 Good morning. Thanks you guys for making it out. Got a big crew this morning. Are we expecting more? No, that's fine. We'll probably just trickle in. I guess the reason I kind of wanted to get started is this section in the BCSE book is just gigantic. So there's just tons of stuff to go through. And I don't think I'm even going to get through all my slides today, but we'll give it a shot. And like usual, just interrupt me. If you have any questions, any thoughts, and if you don't want to talk about, totally fine. It doesn't bother me. Actually, I even have the laser pointer and the clicker today, so that's kind of cool. Alright, so kind of like we did last week, I always just like to start out with just objectives. What do we want to accomplish today? So we're going to talk about clinical refractions. I'm going to try to keep it as practical as possible, but also not just practical, but you do well on OCAPs and boards. So the vast majority of material I have is just from the BCSE book. These of you guys are probably going to be tested on. There are some things that honestly aren't that clinically relevant but are in the book, so I wanted to cover it just to make sure that you weren't taken by surprise. But again, I'll try to make it as clinically relevant as possible. We're going to start with retinoscopy, which is a bit of a lost art. You know, in the days that we have auto-refractors and stuff, a lot of times the retinoscope is just kind of thrown to the side. But it's incredibly useful. To this day, I use it all the time. Obviously, it's really good to get an objective refraction determination, even if you're in the ballpark. It's really good about detecting optical aberrations. There are a lot of times when I'll get a patient, they'll come in and they'll say, yeah, my vision's a little weird and they'll go through all these complaints. I've tried contacts in the past and can't quite get a ride and glasses seem a little off. I'll just do a quick retinoscopy and within three minutes I know they've got care to conus. You can totally tell. You've got the weird, like, scissoring reflex. The reflex is really irregular and weird and you can tell that fast. Like, oh, irregular cornea, they've got care to conus. It happens. It's really good at detecting opacities like PSEs are really easily seen using retinoscopy. Sometimes if you're, you know, before you start a subjective refraction and you do a quick retinoscopy, you can see this big giant PSE centrally and you kind of know, well, you know, if their BCVA is reduced, you'll know why. I mean, you know why even before you start the refraction. Retinoscopy is obviously, whoa, hold on. I just messed something up. Well, laptop page, sorry. Projector on screen. Okay, there we go. Sorry. Anyway, obviously it's really good for infants. We see a lot of infants over at the optometry section. We see a lot of aphacic infants. Obviously that's crucial for that. Or just kids that are wiggly or, you know, we had a patient this week who has a self-induced traumatic cataract. He's also has Down syndrome. It was really sad, really heartbreaking, but he's doing some self-induced trauma. And anyway, I mean, with a patient like that, there's no way you're going to be able to go through subjective refraction and ask him what's better, you know, one or two. You have to rely on your retinoscopy and get as close as you can. Or like I said, there are some adults that are just simply terrible at subjective refraction. Just terrible. And you'll change it by a diopter and they'll be like, oh, it looks the same to me. And you're like, no, it's not the same. I know it's not the same. So when you're using your retinoscope, I guess I probably should have brought one, use the planomere setting. That basically means just put the sleeve all the way down. Have you guys gone through retinoscopy? You guys have, generally? Okay. And I kind of assume that you've really gone through it at least a little bit. Put the sleeve all the way down. Have the patient fixated on a large distance object just so they can relax their accommodation. You know, I have a look at 2400 letter a lot of times. And then you start doing it. And with kids, there are a lot of times you might need to cyclopletch them. You know, you'll get a kid with kind of mushy VA. You know, you're pulling on maybe one diopter of refraction. But their vision is like 2040, kind of a mushy 2040. A lot of times you have to cyclopletch them. You do retinoscopy and then you go, oh wait, they're actually a plus 450 or whatever. That can definitely happen. You know, there's basically 3 types of reflexes there's with and there's against and there's neutral. And all this involves the far point. We'll talk a little bit more about the far point in a little bit. But basically you know, the farthest away, the point farthest away point that your eye can see without accommodation. Like if your patient's totally relaxed, what's the farthest point that you can see clearly? That's your far point. And like I say, we'll go into that in a little bit. In that case, you know, if the far point is between me and the patient, so the patient's far point is between us, then I'm gonna, when I do retinoscopy, I'm gonna see against motion. You know, I'm gonna shine that light and it'll go against the motion that I'm doing. If the far point is behind me, then the light moves in the direction of the sweep, meaning I'm gonna see with motion. You know, you'll see that with hyperopes and embotropes. If you're doing it and you know, you've seen the neutrality, which basically means not much of a motion one way or the other. It doesn't look with, it doesn't look against. It almost looks like there's this kind of bright flash of light. That's neutrality. You know, that's kind of where you want to be. Then if you were doing that and you found neutrality, then if you got closer and closer and closer to the patient, you would see with motion. If you got farther and farther and farther from the patient from that point, you would start seeing against motion. Anyway. Oh, I'm sorry. I think I said that wrong. If you're moving farther back you see against, if you move in closer, you'll see with. Sorry about that. I switched that. Because again, the far point is gonna be either behind you or in front of you, depending on where you're sitting. Sometimes that's a strategy you can use. If you're finding about neutral and you're like, I think about neutral, you can actually scooch up a little bit and see if the reflex changes and then scooch back a little bit and see if the reflex changes and reverses. This is kind of a dumpy drawing, but you'll get the idea. Here's the