![]() Other signs include that the false-positive index is a little high, and the blind spot isn’t as dark as you’d expect it to be. If the total deviation plot is normal and the pattern deviation plot isn’t, something is likely amiss.Īnother clue that something is unusual is that the mean deviation in a normal patient is usually no higher than +2 dB. This should jump out at you as unusual, because normally the total deviation plot shows some depression if the pattern deviation plot is abnormal (except in some rare circumstances among younger patients). It can also be seen in those with milder glaucoma, in which case an examination of the optic nerve will help one realize that the test was faulty, because the optic nerve would look much healthier than a nerve consistent with such a poor visual field.Ĭase 2.Here, the total deviation plot is normal but the pattern deviation plot shows an inferior depression. This pattern can be seen in patients with advanced glaucoma, in which case it can be difficult to know the true status of the peripheral vision. Some patients may repeat this pattern over and over again, either because they don't understand the test, they’re lulled to sleep during the test, they have early dementia or they simply don’t like taking the test. This type of artifact is fairly common in a busy clinic I expect you’ll see it at least a couple of times a month. That’s why you get this four-leaf-clover pattern. Once the technician walks away, perhaps to start another patient on a visual field test, the patient can lose interest in the test and stop responding. Why would this lead to false-negative responses? Usually, while the first four spots are tested, the technician is hovering over the patient and the patient does a good job. Test points spiral out from those central quadrant testing points. The reason this occurs is that the testing algorithm always starts in the center of each quadrant that’s where it does a threshold test, even if you’re using the SITA standard strategy. This is a classic “cloverleaf” pattern (see circled area)-a type of false negative result. However, the central points in each quadrant are much lighter than the surrounding points. See if you can identify the nature of the artifact and its cause before reading the explanation.Ĭase 1.At first glance, the visual field defects look like dense arcuate scotomas. Here, I’ll present a number of visual fields in which something is amiss, and then explain what produced the artifact. It’s important that we remain vigilant for artifacts and errors. On the other hand, some diseases-as well as some types of human error-can produce test results that do resemble glaucoma, giving the appearance of a glaucomatous scotoma. It’s true that some nonglaucomatous problems produce a pattern that’s recognizable as something other than glaucoma. But in the clinic, seeing a host of patients on a busy day, we may be looking through visual fields quickly while simultaneously fielding patient questions, and not always looking carefully at the indices and other details-details that might alert us that something isn’t what it appears to be. However, that can make it easier for us to misinterpret a field we feel comfortable that if there’s an issue, we’ll notice it. Most of us are aware of the issue of artifacts, and we know the patterns of many of them. So, when we’re reviewing field results in an attempt to determine a patient’s condition, and whether or not progression has occurred, we have to expect variability and artifacts. The test subject is a human being, prone to being imperfect and influenced by external factors, and the same is true of the person administering the test. L ike any test, visual field tests can contain artifacts.
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