Visual Field Testing – When it Should be Done

Given how neither patients nor their doctors like visual field testing, we’d all like to do it as little as possible. With that in mind, just how infrequently can one get away with visual field testing? The answer largely depends upon one’s diagnosis. The recommended frequency of visual field testing differs widely depending on whether someone is only a glaucoma suspect; is newly diagnosed with glaucoma; has chronic but controlled glaucoma; has uncontrolled glaucoma; has advanced glaucoma, etc. It’s not possible to cover every patient situation but some general patterns of testing might be as follows: 

Suspicion of Glaucoma 

An individual is considered a “glaucoma suspect” when there’s something about the exam that suggests glaucoma might be present but the evidence is too weak to justify treatment. Because glaucoma might be present it’s important not to let too much time go by before repeat examination and testing. How much time is too much? It varies according to how suspicious one is. In my practice, I will generally recommend visual field testing once or twice a year for those who are only “suspects”. 

At Initial Diagnosis 

When someone is first diagnosed with glaucoma it is important to get a sense of what is called the “rate of progression^[1].” Essentially, we want to know how aggressive the glaucoma might be. This can only be determined by getting multiple visual fields over time. The shorter the time interval between fields the earlier and more accurate will be the determination of glaucoma aggression. In my mind, this is one of the most critical periods to obtain visual fields. As such, I am rather aggressive in my recommendations in that I will recommend a visual field every two to three months for the first year after initial diagnosis. Once I have a sense of how aggressive an individual’s glaucoma might be, only then will I consider reducing the frequency of testing. 

Chronic but Controlled Early to Moderate Glaucoma 

Glaucoma is considered to be under control when both the intraocular pressure (IOP) is at target and there is no strong evidence of progression of the disease by testing. Many doctors will recommend visual field testing only twice yearly in this setting. 

Uncontrolled Glaucoma 

If either the IOP increases beyond target or test results are suspicious for worsening glaucoma, then more frequent testing is indicated until the glaucoma is once again under control.

Advanced Glaucoma 

One of the more frustrating things about glaucoma is that those who have already lost a large amount of their visual field tend to lose vision at a faster rate than those who have less field loss^[2]. Even more frustrating is that visual field performance tends to fluctuate more with advanced glaucoma. What this means is that test results can appear better or worse than prior tests without any real change from glaucoma. How does one control for this? More frequent testing. 

Reasons Why Even More Frequent
Visual Field Testing may be Necessary 

Test-to-Test Variability

Visual field results can fluctuate even when there is no definite worsening of the glaucoma. As just mentioned, this tends to be more common with advance glaucoma but is present to some degree with earlier forms of glaucoma as well. This is one reason why many eye doctors will recommend repeating a visual field test whenever there is apparent worsening of the visual field. 

Poor Quality Testing

Just because someone sits for a visual field does not mean useful information will be obtained. There are many reasons why the quality of the test may be too poor to provide what we call “clinically useful information”. For example, if someone is tired, distracted, or has symptomatic dry eye the quality of the visual field testing can be reduced. If of sufficiently poor quality, the test will have to be rescheduled on another day. 

We Need to “Zoom In” Once in Awhile

The standard visual field test for glaucoma evaluates the central 30 degrees around fixation. However, this testing can miss small areas of central visual field depression. We need our central vision to read, use computers, recognize faces and expressions, and enjoy watching videos on our TV and tablets. Glaucoma affecting the central 10 degrees of visual field tends to be more aggressive. As such, it’s important to periodically take a more detailed look at the very center of the visual field^[3]. 

Summary Regarding Necessary
Frequency of Visual Field Testing 

Essentially, if you don’t look, you won’t find. Given that vision loss from glaucoma is permanent and progressive, it’s important to look often for changes. This tends to be more frequent than the individual with glaucoma would prefer. A simple question can put this preference into perspective: “Which would you prefer more: to keep your vision or to avoid visual field testing?” Given that choice, the preference should be clear. 

References:

[1] Chauhan BC, Malik R, Shuba LM, Rafuse PE, Nicolela MT, Artes PH. Rates of glaucomatous visual field change in a large clinical population. Invest Ophthalmol Vis Sci. 2014 Jun 10;55:4135-4143.

[2] Mikelberg FS, Schulzer M, Drance SM, et al. The rate of progression of scotomas in glaucoma.
Am J Ophthalmol. 1986;101(1):1–6.

[3] Kung Y, Park SC, Simonson J, Su D, De Moraes CGV, et al. 10-2 Versus 24-2 Visual Field Progression Analysis in Glaucomatous Eyes with Initial Parafoveal Scotomata. Invest Ophthalmol Vis Sci. 2012;53:202.

 Related Articles:

1. Visual Field Testing – Why We Do It  
2. Visual Field Testing – What It Is
3. Physical Activity and Rate of Visual Field Loss
4. Why Don’t Glaucoma Treatments Totally Halt Vision Loss?
5. Association Between Rates of Glaucoma Visual Field Progression and Intraocular Pressure (IOP) Measurements Obtained by Different Tonometers