Excimer laser refractive surgery reshapes the curvature of the cornea to correct short sight, long sight and astigmatism. The laser removes a very thin layer of corneal tissue following a profile calculated from your prescription. The aim is to reduce dependence on glasses, not to abolish it as a matter of principle.
Who can be treated
No laser is approved for anyone under eighteen, and the prescription must have been stable for a year. Excluded or treated as high risk: thin corneas, large pupils, pre-existing dry eye, which surgery tends to aggravate, keratoconus, glaucoma, uveitis, herpes simplex, autoimmune disease, immunodeficiency and diabetes. Contact sports are a contraindication, and some employers and armed services prohibit the surgery outright, which is worth checking before rather than after.
What the outcome figures mean
A synthesis of 97 articles covering 67,893 eyes reported 99.5% of eyes better than 20/40, 90.9% within 0.5 dioptres of target and 98.6% within 1.0 dioptre, with loss of two or more lines in 0.61% and dissatisfaction in 1.2%. The verified figure is better than 20/40, not 20/20; where an advertisement claims 20/20, it has misread its own source.
Symptoms that go under-reported
A regulator-run quality-of-life study found over 95% of patients satisfied and under 1% with a lot of difficulty in daily activities. In the same study, among patients with no symptoms beforehand, up to 46% reported at least one new visual symptom at three months, including new halos in up to 40% and new dry-eye symptoms in up to 28%. Patients were more than twice as likely to report a symptom on a questionnaire as to mention it to their clinician, so clinic-collected satisfaction data systematically under-reports. The regulator also states that long-term safety and effectiveness are not known and that severe dry eye may be permanent.