The objective of this study was to determine the correlation between visual function measured with multifocal visual evoked potential (mfVEP) and optic nerve structure measured with Heidelberg retinal tomography (HRT) in primary open-angle glaucoma (POAG) patients. The study brings to our attention the usefulness of these objective tests and their possible future role in the management of optic nerve disease and, in particular, glaucoma.
Since both tests are objective in nature, they eliminate the potential problem of patient error. This can occur when optic nerve function is determined by visual field testing, a subjective method that is the most commonly used type of measurement to diagnose glaucoma and monitor its progression. However, it is necessary to ascertain the accuracy of and correlation between mfVEP and HRT before advocating their use for the management of glaucomatous optic nerve damage.
The study's authors took measurements using both objective testing methods in 35 POAG patients (67 eyes) and seven control subjects (14 eyes). They found a direct correlation between visual function measured by mfVEP and optic nerve structure or damage measured by HRT in 85% of the POAG patients and 86% of controls. More specifically, in the glaucoma group, amplitudes on the superior hemisphere of the mfVEP recordings showed a direct correlation with rim-to-disc area ratio, rim volume, and mean retinal nerve fiber layer thickness and an inverse relationship with cup area and cup-to-disc area ratio all in the inferior hemisphere of the HRT results. Inferior hemisphere amplitudes showed a direction correlation with rim-to-disc area ratio and inverse correlation with cup area, cup-to-disc ratio, cup volume, and mean cup depth in the superior hemisphere of the HRT results.
These results indicate that the structure of the optic nerve head correlates well with visual function in glaucoma patients. The study shows that there is a relationship between optic nerve structural abnormality and failure of conduction of the optic nerve pathways related to this structural abnormality.
However, mfVEP or HRT testing can produce normal results in some open-angle glaucoma patients and false positive results in normal eyes. Using both tests, rather than only one, may eliminate these potential errors. The study results suggest that these objective tests may be particularly useful in those glaucoma patients in whom visual field testing is either difficult or unreliable. Although HRT is used by most clinicians treating glaucoma patients, the correlation with mfVEP may be a useful adjunct.
One shortfall of the study is that it would have been helpful if the authors had provided more information about mfVEP, such as cost, since the test is not commonly used.