Lecture: Advanced Perimetry Interpretation: Recognizing and Dealing With Artifacts

This webinar will discuss artifactual visual fields that can make interpretation difficult. There are several patterns of visual field loss that should make the ophthalmologist wary that the field is not reliable. This talk with focus on the Humphrey Field Analyzer.

Lecturer: Dr. Wallace Alward, Director, Glaucoma Service, University of Iowa Carver College of Medicine, USA


Lee Alward: Well, hello. My name is Lee Alward. I’m going to talk today about Perimetry and particularly dealing with artifacts. So, I have no conflicts regarding this talk. Just to show you where I am, I’m in Iowa City, Iowa which is somewhere most people have never heard off. The nearest big place to us is Chicago 350 kilometers to the east. And it’s supposed to be spring here but we woke up this morning to surprise snowfall. I know a lot of us are socially distancing, trying to stay inside and stay safe. I hope you’re all healthy and your families are healthy where you are.

And just to reiterate the topic of this is dealing with artifacts. So, this is a little bit more advanced than just how to read a visual field, but how to interpret a field or to not interpret a field if it’s not interpretable. So, I’m going to start by asking a few questions that you can respond to. There are four questions and just to get a sense of what everybody, what everybody’s knowledge base is obviously only get a cumulative total from everyone. And then I’ll ask the same questions at the end.

So, question one what is this patients most likely refractive error? -8.75 diopters, -2 diopters, plano or +3.5 diopters. So, question two. What is this pattern most consistent with? False positive responses, false negative responses, fixation issues or inappropriate refraction correction. Same choices for this question and the last question. What is this pattern most consistent with? Again false positive, false negative, fixation issues, inappropriate refraction. And lastly what is this pattern most consistent with? Same four choices. So, I’m going to talk specifically about the Humphrey perimeter.

I think most of what I’m saying is going to be applicable to the Octopus. But at least in where I live in our practice and all the referring practices around us. This is the device that is used. And part of my reason for me giving this talk is that I see a lot of patients sent in who are felt to have glaucoma or worsening glaucoma with visual fields that are really unreadable. And so I really want, I want you to come away recognizing some of these patterns that we just showed in those questions. When to throw a field away and not use it?

So, how do I normally approach the visual field follow up visual field. So, we’ll keep coming back to this particular visual field. It’ll have this reference field at the bottom. So, is a field reliable? So, we’re going to look and see about false fixation losses, false positive, false negatives. We’ll talk a lot more about those. The gaze tracker and then there’s a field stable. I hate to admit that I actually do look at the gray scale. A lot of purists would have you not do that but you’re going to look at things like the visual field index, mean deviation, pattern standard deviation.

And the pattern deviation plot, I think if something is stable and reliable field. It does not take very long to know that things look stable. But there are a lot of numbers on this print out. And do you always need to look at them? And the answer to that is no. But do you ever need to look at them and the answer to that is yes. And particularly if there’s been a change, if there’s been an unexpected change in someone’s visual field then you need to start looking at things you don’t normally look at. And so that’s sort of where this talk is going.
Again if we go back to our reference field at the top, it has some information tells you it’s a single field analysis. We’re looking at the left eye. The strategy is 24-2 again it’s the left eye. It has the patient’s date of birth. So, here’s a patient comes in with the field effect. That sort of looks like an inferior arcuate defect except it looks odd. So, blind spot inferior arcuate nasal stop. But when you look at the Humphrey with 24-2 print out. It’s like the 24-2 accept to get rid of the last row of spots of test sites except for nasally because obviously for a glaucoma field nasally is what’s important. And what you’re noticing is that the blind spot is on the nasal side of this patient’s field.

So, you see I feel like this blind spot here left eye but this is a right eye. And it’s harder in an eye like this that has glaucoma this loss a little easier. That’s the blind spot there. If we look at the overview you can see that in 2017 to 2019, not a whole lot of change. And now this looks completely different but it looks just like the fellow line. So, not a common thing to see but something that you need to recognize a little easier to recognize that if there’s no damage. It’s just a blind spot on the wrong side.

So, again if we come back up here, date of birth but rarely is this a problem. But it can be a problem. And you should, you know, if you’re really struggling you should and you’re digging deep to figure out why this patient’s field has changed. You might want to check and make sure they didn’t miss enter the date of birth. This is a man who drove from very far away because his field was worsening. You can see he has a superior defect there. Mean deviation -6.17 decibels. So, we repeated his field and you can see that the gray scale looks exactly the same. Most things look exactly the same except for the total deviation. Mean deviation though is now – 1.52 instead of – 6.17. Total deviation again looks different but everything else looks identical. And that’s because the wrong date of birth was entered. And so this patient is being compared to a two-year-old who knew that the test could extrapolate back to what a two-year-old’s field should look like instead of a 6 to 9-year-old.

