Are My Corneas Too Thin For Lasik?

The average corneal thickness ranges from 500-550 microns.  Corneal thickness is not the only factor.  Other factors include corneal shape (topography), steepness, pupil size, and eye health.  Your corneal thickness appears to allow you to be a candidate for PRK or LASIK.  And why PRK has been recommended.  Some medical reasons to prefer PRK include corneal erosion syndrome, corneal epithelial dystrophies, and having had previous LASIK surgery.

Your corneal thicknesses certainly seem adequate for LASIK; however, I'd be interested in knowing your full prescription including your degree of astigmatism in each eye. If you were told you are a better PRK candidate you may have some topographical abnormality or some other findings that may make LASIK less safe. You may consider getting a second opinion if you're not entirely confident with your first consultation. At the end of the day remember this is elective surgery.

Most surgeons prefer to leave between 250-300 microns of residual corneal stromal bed after the laser procedure. Based on your prescription, if I understand it correctly, it seems that your corneas are thick enough for either LASIK or PRK. There may be other variables however (dryness, topographic changes etc.) that make you a better candidate for PRK. 

the answer is, if you're asking if your corneas are too thin for LASIK--THEN THEY ARE!:).

Why risk a procedure that will leave your corneas half as thick--and HALF AS STRONG--as LASEK?

Please look at the following QUANTITATIVE explanation so you UNDERSTAND why LASEK is ALWAYS safer than LASIK in terms of leaving you with TWICE as much cornea afterwards.

The strength of your eye after any type of refractive surgery (LASIK, Intranasal, i-LASIK, LASEK, epi-LASEK, PRK) is determined by how much UNTOUCHED corneal tissue you have afterwards.  eye MDs call this the "stromal bed".

A normal cornea is between 500-550 microns thick (500 microns is half a millimeter, or 1/2 of the smallest space on the metric side of a ruler, so you can get some idea of the tiny thicknesses we are dealing with).

If you get LASIK, they'll cut a flap in your eye that's 150 microns thick. in Intranasal or i-LASIK, they cut your cornea with a laser, so they can make the flap thinner, or 100 microns, in an attempt to preserve more tissue, and leave more strength to your cornea.

For every 1 diopter of myopic prescription removed, you need to take off about 8 microns of tissue for low-definition, and 12 microns for hi-def, or CustomVue, or WaveFront.

So let's say your Rx is -6.00

Starting with 500, we subtract 150 for the flap, so we are left with 350 of treatable cornea.

If you're 22, we will have to shoot more like a -7.00 to account for myopic progression, or you'd need an enhancement at 30. so for hi-def, we'd have to take off about 90 microns of tissue. let's call it 100, to allow for a possible enhancement.

350-100 = 250, which is the LOWEST SAFE LIMIT FOR LASIK or you might develop iatrogenic keratoconus, which is the #1 reason to lose a lawsuit as a LASIK surgeon, as it requires a corneal transplant, so you really can't defend doing this to someone:(.

Now let's take the LASEK or epiLASEK example:

Same person, same Rx, same initial starting thickness:

500 - 0 (BECAUSE NO FLAP) - 100 (laser ablation) = 400 OR WAY ABOVE THE SAFETY LIMIT.

In other words, you could laser the prescription TWICE, and STILL be THICKER than after LASIK!.

I did my last PRK when I was a Resident at Harvard, and that was in 1993!  nobody in their right mind, in my opinion, would tolerate the pain, inflammation, and possible scarring of a PRK in 2011, when they could get an ADVANCED surface ablation (advanced COMPARED to PRK), which is a  LASEK or epiLASEK --with NONE of those problems.

In determining whether or not a patient is a good candidate for LASIK or PRK, I look at a number of factors:


Current Prescription and stability

Corneal Topography - a map of your surface astigmatism

Corneal Thickness

Age

Pupil size


These variables give me an indication of how well your corneas will hold their shape after laser treatment.  We don't want to treat people with good correctable vision who are at risk for corneal instability if treated with LASIK or PRK.  While your corneas appear thick enough, the other factors are very important indicators for the long-term stability of your treatment and your ophthalmologists are likely taking those into account when recommending PRK over LASIK.

Looking strictly at the numbers you have provided, it does not seem to appear that your corneas are too thin for LASIK. One of the reasons I say this is that the cornea is thinnest in its center and gets thicker peripherally. The advantage you have is that with a farsighted treatment, the majority of your treatment is going to be in the periphery of the cornea, which is the thicker part. Your surgeon can specifically show you your corneal map and emphasized where, exactly, your treatment will be.