Lecture: Prescribing Pearls

This lecture will focus on spectacle prescribing tips, including, but not limited to, considerations based on age, amount of refractive error, anisometropia, and spectacle design. Case examples will be used throughout.

Lecturer: Dr. Diane Russo, OD, MPH, FAAO, New England College of Optometry, Boston, USA


DR RUSSO: All right! Good morning from Boston, everyone. Or good afternoon, wherever you are. Dr. Diane Russo. I’m an associate professor of optometry at the New England College of Optometry. And thank you for joining me for this talk today. So today this lecture was designed to build on the previous two lectures that I gave on refraction. And so this one is more focused on prescribing specifically, as opposed to the technique of refraction. Like we talked about in the previous two webinars. So we’ll be talking about different variables, like spectacle power and the patient’s age and what their visual demands are, and all the things that you might consider when coming up with a spectacle prescription. We’ll also talk about the challenges to adapting to certain spectacle prescriptions, and using techniques like trial framing to determine your final prescription. I did want to note at this part of the lecture that the lecture is mostly designed to focus on what I consider a primary care eyecare population. So it’s not going to include more sort of complex specialty type cases, like early pediatric cases or prescribing for amblyopia specifically, or even low vision cases. While pediatric care and low vision care may be part of a primary care practice, if I try to include all of that in this lecture, we would never get through it. So I really confined it to probably the majority of patient encounters that you might come across in a primary care eyecare setting. So that is something I just wanted you to be aware of. I will include some reference material for pediatric prescribing, for infants and children. But we will not have time, and it’s not within the scope to really go in depth in that area. Also, that is not my area of expertise specifically. So it would probably be better suited for someone else to go through those types of cases with you. But my hope is that what we will cover today will really cover the majority of spectacle prescribing in your practice. First, if you’ve ever heard anyone talk about spectacle prescribing, you know there’s usually references like: It’s a science and an art. They talk about the art to spectacle prescribing. And the reason that it is referred to as an art is because it is. There are not always hard and fast rules. Do this or don’t do that. It’s multifactorial. There are a lot of things that we consider for each patient case. When we’re determining: Are they wearing current glasses? Are they happy with those glasses? What is the subjective refraction finding? Is it very different? Do we think they’ll have trouble adapting? Because there are so many factors that we take into account. That’s where this art of prescribing comes in. So first we’ll start by talking about things that you would take into account, if you’re going to make a refractive change. So for someone that has an existing glasses prescription, and you’re thinking about changing it, what are some of the things that you should think about before you make the change? First, don’t make a change unless it’s needed. So we can probably find prescription changes for every patient that comes in. There are normal variations that happen. But the first thing I would ask myself, before making a change, is: Is this really needed? So is the patient happy with their glasses? What is their current level of vision in the glasses? And are the changes that I’m finding large or small? And are they actually making a difference? Are they making an improvement? Because if it’s not improving the patient’s vision or the visual function, and they’re happy with their current glasses, then I’m not going to make a change. Even if I did find a change, I will not prescribe that in my final prescription. Some exceptions to this. Might be a case where someone is a latent hyperope, and maybe their distance vision is blurry, but they’re functionally fine. They’re not noticing any difference, and because I’m finding maybe a low to moderate amount of latent hyperopia, I may have a conversation with the patient and say: You know, this type of prescription might be really helpful for you at night. Or if you’re driving at night. Do you ever notice you have trouble seeing things at night? Reading street signs? And then they might say: Oh yeah, you know, I do. So that might be a case. Or a child that might have binocular or accommodative deficits. And so they may not be symptomatic. But I could, within reason, anticipate that they will have symptoms some time in the near future. Those are the times where, even if there are no symptoms, or they’re not having any issues with their current glasses, I may still prescribe. You also want to be aware and careful with patients that seem very sensitive to small prescription changes. That’s indicating that they have a lower tolerance to blur, and so any change that you make while objectively it may seem small — maybe a quarter diopter of sphere or quarter diopter of cylinder — it could be very disruptive for them, and very difficult to adapt to. And this is something that over time you develop that intuition, while you’re going through the refraction, as you’re changing the lenses. You’ll start to notice how the patient is reacting. If you make a quarter diopter change, and it seems very different, they have a big reaction, it made something very clear or very blurry, those are some indicators that they might be sensitive to small changes, and if that’s the case, you have to be very careful whether to decide to make a change or not for the final glasses prescription. So this is also — requires a little bit of math on our end. You’re rarely if ever reducing minus for myopic patients, or reducing net plus power at near for presbyopic patients. We have to be really clear with this and go through some examples so you can see what I’m talking about. With myopic patients, they’re usually used to or habituated to their glasses prescription. And if you lower the prescription, they may interpret that as now it’s blurry. Even if you are getting a lower myopic prescription on subjective refraction. So you may end up giving the higher minus, even though it seems like the patient doesn’t need it, because that’s