So, again like the first rare but you need to start. You need to have those in your thought process. A lot of data here tells you a stimulus size, pupil diameter, background is always the same, the acuity, the refraction and all these reliability indices. So, pupil diameter less of a problem now that it was 20 years ago when we used a lot of pilocarpine. But if somebody has a very small pupil, it will change the visual field. So, this is from Dr. Anderson’s book just showing the pupil at 1.5 millimeters versus pupil of 4 millimeters.

We still have a very few number of patients who are on pilocarpine or echothiophate. And if you do have somebody on a cholinergic, you should dilate them for the visual field. A bigger problem is refractive error. More common problem is refractive error. If the patient’s refraction has changed, that can pose a problem. This is from Dr. Anderson’s book. I have normal in quotes because this is my visual field when I was his fellow. But you could see with my correct – 3.75 diopter correction on the right. And if the technician had actually treated me is how I was a similar amount of hyper myopia instead of myopia.

This is something we see rarely but occasionally. This is a young patient 27-years-old whose field is suddenly abnormal. Minus 4 diopters is fear for the refraction. But then she related to us and then the mean deviation. You could see here – 4.81 diopters. She related to us that she had undergone LASIK since her last field hadn’t told anybody. And so if we repeat the field with no correction, she’s young doesn’t need an add. All of this goes away, mean deviation – 1.02.

So, those are all uncommon things. I think you need to think about them if you’re just puzzling over a visual field. The things that are more common we’re going into now which are the reliability indices and how these can really throw you off. So, fixation losses, dissipate in a patient has no fixation losses. But remember how this is calculated. So, they use a technique Heijl-Krakau technique, I don’t think you need to remember that name specifically. But what the perimeter does is mapped the blind spot early in the task. And then periodically come back and project a spot into the blind spot. And if the patient responds a perimeter assumes that the patient has lost vexation, the blind spot has moved. But sometimes mapping of the blind spot is not accurate. And so if you have high fixation losses but everything else is normal, I usually consider the field to be reliable. And you can use the gaze tracker which is part of the newer not that new but newer software to confirm fixation.

So, this is somebody that’s confusing, right? So, here, there are 7 out of 19 fixation losses. Rest of the false positive false negative look pretty reasonable. But if you look at the gaze tracker, the gaze tracker looks awfully steady. And how would you explain that? Well, this is somebody has just a really tiny optic nerve. And so when the perimeter comes back and projects a spot in the optic nerve is sometimes missing the nerve and getting retina. And so if you this is something that you see not uncommonly that there’ll be a lot of fixation losses but a perfect gaze tracker. You should think about in those situations that this is a patient who has a really tiny optic nerve.

And you can see just the opposite. You can see this person pretty good fixation losses but look at the gaze tracker, the bottom, it looks like he’s watching a tennis match or something. And so this disconnect is usually due to a very large optic nerve or an optic nerve with lots of peripapillary atrophy. So, take the fixation losses with a grain of salt. When you are looking at fixation losses and it doesn’t line up with the gays tracker or if your machine doesn’t have a gaze tracker, but they have lots of fixation losses and everything else looks pretty good, just ask yourself that maybe that’s because they have a small optic nerve. Or the opposite if they have no fixation losses or very few but the field otherwise looks horrible. It may be because it’s a situation like this where they have lots of peripapillary atrophy or very large optic nerve.

So, false positive errors is something that we see a lot of and sometimes you’ll see a field like this. Some of us call this the dreaded White Scotoma because there’s an area here where the gray scale doesn’t have any gray. It’s just perfectly white. And there are numbers 48 decibels which are sort of Superman kind of numbers. So, I think you would hopefully you would look at this, you’d see the 57% false positive false positive rate. You see this white area in the middle and you think you know this is a field I can’t. There’s no point in me even wasting my time looking at this visual field.

But the other thing I want you to notice on this field is this disconnect between total deviation and pattern deviation. Because that disconnect by itself usually almost always means false positives and sometimes it’s much, much more subtle. And most times it’s much more subtle than Superman’s field here. So, why does that happen? If you think about how the pattern deviation is calculated. The concept is that you hear is the hilo vision, right? And so you have something like miosis or cataract usually cataract with the most common thing or corneal edema, all the points are depressed. And so the hilo vision is set down expectation for all the points is set down. And then what the perimeter is looking for is whether or not there are focal areas of laws in this overall depressed visual field.

So, that would be a situation like this. This is a somebody is total deviation. All the points are down quite a bit. But when you correct for the overall depression of the visual field then you see this arcuate scotoma, kind of shining through. Now real honestly, you could see that looking at the gray scale but this helps to pull it out for you. And what it does is it takes the seventh most sensitive non-edge point and sets that to zero, not the seventh most normal point but the seventh most sensitive point. So, in this case, that’s minus six decibel. So, that whole hilo vision, whole expected hilo vision is set down. And then when you correct everything for that, you end up finding the superior RQA defect.

But what happens if somebody is trigger happy and they’re very anxious? They’re just pushing every time they hear a sound then the hilo vision is going to be lifted. And so the expectation is going to be that all the points are super sensitive. And if things don’t — aren’t super sensitive they’re going to show up as an abnormal defect.

