Corneal collagen cross linking procedure combined with PTK and PRK – Cretan protocol plus can improve refractive error (astigmatism). This is based on our experience and a study paper published in the Journal of Cataract and Refractive surgery from Crete, Greece By Dr. Grentzelos.
Corneal collagen cross linking as you may know was invented by Dr. Wollensack. It can halt the progression of Keratoconus. In US FDA has approved Avedro KXL/Photrexa system to prevent progression in post lasik ectasia and progressive keratoconus. The major drwaback has been that patients are still left with refractory error especially astigmatism. Hence vision is not optimal in these teens and young adults. Keratoconus surgeons had been hesitant to apply laser energy to the keratoconus cornea, for fear that tissue removal may further weaken the cornea.
This will also allow us do corneal collagen cross linking procedure combined with PTK and PRK – Cretan protocol plus can improve refractive error (astigmatism ) on patients of forme fruste keratoconus. Such people have been turned down for laser vision correction till date.
Now as may be evident this combined procedure can only be done with epi off technique ( see classification of cross linking/cxl)
Corneal collagen cross linking procedure combined with PTK and PRK can only be done for minor corrections where total corneal tissue ablated is less than 50 microns. And at least 350 microns should be left. Again, judicial judgment by an experienced laser and keratoconus surgeon is very important. We usually have restricted to treat astigmatism in the central 6 mm zone, especially when tissue ablated is away from the thinnest zone.
Vision can be improved. Combination allows rapid improvement of vision, avoiding contact lenses. There is no additional pain. If the two procedures are done separately there is discomfort and healing time for each. Another advantage of using the PTK mode for removal of epithelium is that it flattens the cone decreasing higher order aberrations.
As with any advance we have to be careful of potential side effects. PTK can weaken the thinnest bulging part of the cornea. This may destabilize the cornea.
Please consult with your keratoconus expert if this is a good choice for you.