Surgical Treatments

Potential Side Effects

Undercorrection or Overcorrection

Many factors affect the final results, including

The degree of the healing response of the eye
The hydration of the cornea during the procedure
The individual laser and its calibration
The temperature and humidity of the laser room

If any of these variables results in undercorrection, additional laser treatment can be performed after three months when the results have stabilized.

Induced or Irregular Astigmatism

Occasionally astigmatism occurs in an eye that had none prior to treatment. The cause of this isn't well understood. A combination of factors might contribute, such as the alignment of the patient's eye and uniformity of the laser beam. Fortunately, the amount of astigmatism created is generally small, with little effect on uncorrected visual acuity.

A more serious problem results if the surface is left with any unevenness after LASIK. This will create an irregular astigmatism that will reduce visual acuity. This may require the use of glasses or gas permeable contact lenses to achieve the best possible vision.

Lost of best-corrected visual acuity

It's presumed that following LASIK, patients could wear glasses or contact lenses and achieve the best vision they had preoperatively. For example, if preoperative vision is 20/400 without glasses and 20/20 with them, after laser surgery, uncorrected visual acuity may improve to 20/30, and with a new prescription for thinner eyeglasses the patient could still enjoy 20/20 vision.

However, if a patient sees improvement of uncorrected visual acuity from 20/400 to 20/30, but can't be made to see any better than 20/30 with new glasses, then that patient has lost best-corrected acuity. This occurs less than 5% of the time in patients with low to medium myopia, and somewhat more often in those with high myopia.

Visual Aberrations

Corneal Haze — The normal response of the cornea following LASIK is to heal. If that response is exaggerated, the cornea can develop a hazy, ground-glass appearance; this can be reduced or eliminated with the use of topical anti-inflammatory eyedrops. More dense haze may require retreatment to eliminate the haze and return the proper correction.
Decreased Night Vision, Halos, and Starbursts — The manner in which a LASIK-treated eye refracts light can create an effect similar to nighttime vision with contact lenses. There may be some reduction in brightness, as well as some glare and starburst patterns around lights. These effects are generally mild and most patients have few complaints.
Blindness — Though blindness is virtually unheard of following LASIK surgery, it remains a possibility. A serious and potentially sight-threatening infection inside the eye known as endophthalmitis could occur. The cornea could also be damaged by the cutting procedure during LASIK, or its surface made so irregular that vision could be distorted to the point of legal blindness.

Flap Anomalies

Thin Flap — Very rarely during the LASIK procedure a thinner-than-desired flap will be created. A thin flap needs to be flipped back in position and allowed to heal. There are no reported cases in which this resulted in permanent loss of vision. The procedure can usually be performed again after three months.
Incomplete Flap — If the cutting blade is physically obstructed along its track, a partial flap will be created. This is more likely to occur in deep set, narrow eyes for which adequate exposure is difficult to achieve. The thickness of the cut will be fine, but it will not extend fully across the cornea as needed. There have been cases in which the surgeon has attempted to continue despite a partial flap, and incorrect treatments have resulted.
Flap Striae — Folds or wrinkles in the flap are known as "striae." Striae disturb the smooth refractive surface of the cornea and thereby reduce vision. Any physical contact the eye undergoes, such as getting hit or rubbed, can displace the flap during the first few days after surgery. If any striae are detected, the flap needs to be lifted and refloated into place, with gentle wiping to stretch out any folds. The longer the folds remain in place, the harder it will be to remove them. However, striae have been successfully removed even months after the initial procedure.
Free Cap or Lost Cap — A free cap occurs when the flap is cut completely across the cornea, leaving no connecting tissue (hinge). A free cap may dislodge after surgery and become lost, similar to a contact lens popping out. An experienced surgeon can anticipate and easily manage a free cap. Also, patients have healed normally without the cap and achieved excellent vision.

Change In Corneal Itegrity

"Sands of the Sahara" (Diffuse Lamellar Keratitis) — On rare occasions, a noninfectious substance develops beneath the flap. This cloudy accumulation of inflammatory cells gives the appearance of swirling sand and has been dubbed "Sands of the Sahara." Its exact cause is unknown. Sands of the Sahara is successfully treated by aggressively increasing steroid eyedrops. Severe cases may require lifting the flap and mechanically removing the inflammatory debris with a small surgical instrument.
Epithelial Ingrowth — The corneal epithelium must be cut through by the surgical blade in order to get to the underlying layer of the cornea. As it does so, it's possible that loosened epithelial cells can implant themselves beneath the flap. There they can grow as a cluster or as a sheet of cells. This isn't a problem, but it needs to be observed closely because the growth can continue centrally toward the vision-critical center of the cornea. The incidence of epithelial ingrowth is very low, and most patients who experience this don't require treatment.

Other Effects

Decentered Ablation — If the laser treatment isn't centered around the pupil, the results may be less than desired. It will mean that some of the light entering the eye will be focused properly and some will not. This is why it's so important to fixate on the aiming beam of the laser. Many of today's new lasers have eye-tracking beams that significantly reduce the possibility of decentered ablation.
Increased Intraocular Pressure — Steroid eyedrops are used in the post-operative management of LASIK patients to reduce the potential for inflammation. Steroids have a tendency to increase the natural pressure in the eye. Sometimes, in some patients, it can rise high enough to damage the optic nerve. This is why steroid eye drops are used for no more than 10 to 14 days following LASIK surgery. Discontinuing the steroid drops usually results in the pressure returning to normal levels.
Lens Abnormality — Clouding of the crystalline lens is referred to as a cataract. It's a natural occurrence with age and it can sometimes be hastened with almost any type of invasive ocular surgery. Post-operative steroid use to control inflammation can contribute to this.
Ptosis — A lid speculum is used during LASIK to hold the eyelids wide open. This can stretch or inflame the muscles responsible for opening the eyelid and can result in a droopy eyelid. This usually clears up on its own.
Infection and Ulceration — Rarely, infection leading to ulceration can occur beneath the flap following LASIK. This area is closer to the inside of the eye, raising the risk of penetration of the infection into the eye. Therefore, infection needs to be treated aggressively. Because the corneal epithelium is only minimally disrupted by LASIK, the chance of a corneal infection is very low — about one in 5,000 cases.

The primary source for information provided here is How to See Like a Hawk When You're Blind as a Bat by Dr. Matthew Ehrlich. Consult this book (available at www.lasikbook.com) for even more information about LASIK.