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Lasik Versus PRK Eye Surgery for Preparedness, by Simple Country Doctor
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