what they’re used to. And if you try and lower the amount of minus correction, they might perceive blur at that point. Presbyopes — you have to be careful with the overall effective power that they’re reading through, because if you make changes to the distance prescription, and don’t take into account how that is impacting near prescription, you could be taking… You could be making a larger change to the near prescription, and reducing the actual amount of plus power that they have at near. Which would then result in blur or asthenopia. So let’s go through some examples. So we have a 25-year-old patient. And their current prescription, their habitual Rx that they come in wearing, is -3, -5, axis 180, and they’re seeing 20/20 through that. Their other eye is 3.25, 0.75, axis 170, also seeing 20/20 through that. You go through the refraction process that we went over in the first two webinars, and you get about half a diopter minus in sphere power in both eyes, and they’re still seeing 20/20. What do you prescribe? You may think… Well, maybe they’re overminused by half a diopter. So I should cut back that minus. But if we go back to what we just talked about, you have to be very careful doing that. If the patient is happy with their glasses, there’s no complaint, there’s no headaches, no eye strain, then I would just keep their prescription the same. I wouldn’t make the change. If they were complaining, and saying something like… I have headaches at the end of the day, or if I’m reading with my glasses on for a long time, or if I’m on the computer for a long time, and my eyes start to feel tired, or I start to get headaches, then I would probably prescribe the lower prescription. But I would definitely include, as part of the education, that I’m lowering the prescription so they may need to adjust. Things may not seem quite as clear. But we’re making the change for comfort. We’re not making the change to improve acuity. And so that is something that I would include as part of the education. Oh, let’s go back here. So next example. We have a 54-year-old patient. And they come in wearing a prescription of -3. So it’s the same prescription that I gave for the last example. But the acuities are a little bit different. So the acuity is reduced to 20/30. In each eye, with their current glasses. But their reading, their near visual acuity, is 20/20 with a +1.50 add. Now, with the subjective refraction, we’re finding more minus, and that improves their vision to 20/20. But the question is: What add to we give? In the previous example, with a +1.50 add, we would think… Oh, we’re gonna keep that, because they were reading 20/20 with it when they came in. The problem with that rationale is that really the power they were reading through, if you take into account the distance prescription and the near add, in the right eye, the difference — you take the difference of the minus sphere power and the add power — they’re really reading through a -1.5. And the left eye is reading through a -1.75. But with the changes that we made to the subjective refraction, if we kept that 1.5 add, they would now be reading through a -2 lens, and a -2.25 lens. So now we would have increased the amount of minus that they would have to read through, when looking through the near add, if we kept a +1.50 add. Which — the patient is not going to like that. They would have to accommodate even more. They have less of an accommodative reserve at 54. So in order to keep this effective near power the same, because they were 20/20 when they entered with their +1.50 add, you would actually have to give a +2 add, to keep that effective near power the same. This is — and we’re sort of walking through this step by step. Looking at the math and overthinking this. Clinically, you would not have to overthink this quite as much. Because one of the main things you would be looking at, when thinking about prescribing a near add, would be their age, and thinking about an age predicted add, which we’ll go over in the lecture. But I wanted to walk you through the math step by step, to show you how making a change in the distance prescription affects the near power, and how we do want to make sure that we are not reducing the amount of plus power that we’re giving at near, because of the changes that we may have made in the distance. If you are making large changes to the sphere or cylinder power, you may want to be careful about that. So if you’re getting more than 1 diopter of sphere change, you may not want to give all of it. You may want to give some and then change it, increase it, over time. Using a trial frame would be most helpful in this case. And we’ll do some examples of these as well. If you’re making larger than a half a diopter cylindrical change, you may not want to give the entire change. You may again, similar with the sphere, want to give part of it, and then increase it slowly over time. If it’s a high amount of astigmatism, or if it’s a first pair of glasses for someone, or even if it’s the first time that they’re getting cylindrical correction, if they’ve worn glasses but it’s only been spherical, you do want to proceed with caution. Using, again, the trial frame will be most helpful in this situation, to determine what you’re going to actually end up prescribing. And you may not give the full change. You may give part of it. And then once the patient adapts to that, then you may give them a new prescription later on, over time. But you may initially start with a lower prescription for adaptation purposes. Also, you want to make sure that you’re taking into consideration the sphere power, if you’re making changes to the cylindrical power, and making changes to the spherical equivalent. The calculation we use is that you take the sphere, and you add half the cylindrical power of the change you’re making to the cylinder. We’ll go through a few examples of this. I’m not sure what everyone’s familiarity is with spherical equivalent calculations. So I wanted to make sure we all had a good understanding of the concept, because we’ll be talking about this throughout the lecture. So we have our first question here. A patient’s subjective refraction of the right eye is -3, -2, and axis 180. What is the spherical equivalent? If you were to take all of the cylinder power out, and just give a sphere powered lens to this patient, what would the spherical equivalent be? All right. Excellent. Most of us are on the same page. Great. The answer is -4. The way you do the calculation