What is Post-LASIK Ectasia?
Corneal ectasia is a severe complication occurring after LASIK surgery. The cornea is too thin from the amount of corneal tissue that was removed with the laser procedure or a prior corneal disease and begins to protrude forward.
Symptoms of Corneal Ectasia
Corneal ectasia causes uncorrected blurred vision with an increase in myopia or nearsightedness which may be associated with or without astigmatism. This is due to the steepening of the cornea. There may be a loss of best correctable vision as the ectasia progresses due to irregular astigmatism. There may be an increase in glare and halos around lights at night.
What Causes Post-LASIK Corneal Ectasia?
The central cornea thickness is too thin. This thinning and loss of corneal tissue stromal structure allows the cornea to become herniated forward in a similar manner to keratoconus. There is damage to the epithelial membrane, collagen scarring, thinning of the collagen layers, and lysis of tissue. Either the patient had a cornea disease that contributes to the thinning or too much tissue was removed in order to correct the person’s vision.
Risks Factors for Developing Post-LASIK Corneal Ectasia
Low Residual Stromal Bed Thickness
Most eye doctors fell that having a minimum of 250 microns of tissue remaining in the base of the cornea after the laser treatment is important in helping prevent the development of corneal ectasia. This does not guarantee that corneal ectasia will not occur but anything less than 250 microns increases the risk of developing corneal ectasia.
Low Pre-operative Corneal Thickness
If the person has a thin cornea to begin with, then they may not have enough cornea thickness present to have a LASIK procedure performed and leave the 250 micron bed thickness after the laser treatment. Other procedures such as LASEK may be more appropriate in these cases.
Abnormal Pre-operative Topography
Abnormal findings on the corneal topography such as keratoconus, pellucid marginal corneal degeneration, or forme frusta keratoconus are significant risk factors for developing corneal ectasia after LASIK.
Young patients may be a risk factor as certain corneal diseases may not present until later in life.
Treatment of Post-LASIK Corneal Ectasia
There are a number of different types of contact lenses that can be used to correct the vision after the ectasia cannot be corrected with glasses. Soft contact lenses, rigid gas permeable contact lenses, and hybrid-type contact lenses may be used to correct the vision.
Intracorneal ring segments such as Intacs can be placed in the corneal to support the thinning protruding cornea.
Collagen Cross-Linking of the Cornea
Collagen cross-linking has been shown in studies in the U.S. to strengthen the cornea and stop the progression of the ectasia. This treatment has not been approved yet in the U.S. but has been used in other areas of the world.
Penetrating keratoplasty (corneal transplant) is usually used as the last resort. Replacing the thinning cornea with a new cornea resolves the problem.