250 Cornea Thickness Rule

Post your questions and start your research in this forum if more than three months ago you had any type of surgery to reduce the need for glasses and contacts.

Postby LasikExpert » Sat May 19, 2007 9:14 pm

DryEye wrote:PRK would remove top portion only vs lasik doing it internally with 63 microns of tissue for safety?


PRK removes tissue from the surface. Lasik removes tissue under a corneal flap. PRK on a Lasik flap is possible for enhancement surgery.

DryEye wrote:Can a surgeon get it down (lasik enhancement) to a certain amount of tissue to remove safely when doing an enhancement - say 30 or 40 microns in this case?


Current laser systems are able to provide information regarding the amount of tissue that would be removed prior to surgery. There are some variables, but this is normally within a few microns.

According to the Munnerlyn formul, about 12 microns of tissue are removed for each 1.00 diopter of refractive error. 30-40 microns would be in the neighborhood of 3.00 diopters of change.

DryEye wrote:With PRK they would have more to work with for removal if need be over a period of one's lifetime?


Yes. The difference in untouched cornea between PRK and Lasik would be equal to the thickness of the flap.

DryEye wrote:Do you know what the average (cornea left) is for most people after lasik?


No. The information would be academic as it has no clinical purpose except if under the 250 micron minimum or if ectasia presents.

DryEye wrote:How do the two differ in terms of corneal stability over long run?


A healthy cornea will normally remain stable so long as 250 microns of tissue remain untouched (more is always better) no matter what the procedure.

DryEye wrote:With PRK one can do more than 63 microns if need be?


PRK on the Lasik flap is limited to the thickness of the flap.

DryEye wrote:Also, I read here that once one does PRK over a flap that is the way it has to be done for additional enhancements down the road.


This question was recently asked and I brought the issue to the attention of four prominent surgeons. All agreed that attempting to do a Lasik enhancement (flap lift) after PRK was done on the Lasik flap would not be wise. There are no case histories of this having been done.

DryEye wrote:Would I have had more cornea left if I had chosen Intralase instead of microkeratome (VISX CustomVue)?


Possibly, but probably not. Mechanical microkeratomes are able to create very thin flaps too.

DryEye wrote:I think I would prefer lasik if I decide on an enhancement unless I am told that it isn't a wise choice.


If the advice of your surgeon is that you have a choice, then choose that with which you are most comfortable.
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