Why the cornea
The cornea provides about two-thirds to three-quarters of the eye’s focusing power. A small change in its curve makes a large change in focus. Laser vision correction reshapes the cornea so that light lands sharply on the retina, reducing or removing the need for glasses or contact lenses.
- For nearsightedness, the centre of the cornea is made slightly flatter.
- For farsightedness, the cornea is made slightly steeper.
- For astigmatism, the steeper curve is evened out to match the flatter one.
The laser is guided by a computer and an eye tracker, which follows small movements of your eye during treatment.
The four procedures
SMILE Pro
A femtosecond laser shapes a thin disc of tissue, called a lenticule, inside the cornea. The surgeon removes it through a small opening. No flap is made. It treats nearsightedness and astigmatism.
LASIK
A laser creates a thin hinged flap on the surface of the cornea. The surgeon folds it back, an excimer laser reshapes the tissue underneath, and the flap is laid back down. Vision usually recovers quickly. It treats nearsightedness, farsightedness and astigmatism.
PRK
The thin surface layer of the cornea is removed, and the excimer laser reshapes the cornea directly. No flap is made, which can suit thinner corneas. The surface layer grows back over several days, so recovery is slower and more uncomfortable at first.
PRESBYOND
A laser treatment for people over about 40 who find reading harder. It sets the two eyes slightly differently so the brain can blend near, middle and far vision. See Presbyopia, and reading after 40.
Each procedure has its own page with recovery times, benefits, limits and risks: see NextGen Laser Vision.
Why screening comes first
Not every eye is suited to laser correction. A refractive screening checks:
- That your prescription is stable, usually unchanged for at least a year.
- Corneal thickness. Every treatment removes a little tissue. If too little is left, the cornea can weaken and bulge (ectasia), so thin corneas may need a different technique or none.
- Corneal shape. Conditions such as keratoconus, where the cornea is weak and cone-shaped, rule laser correction out.
- Dry eye. It should be found and treated first, especially in long-term contact lens wearers.
- Your general eye health, including cataract and glaucoma.
Before your screening, leave contact lenses out for the time reception advises. Lenses change the shape of the cornea for a while and can affect the measurements.
After treatment
- Dryness. A gritty feeling, mild blur that comes and goes, and sensitivity to light are common for the first weeks. Lubricating drops help, and it usually settles.
- Regression. The cornea is living tissue. It can thicken slightly as it heals and bring back a little of the old prescription, especially after high nearsightedness corrections. A further treatment is sometimes possible.
- Infection. This is rare, and careful technique and aftercare drops reduce the risk further.
Laser correction treats your prescription today. It does not stop the eye from ageing. Presbyopia and cataracts can still develop later.
This guide explains; it does not diagnose. Your doctor’s advice about your own eyes comes first.