is it’s sphere plus half the cyl. If we’re taking out all but -2, half of that would be -1. So the spherical equivalent would be -3 plus -1, which gives us -4. That’s a big change, though. To take out two full diopters of cylindrical power would almost definitely reduce that patient’s visual acuity. And so more often what we’re doing is just reducing the amount of cylindrical correction, not taking it out completely. That’s our next example. If you take the same patient, but you decide you don’t want to take all of the 2 diopters of cylindrical correction out, just 1 diopter, what would the sphere power — not what would the Rx be, but what would the sphere power be, if you reduced the cylindrical correction here to -1? And this is done very commonly, I’m sure. Most of you are already doing this. Again, I’m mostly including these calculations to be sure that we’re all on the same page, so that I’m not using terms or techniques that anyone is not familiar with. But this is done — I do this on a daily basis, when seeing patients in clinic. Because we want to make sure that the new prescription that we give will be comfortable. Excellent. So most of us put -3.50. That’s exactly right. That will be the sphere power. Again, we’re taking the sphere plus half the cylinder, but in this case we’re only cutting the cylinder by 1. So half that is -0.5, so -3 plus -0.5 is -3.50. So this is what we might end up prescribing for this patient. We’ll do just a couple more examples, using plus powered lenses. Because that changes the calculation a bit. So similar situation, but now the patient’s left eye is +1.5, -1, axis 90. What would the spherical equivalent be? Same thing, if you took out all the cylindrical power, and were just going to give a sphere prescription to this patient? Excellent. Right. Most of us put +1. Perfect. Same concept here. We’re not gonna take out all the cylindrical power. Just half. So what would the sphere power be, if you reduced the cylinder by half a diopter? Great. Most people put +1.25. So this changes the calculation a bit. If we reduce by 0.5, you get +1.25. And this would be the prescription that you might end up with. The reason why I’m including these questions — I see the vast majority of us are getting this right. So you’re already familiar with this. But we’ll build on this, especially when we talk about what we might trial frame. So I wanted to make sure that we were all on the same page with this concept. When it comes to making a change to the cylinder axis, you do have to be careful, if you’re making a larger change, of say more than 15 degrees, if it’s a high cylindrical power, maybe 2 diopters or more, 2.5 diopters or more, you may not want to change the axis at all. You may want to keep the axis the same and just change the power. Or make very minimal changes to the axis. Because 5 degrees for someone that wears 3 diopters of cylindrical correction is a very large change. But 15 degrees for someone that wears half a diopter of cylindrical correction is maybe not quite as noticeable. And I talked earlier that there are normal fluctuations. So keep that in mind, especially if you’re getting a quarter diopter difference between the patient’s existing glasses and what you’re finding on subjective refraction. Again, unless the patient is very sensitive to small changes, I’m going to be less likely to change a prescription by a quarter diopter, unless it’s indicated. Trial framing. So this I do very often. Typically I refract using a phoropter, and so that is not a very good real world simulation. So most often what we’ll do is refract in the phoropter, and when we’re trying to figure out what to prescribe, if there’s a large change happening, like what we’re talking about today, we’ll put that in a trial frame. For those of you who are already doing trial frame refraction, this is even easier, because you already have the lenses in the trial frame. You could have the patient look around, you could have them walk around, if you’re in a room, you could have them leave the room, go into a larger space, so you get a sense of how it feels for them to be wearing the new refraction, especially if it’s a large change. When should you trial frame? Again, there is not a hard and fast rule. I gave you some numbers here. It’s more of a recommendation. If you’re making a change of a diopter or more to the sphere, 0.7 diopters or more in cylinder, 15 degrees or more in cyl axis — this is what we just talked about — or if the patient is coming back with the glasses you prescribed saying that they don’t feel right and they want you to check the prescription, trial framing in that case would also be very helpful. So we have an example. We have a 36-year-old patient that comes in wearing this prescription. Their acuity is about 20/30 and 20/40, +2. So their acuity in the distance is a little bit reduced. On subjective refraction, you’re getting a full diopter more of cylindrical correction, with the 5 degree axis change in the right eye. That does improve their visual acuity. And you’re getting a quarter diopter change of sphere in the right eye, with another diopter change in the left eye, with also a 5 degree axis change. So what could you trial frame in this case? So some of the things you could show the patient — and this is usually the order that I would show the patient. And this is something I talk about with students all the time. Very often, I think my students interpret trial framing as just showing the patient the prescription that they found, or not the prescription, but the subjective refraction in a trial frame. But that’s not exactly what trial framing is. Right? So I would probably start by showing the patient some kind of combination. So cutting the cylindrical power by half a diopter, keeping the spherical equivalent, showing it with the new axis in the right eye, same thing with the left eye. So cutting that cylindrical power. Keeping the spherical equivalent. Showing with the new axis. I asked the patient: How does this feel? How do things look? And then I might show them the same powers, but with the different axes. So show them the difference between the old axis and the new axis, and see if they notice any difference. If they don’t notice any difference, then I might keep their old axis. The 165 and the 140. And then I might show them the full prescription. Right? So I probably in this case, if the patient was complaining that they noticed their vision was blurry, I probably would not show them their