Episode 1: The Basic Eye Exam

This is the first episode of this program, so I’m still putting things together. You can listen to the show with the links above. I’m having the episode transcribed, but this will take a few days. in the meantime, I’ve copied my show outline below in case you want to read it while listening.

EPISODE 1: The Basic Exam

Download the show: EB001-EyeExam.mp3

Also, you can subscribe to this podcast using iTunes … just search for “Eye Basics” in the iTunes store, or go directly to the podcast page here.

Show Transcript (comments below)

This is Eye Basics 101 Episode 1: The Basic Eye Exam

In a world without good eye education, a beacon of hope was born. That beacon is Eye Talk Radio

Welcome to Eye Basics 101. This is an audio program dedicated to teaching you about the eye and ocular disease. No matter if you are a student, a practicing doctor or just a curious person wanting to learn more about the eye, we can all learn more with thoughtful discussion. My name is Dr. Timothy Root, I’m a general ophthalmologist and cataract surgeon. The show notes for this episode are available at eyetalkradio.com, that’s E-Y-E eyetalkradio.com. If you have questions or comments about today’s discussion, just visit the show notes. You can also find it directly at Eyebasics101.com. Just look for episode 1 and leave a comment if you have one.

Today’s topic is the basic eye exam. Now, sight is arguably the most important sense for both survival and quality of life. The eye exam is quite different than a medicine exam. If you are a medical student or practicing doctor, much of your training to this point has probably involved a basic whole body exam. The eye is quite different.

For one thing, it’s much smaller, the eyes are only about one inch in diameter. It’s one of the smallest organs we can actually examine but there is a lot to see. And the reason why is the cornea, that clear window on the front of the eye lets us look inside the eye, so a lot to examine, a lot to document and it’s all crammed into a tiny space.

But before we get going on the basic eye exam, I wanted to spend a little bit of time talking about the motivation behind this program and why are we doing with this. When I was an ophthalmology resident, I had a great fortune of spending a good month up in New York City rotating with a neuro-ophthalmologist. During that time, I had to do quite a lot of self-study to try to understand a very confusing topic, neuro-ophthalmology is one of the more difficult sub-specialties to comprehend.

I found a series of audio lectures recorded by the great neuro-ophthalmologist J. Lawton Smith back in the 70s. They were online so they put them up in a novel website and I downloaded all the mp3s and loaded them on my mp3 player. As I commute around the city, I would listen to this lectures and they were pretty dense. Neuro-ophthalmology, talking about neuro anatomy in an audio format was quite challenging but I did find the experience extremely enlightening and very educational for me. I really enjoyed listening to these lectures and hear Dr. Smith talk to me right into my ears. It was quite moving.

I don’t know if you have ever had any familiar idea with J. Lawton Smith. He died a couple of years ago but he was one of the great neuro-ophthalmologists of the past 50 years. He worked down at Bascom Palmer down in Miami, Florida but he was from South Carolina and he was famous for his teaching style and partly because he just had a really interesting way of speaking, had an extremely dense Southern Carolina accent and he would say things like, pure as Ivory soap and you’re a rube and all these crazy Southern Carolina backward sayings. It’s really funny, it’s strange it can’t come with such an accent and such a great intellect. I found the entire experience very interesting, the audio was fantastic.

I enjoyed the dialogue, I think it made me a better doctor. I’m not saying I’m a J. Lawton Smith, that’s for darn sure, but I did find the experience listening to the audio while walking around quite good because reality is, I do a lot of videos. If you have ever seen my videos online, I do a lot of online video lectures, you’ll find them on YouTube. But people only have so much screen time, so much time where they’re sitting in front of the computer screen or looking on their phone or doing that type of stuff because life is busy. I’m hoping that by putting this in an audio format, it will be portable, you will be able to listen to it while driving around, walking around, cleaning the house doing chores and also maybe a little bit more personal because I can spend a little bit more time talking to you.

There’s also some selfish reasons behind this whole audio endeavor because the preparation time is much less. I put together a video lecture, I try to do a good job and it takes me months to put together lines and record the videos and then edit the audio into it and fix the timings, put it into a down loadable video format, upload it online. It’s a big ordeal and my family is not wild when I go into video mode. But audio, I could probably whip up pretty quickly. In fact, I’m scheduling to do it bimonthly so we’ll see what is quite as useful.

But with that other way, let’s go back on topic. We’re here today to talk about the eye exam, the basic eye exam. Now, this is actually a challenging topic even though it’s supposed to be basic, this is challenging. The reason why is talking about exam techniques is extremely boring. I dreaded doing this topic but I knew I had to get it done because you can’t really talk much about ophthalmology or optometry without learning how to actually looking at the eye itself but extremely boring topic.
In fact, when I was a medical student, they would make us read, I believe it was called the Bates clinical exam, this was this big giant hardbound book on how to examine the human body, how to percuss the lungs and to listen to the heart and t examine the lymph nodes. It was an extremely boring book. I bought the darn thing as I was supposed to but I never cracked it open because it was just overwhelming. How do you learn the body exam through a textbook? In fact, that book was so big they give us a pocket version for carrying around with us which I did look at.

Learning how to do an examination technique is kind of like reading a passenger safety instruction when you’re on an airplane. I mean, who really does that? It’s really boring. Or maybe read a manual on refrigerator maintenance. It’s not the type of thing that necessarily lends itself towards the written, or even the spoken word. These things are important so we’re going to talk about it because we got to do it, you got to start somewhere and this is a good place to start. If you’re going to be an awesome doctor or eye doctor, you got to know how to examine the eye. My challenge, in fact, it’s not even challenge, it’s my responsibility to you, is can I present this information in a way that’s both educational and still entertaining and you’re going to be a judge at that because I don’t know but we’re going to do our best so bear with me and let’s get going.

The first topic I want to go over is vital signs. Now in medicine, the vital signs are the blood pressure, the heart rate, temperature, respirations, these are all measurements of essential body functions. When I say essential, if you have no blood pressure, heart rate, temperature, you are essentially dead, right? Well, oddly enough, despite the importance of these vital signs, in ophthalmology, that nearly is important. I mean, if you could walk into an eye doctor’s office, your vital signs are actually good enough.

