This article is more than 5 years old. Information may no longer be current.
Visual field testing still essential for glaucoma management
OCT analysis may have more value in early disease, but fields should become more important as severity increases.
Click Here to Manage Email Alerts
In recent years, our literature has been inundated with information about OCT. While OCT technology is impressive, we must not ignore threshold visual fields, the functional side of our ongoing discussion about structure and function. While OCT is about to become one generation old, we can be reminded that Hippocrates first described hemianopia during the late fifth century B.C. and, since that time, our understanding and ability to access and understand visual fields has evolved exponentially.
In the 150 years that have elapsed since Von Graefe and Helmholtz, the challenge of eye doctors who diagnose and treat glaucoma and those who develop visual field technologies has been to seek means to acquire data more quickly and repeatably while implementing test strategies that deliver better diagnostic value.
When and how often should fields be performed? Which test strategies are best, and how should we manage our test data in the most meaningful way? Here are a few thoughts to keep in mind when designing your glaucoma testing and analysis protocols.
Frequency
Threshold visual fields (CPT 92083) should be performed with nearly all glaucoma workups and repeated at least twice a year. If initial or subsequent findings show significant change, repeat fields quickly to either validate or disprove the change. If glaucomatous progression is the concern, we must have that validation immediately, so therapy can be appropriately modified.
Test strategy
While frequency doubling technologies such as Pulsar (Haag Streit) and Matrix (Carl Zeiss Meditec) seem to promise aggressive and early detection, white on white 24-2 and 30-2 strategies remain standard of care. Investigators have shown that doubling technologies show promise for earlier detection, but we wait for manufacturers to introduce better progression analysis methods that could elevate these to the standard of care. It is important to try to stick with one strategy for subsequent testing and progression analysis. Randomly mixing strategies on individuals can dampen our ability to recognize and validate change.
Ten-degree fields
While 24-2 and 30-2 fields remain the overall standard, 10-degree thresholds are important in two situations. In advanced glaucoma, where field loss may approach central fixation, they have long been shown to be more sensitive and should be the standard. Ten-degree strategies generally offer about 10 times the number of test points within that important area and give us a far more meaningful appreciation of our patient’s visual status.
Conversely, 10-degree thresholds can offer greater diagnostic value in early glaucoma. Our newfound ability to analyze the macular region with our OCTs has increased our awareness of structural changes that may occur in early glaucoma. In our practice, we add the 10-degree strategy when we observe significant axon layer and ganglion cell layer loss in the macular region. In early glaucoma, the 10-fold increase in test points can yield more meaningful clinical information that may be consistent with early OCT structural loss.
Early, late disease
Which test is better, fields or OCT? The answer seems to be both. While OCT technology is outstanding and getting better, OCTs seem to be limited in their ability to track nerve thickness change below about 50 microns. This makes it more difficult to track structural progression in patients with advanced disease. Conversely, OCTs can give us evidence of progression before we see visual field change. Therefore, OCT analysis should bear greater weight for early disease, and fields should become more important as glaucoma increases in severity.
Test duration
Patients tend not to enjoy visual field testing, and faster test strategies seem to attend to that emotion. Some current test strategies offer 2 minutes per eye thresholds, and it is rumored that other testing systems with similar lower test times are now in development. Tendency-oriented perimetry (TOP) by Haag Streit offers about 2.5-minute per eye test times, and Swedish Interactive Threshold Algorithm (SITA) by Carl Zeiss Meditec offers about 5 minutes. A new strategy soon to be released by Carl Zeiss called SITA Faster takes about two-thirds of the time required by SITA Fast and about half the time required by SITA Standard (about 2.5 minutes per eye).
Test analysis
It has been rumored that eye doctors seldom look at field results. We are too often found guilty of disregarding progression by ignoring previous tests. Current software such as EyeSuite (Haag-Streit) and Forum (Zeiss) allow us to store patient data and effectively analyze trends. For those of us who have suffered the annoyance of shuffling through a stack of old papers, these types of software solutions may be the answer.
How many tests should we look at? It is important to look at the right data. At the test rate of two fields per year, it is best to look at the most recent six tests. Progression can remain subtle for several years and suddenly change for the worse. In calculating either local or global progression rates, we can make the mistake of incorporating too many tests during the prior period of non-progression and are at risk of masking or diluting important progression data.
Global, local defects
Visual field devices measure global and local defect levels. While the software and terminology vary somewhat between manufacturers, the principal is the same. Global values show us the mean loss over the entire field, and local values show us the depth of specific defects. While it is important to look at both, it is essential to understand that while global changes can be nominal, local defects may be highly significant. In glaucoma, it is common for an individual to have a field that, mathematically, looks normal, while having a small deep local defect that is highly significant. The “normal” global defect may mask the local one.
Progression rate
How many decibels must be lost before a test point turns black? Usually, it’s about -15 decibels, and knowing this is valuable when we observe local and global progression rates. We can then see that if, for example, a specific sector of a field is losing 2 decibels per year, then, if left unchecked, the area will turn black in about 7 years.
Visual fields wish list
Visual field analysis has evolved in the past 30 years. Test times are shorter, analysis software has become faster, and our understanding of the data has improved. Given those improvements, the test has not changed much. While, on our ultimate wish list, we hope for some sort of practical objective field test, here are a few things that might happen sooner.
In most devices, patient fixation is monitored using some variation of the Heijl-Krakau blind spot monitoring system. Given today’s computing speeds, it seems likely that we could do better. It is about time that we have machines that can reliably and repeatedly project a test stimulus in the same spot.
It also looks like newer devices and software will bring us faster test times. This will be better for patients and our wallets.
Additionally, while technologies such as frequency doubling offer earlier loss detection, we are waiting for some essential finishing touches to bring these new tests into the standard of care for diagnosis and progression.
- For more information:
- Elliot M. Kirstein, OD, FAAO, is the founder and director of Harper’s Point Eye Associates, which has three locations in Ohio, and was the co-founder of the MidWest Optometric Society. He is also an assistant clinical professor at the Western College of Optometry and the Illinois College of Optometry. He can be reached at: DrKirstein@DrKirstein.com.
Disclosures: Kirstein reports he is on the speakers’ alliance for Alcon, Haag-Streit, Optovue and Reichert. He has served as the glaucoma consultant for Paradigm Medical Industries and the U.S. glaucoma research consultant for Ziemer Ophthalmology.