Laser exposure...

[Externet]

Hi.

Which laser beam does more burning damage to a retina ?

Passing trough a 3 mm pupil opening, both cases same hazardous power :

 

A 3 mm diameter beam, or a 0.5 mm diameter beam ?

 

Does a wider beam damages less a larger retina area, and a smaller beam a worse burn but in a smaller area ?

[Klaynos]

This is not trivial as the eye has a reflex to look away when damage starts. I'm not sure whether that reacts faster to large area damage.

[John Cuthber]

The lens of the eye will focus both beams to prety much the same size spot so it won't matter much (assuming that it's visible light).

[swansont]

Hi.

Which laser beam does more burning damage to a retina ?

Passing trough a 3 mm pupil opening, both cases same hazardous power :

 

A 3 mm diameter beam, or a 0.5 mm diameter beam ?

 

Does a wider beam damages less a larger retina area, and a smaller beam a worse burn but in a smaller area ?

 

There's more subtlety to this than you may realize. The beam diameter for a gaussian beam is typically related to the the 1/e² point of the intensity, so there is a lot of power outside of that. i.e. a 3mm beam does not have a sharp intensity cutoff at 3mm. Further, the beam traveling through an aperture will diffract. So a 3mm beam would have less power focusing on the retina than the 0.5mm beam.

 

However, wider Gaussian beams can be focused down to smaller spots. That makes things worse.

 

http://en.wikipedia.org/wiki/Gaussian_beam

[MigL]

A wide beam laser is used to 'shave' thickness off the cornea for vision correction surgery.

And it does no damage to the retina.

 

I've had laser surgery for glaucoma, both burns around the edge of my iris and a hole burnt right through, in both eyes.

The pin hole burn-through took less than a second.

 

Both lasers are YAG, but I have no idea of the comparative power.

[swansont]

A wide beam laser is used to 'shave' thickness off the cornea for vision correction surgery.

And it does no damage to the retina.

 

I've had laser surgery for glaucoma, both burns around the edge of my iris and a hole burnt right through, in both eyes.

The pin hole burn-through took less than a second.

 

Both lasers are YAG, but I have no idea of the comparative power.

 

The energy deposited is a key. Power, and whether it is continuous or pulsed.

[John Cuthber]

I suspect that the IR produced by a YAG laser doesn't get through the cornea and lens so it won't damage the retina easily.

After all, if they are trying to burn bits off the cornea, they will choose a wavelength that is absorbed by it.

 

Near IR will get through to the retina butt may not be focussed well so it may be less harmful.

 

The sensible advice is to wear suitable eye protection when using lasers.

Edited May 23, 2015 by John Cuthber