Corneal refractive surgery alters the curvature of the cornea to focus light more precisely on the retina. The goal of refractive surgery is to decrease dependence on eyeglasses or contact lenses. Most people who undergo refractive surgery achieve this goal; about 95% do not need corrective lenses for distance vision. Ideal candidates for refractive surgery are healthy people aged 18 and older with healthy eyes who are not satisfied wearing eyeglasses or contact lenses. Preoperative examination excludes people with active ocular diseases, including severe dry eye. Candidates should not have a history of autoimmune or connective tissue disease because of potential problems with wound healing. Latent herpes simplex virus may be reactivated after surgery; patients should be advised accordingly. Another contraindication is use of isotretinoin or amiodarone. Refraction should be stable for at least 1 yr.
Adverse effects of refractive surgery include temporary foreign body sensation, glare, halos, and dryness; occasionally, these symptoms persist. Potential complications include overcorrection, undercorrection, infection, and irregular astigmatism. In excimer laser procedures performed on the superficial corneal stroma, haze formation is possible. If infection, irregular astigmatism, or haze formation causes permanent changes in the central cornea, best-corrected acuity could be lost. The overall complication rate is low; chance of vision loss is < 1% if the patient is considered a good candidate for refractive surgery preoperatively.
The two most common refractive surgery procedures are laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK).
Laser In Situ Keratomileusis (LASIK)
In LASIK, a flap of corneal tissue is created with a femtosecond laser or mechanical microkeratome. The flap is turned back and the underlying stromal bed is sculpted (photoablated) with the excimer laser. The flap is then replaced without suturing. Because surface epithelium is not disrupted centrally, vision returns rapidly. Most people notice a significant improvement the next day. LASIK can be used to treat myopia, hyperopia, and astigmatism.
Advantages of LASIK over PRK include the desirable lack of healing response (the central corneal epithelium is not removed, thereby decreasing the risk of central haze formation that occurs during healing), the shorter visual rehabilitation period, and minimal postoperative pain. Disadvantages include possible intraoperative and postoperative flap-related complications, such as irregular flap formation, flap dislocation, and long-term corneal ectasia. Ectasia occurs when the cornea has become so thin that intraocular pressure causes instability and bulging of the thinned and weakened corneal stroma. Blurring, increasing myopia, and irregular astigmatism can result.
Photorefractive Keratectomy (PRK)
In PRK, the corneal epithelium is removed and then the excimer laser is used to sculpt the anterior curvature of the corneal stromal bed. PRK is used to treat myopia, hyperopia, and astigmatism. The epithelium typically takes 3 to 4 days to regenerate; during this time a bandage contact lens is worn. Unlike LASIK, no corneal flap is created.
PRK may be more suitable for patients with thin corneas or anterior basement membrane dystrophy.
Advantages of PRK include an overall thicker residual stromal bed (thereby reducing risk of ectasia) and lack of flap-related complications. Disadvantages include potential for corneal haze formation if a large amount of corneal tissue is ablated and the need for postoperative corticosteroid drops for 3 mo.
Intracorneal Ring Segments (INTACS)
Intracorneal ring segments (INTACS) are thin arc-shaped segments of biocompatible plastic that are inserted in pairs through a small radial corneal incision into the peripheral corneal stroma at two-thirds depth. After INTACS are inserted, the central corneal curvature is flattened, reducing myopia. INTACS are used for mild myopia (< 3 diopters) and minimal astigmatism (< 1 diopter). INTACS maintain a central, clear, optical zone because the 2 segments are placed in the corneal periphery. INTACS can be replaced or removed if desired.
Risks include induced astigmatism, undercorrection and overcorrection, infection, glare, halo, and incorrect depth placement. Currently, INTACS are mostly used for treatment of corneal ectatic disorders such as keratoconus and post-LASIK ectasia when glasses or contact lenses no longer provide adequate vision or are uncomfortable. Best-corrected vision and contact lens tolerance improve in 70 to 80% of patients.
Phakic Intraocular Lenses (IOLs)
Phakic intraocular lenses (IOLs) are lens implants that are used to treat severe myopia in patients who are not suitable candidates for laser vision correction. Unlike in cataract surgery, the patient's natural lens is not removed. The phakic IOL is inserted directly anterior or posterior to the iris through an incision in the eye. This procedure is intraocular surgery and must be done in an operating room.
Risks include cataract formation, glaucoma, infection, and loss of corneal endothelial cells with subsequent chronic corneal edema that eventually becomes symptomatic.
Because phakic IOLs do not correct astigmatism, patients can undergo subsequent laser vision correction to refine refractive results in a technique known as bioptics. Because the bulk of the myopia is corrected with the phakic IOL, less corneal tissue is removed with the excimer laser, and the risk of ectasia is thus low.
Clear lensectomy can be considered in patients with high hyperopia who are already presbyopic. This procedure is identical to cataract surgery except the patient's lens is clear and not cataractous. A multifocal or accommodating IOL, which allows the patient to focus over a wide range of distances without external lens correction, can be inserted.
The main risks of clear lensectomy are infection and rupture of the posterior capsule of the lens, which would necessitate further surgery. Clear lensectomy should be done with great caution in young patients with myopia because they have an increased risk of postoperative retinal detachment.
Radial and Astigmatic Keratotomy
Radial and astigmatic keratotomy procedures change the shape of the cornea by making deep corneal incisions using a diamond blade.
Radial keratotomy has been replaced by laser vision correction and is rarely used because it offers no clear advantages over laser vision correction, has a greater need for subsequent retreatment, can lead to visual and refractive results that change through the day, and can cause a hyperopic shift in the long term.
Astigmatic keratotomy is still commonly done at the time of cataract surgery. The incisions are referred to as limbal relaxing incisions since the optical zone is much larger and closer to the limbus.
Last full review/revision April 2013 by Deepinder K. Dhaliwal, MD