Should I stop wearing contact lenses before the assessment, and for how long?

It is the most common question before an assessment, and the one whose answer is most often misunderstood. Many patients stop the day before, in good faith, and the assessment has to be done again.

Why this waiting period exists

A contact lens rests on the cornea and presses on it constantly. It slightly alters the curvature of the cornea and how hydrated it is. The effect is reversible, but it does not wear off in a few hours.

Yet the pre-operative assessment measures exactly this curvature, by topography, and the thickness of the cornea, by pachymetry. These measurements decide which technique is chosen and the correction programmed into the laser. A cornea still distorted by contact lens wear gives wrong measurements, and therefore an unpredictable result.

How long to stop

• Soft lenses: stop one week before the assessment.
• Soft toric lenses, for astigmatism: two weeks.
• Rigid gas-permeable lenses: at least three weeks, sometimes longer.
• Orthokeratology, lenses worn overnight: several months, because the cornea is deliberately reshaped.

These periods apply before the assessment, and again before the operation if a long time has passed in between.

What happens if you stop too late

The assessment goes ahead, the measurements are recorded, and the topography shows an irregularity. There are two possibilities. Either the irregularity is clearly due to the lenses, and the test simply has to be repeated. Or it is ambiguous, and it becomes impossible to tell a temporary distortion from a genuine weakness of the cornea.

The second case is the more troublesome. A weak cornea is an absolute contraindication to LASIK. Being unable to decide means postponing, repeating tests, or ruling out, as a precaution, a technique that would have been possible.

A few practical points

You will need to wear your glasses for the whole of this period. It is a constraint, and it is the main reason people stop too late. Plan for it when you book the appointment, not the week before.

If your glasses are not up to date, tell us. It is better to move the assessment back by two weeks than to come with a cornea that has not settled.

Finally, tell us honestly how long you actually went without your lenses. A patient who says one week when they stopped three days before skews the interpretation without realising it. No one will hold it against you: we simply reschedule.

Sources Société Française d'Ophtalmologie (French Society of Ophthalmology), recommendations for the pre-operative assessment in refractive surgery.
American Academy of Ophthalmology, Preferred Practice Pattern, refractive surgery.