little retina scope there. We just got a patient who's just totally plain out. The far point is gonna be behind me as an examiner. As I'm looking at that, I'm gonna see with motion. Because the person is hematropic. And this is assuming that I've got either Plano in the fropter or no fropter at all. I'm just trying to get in their eyes. Same thing with high probes. The far point is technically behind the eye, but it's kind of beyond infinity as well. Which gets really confusing. But basically with the high probe, if you've got nothing in front of them, you're gonna see with motion. Just keep that in mind. You will see with. You shine these little kids. You shine them in. You'll see this really strong with motion. For sure, they're gonna be hyper-opic. And then kind of the most common situation is the patient's myopic. So you can see the far point is between the examiner and the patient. And so in that sense, you're saying against motion. Just to kind of put these things in perspective. So, a quiz. So you're using retina scope on Kloy to your two-diopter myopic patient. If you were sitting 100 centimeters away, what motion would you say? I guess the first thing you want to look at is Kloy, where is Kloy's far point? And because he's myopic, we talked about how Kloy's far point is going to be sitting in front of him because he's a minus 2. So when his eyes are completely relaxed, his clearest vision is going to be about right here. He's a classic minus 2 myope. So you'll say, alright, so his far point is the inverse of that. It's 1 over 2. So Kloy's far point, 1 over 2. So his far point's at 0.5 meters or 50 centimeters. So this is his clearest spot of vision because you just take the inverse of whatever their refraction is in diopters. And so if his far point's at 50 centimeters, but you're sitting 100 centimeters away, you will see against motion. So you're 100 centimeters away, he's got nothing in front of his eyes and you go, oh, I see a little bit of against motion. And so you know he's going to be myopic without him saying a word. Go ahead. It's exactly right. So basically if you scoot it up 50 centimeters and you're at that 50 centimeter far point, neutral. Yeah, you would see no motion. And then I guess if you scoot it up even closer, which would start getting a little creepy, you would start to see with motion. All right. And then, yeah, 50 centimeters you see neutral at any distance closer to 50 centimeters you would see with. Good. So this is really, really important because even if you're not that great at retinoscopy there are some little clues you can pick up to really help you to know how close you are. So, you know, example of the speed. If you go in and, you know, you're doing retinoscopy and you see this really slow kind of mushy against motion, you know you have a ways to go. The closer you get to neutrality, the faster that motion is going to get. You know, you do the sweep and then if it suddenly goes against you, but it goes really fast, you know you're getting close. You know, the closer you are, the faster the reflex speed. Brilliance is really good too. A lot of times we'll have these kids, you know, and they're wearing a, you know, a little 27 diapter contact lens and a lot of times, you know, they're wiggling, they're moving around and you can't really tell much if it's with or against motion but if you can get at least a sense of how brilliant and bright that reflex is that gives you a really good idea of how close you are. There have been times when they're, I mean they're two-year-olds, they're super wiggly and I have to kind of just base it on how brilliant was my reflex, how close are we. And kind of just a little clinical pearl with reflexes are usually brighter than against. And so, you know, if while you're using the feropter, if you give the patient too much minus sometimes that helps because you're like, oh, I see it really bright with reflex. So that means I have to add some plus. And then the reflex broadens as you approach neutrality. That's important. That's a little trickier to kind of get a handle on but that is kind of a good thing to know. It'll get, it'll get a broader and broader the closer you are to that sweet spot. So as you guys all know if you see with motion then you have to add plus. If you see against motion you add minus. That's just a rule of, you know, just to remember. Add plus if you see with, add minus if you see against. So working distance. So this is something that it's really commonly forgotten about. Sometimes you can really mess yourself up if you forget about working distance. And this all depends on how far away you're sitting from the patient. And it's an inverse relationship. So if you see this, this, you know, cool chart here. So if you're sitting 50 centimeters away from the patient then subtract two diopters. Or 100 centimeters away then subtract one diopter. So say you find neutrality at a certain spot but you're sitting 100 centimeters away then the actual prescription is one diopter less. And we'll do an example of that. And I'm sure you guys have gone through this before. So you're examining your patient, Kim. I actually had a friend in college, her name was Kim spelled C-I-M. This is paying homage to her. You're sitting 67 centimeters away and you find neutral with a plus five. So in the feropter there's a plus five in there. And you find neutral it's not with, it's not against, it's this kind of flash of light, it's neutral. So what's Kim's actual Rx? Well, you know, you're sitting 67 centimeters away. So that's 1 over 0.67 1.5 diopters. And so if you're finding a plus five in the feropter you have to subtract 1.5 diopters. So her actual Rx is plus 350. Sure. Correct. So we're going to get into that but when you have, that's a good question, when you have the feropter on, the feropter typically sits about 12 millimeters from the front surface of the eye which is about the same distance as glassy steel. So you want to make sure the feropter's not too close or too far from the patient because that will change. But if the feropter is sitting about the standard 12 millimeters from the eye then yes, you can trust that plus 350. Now in context that changes and we'll talk about that too. But yeah, that's a good way to think about that. And that's a good thing to be careful about because sometimes, you know, I do retinoscopy and then I look over the patient and they're sitting back like six inches from the feropter and I'm like, all right, that's, I cannot trust those numbers at all. All right, and then just another example, you know, you're examining Bertram, you're sitting 100 centimeters away, you find neutral with