So, here’s back to our Superman field. The seventh most sensitive point is 16 decibels above fixation, right? So, this person’s field is normal or higher than normal compared to age corrected normal. But most of the points are depressed because he’s not uniformly trigger happy. This is a more common thing to see. There’s no whiteness here. You know, it doesn’t look that bad. There’s only 4% false positive. But this disconnect should really make you think that this is a field that is a very suspect. These are the kind of fields that I’ll show my residents from across the room and say tell me what this field is showing. And they’ll say hopefully they’ll say false positives. This is someone has a lot of false positives.

So, it’s important though to point out and let me back up to this field. These don’t really line up with anything, right? This is a field of somebody who has more on pattern deviation than total deviation. But this is one of those patients who has perfect vision, you know, test pilot kind of vision. And no false positives up here, all of the reliability indices are normal, and this defect thus follow a pattern that is consistent with glaucoma this loss. So, rarely you will see this in somebody has great vision that the pattern deviation is higher than the total deviation. But I think there would be 50 of the others for this. And again it should follow a glaucoma’s pattern.

Usually like in this patient, it’s a sign of false positive responses. So, I really want you one of the things to kind of, one of the points I want you to take out is this disconnect here. And when you see that thinking I think this is perhaps an unreliable field. We don’t have any zero here is not this is an edge point. So, technically it shouldn’t be using that point. But the whole hilo vision in this person is lifted 4 decibels. And so again look for that disconnect.

Usually these are young and patients who are anxious, they worry that they’re going blind. And so it’s I think it’s usually curable if you reassure them. Tell them that the way the machine is designed is that its thresholding these points. So, it’s half of those signals the patient is going to miss by definition no matter how great their vision is. And so if usually if you tell them that and they try it next time, they’ll do a lot better.

So, false negative errors are occur when the machine has mapped out parts of the visual field. And comes back and projects a point that is a signal that is much brighter than had been previously detected. So, if you’re at a point where it had been 20 decibels of sensitivity and that come back and project a 35 decibel target and you don’t respond to that, then the assumption of the perimeter is that you have fallen asleep or lost interest or for whatever reason are no longer responding.

The extreme of this is the cloverleaf field where the patient responds to these four targets at the beginning and then basically loses interest falls asleep or for whatever reason stops performing. And you can see these are the four initial points that are used to just to start the field. The machine test these points to kind of get its bearings as to how depressed the whole field should be and then it moves on. Just as an aside when you see in the full threshold fields not in CIDA which is has a whole different strategy. But if you’re using a full threshold field and you see numbers in parentheses like this. That means that that’s the point that’s retested. So, if these four cardinal points are retested. And then points like this that are surprisingly different, right? So, this is not surprising go 23 23 21 gets less sensitive as you go towards the periphery. But when you go from 21 to 9, that’s a big drop off so the machine would just reject that point. So, false negative can be seen early in glaucoma. So, you shouldn’t always just blow these fields off.

These are usually patients who are older and maybe tired. Maybe they just drove six hours to get to your clinic. Usually I feel like if there’s not an explanation for it, it’s usually not curable, you usually can’t talk them into doing a better performance, if they’re just too old and struggle with this. Now you can try a Size V target and I do this much more. We’ll talk about that in a second. We have the ability to do Goldmann, most people don’t. But for some people who are elderly or very young and just not facile with interacting with computers sometimes having something done manually with a human being at the other side of the device is a better alternative. And lastly some people just can’t do field. So, on a lot of my charts, I just acknowledge that I can’t follow this person with visual fields.
But let’s talk a little bit about Size V. So, this is somebody with a superior arcuate defect mostly a little bit of lost their inferiorly. Pretty poor performance, 11% false positive errors, 7% false negatives. This is somebody who I switched over Size V, so I used to do Size V with a bigger spot typically only for people who had such severe loss that I just wasn’t seeing anything and I just wanted to increase the range of what I could see. But more and more I’m using it for people who are bad field takers because the bigger spots just give them more confidence often and ability to do the test better.

So, here’s the same patient with a Size V target. And you can see the performances dramatically better. Now we’re not seeing the same degree of loss as we do in the size III that this may be a very small defect that only shows up, this pair of central defect with a small target. But I could use this to go forward and use this as my new baseline because I really not going to be able to do much with someone whose performance is so poor. And I used to think that I mean this is a full threshold field, right? This is a seat up. And so I thought. Well the patients are going to hate the difference in test duration. But you could see that there’s not really that big a difference in test duration because the sheet will move pretty slow if you’ve got a lot of stuff going on.

So, think about Size V not just for people who have lots of loss, lots of damage. But also for people whose performance is pretty shaky. When we do fields, we always check the Fovea. A lot of people don’t. To me the Fovea, of course, is the single most important point in the visual field. But testing a Fovea brings in the possibility of having this kind of a visual field. And what are we seeing here? So, we’re seeing this horizontal that doesn’t really respect the horizontal meridian and we’re seeing a blind spot.

