Thin corneas: when
NOT to operate.

Over the course of my career, I have performed more than 25,000 eye surgeries. A significant part of my work, however, consists of not operating: explaining to the patient why, in their specific case, laser surgery is not the best choice. This is a medical act just as important as the procedure itself.

Among the most frequent reasons for exclusion is corneal thickness. But the concept of a "thin cornea" is often misunderstood — both by patients and, sometimes, by those who advise them.

What is corneal thickness and why it matters

The cornea is the transparent lens on the surface of the eye. It has an average thickness of approximately 540 µm at the centre — just over half a millimetre. Laser refractive surgery works by reshaping this tissue: to correct myopia, for example, the central zone is thinned.

The principle is simple: if too much tissue is removed, the biomechanical structure of the cornea weakens. A cornea that is too thin after the procedure can deform over time — a condition called corneal ectasia. Preventing this is the absolute priority of every responsible refractive surgeon.

The magic number doesn't exist

Many patients arrive for their consultation having read that below 500 µm surgery is not possible. In reality, there is no universal threshold. Corneal thickness is one of the assessment parameters — not the only one, nor even the most important.

How we measure: 25,000 points, not just one

Traditional pachymetry — an ultrasound probe that measures a single point at the centre — is insufficient for such an important clinical decision. In our clinics, we use the MS-39 corneal tomographer, which analyses the cornea with over 25,000 measurement points.

This instrument produces a complete three-dimensional map: thickness point by point, anterior and posterior curvature, elevation profile, epithelial distribution. We do not look at a number: we examine a complete biomechanical profile.

The parameters we assess beyond thickness

The decision to operate or not is based on a set of factors, analysed in their reciprocal clinical context: anterior and posterior corneal topography, epithelial thickness and distribution, the corneal asymmetry index, anterior chamber depth, pupil diameter, the stability of the refractive defect over time, and the patient's age.

Every diagnostic visit in our protocol also includes Peramis aberrometry, which measures the optical aberrations of the entire visual system — not just the cornea. This level of detail allows us to identify at-risk profiles that a traditional pachymeter would not detect.

TransPRK: an advantage for thinner corneas

Not all laser techniques remove the same amount of tissue. TransPRK SmartSurfACE, the technique we use as our primary protocol, works directly on the corneal surface without cutting a flap. This means it saves approximately 100-120 µm of tissue compared to traditional LASIK.

In practical terms: a patient who is not eligible for LASIK due to a borderline cornea could be perfectly eligible for TransPRK. This is one of the reasons we chose this technology as the standard in our four clinics.

ForeSight AI: simulate before deciding

Before each procedure, the ForeSight system integrated into the AMARIS laser produces a predictive simulation of the expected result. The patient sees — literally — what the estimated outcome will be based on their actual data: topography, aberrometry, thickness.

When a cornea is at the limit of eligibility, this simulation becomes even more valuable. It allows us to evaluate different scenarios and make the decision with the patient, not for the patient.

When we say no

There are situations where the answer is clear and non-negotiable. If tomography shows signs of keratoconus — even subclinical — the procedure is not performed. If corneal biomechanics are compromised. If the refractive defect is too high for the available thickness. If the patient is too young and myopia has not yet stabilised.

In these cases, our role is to explain why with clarity and respect, and to propose existing alternatives: specialised contact lenses, implantable phakic lenses (ICL), or simply waiting.

Saying no is an act of medical competence, not a failure. A surgeon who operates on every patient who walks in is not practising good medicine.

What to do if you have been told your corneas are thin

If an ophthalmologist has told you that you are not operable due to corneal thickness, the advice is simple: get a second assessment with state-of-the-art instrumentation. A single pachymetry number is not a diagnosis.

During our diagnostic consultation — free and without obligation — we analyse the cornea with MS-39, Peramis and ForeSight simulation. If the procedure is safely possible, we will explain how. If it is not, we will say so with equal clarity.