a negative 350. By the way, I like, I told you last week I like just putting up unusual names. I don't know why, it's just better than like John and Larry and the typical ones. So same kind of a thing. You go one meters away. So you go one divided by one because it's 100 centimeters and you're converting it to meters. So it's one diopter. So if you're finding a 350, you subtract one, the rx is minus 450. This is for glasses. Same kind of a thing. Okay, so for retinoscopy so the eye is made up of two principal meridians as you guys know and just when you're going through and using retinoscopy you try to neutralize the least plus axis first and then sometimes that's hard because you're like, well, how am I supposed to know that? Well, you know that for when you rotate the streak 90 degrees and then you find with motion. That's when you're refracting in plus cell or doing retinoscopy in plus cell that's what you want to find. You want to neutralize one meridian, flip it 90 degrees neutralize the other meridian but find plus when you're doing that and then add a little to it. So I think I've got... Yeah, here's an example. So you're doing retinoscopy on an apheicic child. So the streak is oriented horizontally so it's like this and you're moving it up and down. So basically what you're doing is you're finding the power in the vertical meridian, right? Even though your streak is horizontal, moving it up and down, you're finding the power in the vertical meridian and you find a neutral reflex with a plus 22. So you're saying, alright, well you guys know what power crosses are, right? You've done that? Okay. Basically it's power cross. This shows the power of the principal meridians of the eye. So your scope is going up and down like this. You find a neutral reflex with a plus 22. So that means you've got a plus 22 here. Then you orient the streak vertically and you get a neutral reflex here with a plus 27. And then you're like, okay. And it's funny to this day, I won't even think about working distance. I'll just write down the numbers that I get and I'll just figure out my working distance later. But in this case, there's a working distance of 50 centimeters. So what is the distance rx of the child? So you figure 50 centimeters, you reverse that. So 1 over 0.5. 1 over 0.5 is 2 and you're sitting 50 centimeters regardless of however you have the streak oriented. So you actually have to take away 2 doctors from each meridian. And so the power cross now looks like this. Plus 20 and plus 25. And so what that means is the final rx is plus 20 plus 5 axis 90. That's the child's rx. Okay. Any questions about that? Kind of straightforward. Okay. Good. Alright. So we had a fun discussion about this yesterday. We talked about the astigmatic dial technique. I'm kind of starting to get into a few other things. How to start finding the amount of astigmatism. I had my two residents and one of my students, we were talking about this yesterday. We were trying to figure it out. I used this once in school. I've never used it again. But there's a section on the book. So I just said, let me just cover it really quickly. Basically, you show them this kind of goofy dial. And then you're going to say, which orientation of lines and blackest. And they'll tell you horizontal or vertical or one of the clock hours. You fog the patient. You identify the blackest and sharpest lines. And then this is having to do with minus cylinder refraction. I sat down and tried to do the optics and the math if you're doing it with plus cylinder refraction. And it's a lot more confusing. You don't just reverse it. Anyway, if you are doing minus cylinder, you add minus cylinder with the axis perpendicular to the blackest and sharpest line. So if they say, that horizontal line is blackest and sharpest, you orient your axis at 90. And then you add minus cylinder until it looks equal. And then you kind of unfog the patient. And that gives you a rough idea of how much astigmatism the patient has and roughly where it's oriented. Again, not really ever used. But you might get a question on it. This is by far the more common method is the Jackson cross cylinder. Well, I mean you guys know that Jackson cross cylinder, that there is a good pointer. That little guy right there. So that's what a Jackson cross cylinder basically is on most poropters. There's a plus 25 there, minus 25 there. And when you're doing subjective refraction, you want to start by refining the axis before you refine the power. So you want to find what the axis of the prescription is before you figure out the power in most cases. So you position the JCC's principal meridians 45 degrees away from the correcting cell. It's called straddle line. So in this case, so you suspect that there are astigmatisms around this 180, you know, ballpark. And so you want to figure out the axis first. So you make it so white dot, red dot. It's kind of right in between the axis 180. And you know, it locks into that little position. And then you know, you chase the white. You ask them what's more sharp and clear, number one and number two. And then you follow the white. You know, say in this case you say what's more sharp and clear, one or two. And like this, they say well, number two, and this is number two here. Well, then you're going to turn this dial like that. So it's going to orient closer towards the 15. And you ask them again, one or two, and you just keep chasing that white there. So that's refining the axis. Now refining the power is, you know, kind of the other one. Basically, you align the JCC with the principal meridian of the correcting lens. So you basically say, okay, now that we know roughly where the axis is, we're going to see how much power is in the cylinder there. So you refine it. You see the white here. And that's parallel here with the axis. And you've got the red here. It's perpendicular. You keep chasing that white. If they like the white, you keep adding more power. And you guys have all done that before, right? Okay, good. When you're finding the axis, what amount of cylinder do you usually start with? So that's a good question. If you have no idea what it is, I always start here with 0.5. Because if you try to find the axis with 0.25, it's a lot trickier. You always have to go at least 0.5 and say they don't have any cylinder at all. Even with 0.5 you'll still be able to find it and eventually you'll kick it out. But always at least 0.5. And sometimes, the reason I said that you almost always start with finding the axis is because say a patient's got four diapters of astigmatism, but you don't know that. And you just pop in 0.5 here. It's going to be tough for