That’s a little bit droopy here. And why is that occur? So, if they’re map, when they mapped a Fovea they can’t project a light on the camera. So, they have the patient looked down and they have them look in the middle to triangulate in the middle of these four points. And then use that area in the center here to test a Fovea. And then the patient is supposed to look back up to this fixation target. And if they don’t, they will do the entire test while looking down below. So, this is at the same patient I just showed you. This is before and after. And once you’ve seen this, you’re not going to miss this, right? You’re going to see that instantly know that this is somebody who failed to re-fixing.

So, gaze tracker at the bottom here and then what the gaze tracker does is in the upward spikes are fixation losses or movement. So, that is using a sensor to watch the cornea and as the cornea moves and downward spikes like this is when they can’t get a signal. So, that’s probably a blink. For people who are — have wandering eyes that usually gets worse as time passes.

So, the gaze tracker to me is just it’s something that I look at in conjunction with as we talked about before with fixation losses. I mean somebody whose gaze tracker looks like this. I would feel is really wandering a lot. And it’s going to make me question somewhat the results. Rim Artifacts, we see like this. And what you see is the sudden drop off to zero or less than zero. So, 25 to zero and then less than zero. So, it has this characteristic pattern. The thing you should always be in your mind whenever you’re looking at a visual field is what the nerve fiber layer looks like, right?

So, if what you’re seeing doesn’t fit the nerve fiber layer pattern, then you should be wondering. And this is something that once you’ve seen it a few times, you’ll instantly recognize it as a rim artifact. Just as an aside what’s the difference between zero and less than zero. And that comes back to knowing what these numbers mean, right? So, this is decibels is 28 is decibels of attenuation. So, that means that you have this 10,000 a [indiscernible] [00:26:56] blight. That’s the brightness of the light, the target light in the Humphrey perimeter.

And you can attenuate that light, you can put neutral density filters in front of that light and attenuate it down 28 decibels and still see the light. That’s what this 28 means that this you can do 25 decibel. So, 28 is more sensitive than 25 which is clearly more sensitive than five or zero. What zero means is that this is un attenuated light. So, it’s a 10,000 [indiscernible] [00:27:26] the brightest light that the Humphrey can make and the patient is seeing it. So, the patient does see this spot.

Less than zero means that they don’t see it. So, there is a difference between zero, less than zero. Rim artifacts usually you see those people with high +4 fractions, people with high plus refractions less so in somebody with a minus refraction or the lens carrier maybe set up too far from the patients eye. Or the patient may have drifted back and so they’re now seeing the edge of the lens.

Lid artifacts are parameters are very good at taping the lid. But not everybody thinks about that. And so you see this very odd field effect and again in your brain you should be thinking, well, does this match the nerve fiber layer? And the answer of course in this case is no. And so here we have the same patient tested after taping up the eyelid.

Remember that there’s a learning curve and so the patients first field may not be completely reliable or believable. But you should usually give them a chance. This is somebody who have horrible performance on their first field. And then you came back and did a really good job the second time. It’s a very unusual experience for patients especially the first time they have a field. One of the parts of our curriculum to teach our residences, all of our residents have to have a visual field performed on one of their eyes. Just so they know what it’s like and partly so that they don’t take somebody who just struggle doing Snellen acuity and put him in a perimeter. I mean it is not something that’s easy. And it’s a lot less easy for people who are not sophisticated with computers and interacting with things that are computer based and there’s not human based. Again if we look at this top field that doesn’t really fit with the nerve fiber layer.

So, a lot of perimetry is pattern recognition. And as I said I often will just show that my residence or fellow field from across the room and say what’s wrong with this field. This one I really want you to remember this disconnect between total deviation pattern deviation you should be thinking. Is this a false positive field? Again, it may be somebody with superhuman vision who has early glaucoma defect but usually it’s false positives. Also the dreaded white scotoma where you have these white spots in the visual field, that’s the field that you should just throw away.

The cloverleaf field, excessive false negative responses someone who’s fallen asleep or just checked out of the testing process the drooping blind spot or failure to respect the horizontal meridian, somebody who never re-fixated after testing their fovea and rim artifact. So, in the end hopefully you’ll have a field that’s believable. Help you provide the best possible care to your patient. And you recognize that this is probably not an arcuate scotoma. This is somebody with a lot of pulse positive responses. And this is not truly a believable defect. And you would in this case I think would rather than referring this patient for a glaucoma evaluation, you would just tell them about how they’re supposed to miss half the spots. That’s a normal thing to do. And then repeat the visual field after a month or two and that would probably go away.

One last thing is this field. So, this is somebody with horrible performance, right? 38 33% false positives, 21% false negatives, five of six fixation losses, but this is glaucoma, right? I mean this is believable that this person has a field defect. They’re not going to make up something that’s so classically glaucoma as this. So, this is real but you wouldn’t want to follow this person for subtle visual field changes. I mean if every time their performance was this bad, I think you’re not going to really pick something up. I would probably try this person with the Size V, see if there’s a way that you can sneak a visual field out of this person. But he may not, he may be somebody who field testing is just not going to be part of their treatment. But this is real and so that I just want to close with that. I don’t want to throw everything away.

