Peter A Netland Visual Fields PAN 2021

My name is Peter Netland. I'm at the University of Virginia. In this video I will be discussing visual field evaluation. My disclosures are shown on this slide. I have no conflicts of interest with the materials discussed in this presentation. Visual field analysis is extremely important in the initial assessment and follow up of glaucoma patients. We use this on a day daily basis in clinics. And the choice of visual field testing does vary to some extent with the clinical setting and individual clinicians have their preferences and we'll try to review these in this talk. So the visual field in glaucoma is important. We're looking for glaucomatous appearing visual field changes. So these characteristically do respect the horizontal midline. We oftentimes have peripheral visual field loss very commonly, perhaps most commonly an arcuate defect or barium scotoma. The nasal area can be affected as well with nasal steps and we can have paracentral defects as well. The central visual field defects can be monitored with a 10, 2 and we can find visual field defects there as well. Generalized depression is very common in glaucoma patients and this can be central or peripheral. And in advanced glaucoma there can be advanced visual field loss with just a central island of vision remaining and a temporal island. And then in end stage glaucoma we can even have loss of this central vision. So over on the right we're showing here a nasal defect and arcuate defects. The one on the left is an inferior arcuate and the one on the right is a superior arcuate defect. And these are very characteristic glaucomatous visual field defects. So the visual field is a subjective test. It's part of our functional testing. So understanding the reliability of the field is important. The visual field reliability is measured with certain indices. The Humphrey visual field does display the fixation losses. Also false positives are tested and false negatives and these are shown to give an idea about how reliable the patient was in performing the visual field. Global indices are useful measurements as well. These can measure the sort of summary values that can measure the overall mean defect, which is the average of all points from the total deviation. The pattern standard deviation is extremely useful. This is points that are significantly different from the total deviation subtracting out background or general depression or background changes. The visual field index is useful especially when Communicating with patients. 100% Visual Field Index is a perfect age adjusted visual field and and in glaucoma patients this is sometimes reduced and it can give an idea about how much visual field is remaining in a patient. The standard full threshold testing algorithm is the classical testing strategy. It's probably still the gold standard does have disadvantages, particularly that it takes a lot of time to do the test. This is a staircase or bracketing strategy. Double crosses the threshold for vision and the steps are 4 decibels increasing until the patient responds by pressing the button that they see the stimulus. Stimulus is then decreased, crossing the threshold until the patient doesn't respond. So this fairly accurately measures the visual field. FAST pack was a variation of this introduced in 1991. And in this strategy the stimulus intensity changed in three decibel steps, but it only crossed the threshold once. So the test was a little bit faster. It did have a higher infra test variability. It is still available on the machines that we can purchase today, but it's less frequently used. The Swedish interactive thresholding algorithm, the CETA strategy, is very commonly used now. Probably most commonly, it was introduced in 1997. It's certainly more time efficient. The test time is cut by about 50% compared with full threshold strategy. And the field starts with prior probability models of normal and abnormal fields and then measures the threshold sensitivities and tries to adjust adjacent points to some extent with the probability models of normal and abnormal fields. The CETA standard test is faster than the full strategy, full threshold strategy by a significant amount, and the CETA fast is faster than the CETA standard by a significant amount. There's now a CETA faster which is about 50% faster than the CETA standard and no doubt will be popular among clinicians because the test time is reduced. Further, the issue with the CETA standard and CETA fast and now CETA faster is that as the test strategies are shortened, sometimes the visual fields do not as accurately depict what would have been detected in a full threshold test. They can underestimate the visual field defects in some instances. And so there is to some extent a departure from the full threshold accuracy to achieve a faster test, which has certain advantages to the clinician and to the patients. So it's a trade off. The test times are important in clinical practice. Obviously you can put patients through the machine more quickly, but also patients are more able to do the test with shorter strategies. And. And the CETA faster is in fact about 50% faster than CETA standard. And the question is how