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My research concerns visual field testing. This is commonly done using a machine (perimeter) which shines lights of various different brightnesses from various directions at the eye. The patient presses a button each time they see a light. In this way, the machine can map out the blank parts of the visual field. Some perimeters are computerized and store the maps of visual fields as grids of numbers. My work mainly involves applying mathematical and statistical techniques to these grids of numbers to detect the development of glaucoma, and to detect any worsening in established glaucoma, earlier than by conventional methods. I am using a computer program, PROGRESSOR, which is an updated, more powerful version of a program originally written by Dr. Fred Fitzke at the Institute of Ophthalmology, London. This program can perform a variety of analyses on visual fields to detect deterioration. Here are some of the results I have presented so far:
At Moorfields Eye Hospital, London we are following a large group of ocular hypertensives. These are people who have raised eye pressure but no visual field abnormalities. They are more likely to develop glaucoma than the population in general. We have found that, in those ocular hypertensives who do go on to develop glaucoma, we can consistently detect the glaucoma earlier than standard methods. Of course, earlier detection means an earlier chance to start treatment. We are working on improving our methods further.
In a group of glaucoma patients with progressively worsening visual fields, we have found that our methods detect the deterioration more than one year earlier than the standard analysis. It is important to detect whether visual fields are worsening and, if so, how fast because treatment may have to be changed to prevent further deterioration.
These are visual field tests done with both eyes open, such as those required by the DVLA for driving. They are not routinely done because treatment for glaucoma must be tailored to each eye individually. However, we have found that the results of binocular field tests tie in well with how people use their eyes for daily activities such as going up and down stairs and finding things that they have dropped. We are able to merge the results of separate tests done on each eye individually to produce an accurate reconstruction of the binocular field test. In this way, the benefits of the binocular test are enjoyed without any extra tests for the patient. Although it will never replace true binocular field testing, this analysis will enable an appreciation of the binocular field as a much more regular feature of a visit to the Glaucoma Clinic than previously.
If it is suspected that a glaucoma patient’s visual fields may be deteriorating they may be asked to have visual field tests more often than if their visual fields are considered to be stable. We have found that, in a group of glaucoma patients with progressively worsening visual fields, testing fields three times a year instead of once a year means that the deterioration is detected more than one year earlier. This demonstrates that having more frequent visual field tests is of benefit if progressive glaucoma is suspected.
Visual field tests are often quite tiring (not to say tiresome) for the patient as a high degree of concentration is required. For this and other reasons the results are corrupted by fluctuation, which may be compared to interference on a television screen. Techniques for reducing this interference are used in other branches of science and Dr. Fred Fitzke and Mr. David Crabb at the Institute of Ophthalmology, London have applied these techniques to visual fields. We have found that we can improve the reliability of information from field tests without compromising the ability to detect deterioration.
