Re: What is the physics behind laser eye surgery?

     I do not have information on the actual calculations used to 
determine how strong of laser, how long of duration, or exactly where the 
laser is aimed at.  However, I can give you some basic information about 
the latest refractive surgery procedure called LASIK, that can correct for 
nearsightedness (myopia), astigmatism, and some farsightedness (hyperopia).
     The idea behind LASIK is to minimize corneal trauma, minimize pain, 
and mazimize the precision of refractive surgery.  Because the corneal 
epithelium is removed prior to using the laser, you minimize the amount of 
post-operative pain and scarring.  The laser actually burns small amounts 
of deeper corneal tissue in strategic areas, that in effect changes the 
refractive power, or the corneal ability to bend light.  In myopes 
(nearsighted), tissue is removed in the center of corneal to flatten it 
more.  This is because myopes usually have steeper than normal corneas 
that in effect, refract (bend) light too much for the light rays to focus 
on the retina, for that particular eye.  Removing (burning) off precise 
amounts of this tissue allows the corneal to flatten, therefore allowing 
the light rays to be focused on the retina.  That is it in a nutshell. 
    I do not know how the amount and strength of the laser is calculated, 
but I know that very expensive computer programs can do it, after taking 
in an extensive history of each particular patient.  You might want to do 
a search on revoptom.com  on LASIK or laser refractive surgery and see if 
there is more information.  Good luck!

Kenton L. McWilliams, O.D.