Corneal biomechanics
Corneal biomechanics plays a fundamental role in the origin and progression of corneal pathologies, such as keratoconus, in corneal remodeling after corneal surgery and helps in the precision of the measurement of glaucoma biomarkers, such as intraocular pressure (IOP) .
Images of corneal deformation induced by a non-contact air-puff reveal information that differentiates the normal versus the pathological corneal response. However, current commercial systems are limited to monitoring corneal deformation only in one corneal meridian (horizontal section).

This article, which is included within the milestones of the project EU Horizon 2020 IMCUSTOMEYE , presents a novel swept-source optical coherence tomography system (SSOCT) custom developed, which together with a collinear air-puff excitation, is able to record dynamic corneal deformation in multiple meridians.

Corneal biomechanics, corneal morphology and intraocular pressure (IOP) are some of the most important factors influencing the balance of forces that help maintain a healthy eye and good vision. Corneal biomechanics play a fundamental role in the genesis of corneal pathologies, such as keratoconus. Various eye treatments are also based on the corneal biomechanical response, including corneal implants for refractive correction or corneal incisions in cataract surgery where the location and geometry of the incision modulates the correction of astigmatism. Furthermore, the precision of the measurement of IOP, a biomarker of glaucoma, is influenced by the biomechanical properties of the cornea.

Keratoconus
Keratoconus is a progressive, non-inflammatory disorder that causes the cornea to thin and bulge into a conical shape. Corneal viscoelastic properties are altered in keratoconus, most obviously with a reduction in its stiffness, commonly in a focal eccentric region of the cornea.
Today, changes in biomechanical properties are believed to take place prior to corneal thinning and steepening, in what is known as preclinical keratoconus. Treatments for keratoconus include, but are not limited to, collagen crosslinking for corneal tightening and intrastromal corneal ring segment implants to flatten the cone, in mild and moderate cases, and corneal transplantat in more advanced cases. Treatments for mild to moderate cases focus on stopping the progression of the disease, as there is no cure available to reverse its course. Therefore, patients will benefit from early detection, before the development of changes in the shape of the cornea.

The early detection of keratoconus, or any corneal biomechanical abnormality, is a difficult task, as it requires probing normal and pathological corneal tissue in vivo.

Optical coherence tomography
Optical coherence tomography (OCT) is a non-invasive diagnostic imaging technique used for detailed exploration of parts of the eye such as the cornea, and this time it has been used in combination with an air-puff stimulus. An advantage of OCT systems is the flexibility of programmable optical beam scan patterns, which can be designed to monitor multiple meridians. However, no system to date has managed to exploit both the axial scan speed advantage of SSOCT and the capabilities of ultra-fast laser scanning systems. A careful choice of scanning and optical system design allowed for the appropriate compromise between temporal and spatial sampling of corneal deformation profiles.

In this article, we present the first multi-section corneal imaging device, based on a scanning source optical coherence tomography system with high cross-scan speeds, to measure a promising early keratoconus biomarker. the asymmetry of deformation induced by the air blast.

The system will serve as the basis for determining the minimum viable specifications for a keratoconus detection device, and as a platform for estimating the specific corneal biomechanical properties of each patient, which can be used in corneal surgery simulators.
Currently, the system is used in a pilot clinical study with candidates for lasik and keratoconus in collaboration with the Fernández Vega Ophthalmological Institute.

Full article

The work is a collaboration between the Institute of Optics, 2EyesVision SL, Biomechanical Engineering Group of the University of Liverpool, Physical Optics and Biophotonics Group of the Institute of Physical Chemistry - Polish Academy of Sciences (Warsaw).