Instead, we have completely different vital signs and I’m not sure if this is something books teach but this is what I teach my own students. The vital signs of the eye are the vision, the pupils, and the eye pressure. I’ll say that again, vision, pupils, pressure. These are the essential ocular functions. They are essential because if you have no vision, what were the eyes for? Pupils are nice objective measurement and pressure is vitally important for glaucoma. Vision, pupils, pressure, vision, pupils, pressure. It’s like a mantra.

In fact, you need to get a patient’s vision, pupils, pressure before you can put dilating drops in which doesn’t sound like important points but when you’re an ophthalmology resident and you get called at two in the morning to the emergency room to see a patient, you have to get their vision, pupils, pressure before you can put those dilating drops in. Those dilating drops are going to take 15 to 30 minutes to work and so if you want to get sleep, you got to get that vision, pupil, pressure first so that you can get those drops in.

And so, I kind of feel like the Dunkin Donut man, I don’t know if you remembered this old commercial from the 80s but he would wake up early in the morning and say, “Time to make the donuts.” It’s the same thing with the eye. “I got to check the vision, pupils and pressure.” Because this is very important, let’s spend some time on each of these vital signs and going to these in a little bit more detail.

Number one, vision. Arguably, of all the vital signs, the vision is the most important function and interestingly, despite its importance, vision is very hard to measure sometimes. It’s inherently a subjective measurement. No one man’s blurry vision is another man’s clear vision. And so, in an attempt to objectify this measure of a patient’s vision, we had to come up with something and so the most commonly used measurement is the eye chart, how good is your vision. Most doctors use the Snellen eye chart. It was invented by Dr. Herman Snellen back in 1862 but it’s basically the eye chart with the big E on the top and as you go down, the letters get smaller and smaller and smaller.

The Snellen eye chart is normally documented as some type of ratio. A patient with 20/20 vision is considered to be a normal person but if someone has, let’s say, 20/60 vision, what that means is if you have your patient standing at 20 feet looking at the eye chart, they could only read the 20/60 line where someone with normal vision standing 60 feet back from that eye chart can read just as good. It’s kind of a ratio of how good is your vision compared to how someone else with normal vision is. We use the 20 foot marking here in America and the US but the rest of the world uses different measurement, they’re on the metric system and so they do a meter convention and they usually do 6 meters. Let’s say 20/200, in other countries would be a 6/60. Same ration number comes out to being the same, just different measurements used.

There is another type of eye chart called a logmar eye chart that is typically used with research. It has a little bit more even progression between the line. Every line has the same number of letters on it so it’s probably more technically accurate but the Snellen chart is pretty much standard so 20/20 vision Snellen, that’s how we document it.

As far as how to measure someone’s vision, it was pretty obvious. You check each eye one at a time, see how well it can read that eye chart. But there’s a couple of points I ‘d like to emphasize here before we move on. The first point is that the corrected vision is really the only important measurement here. People always want to know what’s their vision without glasses. It doesn’t matter because patient’s vision with the glasses or with the best corrected vision is the only thing that’s important because that tells us how healthy the eye is.

Sure, you may be nearsighted or farsighted, it doesn’t matter. We only really check patients with corrected vision. Unless there’s some other reason you need to know what their vision is without glasses, for example, the driver’s license bureau might want to know if this person can drive a car safely without her glasses, so then we check but on routinely, I don’t always bother checking uncorrected version because it doesn’t really tell me anything.

Also, we check one eye at a time typically and you can do that by using the occluder a little paddle that covers one eye at a time. There’s also the paddle that covers both eyes that has a little hole in the middle of it. The important thing when checking someone’s vision one eye at a time is people cheat. They totally cheat. You really have to watch them closely which is why the occluder panels are good because you now they’re not peeking between their fingers. You have to watch little children especially because they will cheat at the drop of a time [0:12:01.6], they are not being malicious, they just do it. Also, some of our older patients especially in glasses, when their hand would drift, they don’t realize it either. So one eye at a time. This is obvious stuff, right?

Another technique we use is the pinhole technique. If you have a patient who doesn’t see perfectly, one trick you can do is have them look through an occluder that has little tiny holes punched through it. By doing that, if they ended up seeing significantly better, this implies that maybe their glasses aren’t quite up to date or they need glasses or change in that prescription. The reason why is when you look through a pinhole, this turns your eye into a pinhole camera. I’m not going to go too much on the optic here to explain how this works but I’ll do it a little bit.

A pinhole camera, I don’t know if you have ever seen one of these things but it looks like a box that’s dark inside with a little tiny hole punched into one wall. You can make one of these using an old coffee tin for example, you just punch a little tiny hole on the lid, put some photographic film on the bottom of the thing and then you set it stable somewhere. The theory behind it is if you have a small enough hole going into this camera, light coming off of specific object will come through that hole inside the camera and hit a single spot on the film at the back of the camera. Light from a different area will always go through that hole and hit a single spot so everything is in focus. It doesn’t matter how close or how far away that object is, light can only split through that little tiny hole so it comes in straight and strikes a single space in the back of that camera.

Pinhole camera is always in focus, distance, near, it doesn’t matter. It doesn’t even need to be focused. Pinhole cameras are nice in that way. A lot of small cellphones have pinhole cameras in them and if you notice, using a cellphone, there’s not a whole lot of focusing, everything is kind of in focus. Nicer cellphones have cameras down and they do focus but little tiny spy cameras, little tiny camera phones, they have pretty good focus.

Compare this to a big giant SLR camera, those things you have to focus perfectly because if you don’t things are out of focus because they have a nice, big aperture. The bigger the hole going into the camera, the more you get to focus. SLRs take great pictures because you get that wonderful blurring effect in the background so you could really focus on your object. But the point being pinhole turns your eye into a pinhole camera so things come on focus. If your patient ends us seeing a lot better when you put that pinhole occluder up there, it kind of implies that maybe, they need to be focused better. Maybe, their glasses are out of of wack because they need glasses. But the pinhole technique, we do that one eye at a time typically. It will all come back to this pinhole especially if we are talking about cataracts but now, let’s move on.

Another technique that we can use on checking vision is called the BAT or BAT test, it’s the brightness, acuity, tester technique. The idea behind it is you check your patient’s vision and you shine a flashlight in her eye, a little pin light right next to their eye and you see if it creates any glare problems, if their vision drops off a lot. If it does drop off a lot, they kind of implies maybe there’s a cataract because a cataract has a cloudy lens inside the eye and if it’s cloudy, if you shine the light from the side, it will glare the whole thing out makes it harder to see so if someone has a lot of glare disability, the BAT technique sometimes pick it up.

