While interpretation of visual field findings often takes center stage in glaucoma management, personalizing testing strategies to optimize patient performance can enhance the yield of perimetry.
When we encounter a new patient with glaucoma, we typically stage the patient's disease and establish a strategy for intraocular pressure (IOP) reduction, whether we target a reduction from baseline (e.g., 25%) or an absolute pressure number (e.g., mid teens). Another question that we might ask ourselves is: how am I going to tell if my patient's IOP lowering is insufficient? Towards this end, we may decide whether to focus on structural measures of progression (photography or optical coherence tomography [OCT]) or functional tests (visual field). It is generally accepted that photographs and OCT perform better in early glaucoma where as the visual field will best demonstrate progression in the advanced stages. But how can we pick the best testing strategies to benefit the sizable number of our patients who will progress despite significant IOP lowering?
To begin with, we should probably put time and efforts towards helping our patients become good visual field test performers. Recall that from the ocular hypertension treatment study, two-thirds of patients with consecutive, abnormal, reliable test results were normal on a third testing.1 As such, we should recognize fluctuation as a part of the glaucoma testing progress. Many unreliable visual field takers will become reliable with experience. Three or so visual field tests in the first year may be a good way to familiarize the patient with the test while establishing adequate baseline data upon which to determine future progression.
To best determine progression, we should pick one testing strategy or test type per patient, and use that strategy consistently. (An exception to this strategy may be applied for patients with central and peripheral damage, for whom alternation between 24 degree and 10 degree fields may work best.) Do take some extra time to explain the test to the patient early on. For example, most patients are relieved to hear that the test presents very dim lights and can be frustrating for many patients, even those with perfect vision.
Next, estimate the likelihood that your patient will progress, and adjust visual field test frequency appropriately. It is easiest to detect progression in patients with less severe damage, who are progressing rapidly, who are reliable visual field performers, who do not fluctuate much between tests and who are assessed more frequently.
When possible progression has occurred, respond by repeating tests and by increasing your frequency of testing to confirm progression. This strategy will be as helpful as escalating IOP lowering therapy, and will allow you to appropriately treat patients who are experiencing true progression while avoiding over treating those who just had a bad test.
In summary, the doctor should take a highly personalized approach towards the optimization of visual field testing for each patient.
1. Keltner JL, Johnson CA, Levine RA, et al. Normal visual field test results following glaucomatous visual field end points in the Ocular Hypertension Treatment Study. Arch Ophthalmol. 2005;123:1201-6.
Nathan Radcliffe, MD, a glaucoma specialist, is an assistant professor of ophthalmology and director of the Glaucoma Service at Weill Cornell Medical College and New York-Presbyterian Hospital in New York.