarly eye drops, two sets in each eye, one is a numbing agent, the other is a paralyzing agent as to dilate your pupils as much as possible to where they stop reacting to light so the doctor can look inside your eye, and take pictures. And so, the experience I had, being a first time thorough eye examination, was pretty unpleasant. I admit, I have looked at the dot from all of my lasers without wearing goggles, but I have not stared at it especially while burning, that's just dumb, right? Well, the doctor shines this light that looks like a nice bar that seems to be like 20Watts of power straight into your eye for long periods of time as he searches for any signs of damage, blood, swelling etc. It felt like if I shined my 225mW green laser at a white wall and put my eye point-blank at the dot and stared directly at the dot for about 5 minutes. The doctor even needed to hold my eyelids open, I told him I could do it but he said that it actually helps him to do it himself. Anyway, my Optic nerve being swollen ended up being his diagnosis, which is a huge red flag for my health, as there are several major diseases which could cause it, although the majority of the causes are unknown. And this is also why I created the "doctor and hospital visit" thread, because my vision has greatly improved since then, almost 100% back to normal. So no, my laser hobby was not the cause of my vision problem, as my retina is 100% fine. Anyway, that's besides the point of this thread. I couldn't believe that amount of light they shine in my eye when they observed me. It hurt so much, I had a few tears, but I guess they should have gave me more numbing drops!

In conclusion, if an optometrist can pump your eyes with so many photons and still expect you to see afterwards, I seriously doubt that any person could ever obtain eye damage from staring at a dot. Does the coherence property have anything to do with it? I would think not, as long as it isn't shined directly at your eye, it would never burn, unless it was a super ridiculous UV, IR, or super powered laser that could burn from scattered reflection of radiation, looking at the dot should not do a damn thing.

Am I saying not to wear safety goggles? NOT AT ALL. Because there's always the chance that you could catch a direct hit by accident, and I'm sure having that many photons hit your retina can't necessarily be good for your eyes, and it certainly isn’t comfortable.

 

[laserlover]

ya they do those drops every time i go to the optometrist, and you get used to them, then they do that bright light thing which is fun, lol, cause your practically blind afterwards

 

[RA_pierce]

Haha sorry to hear about your painful experience.  ;D

Well, I think it's safe to look at a laser's dot. It may be uncomfortable, but at a safe distance, I think you may be ok.

My reasoning is this:

Some people will argue that diffused reflections are dangerous because lasers are coherent and the light will be focused on a tiny region of your poor eye, thus burning a hole through your head.

Your pupil will dilate to about 8mm maximum in low light.
In bright light, I'd put it around 1.5 to 2mm.
When using a laser, even in a dark room, your iris will automatically adjust to let in less light.
When you point a laser at most surfaces (except for reflective ones) the light will be scattered. Obviously. So imagine your entire laser's output spread over an area of 1m. If your laser is 300mW that's 0.3mW per mm (correct? forgive me if I'm wrong, I'm not a numbers person haha).
With your pupil fully dilated at 8mm, you're getting 2.4mW total in your eye. Then, factor in the probability that your eye will not be fully dilated when you look at the dot.
Now, factor in the loss of power from the wall absorbing some, reflection from the lens of your eye, and the fact that a diffused reflection will scatter the light much more than that at 3 feet. Then factor in the fact that most of us don't even own >300mW lasers.
2.4mW maximum (from 300mW) is hardly enough to do permanent damage, especially when from a diffused reflection.  A 5.0mW laser pointed directly into your eye will do no immediate permanent damage.

I think it makes perfect sense.

 

[rocketparrotlet]

FrothyChimp? Your thoughts on this? (I'll stick to my safety goggles until FrothyChimp makes a decision.)

-Mark

 

[kristopher]

I feel your pain!

When I started graduate school, my boss knew I'd be working with lasers so he wanted us to get retinal photographs. They did the same thing, dilating each eye and then taking pictures with a bright flash while holding your eyelids open! It super saturated the cones so when I left, while everything was crystal clear still, the colors were totally tweaked. White walls were yellow, green things were blueish, etc! Nothing was white! Talk about a headache - I took the rest of the day off! Next day it was back to normal, I only have flashbacks once a year or so.

