Hi Windy
The main corneal parameter that is considered in terms of avoiding corneal ectasia is the 'residual stromal thickness' (RST)-which means either the remaining thickness of untouched cornea under a LASIK flap or in the case of epi-LASIK/PRK, the remaining corneal thickness under the epithelial layer.
For many years, the minimal RST that doctors aimed to leave behind was 250 microns. In many cases, significantly more was left eg around 300 microns, so that in case enhancement is needed, it is possible to correct for small amounts of regression or residual spectacle power.
When observing these figures, the risk of ectasia is extremely low eg in a study conducted by the Singapore National Eye Centre, 8 out of almost 38,000 eyes developed ectasia.
Having said that, it is recognised that some eyes are at higher risk of getting ectasia. These eyes can get ectasia even if the RST is 250 microns or more, and are usually found to have certain topographic patterns similar to keratoconus before LASIK. It is routine nowadays to screen for these kinds of eyes before surgery. If these suspicious features are found, the patient is usually told they are not suitable for laser surgery but may consider ICL surgery in some cases. Rarely, on a case by case basis, laser surgery with corneal crosslinking may still be possible also.
In your case, it is likely that you would have already undergone the pre-operative screening and were found to have normal corneas before your surgeon proceeded with surgery. All LASIK surgeons are cognizant of the need to respect a minimum RST after surgery, so you do not have to be concerned about your corneas being too thin after surgery. It is really only a factor during the pre-LASIK planning process.