them because they've got so much astigmatism. Sometimes you have to try to pop in a little bit more power here. And then it gets easier for them to find that axis. You know where that is. But that's rare. If you have no idea, just start with 0.5 and you can usually get there. Now remember, as you're adding power to the cell, don't forget about spherical equivalent. Every 0.5 change that you add of astigmatism, you have to make a 0.25 change in the sphere. And you guys know this equation. Spherical equivalent is the sphere plus the cylinder over 2. So you've got like alzada's arex here is plus 2 plus 3 axis 180. What's the spherical equivalent? Well, you have a plus 2. And then you get the cylinder component plus 3 and you divide that by 2. So 2 plus 3 over 2 is a plus 350. So that's the spherical equivalent. And that becomes important in a lot of things with glasses and contacts. Like for example, we had a patient yesterday. He had 2.75 diopters, plus 2.75 diopters of astigmatism. But I kind of felt like, well I guess he was wearing contacts. But if we gave him that much astigmatism correction right off the bat, I think that was going to drive him crazy. Sometimes you can't give the full astigmatism or else it just really kind of messes people up. So what I did is I cut that plus 2.75 down a little bit to plus 2.25. So I basically took out some plus. And so when I took out some plus basically meaning I went from a plus 2.75 to a plus 2.25. So to compensate for that, I had to give him 0.25 more minus in the sphere to compensate for that. Okay. Yeah, I was just going to ask you about that. So it's the directionality, it must be just adding more plus. Yes, yeah. If you're adding more plus, I guess I think I might have told you on my example. In this case I basically took away the plus. So I added an extra quarter of plus in a sphere. Yeah, so basically if you take away plus in the cell, you add plus in the sphere and vice versa to kind of compensate for that change. Because say you take out 2 diopters of plus cell, well then suddenly you've added a lot more minus than they need. So you need to compensate for that by adding it back into the sphere component. So you're changing the sphere as you're cranking it up on the cell. Yes. So you're checking the system. Yeah, so say they keep wanting cell. They got plus 1, plus 125, plus 150. You know as you're doing that you're adding a bunch of plus. So I'm taking away plus or adding minus in the sphere component. Same thing. Just to make sure the sphere cool equivalent. Like in this case you try to make sure that as you're going through this the sphere cool equivalent stays plus in the sphere. So that's a good thing. Say I decided to change this rx to a plus 250. I'm basically adding minus here. So then I add a plus quarter here, so plus in 25. So there you have it. Alright. So we're finding the sphere. Basically you want the strongest plus or the weakest minus that yields the best VA. So you basically try to reduce the plus sphere until optimal VA is reached. You know watch out because a lot of times patients make this comment. They're like what's better 1 or 2 or what's clear they'll say 2. And they say oh and also it's darker and smaller. You don't really want that. You don't really want the patient to say that it's darker and smaller because that probably means you gave them too much minus. Especially kids. I mean kids will just eat minus. They'll eat tons and tons of minus. I mean your actual rx is like a minus 2. But you know you're giving a minus 3 and you're like oh I love this. This is really sharp and clear. That's just because you're over minusing them and they like that dark and clear appearance of the letters. But ultimately that's not going to do them any good. They're not going to like that. Now one of the tests to make sure that you're not over minusing is called it's the dual chrome test. I actually use this all the time. There's this acronym, RAMGAP. Red ad minus green ad plus. Green has shorter wavelengths. Red has longer. Green wavelengths focus anterior to the red. I'm going to show you a picture of this. So you guys have seen this before. It splits the chart between green side and red side. And then basically you ask the patient, well first you fog them. So first you'll add a quarter of plus and maybe .5 of plus and you'll say alright. Now there's black letters on the red side and the green side. Where do they look darker and blacker? That's what you'll ask him in this case. Like what side do they look darker and blacker? In this case you do want to know that. And if you look at the optics here, so red longer wavelengths focus here. Green shorter wavelengths focus there. So in this case they'll say, hey the red letters on the right side, the red letters are darker and blacker. So what basically you're doing is you've created this. Because this red is right on the red nut. And so the letters look darker and blacker and clear than the green. And so you know we use that Lachlan and Ramgap by adding minus. You're basically pushing both of those lines backwards beyond the red nut. And so basically focuses the green right there. And green becomes darker and blacker as you're adding minus. We'll go back. So in an ideal world in a perfect world you want it kind of exactly right between the red and the green. That's kind of a nice prescription for most people. If they're presbyopes maybe you want to fudge a little bit more toward the red. But this is a really good way to find out if you're giving someone too much minus or too much plus. Sometimes if I have over plus they'll say oh my gosh that red is so dark and black and that green I can't see anything. And I'm like I have to add some minus because I've given them too much plus. Now the ideal prescription is to have what you think is the right prescription in front of the frupture and you'll say okay what's darker and blacker. Usually they'll say well it's pretty close maybe the red. That's usually the best. When they say that that's beautiful. When they say it's really hard to tell the difference but I'd say maybe the red's a little darker and blacker because that means you're not over minusing them. And usually if someone's over plus a tiny bit they usually tolerate that better than if they're over minus at least anyone about 30 years old and older. With kids you know it's not quite as important like if you've got a 15 year old and they're like well it's pretty close but maybe green and you're fine. I mean you're probably right close to there or kind of right in the middle and they'll be fine. So you find them first just to make sure because in an ideal world you'd want them to say