current prescription. If they said their vision was fine, I might have started with this, and then worked my way up to the changes, with cutting of the cyl, and then show them the full subjective refractive findings. But this is usually the stepwise process of what I would show the patient, to determine what they would be most comfortable in. What are they appreciating clear and comfortable vision in? So here we go. We have another question. So if our patient has the following habitual prescription, with some reduced vision, and you find an increase in plus power and an increase in cylindrical power with axis change in the right eye, same thing, increase in plus power for the sphere, increase in cylindrical power, and a change in the axis in the left eye, which improves the acuity, what would you trial frame for the right eye specifically? So again, we’re just looking at the right eye in this case. All right. So we’ve got a bit of a mix here, all over the place. With most people putting C. This is a little bit of a trick question, and I think I usually include something like this in all my lectures, but technically, you could have trial framed any of those options. So there is no wrong answer here. If the question was: If you could only trial frame one of these options, what would it be? Then that may be different. But if you’re just trying to pick what you might show the patient in a trial frame, really you can show them any of these options. So if you showed them A, you would just be showing them what their current prescription is. And you can use that as a reference point, and say: This is what’s in your current pair of glasses. How does it compare to this? And then make a change and show them the change. You could also show them B, which would just be cutting the sphere power, but keeping the cylindrical power and the axis that you found, sorry, keeping the habitual axis, but increasing the cylindrical power, and then just cutting the amount of plus. You could also cut the cylindrical power, keep it at the new axis, but keep the spherical equivalent. And so that’s what most people put. That is probably what I would have started with. Or if I only had one to choose, I would choose C. Or you can show the patient the full — nearly the full prescription. Actually, yes, in the right eye, it would be the new subjective refractive findings. And realistically, you would be showing the patient more than one of these options, and comparing, and getting the patient’s feedback. How does this feel? Is it comfortable? How do things look? Is it clear? Is it clear but uncomfortable? Because if it’s clear but uncomfortable, I’m then concerned about whether or not they’ll adapt to the prescription, and then I might not give that — those refractive findings. I may reduce the prescription even more. So if I were to show the patient D, and they said: Everything looks really clear, but I don’t feel comfortable… If you gave them that as their final prescription, they may have trouble adapting. They may adapt, but you know already in the exam room they’re uncomfortable in it. And so if that were my decision to make, if this was my patient, I would probably go with C. If it was clear and uncomfortable in D, and they said it was clear more or less, but comfortable in C, then I would give them C. That’s why trial framing is so important and helpful. Patient education is… Critical. If you’re making large changes. Pretty much any time I make a large change or I’m giving a new glasses prescription to begin with, I will include education on adaptation. Something like… If you put the glasses on, and it’s not totally comfortable at first, that’s normal. Don’t take the glasses off and not wear them. The more you wear the glasses at first, the faster the adaptation will take place. I’ll tell them: If you wear the glasses all day, every day, for a week, and it still doesn’t feel comfortable, then come back. Because we may need to make a change. And I’m trying to avoid that at all costs. I want the patient to be comfortable. I don’t want them to come back and take the time to come back. So I will always include that as part of the patient education, so that the patient knows what to expect, but also, I’ve taken all these other steps, including usually trial framing, to try and ensure that adaptation is not a problem for the patient. Also something to consider is: Letting the patient know what their prognosis is. So depending on their refractive status, if they have myopia, should they be expecting it to get worse? How quickly will it get worse? Will it plateau at some time? I know this is a very… Hot topic now. So that may come up. But also patients that are presbyopic. Letting them know: You may not need reading glasses for everything now, but at some point, you may be much more… You’ll probably be much more reliant on reading glasses. Or patients that are maybe low hyperopes their whole life, and maybe don’t need any glasses. Usually I’ll tell them… Well, you may not have needed glasses up until this point. And then all of a sudden you needed reading glasses, and now all of a sudden you need glasses for everything. So that would not be uncommon. And so I will usually include that as part of the patient education, so that they know what to expect. Patients also have a right to their own preferences. If they prefer a weaker prescription because it’s more comfortable, and it doesn’t interfere with any of their visual demands, then that’s perfectly fine. Prescribing considerations for the different age groups. So I am going to include some information on considerations for the pediatric patient population. But again, this is really beyond the scope of this talk. So I’m mostly just including this for informational purposes, for reference material. So that if you did want to come back to this talk and refer to the slides, the information would be there. But this is, again, beyond the scope of this talk. Prescribing specifically for amblyopia is not really in my specialty. But again, I felt that I should at least include this information, so that you would have it. So the primary concern with pediatric patient population is preventing amblyopia. If there are amblyogenic risk factors. Because we’re talking about spectacle prescribing here, we would probably mostly be concerned with refractive amblyogenic risk factors. And so I included this table here. Again, just for reference. So if we’re looking at anisometropia or isometropia, this will give you the refractive… The