Ophthalmology · Refractive surgery
Refractive surgery, in 3D
Three techniques, three different locations: PRK and LASIK act on the cornea; the phakic ICL lens is implanted inside the eye. Scroll to walk through all three; rotate the model with two fingers (or by dragging with the mouse) at any time.
1 · The starting point
Where light is focused
The cornea provides about two thirds of the eye’s focusing power; the crystalline lens adds the rest and adjusts focus. All three techniques work on the cornea or in the space between the two.
Cornea: 0.55 mm at the centre · Eye: 24 mm in diameter
Technique 1 of 3 · Surface laser
PRK
Photorefractive keratectomy: the laser works directly on the corneal surface, without creating a flap.
2 · PRK1 / 2
The epithelium is removed
The epithelium is the most superficial layer of the cornea. It is removed over an area of about 9 mm to expose the stroma, the tissue that holds the curvature.
2 · PRK2 / 2
The laser reshapes the surface
The excimer laser flattens the first microns of the stroma within an optical zone of about 6.5 mm. No flap is created: the epithelium grows back over the new curvature within days.
Working depth: 0 – 0.1 mm
Technique 2 of 3 · Laser under a flap
LASIK
The laser works within the stroma, protected under a flap that is repositioned at the end.
3 · LASIK1 / 3
A flap is created
A femtosecond laser traces a plane within the stroma, about 120 microns below the surface, leaving a hinge at the upper edge. The epithelium remains intact on that flap.
3 · LASIK2 / 3
The laser works underneath
With the flap lifted, the laser reshapes the exposed stroma. The treated surface lies inside the cornea, not on its outer face.
Working depth: 0.12 – 0.25 mm
3 · LASIK3 / 3
The flap is repositioned
The flap is returned to its place over the treated bed and adheres without stitches. Because the epithelium was not disturbed, early discomfort and visual recovery are usually milder than with PRK.
Technique 3 of 3 · Intraocular lens
Phakic ICL lens
The cornea is not modified: a lens is implanted behind the iris and the crystalline lens is preserved.
4 · Phakic ICL lens1 / 2
The lens goes in folded
Through an incision of about 3 mm, a folded lens is inserted and unfolds once inside the eye. No corneal tissue is removed and the curvature is unchanged.
4 · Phakic ICL lens2 / 2
It sits between the iris and the lens
The lens rests in the sulcus, behind the iris, and forms a vault that keeps it separated from the crystalline lens. The natural lens is preserved: that is why it is called phakic.
Depth: ≈ 3 mm from the surface
5 · The three, in contrast
What sets them apart
All three correct the prescription, but they do different things to the eye’s tissue. From the outside, once healed, the eye looks the same in all three cases.
- PRK. Removes tissue at the corneal surface. No flap, with the epithelium regenerating afterwards.
- LASIK. Removes the same tissue, but inside the stroma and under a flap that is repositioned.
- ICL. Removes no tissue: it adds a lens inside the eye, and that lens can be removed.
Summary
| Technique | Where it acts |
|---|---|
| PRK | Corneal surface: epithelium and anterior stroma |
| LASIK | Corneal stroma, under a flap of about 120 µm |
| Phakic ICL lens | Inside the eye: behind the iris, over the crystalline lens |
The technique is chosen after the assessment
Suitability for one technique or another depends on the prescription and its stability, the cornea, the ocular surface and the rest of the eye. The assessment first decides whether surgery is advisable; the technique comes afterwards.
To learn more: Guide: refractive surgery options · Guide: surgery day
Also in 3D: the cataract, seen from the inside · Also in 3D: glaucoma, from the healthy eye to surgery · Also in 3D: keratoconus and its treatment
Illustrative 3D model for information purposes; measurements are approximate and thicknesses are exaggerated for clarity. It does not replace an individual assessment by your ophthalmologist.
Authorship, medical review and sources
- Author and medical reviewer
- Dr. Francisco Javier Abellán Martínez
- Ophthalmologist · Medical registration no. 282880215
- The same specialist currently authors and medically reviews the content; this is not presented as an independent external review.
- Last medically reviewed
Sources consulted (2)
- Refractive surgery patient information (Opens in a new tab)The Royal College of Ophthalmologists
- Refractive surgery standards and guidance (Opens in a new tab)The Royal College of Ophthalmologists
General educational content. It does not replace an individual assessment, diagnosis or personalised instructions from your healthcare team.
How these guides are written and reviewed