Refractive errors can be corrected in three ways - Spectacles, Contact Lenses and Refractive Surgery. The most popular refractive surgery worldwide is LASIK.

Other procedures are PRK (Photorefractive keratectomy), LASEK (Laser assisted sub-epithelial keratectomy), IntraLASIK (Femtosecond Laser Microkeratome LASIK) and sometimes intra-ocular lenses (phakic IOL).

Range (Scope)

1 to 20 diopters of myopia
1 to 8 diopters of hypermetropia
Up to 8 diopters of astigmatism

Pre-procedure considerations

More than 18 years of age with stable refraction, should not be pregnant at the time of the procedure.

The eyes are examined for any disease that may adversely effect the outcome of the procedure.

Contact lens users are advised to stop wearing lenses 7 days prior to the procedure in case of soft contact lenses and six weeks or more for hard or semi-soft contact lens users.

Corneal surface mapping and thickness measurements are taken so that the surgeon can decide how much of the cornea needs to be worked on.

An anti-biotic eye drop is prescribed for a couple of days prior to the procedure.

Procedure

The thickest part of the cornea is its middle layer called the stroma. The LASIK LASER (193 nm EXIMER LASER) remodels this area of the cornea under a thin flap of the outer layer of the cornea that is later repositioned after remodelling.

During remodelling the machine uses and eye tracking system to compensate for minute involuntary and voluntary eye movements automatically redirecting LASER energy for placement within the target area.

Generally a mild sedative and anesthetic eye drops are instilled before the procedure.

Difference from LASEK and PRK

In LASEK the corneal epithelium is preserved with a chemical solution, peeled off, and replaced after the laser ablation is complete. In PRK the epithelium removed is discarded and allowed to regenerate

Post-procedure

Anti-biotic and anti-inflammatory eye drops are prescribed for a few days after the procedure.

Some patients may also need lubricating eye drops (artificial tears) for some time.

Complications

3-6% of the patients suffer some or the other form of complications up to 6 months after the procedure.

Immediate complications that are resolved are more common.

Sub-conjunctival hemorrhage
Dry eye
Over and under correction
DLK (diffuse lamellar keratitis - Sands of Sahara syndrome)
Visual disturbances (fluctuation in vision, startbursts, halos, glare, photophobia (light sensitivity), double vision, ghost images.
Flap striae
Epithelial ingrowth under the flap
Displaced flap
Corneal infections
Corneal ectasia
Macular hole

Longterm implications

The CCT (central corneal thickness) is permanently altered during the procedure. CCT is extremely important for accurately measuring the intra-ocular pressure necessary in Glaucoma screening and treatment.

The changes also affect the calculations used to select the correct intraocular lens implant when you have cataract surgery. This is known to ophthalmologists as a "refractive surprise".

Although the cornea usually is thinner after LASIK, because of the removal of part of the stroma, refractive surgeons strive to maintain a minimum thickness to avoid structurally weakening the cornea. Decreased atmospheric pressure at higher altitudes has not been demonstrated as extremely dangerous to the eyes of LASIK patients, however, some mountain climbers have experienced a myopic shift at extreme altitudes.