Myopia in young adults:
when it is stable
and when to operate.

Myopia is the most common refractive error in the world. In Europe, over 40% of young adults are myopic. The temptation to have surgery as soon as turning 18 is understandable — but haste is the worst enemy of a good result.

Why myopia is not stable at 18

Myopia is caused by an eyeball that is too long relative to the optical power of the cornea and crystalline lens. This elongation is an active process that typically begins in childhood and continues until age 20-25, sometimes beyond. Operating on a myopia that is still progressing means achieving an excellent result on the day of surgery — and finding yourself myopic again a year later. Not because the laser did not work, but because the eye continued to elongate.

How to verify stability

The criterion is simple but requires time: the refraction must not have changed by more than 0.50 D in the last year. In practice, at least two refractions are needed — three ideally — spaced 6-12 months apart, showing stable values. A single visit is not enough: a documented refractive history is required.

If the patient is 20 and their myopia has gone from -3.00 to -3.75 in the last year, it is not stable. We send them back and see them again in 12 months. It is not a punishment — it is the guarantee that the laser result will be permanent.

Unmasking accommodation: the true refractive error

The refraction the patient knows — from their glasses — is the subjective refraction. But in young people, the crystalline lens can unconsciously "accommodate" during measurement, masking the true defect. This is particularly critical in young hyperopes, where accommodation can hide entire dioptres of hyperopia — the patient believes they are emmetropic or slightly hyperopic, while their real hyperopia is significantly higher.

Modern autorefractometers use an integrated defocus system to relax accommodation during automatic measurement: they present a blurred image that prevents the lens from contracting. This reduces the risk of overestimating myopia or underestimating hyperopia at the instrumental measurement stage.

During subjective refraction, when residual accommodation is suspected — typically in patients under 30, and especially in hyperopes — we use a manual defocus test: a positive lens is inserted that "defocuses" distance vision, forcing accommodation to relax, and the refraction is refined on this relaxed basis. This test is quick, non-invasive, and in most cases sufficient to obtain the true refraction.

How much myopia can be corrected?

The excimer laser routinely corrects myopia up to -8.00 / -10.00 D, provided corneal thickness allows it. For each dioptre of myopia, the laser removes approximately 12-15 µm of corneal tissue (in the standard 6.5 mm optical zone). A myopia of -6.00 D requires removing approximately 70-90 µm — on an average cornea of 540 µm.

The critical parameter is not myopia itself but residual tissue after ablation. The accepted safety limit is at least 250 µm of residual stroma beneath the ablation. For TransPRK, which creates no flap, the tissue saved compared to LASIK is approximately 100-120 µm — a significant advantage for moderate-to-high myopia. Learn more: Thin corneas: when NOT to operate →

High myopia: when laser is not enough

For myopia above -10.00 D or when the cornea is too thin, laser is not the solution. The alternative is the phakic ICL (Implantable Collamer Lens): a lens positioned inside the eye, in front of the crystalline lens, without removing corneal tissue. The ICL is reversible — the lens can be removed — and preserves corneal biomechanics intact. However, it is essential to be informed that this is an intraocular procedure, with a different and higher risk profile than corneal laser surgery: the risks — although rare — include endophthalmitis, induced cataract, pupillary block glaucoma, retinal detachment and endothelial cell loss. The decision must be made with full awareness.

Our advice to young myopes

Don't rush. Have your refraction checked every year. When you have at least 12 months of documented stability, come for a free diagnostic examination. We measure everything — MS-39 topography, Peramis aberrometry, cycloplegic refraction if needed, ForeSight simulation — and tell you with certainty whether it is the right time. If not, we tell you when to come back.

A year of waiting for a permanent result is a smart investment. A premature correction that needs redoing is an avoidable risk.