optical coherence tomography
Optical Coherence Tomography is one of the most advanced scanning tools used to measure peripheral vision and the thickness of the retinal fibres at the back of the eye.
OCT as an alternative to perimetry
In an extensive study we looked at whether OCT is a more effective way of measuring peripheral vision rather than using traditional perimetry.
Perimetry is a very subjective test relying on people's response. OCT is more objective, using an infrared beam to scan the eye. This gives instant results that are not dependent on people's reactions and could be particularly significant for anyone with slower reaction times or cognitive difficulties.
The study involved 250 patients and found that 65 per cent of those who were not able to be tested via perimetry, could be tested using OCT.
Vigabatrin and loss of visual field
We have also used OCT to investigate the link between the anti-epileptic drug vigabatrin and loss of peripheral vision. Vigabatrin was first licensed in the UK in 1989, but within eight years it was noted that 45 per cent of those taking the drug were experiencing a loss of visual field.
It was generally thought that, once established, the visual field loss would remain the same and not deteriorate further with prolonged use of the drug. But most studies had only assessed people over a short period of time. We wanted to assess the way that visual field loss progressed over a 10-year period in relation to continued use of vigabatrin.
We looked at a group of 14 people who had been taking vigabatrin for at least 10 years and who were still being prescribed the medication. Individuals underwent several visual field examinations. The prevalence of visual field loss increased from 64 per cent from the first test to 93 per cent at the most recent rest. The visual field size was significantly smaller at the most recent test with all participants showing a trend for decreasing visual field size with increasing cumulative exposure to vigabatrin.
We concluded that visual field loss progressed for those people who continued to take vigabatrin over a 10-year period. Although progression may be slow and is difficult to detect, new techniques are needed to monitor the effects of vigabatrin retinotoxicity in those who continue to take this anti-epileptic drug.
Epilepsy and thickness of retinal nerve fibre at the back of the eye
We are now using OCT to assess the thickness of the retinal nerve fibre layer in people with epilepsy who have not been exposed to vigabatrin. This is then looked at in relation to epilepsy duration and severity, drug resistance and localisation of the epileptogenic focus.