The cornea is the transparent outer part of the eye and is the first structure to refract incoming light, playing a major role in visual acuity. It is also a complex, flexible and layered structure that responds to mechanical forces, pressure and small changes in its geometry.

Researchers from ICTER, which operates at the Institute of Physical Chemistry of the Polish Academy of Sciences, describe the system in a paper published in Biomedical Optics Express. The OCT-based technology observes how the cornea deforms after a short puff of air and records the response at nine locations in a single measurement.

Non-contact air-puff testing has been used in ophthalmology for years, including to measure intraocular pressure. A brief burst of air causes the cornea to deform slightly, allowing its mechanical response to be assessed.

However, corneal weakening does not always occur evenly.

In keratoconus, a disease that causes the cornea to thin and bulge outward, changes may initially be localised. A section of tissue may become more susceptible to deformation before the abnormality can be easily detected by standard imaging methods.

The disease can cause increasing vision distortion, astigmatism, light sensitivity and problems with selecting glasses or contact lenses. In advanced cases, patients may require specialised treatment and sometimes a corneal transplant.

Existing methods often assess the overall response of the cornea or track its behaviour in a single cross-section. The new system instead measures the response at one central and eight peripheral points simultaneously.

This allows researchers to determine not only how much the cornea deforms, but also where its response is greatest and whether it indicates local biomechanical weakness.

‘The cornea is one of the main elements of the eye that focuses light on the retina, so not only its shape is important, but also its mechanical properties. It is believed that it is the mechanical state of the cornea that changes in some diseases, such as keratoconus, before the shape changes. Our system, by simultaneously measuring the response of the cornea to stimulation with an air puff, allows us to estimate this asymmetry, which gives hope for earlier detection of changes than in the case of purely geometric methods’, said Karol Karnowski, PhD, from ICTER.

The technology is based on optical coherence tomography (OCT), an imaging method widely used in ophthalmology, particularly for examining the retina and the anterior segment of the eye. It uses light rather than sound and allows eye structures to be viewed at high resolution without physical contact with tissue.

The researchers adapted OCT so that several light beams fall on the cornea simultaneously, with each beam corresponding to a different measurement point. Signals from the different locations are separated using depth coding, meaning that information from several parts of the cornea can be recorded in different depth segments of a single OCT signal.

This is important because the cornea’s response to an air puff lasts only tens of milliseconds. During such a short period, even a small movement of the eye, a blink, a change in the tear film or a delay caused by sequential scanning can distort the result.

‘Because the corneal deformation we want to capture to assess its asymmetry lasts approximately 20 milliseconds and the measurement cannot be repeated, the key to our method is the simultaneous measurement of corneal response in multiple locations. This requires high temporal resolution, similar to a camera capable of taking a large number of images per second. Previous techniques either lacked such temporal resolution or offered spatially limited measurements’, Karnowski said.

The system could potentially support earlier detection of keratoconus, particularly when changes are still subtle. It could also aid in monitoring disease progression and assessing treatment effectiveness, including after cross-linking surgery, which is used to strengthen the cornea.

Another possible application is assessment before refractive surgery, such as laser vision correction, where accurate evaluation of corneal biomechanics is important for patient safety.

The researchers emphasise that the current work is technical and demonstrative. A separate clinical dataset has already been collected, including a control group and patients with early or mildly symptomatic disease. The results of this validation will be presented in a separate publication.

The current system also has limitations. Analysis requires manual segmentation of the anterior corneal surface in OCT images, which is suitable for research but too time-consuming for routine diagnostics.

The team is working on automating the process, including with machine-learning algorithms. Precise eye positioning is another challenge, as incomplete centering, small eye movements and blinking can reduce signal quality and affect the results. Future versions of the device could incorporate additional pupil monitoring, real-time feedback and eye-tracking systems.

Although the study focuses on the cornea, the underlying concept could have wider applications. The researchers have demonstrated that multi-point OCT measurement can be used to observe very rapid, unique mechanical events in light-scattering media, including soft tissues where conventional sequential scanning can generate errors.

PAP - Science in Poland

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