Written by Dr GozlanOphthalmologist, refractive surgery · updated October 26, 2026
The operation
What is measured, why, and what the assessment decides.
No operation is performed without a complete preoperative assessment. It is painless and performed by the ophthalmic surgeon. It decides whether laser surgery is possible for your eyes, and which one: Dr Gozlan chooses the technique based on these results.
| Test | Why |
|---|---|
| Refraction | Precise measurement of the correction needed (myopia, astigmatism, hyperopia), checked after pupil dilation if needed. |
| Corneal topography and tomography | A map of the shape of the cornea. It detects early keratoconus in particular, which rules out laser surgery. |
| Pachymetry | Measurement of corneal thickness. It determines whether LASIK (flap) is possible or points towards PRK (surface). |
| Aberrometry | Analysis of the optical quality of the eye, used to fine-tune the treatment. |
| Pupil diameter | Helps anticipate the quality of night vision. |
| Eye surface and tears | Significant dryness must be treated before any surgery. |
| Eye pressure and fundus examination | Examination of the retina and optic nerve, particularly in high myopia. |
| Near vision and dominant eye | Determines which eye will be set for distance vision, with a micro-monovision trial if needed to check that it suits you. |
Contact lenses temporarily change the shape of the cornea and distort the measurements. They must be removed a few days (soft lenses) to several weeks (rigid lenses) before the assessment; you will be told the exact timing.
The assessment takes place in Paris (16th arrondissement). If you come from far away, it can be scheduled just before the surgery session. The first exchange can take place remotely; the measurements are always taken in person.
See also: the techniques, the day of surgery and the fees.
This general information does not replace a consultation. Like any surgery, refractive surgery carries risks, which are explained during the consultation.