PRK: Another Path to Laser Vision Correction
Lasik Alternatives Photorefractive keratectomy (PRK) uses the excimer laser in the same way as LASIK, and patients' vision correction results are similar. The main difference between PRK and LASIK is that in PRK there is no flap — only the very top (epithelial) layer of the cornea is removed (or moved aside) before the excimer laser sculpts the cornea.
Many PRK surgeons use a blunt, gently vibrating microkeratome to remove the epithelial layer. LASEK and Epi-LASIK, described below, are other PRK techniques. New approaches, such as advanced surface ablation in which the cornea is cooled either before or after surgery, help reduce the discomfort that may occur after PRK. The patient may also be given topical antibiotics and anti-inflammatory medications and oral pain medications to reduce discomfort and speed healing after surgery. A "bandage" soft contact lens is used to promote epithelial healing, which takes about four days.
While LASIK patients often report clear, improved vision by the day after surgery, it may be a few days before vision stabilizes for PRK patients. The cornea's epithelial layer re-grows during this time. The thicker corneal flap created in LASIK is not made in PRK, so if there is a concern about potential flap complications, the surgeon may recommend PRK. If the patient's corneas are too thin to meet LASIK standards, if he or she had LASIK previously, or if other eye health factors are involved, the surgeon and patient may decide that PRK would be a better choice.
Wavefront-guided PRK offers additional vision correction, similar to wavefront-guided LASIK. Though thousands of wavefront-guided PRK procedures have been safely and effectively performed in the United States, the FDA approval process has not yet taken place, so wavefront-guided PRK is considered an "off-label" use of the technology. Professional medical standards permit Eye M.D.s to use this and other "off-label" procedures and medications.
A microsurgical instrument called a trephine is used to create a flap of epithelial corneal tissue, and an alcohol solution is used to loosen the epithelial cells. Once the epithelial flap is created and moved aside, the procedure is the same as PRK. After corneal sculpting, the epithelial flap is repositioned and smoothed with a small spatula, then secured with a "bandage" soft contact lens to promote epithelial healing, which takes about four days.
A special microkeratome, the Epi-keratome, is used to precisely separate a very thin sheet of epithelial tissue from the cornea. This thin sheet is lifted to the side and the cornea is treated as with PRK. Then the thin sheet may be moved back into place to re-adhere to the cornea or removed. A "bandage" soft contact lens is applied and used for about four days to help the epithelial layer heal.
Conductive Keratoplasty (CK)
Conductive Keratoplasty CK is a noninvasive, thermal refractive surgery procedure used to correct mild to moderate farsightedness (hyperopia) in people over age 40. With CK, your Eye M.D. uses a tiny probe that releases controlled amounts of radio frequency (RF) energy, instead of a laser, to apply heat to the peripheral portion of the cornea. The heat then causes the peripheral cornea to shrink and tighten like a belt. This increases the curvature (steepness) of the central cornea, improving the optical power of the central cornea. This refocuses light rays on the retina and enhances vision.
CK can be used to achieve "monovision" (blended vision). With monovision, CK can be used to improve close-up vision in a presbyopic eye with good vision but poor near focus. To maintain good distance vision, usually only one eye is set to near focus (the non-dominant eye), while the other is left or set at good distance vision. CK does not offer permanent correction; for some people, farsightedness may return over time.
Phakic Intraocular Lenses (IOLs)
Phakic IOLs are designed for people with high degrees of refractive errors that cannot be safely corrected with corneal-based refractive surgery. The phakic IOL, sometimes referred to as an implantable contact lens, or ICL, is surgically implanted inside the eye in front of the eye's natural lens. The eye's natural lens is not removed, so patients can retain their pre-existing ability to focus.
During the phakic IOL procedure, your Eye M.D. places the phakic IOL either in front of or behind the iris of the eye. Once the IOL is properly positioned inside the eye, it provides the necessary correction to redirect light rays precisely onto the retina.
Refractive Lens Exchange (Clear Lens Extraction)
With refractive lens exchange (RLE) — also called Clear Lens Extraction or CLE — an artificial lens is used to replace your eye's natural lens in order to improve vision. The procedure is performed much like cataract surgery.
As is an option in cataract surgery, RLE may employ multifocal or accommodative intraocular lenses (IOLs). These lenses allow the ability to focus at all distances.
Some people who have early stage cataracts may choose to have RLE instead of waiting for their cataracts to progress to the point where they should be removed. This is because the lens implants generally provide them with better uncorrected vision at that point, particularly if they currently need vision correction.
RLE may also be an option for people with severe hyperopia (farsightedness), for whom LASIK is not recommended.
RLE is not FDA-approved, however, ophthalmologists legally may choose to perform this procedure in what is called an "off-label" use.
Source: American Academy of Ophthalmology, www.geteyesmart.com