degrees of refractive error that could be amblyogenic for hyperopia, myopia, and astigmatism. Again, just here for reference. This was adapted from a review article looking at prescribing guidelines for infants and children. Again, we’re not going to go through this step by step, but I included it so that you would have it. Also, I included the table — this is the exact table from the review article — so that you could have this to review back to. This is specifically for infants and children. And so I have these tables for myopia. Also for astigmatism. Same thing. This is for infants and children. And then I took the same table, because I sort of made this a little bit easier to see it, by putting it into a table format, but then I copied and pasted the actual table from the review article, so that we would have this in the presentation as well. When it comes to age and astigmatism, as I said before, the priority is on avoiding amblyopia. As children get older, so between the ages of 5 to 10, you could probably give the full cylindrical correction, and children tend to adapt much easier to astigmatic correction than adults do, so you don’t have to be quite as concerned with adaptation issues. Older children, if they’re 10 up through their teenage years, usually you give the full correction. But depending on how high the astigmatism is, you may also be concerned with adaptation. Although it’s much less of a concern in the pediatric population. For adults, definitely you have to consider spatial distortions, or any issues that they might have with adaptation, and this goes back to all the examples we just talked about, with reducing the amount of cylindrical correction. Using trial framing to do that. Making sure that you’re keeping the spherical equivalent. You may increase the amount of cylindrical correction over time, as the patient gets more and more used to having that correction in their glasses. You could try and change or move the axes to 180 or 90, as opposed to more oblique angles, but that may not always be possible. Or as we talked about before, you could keep the same axis that the patient is used to, and just change the power there. Age and hyperopia. There are many more considerations when it comes to prescribing for hyperopia. So how much hyperopia. Do they have astigmatism as well or anisometropia, how old is this patient, do they have any type of tropia, more specifically esotropia, since you’ll be prescribing plus lenses. May that help with the esotropia or not. Do they have amblyopia or are there amblyogenic risk factors, what is their accommodative and binocular status, what are their visual demands, and do they have any symptoms. So this is again that same table. As you can see, I included the table, because it’s a lot of information that’s very condensed. So again, that’s why I included it. There’s also — it says here — outside the 95% range of refraction, and so I included this reference table that gives you the age in months with the 95% upper and lower ranges of refractive findings. So that you could come back to this… So that you could refer back to this. Not that, again, we’re not going to go into the in-depth details in this talk. For the management of older children, and then into the adult age for hyperopia, if there’s moderate hyperopia, they’re more likely to need at least part-time correction. Usually for near vision only. If they have high hyperopia, they may need full-time spectacle correction for distance and near. And the full-time correction also helps to aid in adaptation, so that the eyes can relax, and they’re not used to accommodating all the time. Vision therapy may or may not be indicated. And patients that are in sort of the 30 to 40 — although it’s usually the late 30s to early 40 range — may be more likely to be symptomatic, particularly if it’s moderate to high hyperopia, and are more likely to need correction. And that may or may not include single vision for full-time wear. Or once the patient starts to get into maybe their early 40s, late 30s, early 40s. They may also need a bifocal prescription. If there’s latent hyperopia, you want to be looking for — or listening for symptoms like blur. But then also asthenopia, patients saying they’re getting tired, associating headaches with near work, and the same thing we just talked about. You may prescribe glasses for reading only or bifocals. Presbyopia may necessitate full-time correction. It may depend on the patient’s refractive findings. They may need one for reading only, or two pairs of glasses, one for distance, one for reading, or something like a bifocal/progressive. As we talked about, talking to the patient about what their prognosis is. There’s progression associated with age. And really age is the best predictor of add value. And so I included our table here for reference. That — for what age predicted adds are. And really, when I think about this, the way that I’ve always remembered what the age predicted add should be is by sort of focusing in on… At 45, someone should need around a +1 add, and at 55, someone should need around a +2 add. And then sort of fill in the gaps, the rest of those values between — so between 45 and 55, they’ll need something between a +1 and a +2. And above 55, they’ll need something between a +2 and a 2.50. When someone is older than 65, usually they’ll need at least a +2.50 add, but it could be higher. If they have reduced near vision. This usually happens in cases with pathology present. So if there’s age related macular degeneration or cataracts, something that’s affecting the central vision. But you need to be aware of the impact it’s going to have on the working distance. So the higher the add, the closer the working distance. And so if the patient is not able or willing to hold print closer, then prescribing that higher add may not be helpful. Also lighting becomes very important at this point. So we have another question here. So if we have a 58-year-old patient, they come in, this is their habitual prescription, they’re wearing a +1.50 add, so they have slightly reduced vision at distance, somewhat reduced vision at near, you find — your subjective refractive findings are here. So small increase in distance plus power, some cylindrical power change, a little bit of axis change in the right eye, again, minor changes to sphere, slightly larger change to the cyl, same axis, but it improves the best corrected vision. What would be the most appropriate add power for this patient? All right. So most of us put +2. There’s a mix between 1.75 and 2.25. 