In fact, there is a BAT tester. It’s a little hand held flashlight that has a little dome that shoot to light that lights it up. Our patients hold it and they look through that dome, to the little hole cut out at the middle of it and it’s a little bit more objective way to measure BAT testing, in case you can set the brightness inside that little device to keep it more consistent, at least in your office, the BAT technique.

Another aspect of vision is our patient’s near vision. This is especially important as we get older and develop presbyopia or difficulty reading without reading glasses. And so, we will typically measure that with a near card. We just give the card to our patient and we tell them to hold it at whatever distance they want, it doesn’t really matter. For most people, I tell them it’s probably best to hold it where you like to read that way we can tweak your glasses but when checking your vision, you just try to get an idea how do they see close up. Some people who have very bad distance ratio will do better with the near card and vice versa.

Now, unfortunately, the near card does not use the same Snellen measurement. The near card is developed by a Dr. Jaeger and so we use a Jaeger scale. In that scale, there is a number of numbers called Jaeger 1, Jaeger 2, Jaeger 3. But we’ll typically see a patient with perfect vision as a J1+ which corresponds about 20/20. A J1 is a 20/25, J2 is 20/30, J3 is 20/40 and so on. You’ll typically document neurovision as J1 or J2 etc.

Finally, when we document vision, we typically write it down and there is a convention of OD, OS and OU. In case you don’t know that yet, OD means the right eye, oculus dexter, OS oculus sinister, that’s the left eye and OU, oculus utro, I believe that’s how it is pronounced, OU is both eyes. That’s how we write it down. There’s a couple more vision checking techniques such as the pinhole PAM but we’re going to hold off of that for now because we’re still on the vital signs. Let’s move on to the second vital sign.

The second vital sign is the pupils. The pupils are that black hole you see when you look at the eye, the iris the colored part of the eye has a little circular hole right in the middle of it and that little circular hole can change shape and that’s what we call the pupil. The pupils were like antlers inside the back of the eye that strike the retina in the back. Now, the size of the pupils is an objective measurement of the eyes’ overall afference input. When I say afference, I apologize for using terms like that, I hated these stuff in neurology. But when I say afference, I just mean they eyes’ ability to sense light in general because when the light enters the eye, if it’s too bright, it makes the eye hurt and the pupils will constrict down and if the pupil will constrict, we know the eyes were seeing, so it’s how much the eye can sense.

This is a nice measure, this is the first time we have something somewhat objective because if a patient comes in and say, you know what, I can’t see anything in my right eye, it’s completely black, it’s like I’m in a coma in a thousand feet down but if you shine a light in your eye and the pupil constricts, this is an objective sign that yes indeed, that eye can’t sense light. It doesn’t exactly tells us what the problem is but at least, the pupils give us a nice measurement that there’s something going on here.

This is also useful for people who can’t communicate. We see a lot of people who can’t speak, infants for example or demented or stroke but you can shine light in the eye and you can at least tell that the eye is sensing light. We typically will check the pupil reaction with a penlight but most penlights that people are carrying in their pockets are not quite bright to really get a good pupillary constriction. The brighter the light, the better, either brighter flashlight or we use a muscle light which is a little light ophthalmologists use.

When measuring pupils, we are measuring two things. The first thing we’re measuring is the direct response, how much does that pupil that you’re shining the light and how much is that pupil constrict so it’s direct as it directly respond to you. But we’re also looking for second response. We’re looking for the consensual response because when you shine light in one pupil, the signal goes from the back of the eye up the optic nerve, crosses over and goes to the other eye and both eyes will actually constrict. So really direct in a consensual response. I’m not going to go over the pupillary pathways, it’s not important but just realize when you shine a light in both eyes, both pupils should constrict by roughly the same amount. The consensual response.
This springs up a problem though. We can try to estimate a pupil’s ability to respond and we can try to estimate someone’s ability to detect light in their eye but it’s really hard to measure. For example, let’s say you have a patient come in, a young woman, she has a history of multiple sclerosis and she’s complaining of a vision problem in her left eye and you suspect that there might be some type of afference, some type of sensory problem, some problem with the optic nerve behind the eye. And so what do we do? We check the pupils, you shine a light on the good eye and both pupils constrict from, let’s say 4mm down to 2 mm.

Great, a direct and good consensual response, everything is working properly.

But let’s say you shine the light in her bad eye, in her left eye and both pupils constrict from 4 mm to 3 mm, not quite as much constriction. The question here is was there a pupil defect there or not? Did we actually detect anything or not? I don’t know about you but determining 3 mm versus 2 mm on a real live patient looking at her eye, it’s very hard for me to measure. It’s hard to tell. This is not always an obvious thing.

That brings in our favorite test when checking pupils called the swinging light test. The swinging light test is very good for looking for relative problems. Let’s give you for instance. If you take a healthy patient and you take your flashlight and you shine it in a good eye, both pupils will constrict. Now, as you move that flashlight from the good eye to the other good eye, the flashlight will travel over the bridge of the nose and so both eyes are temporarily in darkness and so it will start to dilate a little bit. And then when it hit the good eye again, both eyes will constrict.

So if you are looking at the eyes themselves during this whole process and you swing your light back and forth every couple of seconds, you’ll see constriction of the pupil, constriction of the pupils, constriction of the pupils, constriction of the pupils as you go back and forth, the initial movement that you see, the first thing those pupils do once the light strikes is they are always constricting, constricting, constricting. Don’t worry about if it constricts and it wobbles a little bit, there’s something called [0:21:52.3] where the eyes kind of vibrate. But you look for that initial movement so the healthy person you get constriction, constriction, constriction, constriction, perfect.

Now let’s take our patient with multiple sclerosis. We suspect the left eye, the one eye has a problem but we’re not sure. Now in that patient, if you take the flashlight, you shine it with a good eye, both eyes constrict down to 2 mm, great. And if you hop over to the other eye, both eyes will actually seem to dilate up to 3 mm, just a little bit. It’s not much, it’s actually just a subtle thing. And so as you go back and forth between the eyes, you’ll actually see constriction, dilation, constriction, dilation because that one eye is just dilating both eyes up to 3 mm. It’s subtle but this is a great way for picking up very mild afferent problems, very mild pupillary defects.