much accuracy is retained in these faster strategies. Certainly comparing CETA faster to CETA faster probably would be a reasonable thing to do. But comparing CETA faster test to a CETA standard test or even a full threshold may not give the Exact results. The common glaucoma programs vary somewhat depending on how far out in the field one wants to measure. In the peripheral field, the 32 takes essentially a circle about 30 degrees from central fixation and can capture that whole area. The 24,2 does extend out to about 30 degrees nasally, but it does cut off one side to about 24 degrees. And so it does cut down the test time because fewer points are sampled in that strategy, although it uses the same testing Strategy. So the 32 program is popular. See the standard here. I guess our full threshold here. This does measure out to 30 degrees from fixation and it does take slightly longer compared to the 24, 2. But it does measure more than one point between the blind spot and the edge of the visual field, which can be, can be helpful in detecting arcuate defects that may swing away from the blind spot a little bit more peripherally. So one of the main uses for visual fields is detecting glaucoma progression. And in the past this was difficult. Multiple exams were required to detect change and there were different ideas about how much change confirmed a change among clinicians. Estimating the rate of progression was difficult in the past, just looking at individual fields. Now there is glaucoma progression analysis software, GPA software, which is built into the Humphrey visual field. This uses the pattern deviation to identify glaucoma specific progression. It is based on the progression criteria from the EMGT study. And there is a curve and a slope that's generated along with variance thresholds so that you can see whether the test retest variability, whether the patient's test point is within the test retest variability or not. So this is a helpful way to pick up progression more quantified and, you know, extremely helpful to clinicians and picking up which patients really are progressing and which ones are not, by taking into account in a, in a standard way what the test retest variability is. The, the GPA analysis is tended to identify progression and it does try to confirm suspicious points over three tests. Triangles are indicated on the printout and as the new points that are varying from the baseline are picked up, they are progressively filled in as they're reproducible up to three times. So when the patient does show that a point is abnormal on three consecutive exams, then the point is filled in and it appears as a solid triangle. There is a GPA alert as well, which is helpful. It puts in plain English whether there's possible progression or likely progression. And this can be a useful flag for clinicians as well. So the printout does show the grayscale and certain critical measurements. There are reliability indices that are printed and warnings whether if these reliability indices are outside of normal ranges. And then at the bottom here there is a interpretation which does indicate whether the patient is likely progressing or possibly progressing. Obviously the clinician has to look carefully at these results and interpret them properly. But you know, can't rely upon the, upon the interpretation from the machine 100% like with any visual field. But it is helpful to have these flags on the printout. So here's an example of progression. You can see that on the right there are some points that are changing, they're not filled in. And with more repeatable changes, the, the points are filled in more. And if in areas where it is repeatable, in this case five points remained consistently depressed, then the machine does indicate that this is likely progression. So the frequency doubled technology is another strategy. These visual field machines are available. They're very useful for screening. There is a threshold strategy that is available with these machines as well. It is very fast. It screens in about 30 seconds per eye, certainly less than one minute even for a strategy that involves more points and at thresholds in about four minutes per eye. So these are relatively fast. They're fairly accurate. They do identify abnormal areas of the visual field. And there is an age related normative database as well. So this strategy has been helpful particularly for screening. The frequency doubling technology shows the patient a doubling illusion that's created by broadband bars on a display that rapidly alternate and create a doubling image that shows a change in the stimulus to the patient. And as long as they can detect this change, they can hit the button and indicate that they can see this. So this, this frequency doubling in theory does measure the ganglion cell responses that are thought to be damaged by glaucoma. So this can be in principle an effective way to identify glaucoma patients. So for screening tests, the time for the testing is less than a minute. And this has been employed in many screening strategies. For glaucoma patients. The results are somewhat comparable. The displays look a little bit different, but the field defects can be mapped out in a