How to choose the most suitable methods of detecting, followingearly glaucoma

São Paulo, Brazil-Early detection of glaucomatous functional loss and its progression are facilitated by reliance on a single test program and use of the computer-assisted interpretation tools available for that technique, said Anders Heijl, MD, PhD, to colleagues at the World Ophthalmology Congress.

Dr. Heijl, professor of ophthalmology, Lund University, Lund, Sweden, reviewed the nature of early glaucomatous field loss and progression, the tests that are available for early detection and identifying progression, some pearls for interpreting the results, and considerations regarding testing frequency.

"The differences between patterns, such as the Octopus Program G1 or the 30-2 or 24-2 for the Humphrey Visual Field Analyzer, are not that great, and so it is unlikely that you will use an unsuitable pattern," Dr. Heijl said.

In following patients suspected to have early glaucoma, threshold perimetry is better than suprathreshold screening tests for early diagnosis because the former technique will detect the early scatter phase better than the latter. However, suprathreshold screening is appropriate in patients for whom there is no suspicion of glaucoma, such as when performing a population survey or when the goal is early detection of normal-tension glaucoma.

In selecting a perimetric test, standard automated threshold perimetry (SAP) with white stimuli remains the gold standard for early detection. Short wavelength automated perimetry (SWAP) is also suitable, although recent research indicates that it is not more sensitive than SAP.

"In a soon-to-be-published study comparing SITA-SWAP, full-threshold SWAP, and SAP, all three techniques were associated with similar glaucoma detection rates although they did not necessarily identify glaucoma in the same patients. Defects in any individual may be detected earlier with one test compared with another so that applying more tests will increase the detection rate. However, it will also increase the risk of finding false positives," Dr. Heijl said.

Frequency-doubling technology (FDT) has many assets-it is quick, convenient, and has very high specificity but there is no convincing evidence that it can detect glaucomatous field loss earlier than SAP, he said.

"FDT is excellent as a screening tool and is a good test for optometry offices. However, it would not be a first choice for an ophthalmology practice," Dr. Heijl said.

The most important pearl for field interpretation in early detection efforts that he offered is to use the same instrument and test program consistently. Available tools for computer-assisted interpretation are valuable as well, and when the goal is early detection, it is better to look at the probability maps than the grayscale maps. That approach is particularly important if using SITA fields and if the defects occur close to the point of fixation, noted Dr. Heijl.

For new users, plain text messages, such as those provided by the Glaucoma Hemifield Test, may be very helpful, and in eyes with cataract, it is important to concentrate on the pattern deviation maps where diffuse loss associated with the lens opacity has been filtered out.

"Importantly, to find the earliest field loss, look not only at today's field, but also at the last few tests to find similar weak disturbances," he said.

Detecting progression

Progression of glaucomatous field loss is characterized by both deepening and extension of defects. Although threshold variability is larger in glaucomatous fields than in fields of normal eyes, the characteristics of test-retest variability have been modeled and are included in the glaucoma change probability maps.