red is darker and blacker first because say you don't they're like green so you have to add plus. Great you have to add plus. You kind of keep adding plus and you can kind of mess up the patient. You want to fog them first basically to knock out accommodation. So accommodation is not a factor there. If you add a plus they're not accommodating anymore because if they accommodate it's going to make it even worse so it forces them to not accommodate. I guess that's the better answer is we're knocking out accommodation and then you add minus from there. No that's more like 0.5 or like if I've got my prescription and I say I think we're pretty close and then I start the red-green test I'll usually add depending on the patient I'll usually add two clicks of plus you know 0.5 and then almost always they'll say oh yeah red is darker and blacker and then I add a little more minus until it's pretty much equal. Yeah so fog them just by a quarter or 0.5 and a lot of these things with subjective refraction you can never go wrong with adding a little extra plus because then it just knocks out their accommodation especially if they're a kid. Because you don't want to deal with this and trying to monkey around with well how much are they accommodating as well. You just want to make it so accommodation is not a factor. Okay there's also now in terms of balancing the eyes this is an issue too because sometimes you have kids where especially if they're hyper-opes you know say you've got a kid who's plus 4 and plus 1.50 and he or she is just constantly accommodating and you find there are rx but this is really a plus 4 but you're finding like a plus 2.50 or a plus 2 and they're like oh that's fine that's nice and clear and they're just actually accommodating through it. You want to make sure you're balancing the eyes. This fogging technique I don't talk about and no one ever uses it. This is a really good way to balance the eyes is using what's called prism dissociation. Basically you're adding vertical prism to each eye and I'll show you an example of this and then you add a plus to the clearest image. So let me show you this. So patient's sitting there you put a base down over the right eye you put a base down over the right eye and you put a base up over the left eye okay. You fogged them a little bit you know again to knock out accommodation I've added like a quarter or a plus 50 and I say alright you're seeing two lines of letters which line of letter is sharper and clearer and in this case this patient says well the top line is more sharp and clear I like that well the right eye is the one that has the base down prism and remember if you have base down prism everything's reversed if it's base down prism the image is up if it's base up prism the image is down always opposite and so in this case the patient says well top line is more sharp and clear the right eye has the base down prism so this is what the right eye is seeing and this is what the left eye is seeing and what you have to do is you add a quarter plus in the right eye until both eyes are equal so basically you're trying to make the right eye just as blurry as the left eye at this point so they're saying hey this is nice and sharp and clear keep adding plus pretty soon they'll both be kind of blurry equally blurry and they'll say hey that's pretty close you take out the prism and then you unfog them you know you add that .25 or .5 of minus to get them where they need to be and this is a good way to make sure the eyes are balanced to each other does that make sense now it's a little confusing you kind of have to run through it with a patient a couple times to kind of get it and to kind of see what's going on but that just is kind of you know that's a really really common way to make sure that they're pretty balanced yeah I'll add .5 alright I probably wouldn't I probably wouldn't I'd probably keep whatever sill I had just the same yeah because the sill axis and power should kind of already be set by then okay good question so just a final word on subjective refraction and I feel like this is extremely clinically important every quarter of change is approximately equal to one improved line in VA so for example you have Hedwig here his habitual Rx and VA in his right eyes a minus 150 so he comes in with minus 150 glasses and he sees 20-30 with them adding a quarter more minus should get him to about 20-25 and another quarter should get him to about 20-20 so when you refract them you'll probably end up with about a minus 2 that every day all the time so roughly for every quarter you add it improves by about a line give or take I mean if a patient comes in and sees 20-70 and usually you throw all the rules out the window you don't really know what but if their vision is approximately 20-70, 20-60 or better then that's a really good rule to follow I work with students a lot over the VA and a lot of times they'll say hey their habitual Rx is minus 150 minus 3 but they came in seeing 20-30 and I'm like I don't think so if they came in seeing 20-30 that's pretty good I doubt you'd have to add an extra diopter and a half to get him to 20-20 you're looking at more like 50 maybe 75 but I was just telling back off a little bit add a little more plus let him sit there for a second I'm sure they'll see just fine yep and of course that's not very common in someone who's 75 years old but I mean they're even Presby hopes that they'll eat a lot of minus a lot of times say in this case the patient sees you're like well they're not seeing quite the sharp 20-20 I want so I kept adding minus a lot of times it just takes a little patience show them the minus to give them a second they're like oh yeah I can see it's 20-20 because basically they're relaxing their accommodation kind of settling in and saying alright I actually can see well so again far point like we said before the farthest away the eye can see clearly with accommodation entirely at rest the book it was all over the whole chapter and that's why I'm covering it a couple times for myopia the far point is between infinity and the patient the apropiate technically the far point is behind the retina it gets a little confusing but basically to correct an eye with any sort of prescription the correcting lens must place its image at the ice far point so basically you know say you got a 2-die after my hope you're basically creating like the image of the street sign or something in infinity here at the patient's far point which is the sharpest vision they can see without accommodation so the image of the far point becomes the object that's focused on the retina let me show you this so classic myopia eyeballs