Refractive Surgery

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 and can usually return to work or other activities. LASIK can be used to treat myopia, hyperopia, and astigmatism.

Advantages of LASIK over photorefractive keratectomy (PRK) include the desirable lack of central stromal healing response (the central corneal epithelium is not removed, thereby decreasing the risk of central haze formation that may occur during PRK healing), the shorter visual rehabilitation period, and minimal postoperative pain.

Disadvantages include possible intraoperative and postoperative flap-related complications, such as irregular flap formation, and flap dislocation. Flap-related complications can sometimes be corrected by another procedure (eg, flap repositioning). Long-term corneal ectasia can occur 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.

There are several femtosecond lasers that have been designed to perform KLEx. In KLEx, a femtosecond laser is used to create a thin, intrastromal lenticule of tissue, which is then removed through a small (2- to 4-mm) peripheral corneal laser incision. KLEx is available to treat myopia and myopic astigmatism in the United States.

The efficacy, predictability, and safety of KLEx are similar to those of laser in situ keratomileusis (LASIK), with the additional benefit that it eliminates flap creation and the attendant risks. Another benefit of KLEx is the reduced degree of postoperative corneal denervation and an accelerated rate of corneal nerve regeneration relative to LASIK.

Disadvantages include increased incidence of suction loss of the vacuum stabilization ring (which may necessitate aborting the procedure) and difficulty with enhancements (additional surgeries to correct residual refractive error).

Phakic IOLs are lens implants that are used to treat moderate to high (eg, 4 to 20 diopters) of myopia with or without astigmatism in patients as an alternative to laser vision correction. Phakic IOLs achieve superior visual quality compared to laser vision correction in patients with moderate to high myopia because they do not alter the corneal curvature. Also, there is no risk of secondary corneal ectasia since this is additive technology and no corneal stromal tissue is ablated. 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 should be performed in a sterile environment such as an operating room.

Risks are low overall but include cataract formation, glaucoma, infection, inflammation, and loss of corneal endothelial cells with subsequent chronic corneal edema that eventually may become symptomatic. Many complications can be avoided with proper sizing and using a phakic IOL that is designed to be placed in the sulcus (just posterior to the iris).

In PRK, unlike laser in situ keratomileusis (LASIK), no corneal flap is created. 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.

PRK may be more suitable for patients with thin corneas or epithelial basement membrane dystrophy.

Advantages of PRK over LASIK include an overall thicker residual stromal bed, which reduces but does not eliminate the risk of ectasia, and lack of flap-related complications.

Disadvantages include the potential for corneal haze formation (if a large amount of corneal tissue is ablated) and the need for postoperative glucocorticoid drops for several weeks to months.

Some surgeons use mitomycin C to decrease the rate of haze formation after PRK, allowing the use of topical glucocorticoids for a shorter length of time (Some surgeons use mitomycin C to decrease the rate of haze formation after PRK, allowing the use of topical glucocorticoids for a shorter length of time (1).

Clear lensectomy can be considered in patients who are already presbyopic and are not at high risk of developing a retinal detachment postoperatively. This procedure is identical to cataract surgery except the patient’s lens is clear and not cataractous. An extended depth-of-focus, trifocal, multifocal, or accommodating IOL—all of which allow the patient to focus over a wide range of distances without the assistance of eyeglasses—may be inserted.

The main risks of clear lensectomy are infection, retinal swelling, retinal detachment, and rupture of the posterior capsule of the lens, which would necessitate further surgery. Clear lensectomy should be performed with great caution in young patients with myopia because they have a higher risk of postoperative retinal detachment than older patients with myopia and cataract.

Radial and astigmatic keratotomy procedures change the shape of the cornea by making deep corneal incisions using a diamond or stainless steel blade or femtosecond laser.

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 fluctuating vision throughout the day, weakens the cornea, and can cause a hyperopic shift in the long term.

Astigmatic keratotomy is still commonly performed at the time of cataract surgery to treat low levels of astigmatism. The incisions are also referred to as limbal relaxing incisions because the optical zone is much larger and closer to the limbus.