A clustered approach to spacing visual field tests, with the first cluster at baseline and then, if progression is suspected, at a follow-up exam, will result in a more efficient use of resources without loss of diagnostic accuracy than regular (and more frequent) testing approaches, said David F Garway-Heath MD, FARVO, Moorfields Eye Hospital, London, UK.
“Glaucoma is a potentially blinding disease, but not everybody becomes blind from it. We have to identify those patients who are at greatest danger,” he told the 7th World Congress of Glaucoma in Helsinki, Finland.
The risk factors for faster glaucoma deterioration identified in peer-reviewed studies include higher intraocular pressure levels, older age and pseudoexfoliation; older patients with higher intraocular pressure progress on average faster than younger patients with lower intraocular pressure, he noted.
The current World Glaucoma Association (WGA) consensus statement on visual field testing recommends first obtaining a collection of baseline visual fields over a short period of time. Afterwards, a yearly follow-up examination is adequate in low-to-moderate risk patients. However, the frequency of testing should be increased as soon as progression is suspected to have occurred. High-risk patients should be tested more frequently.
The WGA’s recommendations are based on studies comparing different visual field testing protocols for detecting a meaningful rate of deterioration, for instance 2dB per year.
“If we assume that the normal visual field is 0dB and that blindness is -30dB, the time from normal to blind, at a rate of 2dB per year, would be 15 years, about the average residual life expectancy of a glaucoma patient at diagnosis. We need to be able to detect such a rate of change,” he said
The clustered wait-and-see approach
The method to identify deterioration applied in the early manifest glaucoma trial (EMGT) required at least five fields, two at baseline and three at follow-up, to identify deterioration. On average, when deterioration was detected, the mean deviation changed by about 2dB. Subsequent research has suggested that, for a new patient with no prior data, if only one visual field is performed per year, with typical variability in the visual field test result, it would take six years to identify a rate of change of 2dB per year; six tests performed over two years will detect that rate of change.
However, there aren’t sufficient resources to perform tests so frequently in all patients. A more efficient approach is therefore necessary. A study published in 2007 showed that testing every three months or testing once every year until progression is suspected, and then repeating the test, could detect progression earlier than testing every six months. Testing yearly until progression was suspected also yielded fewer false positives than testing every three months.
The WGA’s current strategy thus combines the advantages of more frequent testing and a yearly examination until progression is detected approach, Dr Garway-Heath said.
David Garway-Heath: firstname.lastname@example.org