too long you're looking at an image of infinity it focuses in front of the retina the far point for this my hope is actually here so the sharpest their vision is when you know about arms length right there because that focuses everything on the retina you put glasses here and you're basically creating an image here at the patient's far point that hits exactly on the retina that's basically what you're doing with glasses okay vertex distance changing the position of the correcting lens changes the relationship between F2 and the ice far point I'm talking about for right now we'll just talk about glasses we're talking about like where glasses sit on people's eyes it's really really really important if your prescription is any more or any less than about a plus 5 or a minus 5 standard glasses vertex 12 millimeters even more critical for contact lens prescribing which I don't know if we'll get much into that today but anyways we've got a long zone here so we wear plus 10 glasses that sit 10 millimeters in front of his eyes if he prefers to wear those lenses at 5 millimeters in front of his eyes what power should you prescribe so he basically comes in he says doc these glasses are perfect my vision is awesome you know but I wish I could hold them closer to my eyes because when I do that my vision is not as good you say alright well what do I do so first of all I have to figure out the focal length of whatever you're dealing with so we've got a plus 10 lens what's the focal length here's the standard prescription D is 1 over F D is 1 over 10 so his the focal length of the lenses he's wearing is 100 millimeters okay I'm going to show you this kind of horrific drawing go with me here okay go with me this is probably kind of the most arduous part of the lecture so run with me for a second here but again I was going to kind of cruise through this but there was a lot of stuff in the book about this so I felt like if they emphasized it a lot I probably should too so here so we've got the lenses the lens he walked in with right it's plus 10 so if he says hey my vision is really clear with this plus 10 you know that for a high probe the far points at 90 millimeters how do you know that well you know that because this is a plus 10 and we just found that the focal length is 100 millimeters of that lens far point for a high probe is behind the eye but you know this lens is sitting 10 millimeters in front of the cordia and so the far point is 90 millimeters behind the cordia and that doesn't change because that's just where the far point is for this particular patient and if he says alright well I want to move my glasses from that point to this point well the far point doesn't change it's still here and so you're saying well what's this distance here you know you're subtracting it by 5 so this distance is 95 millimeters and so you're saying alright so what the lens has a focal length of 95 millimeters you do the same equation d is 100, 1 over 0.95, 10.5 so basically the glasses that would suit him the best if he likes to hold put it that close to his eyes a plus 10.5 okay because if you're a high probe when you bring glasses closer to you it essentially makes them weaker that's essentially what they're doing and so to compensate for that you have to make the glasses stronger that's why 10.5 so we'll do an example of a mile so you've got Doshi and she wears negative 4 glasses that sit 5 millimeters in front of her eyes due to recent popular trends she wants to wear them 10 millimeters in front of her eyes what would be the best Rx so again she's a minus 4 so where so the focal length of the lenses she's wearing because she's like hey these glasses are really sharp I really like them I just wish I could pull them out but brought over too close to my eyes they my eyelashes brush against them and that's a common thing that happens so the focal length is 25 centimeters okay now with this picture remember with a mile the far point is in front of the cornea it's between infinity and the cornea so patient's vision is nice and clear with the minus 4 lens at 5 millimeters the far point is 30 millimeters in front of the cornea okay so basically here's this here's the cornea minus 4 nice and clear okay the power of the lens so you're basically saying we're moving it from here to here the far point stays the same so the length now here is 20 centimeters and then you're saying alright well power of the lens has a focal length of 20 centimeters it's minus 5 so if she wants to do that and hold it out farther you're going to have to give her a stronger lens if she wants to hold it out farther because it's opposite with hypros with myopes when you bring glasses closer to you they essentially get stronger when you pull them away from you they essentially get weaker so to compensate for that you have to add a stronger lens hence minus 5 alright I know that gets a little confusing you know and I'm more than happy to give these slides out if you guys want to look at them prescribing for children myopia obviously retinoscopy and cycloplegia are critical children tolerate cylinder really well I mean if it's like a 5 year old kid and they've got 2 diopters of the stigmatism all of them don't just give it to them because they can usually tolerate it really well sometimes I will back off a little bit but a lot of times I'll just give it to them obviously you know I'm a contact lens guy consider contact lenses for high minus or a nice and metropic guys contact lenses like we discussed last week are really good really good at helping to balance out a nice and metropic guys you know you've got a minus 2 and a minus 6 with glasses sometimes that gets a little weird with magnification and vertex distance and all this stuff contacts really levels that out a lot better now hyperopia is always a little trickier you know if the hyperopia is high enough the patient can't see distance or near there's also a lot of strap issues combination issues that go with that retinoscopy and cycloplegia are very critical even more so because you know in a perfect world you put them up to an auto refractor and spit out the prescription you're good to go but with hyperops it's usually a lot more complicated than that now this is important except in cases of isotropia cut the plus so like you'll have a kid say 6 years old in first grade he's been kind of complaining you don't know if he's malingering or not but you check the RX and he's a plus 1 and then you cycloplegia when you're like oh shit he's actually plus 5 in both of his eyes at age 6 if there are plus 5 you should probably prescribe something but if he doesn't have isotropia or any sort of strabismus