Eye care providers are on a quest for something that-so far-hasn't been found.
Kinetic perimetry still has an important role, while advances in static automated perimetry have reduced test time without reducing sensitivity, but the ideal tool for evaluating the visual field in the management of ocular conditions such as glaucoma, optic neuropathies, certain retinal diseases, and other intracranial conditions has not yet been found.
"We're always looking for something that's going to increase the sensitivity of detecting early glaucoma. Perimetry is critical both in the diagnosis of and in determination of progression in glaucoma," Dr. Quinn said, adding that doctors should continue looking at new technologies to see how they affect patients.
In glaucoma management, static threshold perimetry is the preferred mode of examining visual fields. It surpassed kinetic perimetry on the strength of its ability to identify or localize scotomas and identify depressions in the hill of vision. Although it is rarely used today in glaucoma, kinetic perimetry remains the better tool for exploring toxic, ischemic, compressive, or infiltrative optic neuropathies, he said.
Full threshold or standard automated perimetry was the first of the newer static tests, although long testing times were a significant drawback. Today doctors have static threshold alternative strategies, such as SITA standard, or Threshold Oriented Perimetry, and fast algorithms that help reduce test time without any loss of accuracy.
And with normalized databases, physicians can make more sense of the threshold values and estimate a patient's statistical chances of having an abnormality at any given point based on deviation from the normal values.
Along with these improvements in functional testing, there has also been a renewed interesting in imaging technology.
"We've got great instruments for structural measurement of the optic nerve that give us a tremendous amount of data," Dr. Quinn remarked. Instruments include optical coherence tomography, Heidelberg Retina Tomography, and nerve fiber layer analyzers.
It is easier for patients to tolerate these tests, which in part explains their increasing use in clinical practice. But their sensitivity in detecting early glaucoma is not much better than functional tests.
"We still have some of the same problems. The main question, then, is which is more important," he said. "Is it more important to look at structure or is it more important to look at function?"
"The answer is that we have to look at both," he continued. Because of the limited sensitivity of full threshold testing for detecting early glaucoma, there is a quest for functional tests to find these patients earlier. Alternatives include short-wavelength automated perimetry (SWAP), which isolates certain types of ganglion cells that react to different colored stimuli, and SITA-SWAP, a faster mode of testing.