The doctor said my cornea’s are too thin for LASIK.  What does that mean?  In order to have LASIK surgery one’s corneas need to be the correct thickness.  This is very important.  In LASIK a cornea flap is created.  This corneal flap is typically around 160 microns thick.  Once the flap is created it is pulled back and the laser will reshape the cornea.  When the cornea is being reshaped, tissue is being removed.  There must be a minimum tissue remaining, bed tissue, to the cornea after the laser reshaping process.  The minimum bed thickness must be greater than 250 microns.  If the bed thickness is less the 250 microns this can increase risk of a complication called corneal ectasia where the cornea bulges out and causes significant distortions in one’s vision.  This can be devastating.

The average person’s corneal thickness is 540-550 microns thick.  For every 1 diopter of prescription power the laser has to take of 12-14 microns of corneal tissue.  Below are two examples.

Here is an example of someone with good corneal thickness:

Patient's cornea is: 540 microns

Flap thickness: 160 microns

Patients prescription: -7.00 diopters (14microns removed per diopter of power)

Bed thickness: 250 micron

In order for the laser to reshape the cornea for -8.00 diopters then 112 microns of tissue must be removed.

540 total thickness

-160 flap thickness

-98 tissue removed for prescription

282 micron bed left over

So the remaining corneal bed is 282 microns which is more than the minimum requirement of 250 microns.  So in this example the patient’s corneas are thick enough for LASIK surgery.

Here is an example of someone with cornea’s that are TOO THIN.

Patient’s cornea is: 490 microns

Flap thickness: 160 microns

Patients prescription: -8.00 diopters (14microns removed per diopter of power)

Bed thickness minimum: 250 microns

In order for the laser to reshape the cornea for -8.00 diopters then 112 microns of tissue must be removed.

490 total thickness

-160 flap thickness

-112 tissue removed for prescription

218 micron corneal bed left over

So the remaining corneal bed is 218 microns which is under the minimum requirement of 250 microns.  So in this example the patient’s corneas are too thin to have LASIK surgery.  However, they still may be a candidate for PRK surgery which doesn’t use a corneal flap.  Refer to PRK refractive surgery.