RK is an incisional procedure for nearsightedness. RK is an older procedure which can produce very good results, but has lost popularity due to the fluctuations patients experience in their vision after the procedure. Compared to PRK and LASIK, the outcomes are generally less reliable.
AK is a very good procedure to correct astigmatism and is sometimes performed along with other eye surgeries, such as cataract surgery and LASIK. In AK, incisions are made in the outside part of the cornea to correct astigmatism. Because of the location of the incisions, AK provides a correction of astigmatism in most cases without fluctuations in vision. There are very specific requirements to be a candidate for AK, and your doctor can discuss this with you.