or anything like that then I'll always cut the plus because there's no way you're going to give that kid a plus 5 pair of glasses and he's going to tolerate it he's so used to accommodating all the time he'll put it on and be like that's just too blurry and I can't relax my accommodation enough so you'll cut the plus so cutting the plus basically means you back off by about a diopter in a lot of cases a diopter and a half sometimes two diopters so in that case I just gave you kid is plus 5 with cycloplegia I'll prescribe him to be a plus 4 maybe even a plus 350 just to get him started just to train his eyes to learn to relax a little bit and down the road maybe next year I'll bump it up to a 4 or a 450 but you've got to cut the plus if they've got isotropia or any sort of strabismus you've got to give them the full to try to straighten out their eyes and then like I say children often tolerate the cylinder I know a nice isotropia well a baby's laughter is one of the most beautiful sounds you'll ever hear unless it's 3am and you're home alone and you don't have a baby just keep that in mind there's nothing else you get from this lecture this is what I want you to remember alright are you guys doing alright? I know there's this lecture I was like oh man I feel bad for these guys because this is a lecture where I kind of wish I could split it up into two different ones but you know you do what you got to do because I mean the section in this book is really big okay so accommodated problems you'll see these so obviously presbyopia gradual loss of accommodative amplitude you all know that there's this thing called accommodative insufficiency basically premature loss of accommodative amplitude they just can't accommodate as well as they probably should be near objects are really blurred they get really fatigued you know they talk about how they have to hold things out here and this is a lot of times this is not even presbyopes you know you can get people in their early 30s even their 20s and they're like man I'm on the computer all day but I get exhausted by the end of the day I am so tired and sometimes the reason why is they just can't accommodate very well you know a lot of times they'll require additional reading plus power if they're already in you know progressive or something like that and a lot of times it's just simply due to uncorrected hypropia actually another patient from yesterday same thing he's just like man I'm on the computer all day I get so tired he was 37 years old and we just found out his Rx is like a plus 50 in both eyes not that bad it's really not but if you think about it you're like well in order to see infinity clearly he has to accommodate by 0.5 diopters and then when he's looking at the computer he has to accommodate another about a diopter and a half so to see the computer clearly all day he has to accommodate his eyes about 2 diopters all day long and he's getting closer to presbyopia so you can kind of see why he'd be getting more and more tired and a lot of times patients come in they're 35 and they're like I'm just not as comfortable as I used to be and it's simply due because they're a plus one and didn't even know it they've been accommodating their whole life through it and now it's kind of coming back to bite them then you have a combination of excess another name for that is ciliary muscle spasm they get a lot of headaches kind of brow aches their distance vision fluctuates a lot and this can be tough because you know fluctuating distance vision that can be dry eye and a bunch of other things but it could be accommodated problems where they're so used to accommodating all the time that it causes even their far away vision to fluctuate a lot and it can occur after prolonged and intense periods of near work so refracting these patients is kind of tough sometimes you sometimes just have to cycle please even if they're adults okay ACA ratio are kind of good topic to talk about okay so basically you can get kind of into the weeds in this a lot but just to kind of take a step back and overall look basically how much do you converge when you accommodate I had a professor that said just keep in mind when you're looking at ACA problems accommodation drives the bus always look at it as accommodation is driving convergence so basically how much do you converge when you accommodate one diopter normal human being the normal ACA is three to one or five or three to one to five to one there's kind of a range there so basically and it's kind of reversal but for every diopter here the second number of accommodation this is how much your eyes are converging anywhere from three to five diopters okay that's normal human being so there's two ways to measure it once the heteroforia method I don't think we'll worry about that it's very rarely used but I wrote it down then there's the gradient method which is much more common and there's kind of two different ways to do it using the gradient method the probably the easiest one is to stimulate accommodation basically what you do so you do the cover tests if you want you're measuring the heteroforia when we'll do some examples of this you're measuring it at distance you add a diopter of minus over that eye or I mean over both eyes so basically you add a doctor of minus so that that stimulates accommodation it automatically stimulates conversions and then you measure it again the ACA is the difference between the two measurements we'll go through an example of that in a second the other one is you can actually relax the accommodation basically you show a target at 33 centimeters so basically if a patient's corrected correctly then to see something at 33 centimeters they have to accommodate three diopters so right now you know right now my vision say I'm amatropic right now to see my hand I'm accommodating three diopters and so what I do set a target there someone measures you know with cover tests what my heteroforia is and Excel will say and then you add three diopters of sphere to the fropter so basically now to see that point I'm not accommodating at all so I've gone from accommodating three diopters to accommodating zero you measure it again you get the difference divided by three ACA ratio and about that one we're going to talk more about the stimulated combination one okay so we got Laquan has a measured Fourier of eight base in so eight prism so eight prism.com is an Excel Fourier at distance so when he looks off in the distance he's Excel four by eight prism diopters okay common when you add minus one diopter you measure two base in so I'm still exophoric but not nearly as much so what's his ACA ACA is six to one