We call this an APD, afferent pupillary defect but more accurately, it’s probably better described as an RAPD, a relative afferent pupillary defect because you can only pick it up, it’s relative to the other eye. If you have a patient who have two optic nerve problems, equally as bad as you went back and forth, the eye, the pupils will look normal. This is a great way for picking up pupillary problems relative to the other eye, the swinging eye test. Some people call the APD a Marcus Gunn pupil but don’t worry about that if that a little confusing, there’s videos online and I’ll cover this a little bit more when we talk about neurology and the pupillary pathway.

The third vital sign is pressure. Eye pressure is another one of those objective measurements where we try to estimate what the internal fluid pressure is inside the eye and this is very important for glaucoma especially. While we think of pressure as an objective measurement, it’s not really that objective. There’s no way to truly know the internal pressure of the eye, drilling a hole through the side of the eyeball measuring the pressure directly. But you can estimate the pressure inside of an eye by pushing on the outside of the eye and pushing on the outside of the eye is called applanation.
The theory behind it is the Imbert-Fick Law. That’s not really a law, it’s more of a rule but the theory behind it is that if you have a sphere of fluid inside of some type of covering like a balloon wall, you can estimate the internal pressure of that sphere by measuring how much pressure it takes to indent the side of that sphere. In other words, just like kicking a car tire, you can estimate the internal pressure of a car tire by kicking out with your toe, you have an idea of how big your toe is, how much force it took to indent it and by using those measurements, you can estimate the internal pressure of that tire. Same thing with the eye. In fact that’s what we do.

It’s called a Goldman applanation tonometer. It’s a little gadget that attaches to the slit lamp microscope that has a little piece of plastic that you illuminate with blue light and it pushes on the surface of the cornea in the front of the eye. It pushes on that eye and you apply pressure until it flattens an area of about 3 mm in diameter. Once the area of the cornea about that size is flattened, the machine has a little measurement, you can tell how much pressure was applied and it calculates the internal ocular pressure. When we do applanation tonometry, we use fluorescein dye, it’s a man-made fluorescein dye that glows bright green under a blue light and a numbing agent because it doesn’t feel good to touch the eyes so we numb the eye up with fluorescein in there and that fluorescein dye makes it easier to measure the exact 3 mm diameter circle and then the machine kind of calculates out what the pressure is inside of the eyes. Goldman applanation, the gold standards still of measuring someone’s eye pressure.

Now, doing Goldman applanation was one of the skills as a med student. I was terrified of it because this is the first time like shoving something into a patient’s eye and it’s sometimes quite challenging to get a good measurement, looking into the microscope, holding your eyelid with one hand, turning it out with the other. But once you get good at Goldman applanation, it’s not that bad which is easy for me to say, right?

There are other pressure techniques for estimating the eye pressure. One of them is the Tono-pen. This is a little electronic gadget that kind of looks like a really big electronic magic marker that’s white and basically, it has sort of like an applanation tip on the end. It is basically held up to the patient’s eye and you tap on their eye and this little gadget will actually sort of estimate the pressure as well. It’s a little hard to use though.

Tono-pens are commonly used in the emergency rooms and because they don’t have training in how to do it, it’s almost like a random number generator. Even for us in the office, it doesn’t give us the most accurate readings not nearly as accurate as a Goldman but sometimes, it is the only way to measure pressure in someone if you have someone who is in a stretcher, at the bedside or maybe in the middle of surgery, or maybe doing an exam or anesthesia for pediatric case for a young kid. There’s only one way to measure that pressure in those settings, you can’t hold their heads up to a microscope, you got to use something handheld, that’s the Tono-Pen.

Pretty expensive device, it only has one button, I guess the manufacturers figured that medical people are smart enough to work more than one button but it’s a little hard to get used to. They are pretty expensive, I see them $2,000 to $4,000, crazy.
There is an older technique called the Schiotz tonometer which basically did something similar to that but had little weights built into it. I have never actually used one of the things but I don’t think anyone’s using it these days.
Another way to check the pressure is the air puff. Basically, it’s a little gadget or a little machine that shoots a puff of air at the eye and it measures how much the cornea distorts and knowing how much pressure pushes the cornea. It’s the same idea as applanation but it’s physically touching the eye and blowing at it. We don’t normally use this in ophthalmology because maybe it’s not as comfortable for the patient because they don’t like the puff. It may not be as accurate, though some optometrists will argue against that, but it is used and because there’s less training involved learning how to do the thing so it’s hard.
Finally, if we have, let’s say, a child and just trying to get an idea what their pressure is, you can’t do any of these tests, then, sometimes we’ll do finger. Have him close his eyes, very gently press on both eyes and try to estimate what their eye pressure is, extremely inaccurate, we say soft to palpation but I can’t, I really can’t tell the difference between high and low unless it’s rock hard versus super soft. Soft to palpation is not the greatest method but sometimes, you don’t have any other options.

That pretty much ends the three vital signs, vision, pupil, pressure. Have [0:28:27.0] to that, I can’t believe how much we’ve talked about it. Let’s move one because there’s a lot more eye exam. Let’s wake up if you can, stretch and we’ll move on to the extraocular movements.

The extraocular movements, also called the EOM is basically how the eyes are moving. The eyes sits inside of an eye socket like a scoop of ice cream inside of a waffle cone and there’s muscles that attach to the eye that pull the eye in different directions so we can see up, down, left and right. Eye movements are very important for obviously seeing what you’re seeing but they are also important for binocularity, how are the eyes moving in relationship to each other.

Typically, when we are documenting or are looking at eye problems, we look for two things. We look for ductions which is how each eye is moving independently, can an eye look to the side and look in every direction. We’re also looking for versions which is how the eye is moving compared to each other. For example, can the eyes converge, can the eyes move inwards, for example, if you read something in a book, your eye is going to turn in a little bit. And can they diverge? Can they move it back outwards for looking far away?

