“Is PRK safe for thin cornea?”

I will often use the analogy of a book to explain how laser eye surgery affects the cornea. The cornea is like a book, typically 540 pages thick, but varies from 440 to 640 typically. The FDA states that 250 pages of cornea should remain untouched, meaning that the combination of a corneal flap and the the tissue layered to correct the prescription should not go beyond this limit. Most surgeons however use 270 to 300 pages as their conservative limit. If your cornea is say 500 pages, 40 pages less than the average person, and the femtosecond created corneal flap is 100 pages, then you have about 100 pages to spare for correction. If you are having PRK, then that only removes 50 pages and you have 150 pages to spare for correction. In general, we remove about 12-13 pages for every 1 diopter of correction. That is the basic laser math involved. More important than the thickness of your cornea, is the shape of your cornea, if you have an asymmetric or atypical shape, then the risks of corneal instability, what is referred to commonly as corneal ectasia, increases. In many cases, even if you have a normal thickness cornea, if the shape is not symmetrical or normal, your surgeon will advise you to have PRK. The safety of PRK or even LASIK on thin corneas, is directly correlated with how normal the corneal shape is. If teh shape is normal, even if the cornea is thinner than normal, I will often perform LASIK because the recovery is so much easier. So the more important question for your eye doctor is whether your corneal shape is normal or not.

Scans need to be completed and compared to the prescription being treated, but in most cases PRK can be a safe option for thinner corneas

It depends on how thin the corneas and how much treatment is necessary to achieve the desired degree of refractive change. In a thin cornea, PRK is safer than Lasik.

It depends on how thin the cornea is and how extensive the nearsighted treatment is. It is definitely safer than LASIK for thin corneas. By thin, we are talking about corneas less than 500 microns thick. For larger treatment, you would need to be over the 500 microns. Today, most refractive surgeons want to leave at least 350 microns of untouched cornea.