similar way. In this case we have squares that are progressively darkened as the patient is less able to identify the frequency doubling effect at the points. And this can reflect fairly well the actual visual field defects that are measured by standard automated perimetry. There is a more standard printout that is available in the Humphrey matrix. This is again frequency double perimetry that is displayed in a more standard way or more, let's say More similar to the standard on white perimetry. So it's available as a 24, 2 or 32 printout. And results are comparable to the standard perimetry Humphrey visual field analyzer in this case. So you can see on the left the Humphrey visual field, on the right the matrix and the scotoma is mapped out pretty well. And so this can be useful to assess or monitor patients. There is another option for evaluating patients short wavelength or blue yellow automated perimeter, so called swap. This in principle isolates and measures the blue cone function more. It uses a larger target size, yellow background and a 440 nanometer blue target. So in studies it has been found to be able to detect glaucoma damage perhaps earlier in some patients, maybe even up to three to five years in some studies, compared with monochromatic perimetry. But there are disadvantages. The test is more time consuming. It's 15 to 17% longer at least. There is a general depression of the hill of vision using the swap and so it has a smaller dynamic range for detection. It is more sensitive to media opacity such as cataract. And there is a larger inter subject variability for the threshold values. So oftentimes with SWAP we'll see a relatively dark field compared with white on white perimetry. And this may limit the use of the test in older patients, say for example with cataracts, other patients, but still with younger patients, more clear media and perhaps have early glaucoma changes or glaucoma suspects. This can be employed in that situation with, you know, and it can be helpful. Visual field testing is used for glaucoma severity coding. This coding requirement has been in effect since October 2011. Now it's fully in effect. First of all, to code for glaucoma you have to have the optic nerve findings consistent with glaucoma. And then we're required to use a visual field to stage the glaucoma. There are certain types of glaucoma that don't require staging. For example, anorrhytic glaucoma doesn't require a stage, but most types do require staging. Now stage zero is an unspecified. Staging level and that is when the stage is used, when the stage is not recorded in the chart. Stage one is early glaucoma where there is no visual field defect. The visual fields have been measured, but there's no defect. Stage two is moderate glaucoma with a visual field defect in one hemi field not extending to within five degrees of fixation. And stage three is advanced glaucoma. The visual field loss is in both hemifields and or extends to within five degrees of fix fixation. Stage four is indeterminate. And this is when the visual field is not yet measured or a patient is unable to do a visual field. So these different stages are indicated on the coding and often required with a number. The number is at the end of the code there, that's an ICD9 code. I guess the numbers indicate whether the patient is stage 0, 1, 2, 3 or 4. So this is, you know, visual fields are required for coding. So the visual fields though for clinicians really are extremely useful for all stages of glaucoma. It used to be thought that, you know, we didn't have to do visual fields in early glaucoma so much, but the results of clinical trials in early glaucoma patients have indicated that we really do have to pay attention to the visual fields at all stages of glaucoma. In the OHVS study, for example, up to 50% of patients that did progress were detected using visual fields, up to nearly 50% here. So almost half the patients in some of these groups were identified using visual field testing. And so we do have to check the visual fields really at all different levels of glaucoma progression. So Goldmann perimetry, I wanted to mention, this is a manual perimetry. It requires a skilled observer to map out the defects. The observer moves the stimulus, which varies in intensity and size on a map and manually maps out the visual field. And this is not very commonly done now, but can be, can be helpful in patients that can't do automated perimetry and is still used to some extent, although much less frequently now as automated perimeteries become more flexible and easier to use by patients. So in conclusion then, the harmful visual field CTA now in particular, and in my case the 3, 2, but 242 is also commonly used, is useful for routine clinical use, which includes initial assessment and follow up of glaucoma patients. Software can be helpful now in detecting progression. It's commonly used. The glaucoma progression analysis has been a benefit to clinicians. SWAP can be useful, but is less commonly used. And also we have the FDP which has been helpful for primarily for screening purposes. So I hope this gives you an overview of the use of visual fields in glaucoma patients. Thank you very much for your attention.