1.75? Possibly. If we go back to… That age is the best predictor of the needed add, then since this patient is 58, so at 55, you need around a +2, so somewhere between a +2 and a +2.25 might work. But the +1.75 could potentially work, considering we are giving more plus power at distance. So that’s already going to be increasing the plus power at near. So this is where showing the patient the difference between the +1.75, +2, or +2.25 would be the most efficient way of figuring out what your plus power should be. But somewhere in this range is what you should be aiming for, for this patient. Environmental considerations. Knowing what the patient’s visual needs are, their work environment, their life environment, what are their working distances, what are the tasks they may be doing, how do they plan on using the glasses. A lot of times I’ll ask a patient: Do you want to wear the glasses all the time? Or do you just want to put them on for certain tasks? Some patients will say no, I don’t want to wear them all the time. Some may say: I sew and do a lot of detailed sewing work, so I just want to put the glasses on for that, but I don’t feel like I need them for anything else. That’s fine. Other patients may say: No, I want to put the glasses on, wear them all the time, because it’s easier to keep track of that way, and if that’s the case, I may prescribe something like a bifocal or a progressive lens, depending on the patient’s distance and near refractive findings, as well as their visual demands. What if a patient is aphakic? So it depends if it’s monocular or binocular. If they’re aphakic only in one eye, that necessitates a high plus spectacle lens. Which is going to be extremely difficult to adapt to, optically. And so in that case, contact lenses may be an option. To reduce some of the prismatic difference that is experienced with spectacles. But realistically, what you may end up needing to do is prescribe a balance lens for the eye that’s aphakic. Again, all of this is if only one eye is aphakic. If they’re both aphakic, then it’s a bit different, because then you would have high plus power lenses in both eyes. Cosmetically, it would be very noticeable, if you were wearing those high plus power spectacle lenses, so you may opt for contact lenses, if that’s possible. But if only one eye is aphakic, you have all those other adaptation challenges, because of the optical system. Pseudophakia is something else to consider. If they have an intraocular lens implant, regardless of age, usually they’ll need a +2.50 add, unless the IOL is multifocal or monovision design, where one eye is correctable for distance and one eye is correctable for near. When we talk about spectacle design options, there are a few different options out there, but they’re very rarely prescribed. So I chose to focus mostly on task dependent spectacles. So what is the working distance? What is the visual demand? And how do we determine the power that’s needed for a specific working distance? The way you do that is taking the reciprocal of the working distance in meters. And so I included some calculations here. So if someone has a working distance of 40 centimeters, which is usually by convention at least in the US where we measure near acuities, the working distance — the demand, the accommodative demand for working distance of 40 centimeters is 2.5 diopters. For a working distance of 33 centimeters, if we do the calculation — that’s about a 3 diopter accommodative demand. So if we have a patient, patient A is a 67-year-old male, he’s still working, works all day at a computer, so computer distance, and then up close reading, he’s been noticing some blur while using the computer with his current glasses. And so the first question that I would ask this patient are: What is the current glasses prescription? So if the patient had the glasses, that would be the best option, so that we could do lensometry to find out what power he’s currently wearing. How far away is the computer? So that’s determining the working distance. And then what type of glasses is he currently using? Is he using distance only, near only, a bifocal? What is he currently using? And we would need to know all this information so that we don’t end up giving the patient exactly what he already has, which clearly, according to him, is not working. So here’s the question. So you are asking more questions and trying to find out what the patient’s working distance is for his computer, and find out that the working distance is 65 centimeters. So what would the accommodative demand be for this working distance? Excellent. So most people put 1.5 diopters, and this is correct. So this gives us more information about what add power he would need for something at an intermediate distance. The next measurement that’s also helpful is knowing the range. So knowing how much flexibility the patient has with their current glasses. And so if we measure patient A’s range of clear near vision through the following prescription, so let’s say these are our distance refractive findings from the exam today, and he was given a +2.50 add, so it’s through the +2.50 add, the range of clear vision is 35 to 45 centimeters. Could the patient use this prescription as a bifocal? If we’re considering giving this as a bifocal, could he use this for the computer? And remember the computer working distance was 65 centimeters. Okay. So most people said no, and there was a mix between yes, no, and need more information. So realistically, no. Since the add power — the range of clear vision does not include the 65 centimeters, he’s not gonna be able to use the bifocal to see through the glasses. And if you were thinking maybe he could use his distance portion of a bifocal to see the computer, that’s probably not going to happen either. Because he needs, as we said, at least a diopter and a half of accommodation to be able to see at the computer distance. Where his working distance is. And even if he could squeeze out just enough accommodation to clear that diopter and a half, he’s definitely not going to be able to do it all day, since he said he’s on the computer and reading all day. So realistically, he’s not going to be able to use the distance portion of the glasses for the computer. He’s not going to be able to use the near portion of the bifocal for the computer. So this is not going to help him. So if we updated his glasses prescription and gave him a new bifocal