I’ve been reading through the survivalblog archives. I happened across a letter recommending Lasik for folks with significant refractive errors. I’m not an ophthalmologist, but I am a family and emergency medicine doctor, and I did a lot of research into refractive surgery before I had my significant nearsightedness corrected. I started out with [seeing only the] ‘big E’ [on the eye chart] (20/200) in one eye and [seeing] ‘white rectangle’ (worse than 20/200) in the other. I was always afraid I’d lose my glasses/contacts while out in the backwoods on one of my frequent solo adventures. I finally took the plunge six years ago. After careful consideration, I did not go with Lasik, but [instead] had photorefractive keratectomy (PRK) done. The main reason I chose PRK over the more popular Lasik procedure was fear of ‘losing the flap’ on a blow to the head during a martial arts class, or worse, an actual confrontation. There are advantages and disadvantages to both procedures. With Lasik, a thin ‘flap’ is cut almost completely free from the anterior cornea, and a laser is used to reshape the cornea underneath. The flap is then laid
back down and the cornea allowed to heal. With PRK, the laser is used to reshape the front surface of the cornea after removing the single layer of epithelium from the cornea (the place I went to also used a laser to remove the epithelium). The epithelium then grows back. Advantages to Lasik are several. The ‘wow!’ factor is significant; as soon as they lay the flap back down, your vision is significantly improved — usually pretty close to 20/20. Its a pretty accurate procedures, and final visual acuity of 20/20 or better is not unusual. Recovery time is brief and not uncomfortable. This is all because the epithelium (the ‘skin’ on the front of the cornea) is only minimally disturbed. The work is all done deep in the cornea where there is no sensation.
The problems that can come of Lasik come from the same characteristics. It is possible to ‘lose the flap’; have the corneal flap come off. Only about the outside one-third of the corneal flap ever heals, and there are stories of people losing the flap even a year out from surgery, due to fairly minor head or eye trauma. The only treatment possible at that point is a corneal transplant. Revisions are seldom necessary, but are technically difficult because you can’t re-cut the flap exactly the same a second time — usually another procedure like PRK is used if a revision is required. There are more immediate concerns with infection and other flap-related problems just out from surgery. After Lasik, your vision may change significantly with elevation/reduced air pressure (mainly a concern for mountaineers who go well over 14,000 feet). PRK’s advantages and disadvantages look like the opposite side of the Lasik coin. For technical reasons, some refractive errors that Lasik can’t correct can be handled with PRK. PRK is fairly accurate, but may not be as accurate as Lasik (numbers are hard to come by here; I went from 20/200 to 20/25 in one eye with PRK, still slightly nearsighted; the other went from 20/400+ to 20/35 — this was my dominant eye so I had it revised and now have 20/17 in that eye with a little farsightedness. Both eyes still have slight astigmatism, but less than prior to surgery.) It takes 24-to-72 hours for the epithelium to grow back on the front of your eye; this makes it feel like you have an eyeball full of gravel. Its pretty
uncomfortable, but bearable (for most people). You have decent vision after 3-7 days (I was able to drive in about three days), but it takes months for it to completely stabilize. It is possible to have problems like delayed healing of the epithelium, which is pretty uncomfortable. On the flip side, you will never lose the flap, because there isn’t one. If you have to have a revision, they can do the same procedure. There’s no shear face inside the cornea, so no variation in vision with elevation.
If you have dry eyes prior to surgery, they will be worse after Lasik because of disturbance of the tear layer. They may be completely unbearable after PRK, and while this effect may reduce with time it may never go away completely.
Another concern that some don’t stop to consider: your lenses harden with age, which reduces your ability to focus up close (if you have good
distance vision). If you are near sighted now and you get your vision corrected to perfect 20/20, you will most likely need reading glasses by the time you’re 50. Life is full of trade offs. Note that I now have slight far-sightedness in one eye (an annoyance that inhibits close-up focusing in that eye) and slight near-sightedness in the other (but I can focus pretty close with that eye. More idea would be perfect uncorrected vision in my dominant (shooting) eye and slight near sightedness in my non dominant (close) eye — monovision. Even when I lose my ability to accommodate (focus), I’ll be able to read without glasses with my ‘near’ eye and see to shoot with my ‘far’ eye. A lot of folks walk around with this and do quite well. I find it annoying, so I wear glasses to correct
this — but if I lose my glasses, I can still function quite well for both near and far vision, unlike the blind fool I would have been without lenses six years ago.
A slightly more obscure concern is aspherical errors; getting the cornea slightly out of round. I notice that, on a dark night, the dimmer stars appear slightly out-of-round or even double from my ‘far’ eye; this is not uncommon. The lens isn’t quite perfectly round after the surgery. This effect can be much greater, and is very hard to correct for with lenses or
surgery. An even more obscure problem is contrast discrimination; this is what allows you to distinguish a white rabbit on a background of white snow.
There is some evidence that loss of contrast discrimination is significant with Lasik, probably less so but still evident with PRK. Most people never notice it, because they don’t notice what they don’t notice. But if you’re ever in a position where you need to distinguish, say, Mossy Oak Breakup from the mossy oaks behind your house, it could be a factor in your continued presence in the world.
Obtain and understand as much information as possible before you let someone alter your anatomy, and understand that problems can and do occur, and it is usually impossible to tell ahead of time who is going to have problems with a particular procedure. Surgery always has risks (but so does being nearsighted in a world with no functioning opticians). – Simple Country Doctor
Lasik Versus PRK Eye Surgery for Preparedness, by Simple Country Doctor
