Stimulating the cornea with air and sound

by Andrew Nolan, Postdoctoral Researcher at National University of Ireland Galway

It has been noted in previous blog posts that an understanding of the biomechanics of the cornea is fundamental in the detection and treatment of corneal abnormalities such as keratoconus or corneal ectasia. The typical approach to measuring the mechanical properties of an object is to stimulate the object with some external force and measure the response of the object. 

Since the 1950’s, Goldmann tonometry has been the gold-standard in the measurement of intra-ocular pressure. This involves applying an air puff to the eye and measuring force required to flatten, or applanate, the cornea. 

Analysing high frequency OCT images of the deformation of the cornea in response to the applied air puff, information about corneal biomechanics, corneal stiffness and viscoelasticity, can be obtained. A clinical device capable of providing such corneal biomechanical information, based on two trusted and well-established technologies, air-puff tonometry and OCT, would be of great benefit to clinicians in diagnosis and treatment planning. 

Figure 1. Schematic of experimental setup

​​In parallel to this, much can be learned about the mechanical properties of an object by observing the frequencies at which it responds to a stimulus. In work being carried out here in NUIG, in collaboration with our partners in CSIC and 2EyesVision, a system is being developed to stimulate the cornea over a range of frequencies using sound excitation. By exciting the cornea over an appropriate range of frequencies using a speaker and measuring the response of the cornea using OCT or other interferometric systems, a full picture of the frequency response of the cornea can be formed. 

Figure 2. Frequency response of ex-vivo porcine eye

​Based on simulations carried out by our colleagues in the University of Liverpool, a possible biomarker has been isolated which would relate corneal frequency response to corneal abnormality. Developing our stimulation and measurement technologies further, we hope to produce a hand held, low cost screening device for corneal abnormality. This device will provide a valuable tool for community screening of diseases such as keratoconus which can cause such difficulty if not detected early.