Measuring corneal biomechanics in vivo
Measuring biomechanical properties clinically is currently one of the most exciting fields in modern ophthalmology. Biomechanical properties are defined as the response of a biomechanical tissue to a force. The cornea is visco-elastic which means that it exhibits both viscous and elastic biomechanical behaviour.
The applications of measuring these features in clinical practice are numerous since several diseases such as keratoconus have their origin in the change of biomechanical properties. Before corneal curvature or thickness changes due to the disease, the corneal stiffness and elasticity is already altered. Therefore, measurement of biomechanical properties is crucial for the detection of subclinical keratoconus.
For a refractive surgeon taking biomechanical properties into account therefore leads to:
- A higher safety, as patients at risk for developing ectasia after LASIK can be excluded
- A higher efficiency, as surgery can be performed when patients have a stiff and stable cornea
Moreover, many corneal treatments such as laser vision correction (LVC), corneal cross-linking or corneal incisions lead to an altered corneal biomechanical response which finally influences the vision of the patient.
IOP-Measurements: closer to the physiological IOP
The intraocular pressure measurement by applanation tonometry is highly influenced by the biomechanical properties. Therefore, taking biomechanical properties into consideration will provide a much more accurate IOP reading, closer to the physiological IOP. In conventional Goldman tonometry IOP readings can be completely off when the biomechanical properties of the cornea are altered – as for example after LASIK. This could lead to wrong decisions in the diagnosis and management of glaucoma.
Biomechanical properties as independent risk factors for glaucoma
Despite leading to a more accurate measurement of IOP the biomechanical properties of the eye ball are supposed to be independent risk factors for glaucoma. This allows screening for normal tension glaucoma by biomechanical parameters such as stiffness.
The biomechanical properties of the cornea can be measured by the evaluation of the response of the cornea when placed under stress. This can be achieved by an external force such as an air pulse – as done with the Corvis® ST.