I used to use MMC for Rx above -5, then had some late (>3 mo out) haze for -4, and rarely had it for -3 something
so i reduced my limit for MMC (since it is really perfectly safe if diluted properly and applied on a sponge) to > -3
this depends where you are, like if in an area with more sun/UV/wind/etc scarring is more likely, so need MMC more, i tried through epi PRK years ago, i’m on a VISX, there is an (old) software setting for this (“laser-scrape”)the reason we called it “laser scrape” is that you always get a ring of residual epithelium that you then need to scrape off which defeats the purpose of using the laser to remove the epi (over Amoilis brush) to make it less traumatic/cleaner, the reason again for this optically is the laser becomes more tangential/less orthogonal to the cornea towards the periphery, so the efficiency is decreased, so you get central breakthrough before the periphery.
i understand that modern software algorithms add energy to the periphery to try to obtain uniform epi removal/breakthrough however, there still aren’t great methods that are always used to measure preop epi thickness (preop OCT isn’t common) so then we are reduced to visualizing removal by looking for visual breakthrough i also think that the energy of the eximer on the epi is probably imparted somewhat onto the underlying cornea so that you are probably adding energy/trauma to the underlying cornea while you are doing a laser epi removal which is another reason why you might want to use MMC for -3, especially if you are emplying laser-scrape.