So, let me go back and see if we’ve learned stop here. So, this patient’s most likely refractive error. Yes – 8.75, – 2, plano or + 3.50. So, most of you got that right. +350 so this is rim artifact that you see in patients who have typically usually hyperopic refraction often affected patients. What is this pattern most consistent with? False positives, false negatives, fixation issues or inappropriate refraction? Right. So, most of you again got false positive responses. This disconnect between total deviation pattern deviation. How about this pattern? Same four choices, false positive, false negative, fixation issues or refraction issues. Right, so fixation issues patients looking down to mapped their Fovea and failed to re-fixate. And lastly this pattern, what is that most consistent with? Same choices again. False positive, false negative, fixation issues, inappropriate refraction. Right. So, again the vast majority of you got this right. False negative responses, this classic cloverleaf field.

So, all of this material I have a website called iowaglaucomacurriculum.org Orbis has translated this now into Mandarin. So, chapter six really is pretty much what I just told you. But also about how to interpret a field. And so if you have any, if you want to hear this again that’s a place to go if you want to learn more about Perimetry. Thanks for listening. Let me look at some of these questions. What is the cloverleaf pattern mean in a visual field? Is there any scientific explanation? Evidences explain this I think we answered that basically cloverleaf means that you tested the first four spots and then the patient stopped paying attention.
Is it compulsory to correct for both distance and near? So, typically yes. And so you would take the patient’s distance correction and then add an add for the distance to the bowl. And so for somebody who’s young, has no refractive error, they wouldn’t use anything, they would just use your own accommodation. But for somebody who’s 50 and is a plus five then you would use that plus a reading add for the distance of the bowl. So, yes, you need to correct both.

So, how do you deal with cases where fields were consistently unreliable and unequivocal optic has changes at OCT? But as I said I mean you sometimes you can’t do visual fields on patients. So, I would definitely try a Size V. I think you might find that to be tremendously helpful. And, you know, if you have the ability to do Goldmann visual fields or something that is where the patient is interacting with a human being, then that would be another possibility. Most places can’t do that, they don’t build Goldmanm anymore. There are kinetic programs and Humphrey and Octopus. I haven’t found those to be helpful. I think the people struggling with Perimetry, the 88-year-old patient struggling with perimetry is struggling with the interface with a computer more than they’re struggling with the technique. And so for us we would have a human do a field. But that’s not available for most people. So, try the Size V, I think that you would find that helpful.

How do we explain to the patient the difference between III and V, Size III and Size V is it a reliable test? Well, yeah I think it is reliable. It’s, I just tell patients that sometimes it’s easier for them to see a bigger spot. I mean it’s no shame that they can’t perform well on a Side III Humphrey. I think for all of us all of you as well as me. It’s good to take a field test to realize how difficult it is. But what I wouldn’t do and I think this, when I talked to people who are really gurus of visual fields and do visual field research. I think you should do the same thing over and over again, right? So, I wouldn’t do a Size III today and do a Size V next time. If I feel that somebody is really failing on a size III, I would in one of their visits maybe do both the III and V in the right eye. The III to see if there’s been any progression and the V as a new baseline. And then I would just do V from then on. I think if you toggle back and forth between size III and Size V and between 24-2 and 10-2. You get less information than if you do the same test over and over and over again. And I think people who do a lot of visual field research would tell us that.

So, if patients macular apathy can you confidently performed perimetry? Sometimes no, sometimes if someone has poor really poor central vision, they cannot fixates centrally and so their eyes wander that’s obviously difficult for them. When we do Goldmann perimetry, sometimes the perimeters will put a cutout X made out of X ray film. Of course, X ray film doesn’t exist anymore and have the patient triangulate towards the center so we can do that in patients who have terrible macular degeneration or whatever reason don’t have the ability to fixates centrally.

When do I use a 24-2 program? I don’t, so the 24-2 was the program we always used. And the problem with it was that there are a lot more issues with the last row of test points having artifacts from of rim and other things. And so we most people moved to the 24-2. But as I showed you earlier in the talk, we still keep the nasal points because those nasally is the part of the field that you’re most interested in, right? So, it’s kind of worth it to have those points out there.

What percentage of patients do we need to change the stimulus size because of poor performance? It’s not high but I would say maybe five or 10% of my patients. You know, I have a referral practice where people come often from very far away and often have very poor very badly controlled glaucoma or very severe glaucoma is better way to state that. So, I used Size V in those patients. And then I use it for performance problems more and more often as time goes on, but I would say maybe 5% of my patients.

