The consulting room: Visual fields – a forensic approach

Few areas of eye examination have transformed more than visual field testing over the past few decades, moving from a piece of felt on the testing room wall, to the computerised, statistically analysed, multiple strategy machines available in practices today.

This evolution has enabled a standardised assessment to be delegated and performed in a matter of minutes. Visual field testing by optometrists has long been advocated as a routine screening tool for glaucoma, so many optical practices duly carry out some form of field testing as part of the routine eye test. But this approach does have its downside. Practice resources are expended, patient time and effort are spent performing the tests and ultimately, field defects form the basis of a number of unnecessary false-positive referrals. This was highlighted in a 1998 study, which found the positive predictive value of an isolated visual field defect in the detection of glaucoma was zero. In other words, none of the patients referred for suspect glaucoma based on abnormal fields alone went on to be diagnosed with glaucoma. A similar study published around the same time exploring optometrist glaucoma referrals found that optometrists reported a visual field assessment in a measly 19% of glaucoma referrals. Considering glaucoma is defined by the existence of field defects, it is worrying that the majority of optometrists didn’t appear to value its measurement. So should we be bothering to test visual fields?