that's a high ACA so basically for every diopter that I accommodate I converge a ton I converge six diopters and that can lead you to problems especially up close like if I'm looking at something really up close I'm converging just like crazy that can cause double vision that can cause eye strain and driving nuts philosophy let's do another example has a measured Fourier of four base out so you know I'm esophoric in distance after having a diopter you measure six base out so basically you're saying wow you know even though I added a diopter of accommodation boy their their their head or Fourier didn't really change much I mean they're still esophoric but not that much different so what's Flossy's ACA two to one so the patient doesn't really tend to converge a lot for accommodation for every diopter of accommodation and again plane of eye strain in here in this case you have some people that are it's called divergence insufficiency meaning because their ACA is really low they don't diverge very much when they're looking out for the distance and so they can have distance vision problems sure oh I put that in wrong sorry I had copied the the previous slide I'm glad you got that so sorry so that should be the top one four prism diopters of esophoria six prism diopters of esophoria thank you for catching that in fact I should make myself a note about that while I'm thinking about it because I'm just gonna stop this lecture and I I'm gonna not remember okay good thank you alright so how much time I have left holy cow alright so the question about that sure so the honestly the best thing to do is send him into a binocular vision specialist like a vision therapy optometrist who there's a lot of vision therapy techniques to kind of help train patients to converge better or converge less or to control the accommodation and convergence better there's a lot of methods you can do like for example just you've got someone that got a low ACA ratio and so they're not converging a lot when they're looking up close what I'll what I'll talk to patients about is doing pencil push-ups I know you guys never heard of that so you get a pencil hold out arms like you stare at it like the tip of it and you bring it closer and closer and closer and you try to keep it nice and sharp and clear it's gonna suddenly go double once that happens bring it out try it again you're basically kind of teaching your eyes to kind of converge better and the accommodation to work better that's kind of a Mickey mouse thing that I prescribe but they have found that pencil push-ups can actually honestly help patients but that that's something where you just kind of just send them into a vision therapy you know I mean you can do a few other things like for example say a patient doesn't converge very much with every diapeter of accommodation if you have to over minus in that case maybe a little bit to kind of force them to accommodate a little bit more to kind of push convergence you can do that or say they don't accommodate quite or they accommodate too much we'll say so say their ACA ratio is 6 to 1 they accommodate way too much for every diapeter you want to make sure that you don't over minus that patient if anything maybe over plus just so you don't stimulate too much accommodation so it just drives them crazy but bottom line I don't even mess with these patients a lot I'll just say you know what there's a couple optometrists I know I do a lot of vision therapy they're great I'll send them over to them but yeah I mean pencil push-ups though it helps a lot of kids especially since it's really common for kids to not be able to converge very well and sometimes their accommodation is a little off good question so I do have a few more minutes do you have any questions because I can go through a couple other things but let's you want to ask questions first we can just ask a few questions we can call good you're good okay so this will probably be the last thing I'll get to basically accommodate of amplitude basically how much can a patient accommodate what's the strength of their accommodation that it's the diopter difference between the near point and the far point now the near so we talk about the far point far point is how clear can you see without any accommodation at all for myops it's right here you know for two to after myop the near point means if you are giving max amount of accommodation how clearly I mean how closely can you see when you're maxing out your accommodation that's your near point when you can still see things clearly with full accommodation so myop so yeah so here's the far point of myop so the patient says hey you know three centimeters whatever from my I can still see clearly because I've accommodated like crazy that's their near point closer than that it's all blurry because they just they maxed out their accommodation hyperopia so you know we talked about how their far point is behind the eye when they accommodate it is it essentially brings their far point up to the retina so in their case it's a little goofy but their near points actually you know it's here but you're kind of you're kind of doing that um let's skip that one last thing to kind of think of mine I think we'll just do this for from the patients measure to accommodate of amplitude allow half to be held in reserve so if you measure a patient and you find out hey this person can accommodate two diopters that's the max they can do it then they can usually comfortably throughout the day accommodate half of that so say you know this patient has two diopters a max combination they can accommodate one diopter comfortably you determine that Sinandra has 1.5 diopters a max accommodation 0.75 maybe comfortably contributed by the patient but say she's like you know what I really like to read up here up close I like that and that's 40 centimeters away basically she's saying boy 2.5 diopters is what I really like well in this case she needs 2.5 diopters she can comfortably add 0.75 that helps you determine the ad so in her case you'd give her about a 1.75 ad because she can contribute 0.75 but she really needs a 2.5 okay anyway so if any of you guys want you know these slides just let me know um you know there's a bunch of stuff obviously we didn't get to um but uh you know the book is honestly really good it's just kind of a long section I've tried to really condense it and make it as kind of simple and clinically applicable as possible but if there's no other questions I think we'll just call that good thanks for sticking with me I know a lot of these things you know you kind of have to trudge through a little bit but I appreciate your patience okay thanks guys