 

[FrothyChimp]

I can't make any determination unless I know the output of the light in power and wavelengths (as far as comparisons go). Just keep in mind that a white light is by definition not monochromatic and therefore not coherent so wavelength interference (both constructive and destructive) is the rule. A laser, by definition, is coherent, thus the amplitude of the wavefront is significantly higher due to only constructive interference. Because the beam is coherent (the waves are in lockstep) they can be focused to a much smaller point than any non-coherent source.

Staring into any sufficiently bright light is not good as there is a limited supply of photopsins available to each cone. If a white light source is used, all three photopsin varieties are spent leaving the subject with what is commonly known as flash blindness or snow blindness. The photopsins gradually replenish particularly with sleep. You can get a pretty good idea of what wavelengths you have been subjected to based on the colors you can see after the incident.

Now onto the soap box. This is not directed at any one person but to the group overall. I feel the guilty will know who they are.

I would be happy to run all the calculations and demonstrate clearly that laser light is much more dangerous to eyesight mW for mW but based on posts I have seen (particularly the make your own goggles thread) it won't make any difference. I understand there is a worldwide conspiracy to keep laser protection as expensive as possible for people who were never intended to have such systems and my mathematics will clearly indicate such a conspiracy, but please allow me to reiterate my position...once again:

1. Laser light not compatible with vision. If you think otherwise don't bother replying to my assertion because you are an idiot. I have mathematics and physics on my side. Your gut feelings don't count. I know all those Ph.D. physicists, chemists, biologists, and MDs aren't nearly as smart as you, but give them a break, they get some stuff right.

2. Operating laser systems without proper eye protection is stupid. Take a course in statistics and probability. If it can happen, it will happen.

3. It costs money to research and develop protective dyes. No company is going to give you protective glasses for free particularly in some form you find stylish.

4. If you don't think the proper safety equipment is necessary because you are different than others, and warmed by your own hubris, you are an idiot and you can join the rest of the ignorant bafoons at the shallow end of the gene pool.

5. Finally, if you can't afford laser eye protection yet you spend hundreds of dollars building or buying lasers you are an idiot and should not be in this hobby.

I'm sorry if you think I am harsh. I'm sorry if I hurt your feelings. But I cannot say it in simpler terms. Get the eye protection! If you don't find any documentation that a particular plastic or gel or sunglasses or contact lenses or 3d glasses or what-have-you complies with ANSI Z.136 or CE EN207/208 or CSA Z386 you DO NOT have an item that will protect your eyes from laser light! I can see it now...."but, but, my sunglasses have a VLT of 10% across the visible spectrum." If you have to bring up something like this then ask yourself one question: "Does my sunglasses (insert any other supposed optical blocking device here) comply with the above standards? If you answer no then the item is not laser protective. PERIOD!

/rant off

I think I'm done with trying to save people from themselves. You get what you deserve.

 

[LRMNmeyer]

^^^Well said. +1 [smiley=thumbsup.gif]

 

[hashlasersdosei]

1. Laser light not compatible with vision. If you think otherwise don't bother replying to my assertion because you are an idiot. I have mathematics and physics on my side. Your gut feelings don't count. I know all those Ph.D. physicists, chemists, biologists, and MDs aren't nearly as smart as you, but give them a break, they get some stuff right.

2. Operating laser systems without proper eye protection is stupid. Take a course in statistics and probability. If it can happen, it will happen.  

3. It costs money to research and develop protective dyes. No company is going to give you protective glasses for free particularly in some form you find stylish.

4. If you don't think the proper safety equipment is necessary because you are different than others, and warmed by your own hubris, you are an idiot and you can join the rest of the ignorant bafoons at the shallow end of the gene pool.

5. Finally, if you can't afford laser eye protection yet you spend hundreds of dollars building or buying lasers you are an idiot and should not be in this hobby.

Couldn't agree more  [smiley=thumbup.gif]