What’s the difference between 24-2 and 10-2? So, these numbers 24 is the degrees of visual field. So, 24 degree field is measuring 24 degrees plus those little points nasally. 10-2 is measuring more central just the central 10 degrees. We’re learning more and more that there’s loss early on centrally. And so some people are fixating focusing more on the central 10 degrees. The -2 in 24-2 and 10-2 refers to where the points are lined up. This may be trivia but the original points it was 30-1 which was all that they had points lined up on the vertical and the horizontal meridian and then every six degrees. But the problem with that is if you had a horizontally respecting defect or in a neuro-optic case, vertically respecting defect sometimes they would be on that point, sometimes they wouldn’t. So, the perimeters have shifted the points three degrees off of the vertical and the horizontal. And that’s the -2. So, you almost never see a -1 anymore. But so the 24 refers to the degrees that are being tested and the 10-2 the two refers to the fact that the points are offset from the horizontal and the vertical kind of attribute point I guess. And, you know, you can go beyond 24 or 30. There’s a 30-60 that would measure more perfectly. But the automated perimeters are not great out in the periphery. So, I never use that. And I’m not sure I’d recommend ever using that.

Can you explain again the difference between zero and less than zero? So, again you know I think I probably didn’t know this until a few years ago because I just assumed that how can you get less than zero, right? But a zero means that the patient is seeing at that point had less than zero means that they’re not. Zero means for seeing the brightest light that the machine can make but it’s not totally blind. So, if you have a field that has a lot of zeros, I mean it’s close to being blind but it’s not totally blind. Less than zero means that spot does not is not seen at all.

What difference does it make leaving the Fovea on or off? So, you know, I would say most people who send patients in when they send in their fields from the outside don’t usually test a fovea. I think the Fovea is the most important point on the perimeter and I think it’s helpful for me to see the Fovea threshold. The only reason I brought this up in relation to Fovea is because if you don’t ever test a Fovea, you’ll never see that drooping blind spot or the low hanging horizontal.

Are the rim artifact is it always related to high propia? No, I mean it can be related anything that brings the edge of the correcting lens into view. So, that could be that if you have an inexperienced perimetry and they put the lens carrier too far from the patient. Or if the patient has backed up then you can you can see that.

Is it possible that a scotoma will improve with control glaucoma? Absolutely, you know, some people Dr. Spaeth (phonetic) in Philadelphia would argue that. Unless we see improvement we haven’t really controlled glaucoma, I think I don’t — I’m not quite — I don’t quite feel that way but yeah I’ve definitely seen fields get better over time, particularly after trabeculectomy where the pressure has been dramatically lowered. So yeah you can definitely see that.

How do we interpret mean deviation? So, mean deviation is the center. So, in the perimetry print out lower left. It has the points that are comparing this patient to age corrected normal, right? So, it’s comparing somebody who is 54 with other normal people who are 54 and giving you a deviation from normal. So, the mean deviation MD which is in the right hand side of the field print out is a center weighted average of those points. So, if somebody’s mean deviation is down 6 dec, – 6 decibels that means on average their whole field is depressed by six decibels. And that could be cataract, it could be other things but that’s a measure of glow, it’s a global measure of patients loss.

Patients considerations aphakic/pseudophakic patients not really, they definitely need a full correction for near. Please explain the nasal step finding. So, the nasal step just means that if you know again when I emphasizes I was talking should always have in your mind the pattern of the nerve fiber layer. But, you know, the nerve fibers arc over but they don’t on the temporal side of the retina, the nasal side of the visual field. They did not cross the horizontal meridian. That’s not true on the other side but that’s true where most damage occurs in glaucoma is on the nasal side superior arcuate almost it should respect the horizontal meridian. And that’s called step if it travels right along the nasal meridian.

When do we use in a field test other than white on white? I don’t the swap, the Short Wavelength Automated Perimetry which is blue on yellow, that is felt to maybe pick up very early defects I think patients find it tedious to do. There are frequency doubling perimetry. There are other technology to techniques. I think one of the things again that I’ll emphasizes I think it’s important. I think it’s important to do the same thing over and over again. If you find something that works in this patient if you have somebody who you’re following the 10-2, I would stick mostly with the 10-2. For me it’s usually a 24-2. There’s a new 24-2 that test points now around the ads points in the peri-central area. And we’ll see how that works. We’re just now trying that.

How do we analyze the 60-2 field since there’s no database? You know, I don’t think the 60- field is very helpful. And the time I might use that is if you see something on the very far periphery of the 24-2 that you’re wondering why I wonder if this extends out farther. Again I’m spoiled and that I could do Goldmann test. But you might try a 30 60-2 to see if there’s something out there in the periphery. Early on when automated primary first came out, you know we’re testing back then the central 30 degrees. Dr. Bruce Shields did a study comparing Goldmann’s to automated perimetry to see if we’re missing stuff just by hanging around in the central 24 30 degrees. And really you’re typically not missing much. If you see somebody for us we see somebody with end stage glaucoma that just has a little central island. We might want to see those peripheral islands and then we would do Goldmann perimetry. But I think the amount of artifact that you’re going to get into with the 60-2 field is just going to make it not worth doing for me and my experienced.

