How to read the report
of your preoperative examination.

After the diagnostic examination, the patient receives a complete report on their patient portal. The numbers are not random — each one contributes to the decision whether to operate or not, and to the choice of ablation profile. Here is how to read them.

Refraction: sphere, cylinder and axis

The line you see on the spectacle prescription — for example -3.50 -1.25 × 175° — contains three pieces of information.

The sphere (first number) indicates the main defect. A negative number (-3.50) means myopia: the eye is too long and the focus falls in front of the retina. A positive number means hyperopia: the eye is too short. Zero means emmetropia — perfect distance vision.

The cylinder (second number) indicates astigmatism. -1.25 D means the cornea is more curved in one meridian than the other, creating two different focal points. The higher the number, the more distorted the vision.

The axis (175°) indicates the direction of astigmatism — at how many degrees the flattest meridian lies. This data is critical for the laser: an axis error of 10° leaves one third of the astigmatism uncorrected.

Keratometry: K1, K2 and Km

Keratometry measures the curvature of the cornea, expressed in dioptres. K1 is the curvature of the flattest meridian, K2 that of the steepest meridian, Km is the average. Normal values range between 42.00 and 46.00 D.

The difference between K1 and K2 is the corneal astigmatism. If K1 is 43.00 and K2 is 44.50, the corneal astigmatism is 1.50 D. If the difference between K1 and K2 does not match the cylinder of the refraction, it means there is an internal (lenticular) astigmatism in addition to the corneal one — an important piece of data for treatment planning.

A Km below 41 D or above 48 D deserves attention: corneas that are too flat or too steep may have less predictable postoperative behaviour.

Pachymetry: corneal thickness

Pachymetry is the thickness of the cornea, measured in micrometres (µm). The average central value is around 540 µm. But the value that truly matters is the thinnest point, which may be located 1-2 mm from the centre.

The laser removes tissue to correct the defect. The residual thickness after ablation must not drop below 250 µm of stroma. If your report shows a pachymetry of 490 µm and a myopia of -8 D, the calculation may not work — and this is why not everyone can have surgery. Learn more: Thin corneas: when NOT to operate →

Mesopic and dynamic pupillometry

The pupil diameter changes with light. The report shows the diameter under mesopic and dynamic conditions. A very large pupil in low-light conditions (greater than 7 mm) means that at night the pupil could exceed the optical zone treated by the laser — causing halos around lights. The surgeon takes this into account when planning the optical zone.

The topographic map: the colours

The colour maps of the MS-39 report show corneal curvature point by point. Warm colours (red, orange) indicate more curved zones — higher refractive power. Cool colours (blue, green) indicate flatter zones — lower power.

A symmetrical map, with a yellow-orange centre and green-blue periphery, corresponds to a normal cornea. An asymmetrical map — with a lower red island, for example — may indicate subclinical keratoconus. This is why tomography with 25,000 points is superior to simple keratometry: the anomalous patterns emerge from the map, not from the numbers.

Aberrometry

The Peramis report shows the optical aberrations of the entire eye: lower-order aberrations (sphere and cylinder — those corrected by glasses) and higher-order aberrations (coma, trefoil, spherical aberration — those that only wavefront-guided laser can treat). A high total aberration may lead the surgeon to choose a personalised ablation profile rather than a standard one.

Ocular dominance

The report indicates which eye is dominant — the eye the brain prefers for primary visual information. This data is decisive for presbyopia correction with PresbyMAX: the dominant eye is corrected for distance vision, the non-dominant for near vision.

The ForeSight simulation

The last element of the report is the ForeSight simulation: a map of the cornea after the procedure, calculated from your data. It is not a generic prediction — it is an individual simulation that shows the expected postoperative keratometry, the resulting aspheric profile and the safety margins. It is the document that allows you to decide with data, not with trust.

In summary

The preoperative report is not a bureaucratic document — it is the X-ray of your decision. Every number has a direct clinical meaning. If something is unclear, ask. The optometrist and Dr Mossa are available to explain every detail. A patient who understands their data is a patient who makes better decisions.