Irish researchers are studying very rapid and involuntary movements of the eye, with a view to measuring the level of patients' consciousness when in a coma, under anaesthetic or suffering a neurological disorder, writes Ashok Jansari
DID YOU REALISE that while you look at this page, your eye is fluttering 80 times a second with the flutter being less than the thickness of a human hair? But why do Irish researchers care about this minute and imperceptible flutter if it is so small and unnoticeable?
Dr Gerard Boyle, a medical-physicist, and his colleagues at St James's Hospital in Dublin are working on the development of new technology to measure what he calls "ocular-micro tremor or OMT".
They hope that measuring this movement, which has an amplitude of a micron (one thousandth of a millimetre) could help clinicians measure levels of consciousness in coma, anaesthesia and a range of neurological disorders.
Pioneering work in the 1970s by Dr Davis Coakley, Professor of Gerontology at Trinity College Dublin, showed that "there are clinical conditions that affect the frequency of the OMT" according to Boyle. The OMT "slows down in a number of conditions related to changes in consciousness or arousal.
"The physiological reason is that the eye muscles that are controlling your eye are wired into the part of the brain that is close to the centres that control your level of arousal or consciousness," says Boyle. This is in the posterior parts of the brain in an area known as the brainstem and Coakley found that anything that changed a person's level of arousal changed the rate of their OMT.
"In particular, [Coakley] found that in coma, patients who were deep in coma would have a slower OMT than a normal person," according to Boyle. And importantly, "people who were likely to emerge from coma and survive coma tended to show an increase in the rate".
As a result of this, an accurate measurement of the OMT could prove to have "prognostic potential" for the level of coma, something that has massive implications for decisions on treatment and care. Subsequent work has shown that the OMT also changes in other clinical conditions such as Parkinson's disease, multiple sclerosis, head injury and stroke.
Currently, the OMT is measured using a "piezo-electric probe", which involves the eyelids being taped back, a small amount of anaesthetic being put on the surface of the eye and the probe being placed directly on the surface.
The mode of operation is "the same as an old-fashioned record player and little movements produce a movement in the probe", he says. This creates an electric current that can be converted to a measurement.
Another medical physicist at St James's, Dr Noirin Sheahan, originally validated and developed the piezoelectric probe approach to OMT measurement, and it has been very useful for collecting data in scientific settings.
However, due to the need to tape back the eyelid and anaesthetise the eye itself, using it clinically has proven more difficult.
It is for this reason that Boyle has been awarded a three-year Science Foundation Ireland grant of €129,000 to look into developing a more clinically useful system. To do this, Boyle will further work that he undertook for his PhD at TCD where he investigated a "non-contacting system" using a method known as "speckle interferometry".
Speckle interferometry "uses laser beams scattered off the white of the eye", explains Boyle, and by "detecting scattered light which is called a 'speckle pattern', it is possible to detect extremely small movements".
Boyle and his colleagues, Dr Niamh Collins, a physician, and Mohammed Al-Kalbani, an engineer, are leading a group that aims to improve and refine the current piezo-electric system.
The work is underway at St James's in the Mercer's Institute for Research on Ageing (Mira) and in the Department of Medical Physics Bioengineering.
The group plans to collect more clinical data using the currently-available systems whilst at the same time looking at the fundamentals of how light is scattered by the eye.
The eventual aim of the project is to create a portable non-contact system for measuring the OMT.
• Ashok Jansari is based at the University of East London and is on placement at The Irish Timesas a British Association for the Advancement of Science Media Fellow