Corneal topography MS-39:
why 25,000 data points
change the diagnosis.

In refractive surgery, the quality of the diagnosis determines the quality of the result. Not the surgical gesture — which takes 20 seconds — but the micrometric understanding of the cornea — to the thousandth of a millimetre — on which that gesture is performed. The corneal tomographer is the instrument that makes this understanding possible.

In our clinics, we use the CSO MS-39, distributed by SCHWIND as an integral part of their diagnostic ecosystem. It is the instrument on which every one of our clinical decisions rests.

What the MS-39 measures

The MS-39 combines two complementary technologies in a single device: a Placido disc for anterior surface topography and a spectral-domain OCT (SD-OCT) for tomography of the entire anterior segment. The result is a three-dimensional map of the cornea with over 25,000 measurement points, an axial resolution of 3.6 µm and cross-sections over a diameter of 16 mm.

In clinical terms, this means the MS-39 simultaneously produces: the curvature map of the anterior surface (from the Placido), the curvature map of the posterior surface (from the OCT), point-by-point pachymetry across the entire cornea (not a single value at the centre), the anterior and posterior elevation profile, the epithelial map separate from the stromal map, and high-resolution imaging of the anterior chamber, iris and crystalline lens.

1 point vs 25,000 points

An ultrasound pachymeter — the traditional instrument — measures corneal thickness at a single point in the centre. The surgeon obtains a number: 540 µm, for example. But the cornea is not uniform. The thinnest point can be located 1-2 mm from the centre, in a position that the traditional pachymeter does not reach.

A classic keratometer measures corneal curvature at 4 points. The surgeon obtains two radii of curvature (K1, K2) and an axis. But a localised asymmetry — early ectasia, a post-traumatic irregularity — can lie between those 4 points and go unnoticed.

The epithelial masking effect

This is the most important concept that the MS-39 has made visible in daily clinical practice. The corneal epithelium — the most superficial layer, approximately 50-55 µm thick — has a natural ability to compensate for irregularities in the underlying stroma. Where the stroma thins or curves (as in early keratoconus), the epithelium thickens to fill the depression. The result is an anterior surface that appears more regular than it actually is.

This effect — called epithelial masking — means that a topographer measuring only the anterior surface (like an isolated Placido or a keratometer) may not see subclinical keratoconus. The anterior surface appears normal because the epithelium has compensated. But beneath the epithelium, the stroma is already altered.

The MS-39 solves this problem because it measures separately epithelial thickness and stromal thickness. An epithelial map showing localised thinning above the cone — typically infero-temporal — is often the first clinical sign of a keratoconus that anterior topography does not yet show. This finding can change the decision: from "eligible" to "not eligible".

The posterior surface: the early signal

The posterior surface of the cornea is the second critical indicator. In subclinical keratoconus, the posterior surface deforms before the anterior one. An abnormal posterior elevation — even of a few microns — is an alarm signal that a Placido topographer alone cannot detect, because the Placido measures exclusively the anterior surface by reflection.

The MS-39, thanks to the OCT, directly measures the posterior surface with the same precision as the anterior. The combined analysis — anterior elevation + posterior elevation + epithelial map + differential pachymetry — produces a diagnostic picture that no single parameter can provide on its own.

Technology comparison

Integration into the SCHWIND ecosystem

The MS-39 is not an isolated instrument. Its data directly feeds the SCHWIND CAM software for ablation profile calculation, the ForeSight system for predictive simulation, and the AMARIS 1050RS laser for treatment. The data flow is native: no format conversion, no approximation, no manual step. From measurement to simulation to laser, the data travels within a single ecosystem.

Per approfondire come ForeSight utilizza i dati dell'MS-39: ForeSight AI: simulare il risultato prima di operare →

What this means for the patient

The patient does not see the MS-39 as a complex instrument. The examination takes 2-3 seconds per eye. The patient fixates a light, without contact, without drops, without discomfort. But those 2-3 seconds produce a volume of clinical information that no manual examination could match.

If you have been told you are not operable — or conversely that you are operable — based on a 4-point keratometry and a contact pachymeter, that assessment may be incomplete. A complete MS-39 tomography can confirm the diagnosis or change it. In our experience, approximately 5-8% of patients who arrive with eligibility declared elsewhere present anomalies visible only with OCT tomography and the epithelial map.