Localized on Global Irregularity
A combination of the two problems above.
The last case is of a 30year old male dentist who had LASIK 10 years ago. He then developed LASIK ectasia as a result of older flap technology. The old Hansatome flap created was simply just too deep for his cornea. He underwent crosslinking which stabilized the cornea beautifully (not much shape change with this process expected), but unluckily developed a corneal ulcer after the procedure. With scleral contact lense he was still able to get to 1.5 (6/3) vision. But became intolerant to them and seeked further help. BCVA with specs before surgery was 0.3 (6/18). Post-surgery he could see 1.5 (6/3) with spectacles or soft contact lenses.
The corneal ulcer left a "valley" in the cornea adjacent to the "peak" of the ectasia. Together this formed the global irregularity. The crosslinking (which needed to be done) or previous poor flap positioning caused a "flap crunch syndrome". Essentially the flap shrinks with microfolds forming at the level of Bowman's layer, just below the epithelium. A laser profile to take care of the global irregularity was done first, then a smoothing type of laser. All within 5 minutes.
We can consider a second laser to remove even more of the global irregularity. Attempting this at the first setting is possible, but can be tissue heavy. Safer to then split the two procedures.
Notice the difference with the second case. In the second case the global irregularity is much worse (21D to 105D). Here it is only 34D to 51D, but the vision in case 3 was worse before surgery. This is as a result of the microfolds causing local irregularities, as in case 1. This again proves: irregularity is worse than opacity for vision.