When we measure eye movements, it’s not that complicated but the main thing we check is a couple of positions. We want to check how are the eyes moving in primary position, looking straight ahead. Arguably, the ability to have straight eyes looking straight ahead is the most important thing so we check the primary position, are the eyes crossed, are they out, how are they looking? Then we check the cardinal directions. The cardinal directions are the most important physiologically. Think of a big H in the air. We check how the eyes look side to side and in the upper corners. Directly up and down is not as important but basically, we just have to look at our fingers as we move around in these different directions so we check primary first and then we check the cardinal directions.

If there is an eye problem, if the eyes appear to be maybe out of synchrony or we have a patient who is complaining of double vision, there are a couple more tests. One is the cover-uncover test. The idea behind it is you say look at my nose or look at a spot on the wall behind me and you take a little paddle and you cover one of the eyes and then you uncover that eye. You repeat a couple of times and you look for the eyes moving. If the eyes shift, then you know that the one eye is basically resetting or re-fixating on that object. You know that the eyes must be out of alignment.

Another test we do is a cross-cover test and there’s where we try to break the fusion of the eyes down because someone may have a tendency for their eyes to turn in, they may have a tendency towards cross-eyed and yet, they have got pretty strong muscles and they are able to avoid cross-eyed most of the time because both eyes can fixate on the same object. Except when they get really tired and start complaining of eye strain. We can do a cross-cover testing where you can break the fusion, you break the ability of the eyes to work together like covering one eye and then instead of uncovering the other eye, you immediately move your paddles it covers the other eye. You’re hopping back and forth between both eyes and never really have the chance to work together and you look for eye movement problems there. If their eyes start to re-drift and re-fixate a lot, then you know that they have the tendency towards having what we call phoria which is when the eyes went to wander off especially if they get tired.
Eye movements can be very confusing especially looking at tropius forius, cover-uncover, cross-cover testing. Don’t worry, if you really want to learn more about this topic, I have a pretty good video online at ophthalbook.com or look for tropius versus forius on YouTube and usually, I’m the first video there. I’ll put a link to that on the show as well.

The next thing we look for on an eye exam are confrontational fields, how is someone’s peripheral vision because a third of the brain is devoted to vision and if there is a problem in the brain in the visual pathway, we ca often pick that up which is important for someone who has had a stroke or advanced glaucoma. We normally do this at the bedside or in the chair with finger counting. Can you count how many fingers I’m holding when I hold it in different areas in your peripheral vision.
Once again, we do this one eye at a time, both eye binocularity not that important for the most part. Have them cover one eye and make sure they don’t cheat because if they’re going to cheat, especially those kids, and you say, just look right into my nose. As you’re looking at my nose, what you’ll do is you’ll hold up your hand and you hold up either one or two fingers in different areas in their side vision and you see if they can tell you how many are these.

Don’t go try and doing three, four, five fingers because it’s just going to confuse everyone, you’re getting arguments whether the thumb is truly a finger and it’s hard to tell two versus three so just stick with one versus two fingers and move your hand in different areas to see if they can count it. A good thing about having them watch your nose is you can watch their eyes while they’re doing this to make sure they’re not cheating.

Also, if they have an intensity to cheat, this can’t help themselves, they look over towards your hands and people do this, some people just don’t have the mental faculties or concentration skills to keep staring straight ahead. Then what you can do is you can hold up two hands, one on either side, your right and your left hands are up and you don’t tell them which one’s going to come and then one of the hands should have one or two fingers and you kind of alternate it every once in a while. You never know quite where to look so they look at your nose and you can really tweak this out.

Another tip is you may want to hold your hands at an equal distance between yourself and the patient. The theory there being if you can see, the patient will be able to see it too because if you hold it, there’s no way to know otherwise. You can even try closing one of your eyes so that you’re getting almost a mirror image of what the patient ought to see and then you document things. There are other ways of getting visual fields, there are more exact ways. The one we use most often in the office is called the Humphrey Visual field. It’s a computerized machine that patients sit in front of, they put their head into this whole bowl of light, one eye at a time, having eye patch on the other eye and the computer shoots the lights in different areas of the peripheral vision randomly and have a little buzzer and they click it every time they see the light and basically, the computer tries to map out any problems in the periphery. Humphrey visual field, we use it a lot. Every eye doctor probably has one because it’s very important for monitoring for glaucoma in particular.

There’s another machine that is becoming less often used. It’s called a Goldman Visual field. That’s a really big machine, it has a big giant bowl of light and your patients once again sits there one eye at a time, stares straight ahead. But this machine has almost like a flashlight or a laser pointer that moves around and makes the actual light move. It’s not coming on and off, it’s actually moving into the peripheral vision and as soon as they can see it, the patient hits a buzzer and you have to physically draw out on a little map the peripheral vision with different side light, different powers of lights. It’s pretty good for patients with really, really bad glaucoma. Some people has such bad vision or bad side vision that they just can’t do a visual field test. The machine, it just can’t be done. Or maybe they have a concentration issue and you really need to do this manually. So that’s why we do the Goldman field.

The Goldman is a big bear. As a resident, they made the residents do, because I don’t think the technicians wanted to do it, and so we will hate our Goldman days doing these fields because everyone had terrible vision and it would take 20-30 minutes sometimes to get a good field out of it. It was good practice, I’m not complaining but Goldman field’s a little bit of a pain. And also, I don’t think they’re making a machine anymore. They are slowly breaking down across the country, it’s hard to get parts, you look on eBay for the stuff but a Goldman Visual Field. Confrontational fields, hand movements, most people do Humphrey visual fields with glaucoma and finally, Goldman’s for specific cases.

One final tip though on the old visual field, so far when we document things on an eye chart, we pretty much document, like when you draw a picture, you draw a picture of an eye as if it was looking at you, like you’re staring at them almost like you’re an artist. On your piece of paper, the patient’s right eye is actually on the left part of the paper and the patient’s left eye is on the right part of the paper. That’s how we document everything pretty much except for visual fields.

Visual fields you document not that they’re staring at you. You document it as if you were the patient drawing out what you see. You draw the right eye on the right side of the paper and the left eye on the left side of the paper. The reason why is probably because they used to do visual field using tangent screens, they are big screens on the wall and you sort of sit behind the patient and they would bring one with a light in it so they could see it. Also, it gets really confusing otherwise. For example, if you have a patient who has lost the upper right quadrant of their vision in the right eye, so the right eye couldn’t see anything up into the right, on your piece of paper, you’re going to have two circles and then the right circle, the right eye in the upper right quadrant, you are going to have a black area drawn in there. So everything is as if you were the patient staring at the piece of paper describing what you can see. Anyway, that’s confusing, I just write OD and OS over the circles so there’s no confusion but it’s written backwards.

