Post-LASIK ectasia—or corneal ectasia—is a rare but serious complication of LASIK laser eye surgery. The condition is due to the weakening of the inner layers of the cornea, which occurs during surgery. Over time, the weakened cornea loses its shape and bulges forward, resulting in distorted vision that cannot be corrected with eyeglasses.
The exact risk for post-LASIK ectasia is unknown and difficult to estimate, given advances in LASIK technology and treatment protocols. Studies suggest it may occur in roughly one of every 2,000 LASIK procedures.
The appearance and progression of post-LASIK ectasia are similar to a degenerative disease of the cornea called keratoconus.
Though post-surgical corneal ectasia most often is associated with LASIK, it also can occur after other corneal refractive surgery, such as PRK, LASEK or epi-LASIK.
What Causes Post-LASIK Ectasia?
Corneal ectasia following LASIK surgery is believed to be caused by removal of too much corneal tissue during LASIK, which weakens the structure of the remaining cornea.
The eye is filled with a fluid that creates a certain amount of internal pressure (intraocular pressure, or IOP). If the structure of the cornea becomes weakened, the IOP can force an outward bulging of the cornea (ectasia).
If not prevented or successfully treated, ectasia can cause permanent vision loss and may eventually require a corneal transplant.
The risk of post-LASIK ectasia is particularly a concern when high amounts of nearsightedness must be corrected, which requires the removal of more tissue from the central cornea than correction of lower amounts of myopia or correction of farsightedness or astigmatism.
A second important consideration is the patient's central corneal thickness prior to LASIK surgery. A person who has a thinner-than-average cornea and moderate myopia prior to surgery might have greater risk for corneal ectasia after LASIK than a person with high myopia who has a thicker-than-average cornea before surgery.
The key risk factor is the thickness of what is called the residual corneal bed—the remaining corneal tissue under the LASIK flap—after LASIK surgery. If the residual corneal bed (also called residual stromal bed, or RSB) is too thin, this increases the risk for corneal ectasia after LASIK.
To avoid post-LASIK ectasia, refractive surgeons take precise measurements of central corneal thickness prior to surgery and calculate how much corneal tissue must be removed to fully correct the patient's myopia. This information then allows the surgeon to calculate the expected residual corneal bed thickness after surgery.
It appears that some people with normal central corneal thickness, but atypical corneal shape prior to LASIK surgery, also have a greater risk for post-LASIK ectasia. To identify these cases, refractive surgeons take detailed measurements of the curvature of both the front and back surface of the cornea prior to LASIK surgery. This automated process, called corneal topography, can identify abnormalities that might pose a greater risk for post-LASIK ectasia.
Also, studies show younger patients appear to have greater risk of post-LASIK ectasia than older adults.
Patients with a significant difference in the central corneal thickness of their two eyes also may have a greater risk of ectasia after LASIK surgery.
Symptoms Post-LASIK Ectasia
The primary symptoms of post-LASIK ectasia are blurred and distorted vision due to increasing myopia and astigmatism. Often, these vision problems cannot be fully corrected with eyeglasses or soft contact lenses.
The onset of ectasia symptoms varies widely. One study found that the average time to development of post-LASIK ectasia was approximately 16 months after surgery, but some patients showed signs of ectasia as early as one month after surgery, and it took more than three years for post-LASIK ectasia to appear in other patients.
Routine eye exams are essential after LASIK surgery to monitor your visual acuity, the shape and health of your cornea, and the overall health of your eyes.
Treatment of Corneal Ectasia
Most cases of post-LASIK ectasia can be successfully treated. The treatments are similar to those used to treat keratoconus. In the past, the primary treatment options were rigid gas permeable (RGP or GP) contact lenses and implantation of intrastromal corneal ring segments, such as Intacs.
(Not surprisingly, patients who required contact lenses after LASIK because of post-surgical ectasia often were very unhappy, since they often chose to have LASIK surgery to eliminate their need for contact lenses in the first place.)
More recently, a procedure called corneal collagen cross-linking (CXL) has shown promise for the treatment of post-LASIK ectasia and is fast becoming the procedure of choice for many refractive surgeons.
In CXL, the surgeon applies a solution of riboflavin (vitamin B2) to the surface of the eye and exposes the eye to controlled ultraviolet (UV) light rays for approximately 30 minutes. The UV radiation stimulates the riboflavin to create new bonds—or "cross-links"—between the linear connective tissue in the cornea (collagen) to strengthen the cornea so it can maintain a normal shape for clear vision.
A recent study published in 2011 found that corneal collagen cross-linking was safe and effective in improving visual acuity and corneal shape in patients with post-LASIK ectasia over a one-year period.
LASIK Alternatives That Reduce Risk of Ectasia
If pre-operative calculations for LASIK indicate your residual corneal bed might be too thin, causing an unacceptable risk of post-LASIK ectasia, your surgeon will inform you of this finding and that you are not an ideal candidate for LASIK.
In such cases, your surgeon might recommend other refractive procedures that will preserve thickness in the residual cornea bed.
Options include surface-based corneal laser surgery procedures such as PRK, LASEK and epi-LASIK. These are called "surface ablation" procedures because: 1) a corneal flap is not created (PRK), or 2) only an ultra-thin flap of corneal epithelium is created (LASEK or Epi-LASIK).
In either case, more underlying corneal tissue (stroma) remains intact for the excimer laser to reshape, thereby resulting in a thicker residual stromal bed after surgery, compared with LASIK.
If your risk of corneal ectasia after LASIK is high, your refractive surgeon also might recommend a lens-based vision correction surgery as an alternative, such as phakic IOL implantation or refractive lens exchange. These procedures do not remove any corneal tissue, thereby avoiding the risk of post-surgical ectasia.
Lens-based refractive surgery procedures have their own set of risks and rewards, which you should discuss thoroughly with your refractive surgeon prior to deciding if this is a good option for you.
Recently, some refractive surgeons have begun performing a combination PRK and corneal collagen cross-linking procedure for patients who may have an elevated risk of corneal ectasia after LASIK. This combination procedure both leaves a thicker residual stromal bed than LASIK and strengthens the corneal tissue as a precaution to reduce the risk of post-surgical ectasia.
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Note: This information is for general education purposes only. It is not to be used as a substitute for medical advice from your eye doctor or refractive surgeon.