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Dr Kirsten Hamilton-Maxwell 


Research Topics and Related Projects:

Understanding intraocular pressure (eye pressure)

According to the World Health Organisation, glaucoma is the leading cause of irreversible vision loss worldwide.  The pressure within the eye is the most important risk factor development and progression of glaucoma; reducing eye pressure, either by eye drops or by surgery, is the only recommended treatment at the current time.  Even if your eyes are completely healthy, your eye pressure will not be a fixed number – in fact, it can fluctuate for a large number of reasons including the time of day, if you hold your breath, exercise, or even what you had to eat and drink.  It is therefore very important that researchers, such as myself, are fully able to understand how and why eye pressure varies so that your optometrist or ophthalmologist can measure and interpret it confidently.  Examples of my research projects in this area include:

  • Eye pressure is usually highest when you first wake up in the morning.
  • Eye pressure can fall if you have been for a short walk, such as if you walked from the nearest bus stop, on your way to your sight test.

Improving tonometry, the measurement of intraocular pressure

Once we have sorted out what the “normal” eye pressure should be, we need an accurate way of measuring it.  Eye pressure is usually measured by an instrument called a tonometer and the process is called tonometry.  The problem with trying to measure the eye pressure is that we cannot measure it directly because it exists inside the eye, but instead need to rely on tonometers that assess it indirectly by measuring the force needed to flatten a small area of the cornea (the clear dome at the front of our eye).  This means that the accuracy of tonometry depends on the properties of the cornea through which it is measured.  Work is underway to identify the relevant factors and to determine what this means for eye pressure measurement, including:

  • A small amount of clinically invisible corneal swelling, such as the kind that occurs while we are asleep, causes tonometers to overestimate the eye pressure.
  • Tonometers are not only sensitive to the thickness of the cornea in its centre, but also in the surrounding areas.
  • Many types of tonometer are sensitive to corneal properties including Goldmann applanation tonometry (the “blue light test”) and non-contact tonometry (the “air puff test”).  In fact, even a new type of tonometer known as the Pascal Dynamic Contour Tonometer is not immune to this problem.
  • Corneal biomechanical properties, although completely invisible to most clinical instruments, can cause tonometers to read incorrectly.

Corneal size, shape and its other properties

Given that the cornea has such a large influence on eye pressure measurement (tonometry), another area of my work includes defining and quantifying corneal characteristics, including biomechanics and thickness, in health and disease.  Most recently, we reported that a single drop of anaesthetic (commonly used to help your optometrist or ophthalmologist measure the thickness of your cornea) was enough to cause a temporary increase in corneal thickness.

 

Funding:

  • Cardiff University Research Opportunities Programme (2013)
  • Nuffield Foundation Vacation Studentship (2007)
  • OVRF-Maki Shiobara Scholarship (2006)
  • Australian Postgraduate Award (2003)