prescription, we didn’t really solve the problem. So what are some of his options? Progressives. Right? So that would include that intermediate distance. Power lens. Or trifocal. That would definitely work well. Usually a trifocal is about half the power of the full power add. So in this case if the full add that we’re giving is +2.50, the full trifocal power would be about +1.25, which would probably be adequate. So trifocal is an option. He could use computer only glasses. So if you gave him a single vision pair of glasses, that could just be for the computer, but the problem with that is that it wouldn’t include distance or near. So if he’s working at the computer distance and up close for reading, then he wouldn’t be able to read. So another option, if you did want to go with the bifocal, you could, but only if the top portion of the lens was for an intermediate distance. So if it was for the computer, and then the near portion was for closer, for reading. So you couldn’t give the bifocal for distance and near, but you could give a bifocal for intermediate and near. And so these are pretty much all the options that he has, although the computer spectacles — I probably would not do in this case. Again, because that would really only limit him to the computer distance. If he said he was only working on the computer, maybe. But that’s less likely. So really the progressives, trifocal, or intermediate near bifocal would be the best options for this patient. All right. So I did want to leave a little bit of time for questions. So I will work my way through as many questions as I have — as many questions as I can at this point. I saw earlier in the presentation someone asked about using the duochrome test. And I think that was in reference to… If we suspected that someone was overminused, when I had recommended not reducing minus for myopes. You could use the duochrome test, but I think in all likelihood, you might find that they are overminused. I think the thing to consider is whether or not they are used to being overminused. And are comfortable in that. Because even if you use the duochrome and you are feeling comfortable in determining that they’re overminused, you still might keep the prescription the same, because you run the risk of — if you reduce the myopic prescription that they may start to experience blur, because they are so used to having that slight overminus. And again, this is if they are not symptomatic. If they are symptomatic for asthenopia or headaches, then I’m much more likely to lower the prescription and to explain to them why I’m doing that. Someone else asked a question about trial framing. If it’s done monocularly. After binocular subjective refraction or binocularly. So usually I only trial frame binocularly. And this is something I know I talk about a lot when I’m in clinic with my interns. The purpose — so the subjective refraction is to help us to find out what the best corrected acuity is. The trial framing is helping us figure out function, not necessarily acuity. So I want to know if the patient’s comfortable. So I’m doing this trial frame binocularly, if I’m taking acuity, which most of the time I’m not, but if I am, it would also be binocular. Because trial framing for this purpose is to determine function, not necessarily best corrected acuity, because we’ve already done that. So the next question is: What is the importance of trial framing for prescribing new correction? So I think it depends on the power of the new prescription. If it’s a low prescription, low plus, minus, or astigmatic correction, it may not be necessary. But if it’s a bit stronger, and you’re questioning whether or not the patient will adapt, then trial framing will be helpful in that process. So it’s not necessary, but it could be important if you’re concerned that because it’s a first prescription the patient may have difficulty adapting to it. Is trial framing useful in children? Usually not. So usually with younger patients, we are basing our prescribing on objective findings. So not even the subjective findings. If you are able to get any… 7, I mean, from a 7-year-old patient… You’ll probably be able to get subjective findings. But trial framing probably won’t be as useful. So in the pediatric patient population, I’m less likely to trial frame. Although it’s not… Not that you shouldn’t at all, but it will be less helpful, because we’re not as concerned about trial framing for adaptation. So we’re not necessarily trying to figure out function. So a lot of times our findings are based on objective findings, and that’s about it. And we’re not as worried about adaptation. So trial framing in that case is not helpful. Although doing a trial frame refraction is much more common in the pediatric patient population. So you may be — the patient may already be in a trial frame, but for subjective refraction, as opposed to because you are trial framing to try and figure out what you want to give as your final prescription. Let’s see. We have what looks like a little case here. If the patient is 30 years old and had surgery for congenital cataract, before surgery he wore -1.75. After the surgery he’s -1.75 in the right eye, 20/20, and plus… I’m guessing 1.75 minus 1, axis 175, and is 20/60? What would you recommend for this patient? So because you have the antimetropia there, one eye is minus and one eye is plus — I’m assuming the congenital cataract was just in the left eye — in all likelihood, this is gonna be uncomfortable. You could show it to the patient, but the likelihood that I would prescribe this is very low. I would probably end up giving a balance lens in the left eye. Again, this is where trial framing is very helpful. But potentially a contact lens could be a consideration. Or using a balance lens. So this is almost sort of similar to if your patient was aphakic, although the prescription is much lower. So it’s much more likely that the patient could tolerate the difference. So trial framing will be really helpful here, but because of the antimetropia, it could be optically difficult to adapt to. So I would show the trial framing options, like we talked about before. But sort of always knowing in the back of my mind that I may need to consider a contact lens. Or a contact lens fit. Or a balance lens in that left eye. Let’s see. What is the time between changing the Rx and increasing power? So that’s a really good question. Because I know I didn’t talk about that at all. Usually unless the vision is very reduced