This brings us to one of the more intimidating areas of the eye exam, the slit lamp eye exam. The slit lamp microscope is kind of intimidating because it’s a big complicated microscope. Most medical students or optometry students, I never really worked with one of these things before. You may have played with a microscope in high school science class but one that’s on the side, it’s quite different.

The microscope, there’s different makes and models, Haag-Streit is one of the more classic ones, that’s where I’m trained with, the Zeiss, I’ve used this as well. In my office, we’re using Topcons but they all pretty much have the same features. They have a microscopic binocular head so basically a microscope with two eye pieces. There’s a light source that can create a beam or slit of light like a very thin sliver of light and both microscope and that light source intersect at a certain point in space. That little point in space can be pushed on to the eye and allows you to look at different structures.

The eye is pretty cool because it’s not flat like a pathology slide. The eye has a lot depth to it. It’s a 3D structure, there’s cornea, there’s lenses, there’s iris looking back to the retina and because of that, the microscope has designs that slit that beam of light, can be shot into the eye to create cross-sections. You can actually see a cross-section of the cornea or a cross-section of the lens just like a CAT scan can give you a cross-section of the body which allows you to tell the depth of problems. You can see where an infection is, is it in the superior cornea or the back of the cornea. You can see where a cataract is, is it in the middle of the lens or is it coming in from the sides? You can really see the depth of objects and so the slit-beam microscope is quite a useful device and what we spend most of our time doing an eye exam doing.

When you’re documenting an eye exam using the slit lamp, there are a number of things you need to write down. In fact, there’s eight structures you really need to comment on on your note. I’ve never really come up with a good mnemonic on how to remember these eight structures but it’s probably best just to think working your way from the outside, working your way to the back of the eye, that way you don’t forget anything. I’m going to list this out real fast and then we’ll go through each of these structures real quick and sort of things that we might see and how we document it. I’m not going to [0:40:00.0] this because I have a pretty good slit lamp video online in YouTube, just look up slit lamp exams and I’m usually the first result there too. It kind of goes this more detail and shows you what the slit-lamp looks like, how to use it and the different things we may see.
Anyway, the eight structures back on target here. The first one is EXT, that’s the external, the second one is LL, lids and lashes, the third one is C/S, that’s the conjunctiva and the sclera, the fourth one is K, the cornea, fifth one is the AC, the anterior chamber, the sixth one is the I, the iris, the seventh one is L for lens and finally, eight is V for vitreous. Let me go over each of those once again if you don’t mind but like I said, just start from the outside, work your way back and make sure you have eight things written down.

Number one, EXT, external. We’re usually talking about the eyebrows and the skin around the eye but not really the eyelids themselves. We’re looking at the cheek, we’re looking at the nose, we’re looking at the brow. You don;t really need a microscope to do that. In fact, the microscope is not actually that good in looking at the nose, cheek or brow. It’s good to document it anyway. We’re looking at different things like zoster, if they got shingles on their forehead or sometimes a big bug bite on their eyebrow or maybe they got rosacea on the nose like it’s really obvious, that might cause blepharitis or some type of eye problem. Normally, almost always, we just document this as normal or within normal limits, WNL.
The second structure is the lids and lashes and we’re basically looking at the outer eyelids and the inner eyelids. On the outer we’re looking at the eyelashes, looking at the meibomian glands, looking at the oil that run inside the eyelashes. We’re looking at the punctual drainage, there’s this little punctum, little tiny holes where the medial lids that drain tears from the eye into the nose itself making sure that those look normal. We flip the inside that leads outwards and we’ll look the inside of the lids and that’s called the papebral area or papebral conjunctiva. If someone is complaining of eye irritation or a [0:42:00.0] sensation, we’ll flip the upper lid too which is a lot of fun but normally, if there’s no problems, then we would say that lids and lashes normal.

The third thing, the conjunctiva and the sclera. We have only gone a whole lot of our anatomy and I’m probably going to do that in the next lecture but the conjunctiva is that thin layer of skin on the surface of the eye. When people get conjunctivitis, it’s an -itis, an inflammation of the conjunctiva, that skin gets irritated, the blood vessels dilate, you have a ink eye. The conjunctiva, that thin layer of skin. We look to see if it’s injected, that’s when usually 1+ injection, 2+ injection, are the blood vessels injected, are they dilated as it is red. You might also see things like hemosis which is the swelling or fluid collection underneath there. You might see a subconjunctival hemorrhage that’s just blood underneath the conjunctival skin. It looks really impressive.

As a med student, I was always documenting icterus, the yellowness of the eyes looking for jaundice. I guess it’s a big deal in the medical world but we hardly ever see in ophthalmology, I don’t even think about icterus. Normally, when the conjunctiva and sclera, the white part of the eye, if they look normal we’d write “white and quiet.”

the fourth thing we look at is the cornea and for some reason, the abbreviation we use is K, so cornea with a K. We are looking for the cornea for clarity, abrasions, scratches and that’s really where the slit comes in handy. I’ve already mentioned this, the slit of light can create a cross-section, you can sweep across the cornea and make sure everything looks clear. We’re looking for scars and ulcers and we also use flourescein on the surface of the eye to look for spots of dryness for example. But if the cornea is normal, we would document that as cornea clear.

The fifth thing we look at is the anterior chamber, usually we document as AC. That is the space between the cornea but in front of the iris. It’s a little pocket of water there where things can potentially occur. The main thing we are looking for is cell and flare. Basically, the eye is the only structure we can actually see inflammation there. People have inflamed knees, you just go off with the symptoms but the eye, you can look in there and you can see individual cells floating in the anterior chamber, little macrophages or white blood cells just floating around in there or even blood cells, you can see little tiny blood cells and they look like dust floats in a movie theater. If you have been to a movie theater recently, just look up at that projector being right when it comes out of the projector booth and if you see little dust floating in there, those little spots floating in that beam, that’s what it looks like when you look inside the eye. That’s what we call cell.