What is the best duration to repeat perimetry one is worried about learning curve? That’s a good question I would say for my practice I typically if somebody has been stable for years and years. I typically do perimetry once a year. You see stable patients twice year and one of the visits with the OCT and perimetry the other visit. We just check the pressure, look at the nerve. If it’s a new patient and you’re trying to establish a base, I don’t think it’s unreasonable to do field. Then redo it in three months or so and then maybe again in three months and get a really solid baseline. Again the people who do visual field research I think would have us do more visual fields. I think the patients would rather we did fewer and in the US our insurance companies they’re not excited about us doing too many visual field. So, I think though it’s good to get a really solid baseline to do enough visual fields at the beginning that you A) that the patient gets used to doing them. They become good at performing fields. And B) that you have a really solid baseline.

Can the mean deviation have a positive sign? Absolutely. Something you know it’s a mean deviation compared to normal. And so that’s a bell shaped curve. So, some people have better than normal vision. You know the people who are seeing the last line on the Snellen chart with no problem. And so they can have a plus sign. You can also have a mean deviation that’s positive in somebody who’s trigger happiest false positivity.

Patients are part of the world don’t really know their real date of birth. That’s an interesting question. I would just think you would approximate it. You would put January 1st 2004. I mean if they don’t know. But, you know, a year or two is not going to make a big difference. A couple people asked is it okay to do perimetry in a dilated pupil? Yes. I mean you can obviously need the full correction even if it’s a young patient for the working distance. But yeah, you could do that. The problem is going to be a little bit comparing it to previous and subsequent fields.

When would I use a 30-2 versus a 24-2? I don’t really use the 30-2 anymore. I found that those peripheral points were so. We had so many rim artifacts with the 24- with a 30-2 that I didn’t mind losing those that last round. When would I use a full threshold? I don’t typically use a full threshold field. I use Sita, I think that, you know, Sita that makes a lot of assumptions. I was a little uncomfortable with that at the beginning but I think Sita does a great, a great job. And I think the patient’s performance is better because the field is faster. Especially if it’s a near normal field or just a little bit of a visual field defect.

What about media opacities? How reliable is your test? Well, it’s harder for the patients, of course, to do a field test with media opacities. But again that the pattern deviation will extract the media opacities for you to show you things that are focal defects in that patient. You can do that certainly with cataracts and other things. But you have to correct for it and the machine does. There’s actually a pretty good job of correcting for it.

In the case of macular disease, can we do Humphrey Field with the Fovea? Absolutely, definitely could do that. A few people asking about fields and patients with the nystagmus. You know, that’s a great question. I think there are again patients who can’t do visual fields. I might try it but it may be unreliable especially the severe nystagmus but we do fields on patients with nystagmus who have nystagmus. You just, you know, obviously any time you do the patient is going to have poor performance. You need to take the results with a grain of salt. You know, you wouldn’t be acting on a two decibel change and someone who has 10 decibels of range of performance issues.

When do I use see the fast? I don’t really you see the fast. I don’t have an issue with it. It’s just you know my practice. We typically just use regular Sita. A few people are asking me to explain the -2 part again. And since we don’t use the -1 anymore it’s kind of it’s of historical interest. But the -1 the original octopus was lined up along the vertical and along the horizontal. So, they tested points along the horizontal. But if you had an arcuate defect that came to the horizontal and you’re testing right along the horizontal, you might see that or you might not. And so what they did was they moved the horizontal points three degrees above and three degrees below and so that became the -2 technique same with the vertical. So, nobody uses the -1. You can get it on your perimetry or you can ask your perimetry to do a 30-1 or 24-1 and you could do a 24-1 and a 24-2 and merge them. But the patient wouldn’t like you going through all that. But, you know, I think you see these numbers like -2 and you’re thinking what does that mean.

So, I just wanted to know what that meant. Can I explain the seventh best point again? So, the seventh most sensitive point is used to correct the total deviation to the pattern deviation. And so it takes the seventh most sensitive point and either moves usually moves the hila vision down, the expected hila vision down. Somebody’s got a bad cataract, they moved the hila vision down. And then if you move the hila vision down, other parts that are still depressed below that newly reset hila vision and those are the things they’re going to show up in the pattern deviation and allow you to pick out a glaucomist defect from within an overall depressed field. I would like to hear the whites scotoma. Yes, I mean it’s a white scotoma. It’s truly not a scotoma. It’s just kind of — it’s a spot on the field that is completely white. There’s no gray scale and there’s no point showing up. And so, I called that a whites scotoma. Clearly, it’s not a scotoma. It’s just, it’s just sort of playing words. So, we called the dreaded white scotoma. That’s just somebody who their sensitivity at that point is off the scale of the gray scale. And so there’s no pattern there. It’s just white paper. And that just means that it’s crazy excessive false positive responses. If you see those white patches in a gray scale, it’s unbelievable field. You cannot, you can never hang your hat on that field.

