The continued relevance of VFT

With other imaging technology options, what role does visual field testing play?

By Karen Blum, Contributing Editor

Physicians have used visual field testing (VFT) as a central and peripheral vision diagnostic tool for centuries — visual field recognition dates back more than 2,000 years to the time of Hippocrates, who identified a hemianopsia.¹ However, with the advent of imaging technologies like optical coherence tomography, is VFT still germane?

“There is no doubt that [VFT] is relevant,” says Rohit Varma, MD, MPH, professor and chair of ophthalmology and director of the University of Southern California Eye Institute in Los Angeles. “It is essential. It may be more important in some ways than imaging instrumentation because you can get a reasonable idea about structural damage by just directly examining the optic disc and the nerve fiber layer; there are no simple, accurate ways of assessing the central and peripheral visual field other than a white-on-white perimetry.”

Alan Robin, MD, agrees. “It is the best test we have currently for assessing optic nerve function, allowing us to set the therapeutic goal for the patient, and assessing whether the patient is stable or needs more advancement in therapy,” says Dr. Robin, founder of Glaucoma Specialists in Baltimore, an associate professor of ophthalmology at Johns Hopkins University, and a professor of ophthalmology at the University of Maryland.

Various visual field tests from the early 1900’s.
ALL IMAGES COURTESY AMERICAN ACADEMY OF OPHTHALMOLOGY

DOWNFALLS

George L. Spaeth, MD, acknowledges the importance of VFT but sees its downfalls. “It’s time-consuming, it’s expensive, and the results of the field are strongly related to the instrumentation used and to the technician running the instrumentation,” says Dr. Spaeth, Louis Esposito Research Professor in Ophthalmology at Wills Eye Institute/Jefferson Medical College, Philadelphia. Thus, false positives or negative can occur, and the results might not be indicative of the patient’s functioning, he says. Some patients have bad fields yet their brains fill in missing areas to maximize the vision they have; others have good fields yet don’t function well. The Ocular Hypertension Treatment study, which measured visual fields to determine whether enrolled subjects were worsening, found that of the visual fields indicating the patient had worsened, 86% were invalid.³ Dr. Spaeth predicts visual fields will be used less often a decade from now.

Physicians use VFT to derive information that will influence their treatment or management decisions. “That’s the only purpose of the test,” Dr. Spaeth says. “If a person has far advanced visual field loss I think it’s unnecessary to do visual fields: They are often not useful in detecting worsening of vision, they cost the patient something, they cost the system something and the system already is unsustainably expensive. Anything you can do to reduce costs without reducing quality of care is important.”

On the other hand, if a patient is asymptomatic and has no visual complaints and a healthy optic nerve, some experts say it’s necessary to get a baseline visual field. “I would challenge that because you know it’s going to be normal, so why do it?” Dr. Spaeth says. “If it’s not normal, you know it’s not a valid field: Something else is happening, or you’ve missed something.” Instead, he recommends a baseline optic disc photograph.

Dr. Varma concurs that VFT is not an easy test and open to many variables. “But it is the only good measure of functional loss from glaucoma.”

Dr. Robin concurs. In 35 years of practice, he has not found a patient who liked the test. At one time he volunteered for a study requiring VFT once a year for 10 years, and hated it. But, “Without it, there’s really no way to assess optic nerve function.”

VFT’S SPECIFIC ROLE

Angelo P. Tanna, MD, says that both VFT and imaging play an important role in diagnosing and monitoring glaucoma.

“We know that early in the disease course in patients with mild to moderate glaucoma, imaging is very useful for detecting progression,” says Dr. Tanna, vice chairman and associate professor of ophthalmology, and director of the Glaucoma Service at the Northwestern University Feinberg School of Medicine in Chicago. “In fact, in the early stages of disease, imaging the nerve fiber layer and ganglion cell complex is probably more sensitive than detecting visual field progression. But once you get into the later stages of the disease, you hit a floor where nerve fiber layer measurements are no longer helpful in looking for progression. In those patients, the emphasis has to be on standard automated perimetry. That’s our best approach now in patients with advanced stages of glaucoma, for detecting progression. [The techniques] are complementary.”

DISCERNING CONTRAST

Dr. Spaeth maintains that the ability to discern contrast is the most fundamental aspect of vision. So he and Jesse Richman, MD, developed Spaeth/Richman Contrast Sensitivity (SPARCS), a contrast sensitivity test that measures general eye health and acts as a preventive tool for specific diseases. The test (https://www.sparcscontrastcenter.com/home.php) is free, takes three to five minutes and can be done using any computer with Internet access and a 15-inch or larger monitor.

During the test, patients see five black bars on a white background, in one of nine sections on a 3 in. x 3 in. grid. The bars gradually lighten in color and pop up in different sections of the grid, representing five areas of vision, testing peripheral and central vision.

A recent study compared SPARCS and the Pelli-Robson contrast sensitivity test by testing contrast sensitivity. A prospective, cross-sectional study of patients with glaucoma and controls was performed.⁴ Researchers found comparable results: an intraclass correlation coefficient (ICC) of 0.97 for SPARCS and 0.98 for Pelli-Robson, and a 6.7% coefficient of repeatability for SPARCS compared to 6.4% for Pelli-Robson. Researchers identified glaucoma patients using the SPARCS test with 80% sensitivity and 93% specificity, and patients in the control group had significantly higher SPARCS scores than those with glaucoma or suspected glaucoma. Unlike Pelli-Robson, which uses letters, patients do not need to be literate to complete SPARCS.

A follow-up study of 35 patients with AMD and 34 controls found the test valid in assessing contrast sensitivity in AMD patients.⁵ The ICC for SPARCS was 0.87; Pelli-Robson was 0.92.

USING VFT

VFT is recommended by the AAO’s preferred practice pattern, which requires it during glaucoma diagnosis and follow-up exams at least twice a year, says Dr. Robin. He says he strives for this frequency of VFT and conducts tests more frequently in patients with more advanced damage. Dr. Varma orders the tests every six months in stable glaucoma patients, every year in high-risk ocular hypertension patients and every three to four months for high-risk glaucoma patients. However, Dr. Spaeth recommends individualizing VFT for each patient — it may not be necessary for stable patients, but those who are unstable and progressing rapidly may need to be done every few months.

In patients with severe disease, standard perimetry may no longer be useful, says Dr. Tanna. “We usually will switch to using a size V stimulus or measuring the central 10 degrees, depending on which approach is more useful for a particular patient. In those who have good visual acuity but severe loss in the central 24 degrees, but some preservation of central 10 degrees, we’ll switch to 10-2 perimetry, and in patients with even worse damage we’ll switch to kinetic perimetry.”

Dr. Spaeth instructs patients to test their vision at home, in a standard way: one eye at a time, comparing one eye with the other, and noting any changes. “When patients already have far advanced visual loss, they will notice changes in their visual functioning that you can’t pick up on a visual field.”

To reduce variability during follow-up VFT exams, Dr. Robin recommends using the SITA-Standard C-24-2 program. For patients who easily become tired or confused, he recommends periodically pausing the test by keeping the clicker that records responses pressed in, to let patients rest. “Also make sure your technician explains the test to patients, and make sure they understand there will be a lot of spots that are missed,” so they will understand if there are blank periods that’s normal, and they won’t get scared. OM

Dr. Spaeth holds a patent on the SPARCS test.

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