We also look for something called flare which is more of a general haziness. It occurs because of protein from inflamed blood vessels maybe released. Protein is much smaller than cells obviously so you’re not going to see individual proteins floating in there but you will see haziness to the beam of light as it goes through it. If you go back to our projector beam analogy, flare, that protein, looks like smoke. If you’re in a smoky theater with lots of dust, cell looks like the best particles and flare is the smoky appearance of the beam itself. We look for cell and flare. But if the anterior chamber is quite, there is nothing going on, then we would document that as “deep and quiet.”

The sixth structure we’ll look at is the iris and that’s probably the easiest thing to look at because for the first time we have something relatively flat and it’s easy from microscope to focus on things that are flat. And oddly enough, you would think there’ll be lots of pathology here but the iris is almost always pretty benign. People can get nevi and even melanomas on the iris but much less common than on the skin. We look for things like neurovascularization, patients with diabetes, they have a tendency to grow abnormal blood vessels inside the eye. So that’s one of the places we look as on the iris. But for the most part, irises are normal so we document as normal.

The seventh structure is the L, the lens. In here, we’re looking for things like cataract and the cataract is when the lens becomes cloudy as we get older and that cloudiness causes blur. Most people at the age of 40 or 50 had a little bit of cloudiness and we usually call that NS or nucleoscleratic cataract. Or they may have a cortical cataract coming in from the side like spokes on a bicycles wheel. This is usually documented on the 4-point scale. If you have a person with a moderate cataract, you may say they have a 2+ NS, nucleoscleratic cataract. But if the cataract that the lens is clear, then we would just say clear. Lens clear.

The eight and final thing, documenting on the slit lamp exam is the V, the vitreous. The vitreous is that big area behind the lens that fills up most of the eye. The vitreous is a fluid that has the consistency very much like jell-o dessert. If we look at the vitreous, we’re basically just focusing behind the lens and we’re looking for cells which could be inflammation or blood back there. You might be looking for pigments floating in there which looks a lot like the cells in the anterior chamber. A pigment might occur if you have a retinal attachment but almost always, the vitreous is normal and so we would just say vitreous clear.
Those are the eight structures we look for with the slit-lamp exam and once you get good at it, you can blast on pretty quickly and really hone in on problems. This brings us to the final exam thing, the retina. The retina is the light sensing structure in the back of our eye. You can think of it like film in a camera. The retina is quite unique and pretty darn interesting if you ask me. It’s the only place in the body that you can actually see blood vessels directly. Everywhere else is pretty much covered by skin. I guess you can sort of see veins in the surface and maybe some stuff in the cuticles but the retina, you can actually look directly at blood vessels. In this case, it is sort of an indirect view of how the vascular system for the entire body. You can look for emboli, plaques, atherosclerosis and signs of hypertension and etc.

the retina is also the only place in the body that you can actually look at the nerve directly because the optic nerves, and it’s right into the retina. You’re looking head on at a nerve and you can see signs of papilledema or swelling of the nerve or the issues there. The retina is a pretty neat thing. Unfortunately, it’s quite hard to see because you had to look through the pupil and into the back of the eye and the retina is not easy. In fact, this is another place that most students struggle with at first.

There are several tools for looking at the back of the retina. The first one we ought to talk about is the direct ophthalmoscope. The direct ophthalmoscope is the little handheld thing that most primary doctors and med students carry around with them. It’s basically a little tiny microscope that you hold right up to the eye and look at you with a view of the retina. It’s extremely hard to use. I remember as a medical student, we would all sit in a big circle and they would give us a direct ophthalmoscope. We would try to look in the back of each other’s eyes and I don’t know, I don’t think I actually saw anything back then. I just had to sort of fake it and pretend like we did. The direct ophthalmoscope, very hard to use, even for an ophthalmologist especially in an undilated eye, extremely hard to use to see what’s going on back there. Part of the difficulty is lining the thing up to the patient. The biggest problem in my opinion is that the view you get of the retina is so narrow and so small it’s really hard to find your bearings if you get where you are because it’s like looking at a painting of the Mona Lisa through a straw. Okay, is that a forehead, is that the mouth? It takes a while to find your bearings especially if you’re not really comfortable with the anatomy to begin with. Normally, what we’ll do is we’ll try to find a blood vessel and hopefully work our way in one direction until you find the optic nerve and see if you could see it back there.

I’m not going to give you a whole lot of tips for using the direct ophthalmoscope other than good luck. The one thing that’s going to help you the most using this tool is to get it as close as you can to the patient’s eye without touching your eye. The closer you can get that instrument through the patient, the better the view, the larger the view, the easier everything is going to be. What I tell people to do is just create a sandwich. Hold the ophthalmoscope, the direct ophthalmoscope in, let’s say, your right hand. Take your left hand and your thumb and stick your thumb right on your patient’s eyebrow, right on it and then take your direct ophthalmoscope and rest it on your thumb. You got a sandwich, forehead, thumb, instrument because by doing that, you can get really close to the eye without worrying about actually bumping into their eye and then look inside the eye. The closer you get it, the better you are going to see.

Also, just set your instrument to zero, others in whole numbers, they try to tell you that the offset to your prescription. Just set to zero and then flip up and down to get a good view but the direct ophthalmoscope. I don’t use it that often quite frankly. In fact, I don’t think I’ve used a direct ophthalmoscope in six months. I know a lot of neurologists would use them because they don’t want to dilate the pupils and they want to see what’s going on with the nerve but for the most part, not that useful in ophthalmology and optometry.

A more useful tool is called an panoptic ophthalmoscope. This is also another handheld device that’s quite a bit larger and gives you a little bit wider field of view and makes a little bit easier to see in the back of the eye. I didn’t have one of this when I was a medical student, only the rick kids and neuro- ophthalmologists had one because they’re so big and they’re so heavy that I should have weighed my white coat down so I never really have one of them. I do know a couple of neuro ophthalmologists that use them for the same reasons. I guess it has a little bit wider field of view. It’s a bit easier to use in the direct but it’s bulky, it’s more expensive, it’s hard to transport to the bedside for the most part but the panoptic.
The most useful way that we use in ophthalmology and optometry for looking at the retina is right at the slit lamp. We could actually use a 90 diopter lens. It’s a little tiny, very powerful magnifying glass that we hold up in front of the eye and coupling that with the slit lamp microscope. We can actually get a really excellent view of the retina. It’s a much wider fields of view than you get with the handheld stuff and is great stereoscopic as you can really see elevations like retinal detachments or elevated optic nerves or swelling in the retina.