How many tests do you do before starting treatment? You know that’s a good question. It depends, I mean if somebody you always the perimetry is never in a vacuum, right? And so if you see somebody who has a notch in their optic nerve OCT arcuate defect, they have a visual field defect on perimetry. It all lines up. I don’t one field is all I need. If there’s some little tiny change in the visual field and there’s not a lot of other stuff to line up with it then it’s something I would repeat. So, it depends on the severity and how clearly it reflects damage. So, if somebody has a high pressure notch and OCT change, I’m done. If it’s something that’s kind of a change in the field that not obviously glaucoma, this doesn’t for example doesn’t clearly follow the nerve fiber pattern. Then I’m going to repeat that. I’m not going to act on that.

What are the age groups of age matched control? So, it’s usually by year. It used to be in the original octopus perimeter back 30 years ago. It was by decade. And so the then suddenly someone’s mean deviation would suddenly improve because they weren’t 59. Now they’re 60 but it’s every year. So, in the software, there is a normal 58 year old data set. And if you’re testing a 58 year old so the lower left part of your print out is going to have them compared to people their age.

Is correction necessary always for performing perimetry? Absolutely, definitely necessary. Is the Humphrey visual field analyzer necessarily better than OCT in progression? So, this is a really good question. I don’t think we know the answer that. I would say that for me early in disease, like people who are ocular hypertensive just drifting towards glaucoma, the OCT is really, really helpful. When we’re seeing people who are far along in glaucoma, I often will stop doing OCT because it feels that they’ve reached the floor. They’re not going to get any worse. I’m not going to see much. So, I sort of stopped doing the OCT. So, I would say that early on, I find the OCT is more helpful in the field and then later in the disease just the opposite.

Is it okay to wear glasses in the field tested? I don’t think they’ll fit in the machine so that you have to use lens. Can we do perimeter testing for children? Well, it depends on the child. I mean I have had kids who are just amazing who could do fields when they’re very young. Again, we have the advantage to do a Goldmann field sometimes a really great perimetrist can pull a field out of a very young child of five-or-six-year-old child. And there’s some kids who are very precocious who are six or seven who can do a field. But it’s kind of unusual. You just judge that from being in the room with him just like you do for an elderly patient, right? I mean some elderly patients you’re talking to him and you realize this is not something you can do a field. You just know from talking to them that they’re just not with it enough to do a field.

Do I request a frequency doubling perimetry if I get a normal field but an abnormal OCT? I don’t usually — again I love the mind that I want to do the same test over and over again if I can and you were limited by the patients, the patient’s patients and by the fact that our people who pay for visual field. So, I could pay for us doing 50 different fields. So, if I have a abnormal OCT and a normal Humphrey, I would follow them with my Humphrey and the OCT and see if they change. You could try a frequency doubling perimetry. I just — I haven’t found it to be as helpful as some people have. But, you know, I’m just one opinion.

Can you again explain the pattern of the nerve fiber layers in relation to field? I can’t emphasize this enough. You should, just in your brain or on your cell phone or on a piece of paper in your office, have a print out of what the normal nerve fiber pattern is. And your visual field loss for glaucoma, not for neuro ophthalmology things or other things. But optic nerve disease should follow that pattern. So, going out temporally it’s arcing and it stops at the horizontal, right? So, if you have a field the effect that goes past the horizontal, well, that’s not in neuro fiber layer defect. That doesn’t make sense unless you can, of course, have a superior one inferior one that touch, that’s possible. But also on the opposite side of the optic nerve, the fibers that go out nasally just go out like a wedge, right? So, you can have a defect that’s just a wedge, a temporal wedge because that’s the pattern of the nerve fiber layer on the nasal side of the retina temporal side of the visual field and temporally on the visual field that does not respect the horizontal, right? It’s just a wedge. So, find in a book somewhere the nerve fiber layer pattern always have that in your mind. If it’s a glaucoma or it’s optic nerve head druze and other things in the optic nerve. It’s got to follow that pattern. If it doesn’t follow that pattern you should be thinking about other things.

How often do I do OCT and visual fields together? I always do them together. There are people who separate them. So, you know, if you have a patient is stable and you see them every six months, then you might do Humphrey one time and an OCT the other time. I don’t like doing that because in my practice. I like for patients to know that this visit is going to be intense. You’re going to have to do field. You’re going to get dilated. You’re going to get OCT. And then the next visit is going to be just hi, how are you looking at there. Always look at their nerve. Maybe we do a corneoscopy at that visit. Check their pressure and then we’re done and it’s hopefully a fast visit. But the other reason I don’t like to separate them is if I see a change in the OCT, I want the visual field. And if I see a change in the visual field, I want the OCT. So, I find I would find that very unsatisfying to me to have only one and not the other. And again sometimes you’re just following OCT because the patient can’t do visual fields. Sometimes you just following visual fields because the patient they have hit the floor of the OCT or they have nystagmus and they can’t perform OCT.

Is there an aged match control for children? No, I mean there’s not. They didn’t take a bunch of two year olds and put them in a perimeter. I think it’s just extrapolated back down there.

Thank you all for being there. I hope everyone stays inside, stays safe in this rather challenging time. And feel free to go the curriculum website. If you want more, it has all these examples are there. So, take care and I appreciate everyone tuning in.

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April 17, 2020

Last Updated: October 31, 2022

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