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PHOTOREFRACTIVE KERATECTOMY (PRK)
PRK is a method of vision correction
which uses the excimer laser to remove corneal tissue
directly from the surface, without the benefit of a
protective corneal flap or cap. PRK can be used to treat
nearsightedness, farsightedness, and astigmatism.
Images #1-4
In PRK, the excimer laser is directly applied to the
surface of the cornea, without making a corneal flap.
For someone who is nearsighted, more corneal tissue
is removed from the center than from the sides (peripheral
cornea). This flattens the cornea and corrects the nearsightedness.
Images #5-8
For someone who is farsighted, more corneal tissue is
removed from the sides (peripheral cornea) than from
the center. This is like removing a "doughnut"
of corneal tissue, making the cornea steeper, and thus
correcting the farsightedness.
The amount of prescription correction that can be safely
treated with PRK is debatable. Most surgeons feel treating
up to 6-8 diopters of nearsightedness is safe with PRK.
There is an increased risk of developing corneal haze
when treating large amounts of prescription with PRK.
This corneal haze is almost like scar formation; usually
it fades over time, but can cause loss of best-corrected
vision.
The drawbacks of PRK as compared
to LASIK are, in fact, healing issues. At the completion
of PRK, a large part of the cornea is abraded. More
healing is necessary. It may take several days to get
back useful vision, and there can be some degree of
discomfort until the surface heals, usually 1-3 days,
but sometimes longer. A "bandage" soft contact
lens is inserted into the operated eye to make it more
comfortable; it is removed after the abrasion heals.
Weak anesthetic eyedrops can sometimes be cautiously
used to numb the eye until it heals. Because of the
temporary visual handicap, only one eye at a time is
treated, which may require use of a temporary contact
lens in the unoperated second eye (so the patient can
function with both eyes), until the patient feels comfortable
enough to proceed with second eye treatment. Steroid
eyedrops are usually used for a much longer time than
with LASIK, up to 4 months.
Despite what sounds like a long
list of disadvantages, PRK is sometimes an excellent
option for those patients who are not candidates for
LASIK. Because no corneal flap needs to be made, PRK
is arguably safer than LASIK. Patients, appropriately
chosen and treated, can have excellent visual outcomes
with PRK.
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