How laser eye surgery works: LASIK, LASEK, SMILE and Presbyond explained by a UK consultant

Laser eye surgery works by using a cold ultraviolet laser — the excimer laser — to remove microscopic amounts of tissue from the front surface of your eye (the cornea), reshaping its curvature so that light focuses precisely on the retina. In a short-sighted eye the cornea is flattened; in a long-sighted eye it is steepened; in astigmatism it is smoothed out. The excimer laser removes tissue without generating any heat and is accurate to a fraction of a micron — which is why it can safely reshape a living cornea.

There are now four widely used ways to deliver that reshaping to the cornea: LASIK, LASEK/PRK, SMILE and Presbyond. Each achieves the same goal — reshaping the cornea — but uses a different method to access the layer of cornea being treated. Choosing between them is a consultant decision based on your corneal thickness, prescription, tear film and lifestyle.

If you would like to talk through which technique is right for your eyes, you can book a free 15-minute call or read the full laser eye surgery service page and 2026 UK price guide. For a plain-English discussion of the risks, see our companion post is laser eye surgery safe?.

The physics: what an excimer laser actually does

An excimer laser produces a pulsed ultraviolet beam at 193 nm. At that wavelength, each pulse breaks the molecular bonds of a paper-thin layer of corneal tissue and vaporises it, with essentially no heat transferred to surrounding tissue. A modern laser fires 400–1000 pulses per second, each removing about a quarter of a micron of tissue — approximately 1/400th the thickness of a human hair. Wavefront and topography-guided software delivers a bespoke ablation pattern that corrects your specific prescription and any subtle higher-order aberrations of your eye.

LASIK — how it works step by step

LASIK (Laser-Assisted In Situ Keratomileusis) is the most widely performed refractive procedure in the world. The surgeon first uses a femtosecond laser to create a thin, hinged flap in the front of the cornea — about 100–120 microns thick and roughly the size of a contact lens. The flap is gently lifted back to expose the underlying corneal stroma. The excimer laser then reshapes the stromal bed for 15–40 seconds, depending on prescription. The flap is repositioned and adheres without stitches within minutes. Total procedure time: around 10 minutes per eye. Functional vision by the next morning is typical.

LASEK and PRK — the surface techniques

LASEK and PRK are surface treatments that do not involve a flap. Instead, the very thin outer skin of the cornea (the epithelium) is gently removed or lifted, the excimer laser reshapes the cornea directly, and a protective bandage contact lens is placed on the eye for 4–5 days while the epithelium regrows. Visual recovery is slower and more uncomfortable than LASIK for the first week, but the long-term result is identical. Because no flap is created, LASEK is often the safest option for patients with thinner corneas, borderline topography, or high-impact professions (military, contact sports, martial arts).

SMILE — small-incision lenticule extraction

SMILE (SMall Incision Lenticule Extraction) is a flapless keyhole technique performed entirely with a femtosecond laser. The laser sculpts a thin, contact-lens-shaped disc of tissue (a lenticule) within the intact cornea and creates a small 2–4 mm side incision. The surgeon then removes the lenticule through that keyhole opening, and the cornea's shape changes to correct the prescription. Because more than 80% of the corneal surface is left untouched, SMILE preserves more corneal nerves — which is why it typically produces less post-operative dry eye than LASIK. It is currently approved in the UK for myopia and myopic astigmatism.

Presbyond — blended vision for patients over 45

Presbyond is a LASIK-based protocol designed for patients in their mid-40s and beyond who are starting to lose their near vision (presbyopia). It uses a customised, micro-monovision ablation profile — the dominant eye is set slightly for distance, the non-dominant eye slightly for near — with a controlled increase in depth of focus that the brain blends into a continuous range of vision. Around 95% of well-selected patients achieve spectacle-free distance and intermediate vision, with most also managing everyday near tasks without glasses.

What happens on the day

The day of surgery is straightforward and quick. Anaesthetic drops numb the eye so you do not feel the procedure; you are awake throughout and asked simply to look at a fixation light. A soft suction ring gently holds the eye still for a few seconds while the femtosecond laser does its part; the excimer laser then reshapes the cornea for 15–40 seconds per eye. Most patients describe the treatment as strange rather than painful. You walk out of theatre with functional vision, dark glasses to reduce glare, and a plan for aftercare drops. Same-day follow-up or a next-day check is standard.

Recovery and results

With LASIK and SMILE, most patients drive and return to work within 24–48 hours. With LASEK, the first 3–5 days are more uncomfortable and vision fluctuates for 1–2 weeks. All techniques reach their final refractive result by 3–6 months. Enhancement (a small retreatment) is available if the initial result is not quite on target — usually in 1–3% of eyes.

Am I a candidate?

Suitability depends on age (usually 21+ with a stable prescription for at least 12 months), corneal thickness and shape, prescription range, tear film health, general medical health and realistic expectations. A full 60–90 minute assessment including corneal topography and tomography is the only reliable way to answer 'am I suitable?' — for a plain-English list of who should not have laser surgery, see is laser eye surgery safe?.

Related reading: is laser eye surgery safe?, the Snellen chart and vision correction guide, our laser eye surgery and lens replacement surgery pages, the 2026 UK laser price guide, our full service list and the consultant ophthalmologist overview. Related condition post: keratoconus — the condition that must be excluded before any laser treatment.

To find out which technique suits your eyes, book a free 15-minute call with a UK consultant or request a full consultation.