because of the amount that you cut, which usually I will not do that… I will usually keep the patient in the prescription for a year. And have them come back and see how they’re doing. But in the pediatric population, you might make changes more often than that. But in the adult population, usually I will probably not make changes until the next year. Let’s see. For hyperopes in their 20s and early 30s, that can’t adapt to even the most modest of plus correction — I know exactly what you’re talking about there — I prescribe lenses and usually these patients are satisfied, however I’m generally not sure how much hyperopia I should correct using lenses. Any recommendations? Yeah, so that’s going to be so variable based on the patient and the amount of hyperopia. One of the things… If the amount of plus will improve their — either acuity or improve their symptoms, I will usually take into consideration the dry refractive findings and the wet refractive findings. Wet being a cycloplegic refraction. And see: Is there some latent hyperopic component? So then comparing the two, see how much plus I might end up prescribing, but usually I think the most important thing to include is the patient education. And a lot of times I’ll tell these patients: When you put these glasses on, it will probably be blurry. And your eyes will need time to adjust and relax, so that they accept the glasses power, and then things will get clear. But it will probably be a little bit blurry at first, and that’s part of that adaptation. But usually I will probably go with a lower plus power, but I think an important piece to know is if there is any latent hyperopia there. Because you could probably push a little bit more plus for someone that has some latent hyperopia than for someone that doesn’t. So it really depends on the case. And I hope I included enough information there. So for a seven-year-old child, their vision is 20/20 in the right eye and has a cylindrical correction of -1, axis 90, and is 20/20. Do we prescribe glasses or follow the child? So I would… First I would recommend going back to the table that I included sort of as reference. Because a 7-year-old would be sort of that older child demographic. But in this case, if the child is already 7, that 1 diopter of cyl is… Just below the amblyogenic risk factor. And we already know that they’re able to receive 20/20 vision. So in this case, I think again one of the things we’re trying to consider is: Is there an amblyogenic risk factor? And in this case, no. The child is already 7. They’re able to be corrected to 20/20. So in this case, you may not need to prescribe the glasses. But I would definitely… This is just my general answer… But I would refer you back to the table from the presentation with more specifics on that. You could… One last thing I would say about that is… If they’re older now and becoming school aged, which around 7 usually they are, you may prescribe it if they have symptoms. And in that case, you could give the full cylindrical correction. So some of it will also depend on function there. Okay. Please show the references again. I don’t know which one specifically… So I think I have time for maybe one or two more questions. So I’m not sure… Someone asked if I could show the references again. Did you mean just the references slide? Because if that’s the case, then I can definitely do that. But then I would just sort of recommend going back to the recording of the webinar, and to look at the specific slides. But these are just the general references. The number three reference is the article with prescribing guidelines. It’s a great reference article. When do you binocular balance before and after trial framing? So that would be done before. That would be done usually because I refract with a phoropter, at the end of subjective refraction, so I have those findings, and then after that I would trial frame. Would you recommend a difference in near addition power for presbyopes between eyes? Usually not. Usually — and I think a lot of this somewhat is by convention — but usually you would not prescribe different adds, and part of that has to do with balancing accommodation. Even if someone is a presbyope, if they’re an early presbyope, they are still able to accommodate. And so assuming that you’ve done your proper distance subjective refraction, you have now balanced out the accommodation, and if you introduce different power adds, then you’re creating an unequal amount of accommodation, which could be uncomfortable for the patient. So usually the add power is given equally between the two eyes. There could be an exception to that, but most of the time the power is going to be the same between the two eyes. So the last question I think I’ll answer… Because of time… Is: What is the difference between progressives and trifocal glasses? So the progressive lenses are a no-line… Well, we sort of refer to it as a no-line bifocal. But it’s much more than that. So the progressive lenses have your distance prescription at the top of the lens, and then gradually there is an increase in addition power from the top of the lens down to the bottom. So in between you get this gradation of near addition powers. And so if the patient sort of adjusts their head, and where they’re sitting, and their working distance, they can find a clear portion of the lens to look through, to see clearly through the glasses. But there’s a gradation. So pretty much every amount of near add power between what your distance prescription is and the full near add is included in a progressive. Whereas the trifocal is lined, so it has the distance prescription on the top, that intermediate add in the middle portion, and then the near portion in the bottom. So there are very discrete differences between those three levels, whereas the progressive — there’s more of a gradual gradient between them. And so that’s why the progressive is usually the most useful, because if you move your head and adjust where you look through the lenses, you can find a power that is helpful, whereas the trifocal, again, because of the power, is going to have very discrete differences between each segment. All right. So I’m sorry I did not get a chance to get to all of your questions, but thank you so much for joining us for this webinar, and I hope that it was helpful. All right? Thanks again.

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November 6, 2019

Last Updated: October 31, 2022

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