Which form of laser eye surgery removes the least amount of tissue?
I was recently asked to answer the following question that appeared on the Quora website: “Which form of laser eye surgery removes the least amount of tissue?”
Here is my answer: For a given refractive error, the “amount” of tissue removed is roughly the same for the two primary methods of laser refractive surgery: LASIK and ASA. Both methods use an excimer laser to remove a given amount of tissue to better focus incoming light on the retina. The difference in terms of tissue removal is the effect that each technique has on residual stromal bed. The residual stromal bed is the amount of tissue remaining after a laser procedure that contributes to the overall strength of the cornea.
At Kugler Vision, the first step in LASIK is the formation of the LASIK flap uses a femtosecond laser. For the sake of discussion lets assume that the average flap thickness is 120 microns. Let’s also assume that the average corneal thickness is 535 microns. If a patient has a refractive error of -3.00D, then the amount of tissue removed will be roughly 33 microns (this varies depending on the laser platform, but for the sake of this dissuasion let’s assume 11microns per D).
So if the cornea starts with a thickness of 535, then a 120 micron flap is made, we are left with 415 microns after the flap is made. Subract another 33 microns after the laser is performed, and we are down to 382 microns of residual stromal bed.
Let’s say the same eye had ASA, (also known as PRK). There is no flap made in ASA, but the outer layer of the eye, called the epithelium, is removed prior to laser. The epithelium is approximately 50 microns. So for the same eye: 535 – 50 (epithelium) = 485. 485 – 33 (laser) = 452. So in this example, LASIK would leave the eye with 382 microns of RSB whereas ASA would leave the eye with 452. There is much debate amongst LASIK specialists as to whether this difference matters clinically, but the general consensus is that it is best to avoid a RSB less than 250 microns. For a more in-depth review of this subject, read here.
Lance Kugler, MD, is a specialist in LASIK and vision correction surgery and CEO of Kugler Vision. A proud Omaha native, he is passionate about improving lives through clear vision. Dr. Kugler serves on several national boards, and his practice is recognized internationally as a center of excellence. Dr. Kugler is one of the original founders of the Refractive Surgery Alliance, an international organization comprised of over 350 of the world’s leading vision correction surgeons; he also served as its first president. In 2019, Dr. Kugler was selected as a TEDx speaker, and delivered a talk in Omaha about the worldwide epidemic of nearsightedness and refractive solutions. Dr. Kugler is an Associate Professor of Refractive Surgery at the University of Nebraska Medical Center’s Truhlsen Eye Institute, has been published in many medical journals, and participates in numerous clinical studies to advance the field of vision correction surgery. Dr. Kugler and his wife are proud parents to five active kids. When he has a spare moment, he enjoys skiing, tennis, travel, and fine coffee.