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The pre-operative assessment for refractive surgery
An hour of tests that decides everything: whether you are eligible for surgery, which technique, and what correction. It is the only appointment that can answer these questions.
Why it cannot be shortened
None of the questions you are asking can be settled by a single test. The thickness of your cornea determines what is possible, its shape determines what is safe, your prescription determines what is needed, and the condition of your retina determines what must be treated first.
A rushed assessment leads to one of two mistakes: operating on an eye that should not have been operated on, or turning down an eye that could have been.
What is measured
Corneal topography
It maps the curvature of your cornea, front and back surfaces, point by point. This is the test that detects keratoconus or early weakness of the cornea: the most important contraindication to know about, because laser treatment on a weak cornea can make it worse, irreversibly.
Pachymetry
It measures the thickness of the cornea to the nearest micron. From this we work out what will remain after treatment: this figure decides between LASIK and Trans-PRK, or points towards a phakic lens if the cornea allows neither.
Refraction, with and without cycloplegia
Your prescription is measured twice: under normal conditions, then after eye drops that temporarily block accommodation (the eye's focusing effort). This second measurement reveals your actual prescription, which focusing effort can mask, especially in young people with hyperopia (long-sightedness).
Aberrometry and pupil size
Aberrometry analyses fine optical defects, beyond the basic prescription. The size of your pupil in low light is also measured: a large pupil makes halos at night more likely, and this influences the optical zone programmed into the treatment.
The tear film
Existing dry eye gets worse after surgery, especially after LASIK. It is checked for every time and, if present, treated before the operation rather than after.
Dilated eye examination
The peripheral retina is examined for a tear or a weak area, particularly in people with high myopia. Any lesion found is treated with laser first, and surgery is postponed while it heals. That is the whole point of this examination, which is often seen as an optional extra.
Stop wearing your contact lenses before you come
One week for soft lenses, two for toric lenses, at least three for rigid lenses, several months for orthokeratology. A cornea still marked by the lenses gives wrong measurements. Why this delay matters.
How the appointment goes
Allow about an hour. Dilating the pupils, which is needed for the retinal examination and for refraction under cycloplegia, makes your vision blurred and light dazzling for three to four hours. Do not plan to drive home, and avoid scheduling a meeting straight afterwards.
Bring your old glasses prescriptions if you have them: they show whether your prescription is stable, which is essential before any surgery.
What you leave with
A clear answer: eligible or not, by which technique, with what expected result and what risks. A detailed written quote that you can send to your top-up health insurer (mutuelle). And time to think it over: no decision is made on the day.
The assessment is charged even if surgery is not recommended. It belongs to you, and its measurements remain valid if you consult elsewhere.
Dr Emmanuel Halimi
Ophthalmic surgeon · RPPS 10100555084 · Medical Council of Hauts-de-Seine no. 92/23003
Page written and approved by the surgeon.
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