Every patient pretty much will get viewed with one of these 90 diopters during a routine eye exam. Other people have preferences, there are 70 diopters and different brands but I think most people use the 90 diopter for the most part.

One of the challenges using a 90 diopter lens though is that the view you get is flipped, it’s reversed. Up is down, down is up, left and right is flipped as well and so you have to kind of get used to looking at the retina backwards. In addition, the beam that you shoot into the eye normally still shoot a slit lamp in because the bigger the beam, the brighter it is and the patient is squeezed down, it’s hard to see. It takes some getting used to and also you get to learn how to focus back there. But once you get the 90 diopter lens, it’s what most people use.

The final lens that we use is the indirect lens and this is for looking into the periphery for retinal detachments. The indirect ophthalmoscope is a head mounted microscope that basically goes on your head and it has a beam of light that shoots out. We’ll hold a big 20 diopter lens in front of the eye and have our patients look up, down, left and right. It allows us to see back there. There is a much, much wider field of view than anything else. The downside though is it is hard to get used to using it, you can’t see that well with it.

The view doesn’t have quite the same stereo [0:53:23.4] it’s not good for looking for little things like macular degeneration or optic issues but if you’re looking way in the periphery, it’s really the only way to do it easily. Sometimes, you can’t even get out of to the periphery, can’t see the edges, the retina for small tears or holes. In those cases, we’ll do something called scleral depression or kind of pushing of the eye with a little cue tip or long metal device to kind of indent the eyes so we can see way out to the side. Patients don’t really like that but the indirect ophthalmoscope, probably in previews of a general practitioner but certainly use this on a daily basis with our patients in optometry and ophthalmology.

As far as evaluating the retina, there’s really only four structures you need to document. And I have come up with a mnemonic for this. I call it the MVPD, the most valuable player dude. This is the only way I can remember it but the M is for macula, that’s the central vision, V is for vessels, P is periphery looking for retinal detachments or holes and D is for disk, the optic nerve itself. So MVPD, most valuable player dude, if you have to remember somehow but that’s the only way I can remember it.
M, macula. You are looking for signs of macular degeneration, looking for good reflex but if it is normal, just say macula normal. V is for vessels and we’re looking at the blood vessels, the arteries and veins coming off the optic nerve and spreading through the retina itself. We’re looking for emboli and clots and other abnormalities but for the most part, we’ll write down normal if it’s normal.

P is for periphery and we’re looking for retinal tears or holes or other issues out there. I usually document flat 360, no tears, no holes, something along those lines. And finally, D is for disk, the optic nerve and I would document normal, pink and healthy. We usually come up with a cup to disk ratio. The disk is the size of the optic nerve, the optic disk. You don’t need to know the exact size but if there is a big cup in the middle because there is usually indentation inside of it, the cup to disk ratio is a sign usually of glaucoma. People with glaucoma, they lose a lot of nerves in their optic nerve and so you get an enlarging cup to disk ratio. We’ll talk more about this in glaucoma. But we’ll usually document it as a ration. For example, a normal cup to disk ratio, 0.3, meaning that the cup is 30 percent the size of the overall disk itself. Once you get 0.5 or higher, you start getting nervous with glaucoma but it really kind of depends on the appearance itself. MVPD, most valuable player dude, I hope that will help.

Now, we’re winding down to the end of this little talk. But before we do, I’d like to go over a couple of reader questions that I pooled from ophthalbook.com, my website, because I think it’s useful sometimes, especially a topic like this to hear other people’s questions. [0:56:16.1] is very useful for honing in on important theories, important talks.

Our first question is from Loretta and she asks, “What does it mean by fundus not visualized? Is this a normal or abnormal finding?” that’s a good question. Fundus is typically talking about the retina. Fundus is actually Latin for bottom and there’s a fundi or fundus in mini organs in the body. For example, the stomach has a fundus, the gall bladder has a fundus, the uterus has a fundus, anything that has sort of a ball like internal shape to it, it’s usually described as a fundus. When it comes to the eye, we normally describe the fundus as the retina in the back of the eye especially the area that is easy to see using a 90 diopter lens.

Another way to call this is the posterior pole. If someone says the fundus is not visualized, that usually means they can’t see in the eye. Let’s say someone with a really bad cataract, I can’t see the retina, the fundus is not visualized. Or a kid or [0:57:11.6] they won’t let you look inside them, fundus not visualized. Someone mentally retarded or just moving around so much or squeezes her eye shut, you might document it as fundus not visualized. Another way to document this will be posterior pole, something with line. So fundus is how we describe that. Also when we take photographs of the retina, it’s usually called fundus photographs because that’s where we’re taking the photo up so good question.

The second question is from Mahmood who asks, “What about the red reflex? My professor is obsessed about it. Would you please make a video about it doctor?” Okay, the red reflex is basically what the retina looked like when you shine the light at them. You just hold the flashlight right next to your eye and see what their red eye looks like. Quite frankly, I don’t use the red reflex that often but it is kind of useful. Normally, I’m doing a complete eye exam anyway so I’m going to find any problems.
But there is a couple of places that the red reflex is important. Certainly, pediatricians use it because they can look for red reflex in a child. If you have a child with no reflex at the one eye, you kind off get nervous that something is going on like a retinal detachment back there so you’re not going to get red eye or a retinal blastoma or some terrible tumor. Certainly, pediatricians do the red reflex a lot. They are also good if you have a patient who you are trying to figure out why the can’t see and it’s in the middle of the night and you haven’t dilated them yet but you kind of know what’s going on, check the red reflex. If they really have bad vision and no red reflex in one eye, they happen suddenly, it’s probably the retinal detachment or the eyes full blood or something. It’s kind of like getting a preview of what else is going on. The red reflex is also somewhat useful for strange cataracts, for example you have a patient who has got a little bit of cataract but they got a lot of complaints. They are really complaining of problems with their vision. They can’t see or [0:59:06.5] any better, why do red reflex and everyone almost say, oh my goodness, you’ve got this weird apasty [0:59:09.7] right near the middle of your lens. I didn’t even notice it under the slit lamp microscope. It’s almost like you got a bubble of oil or something in the middle of your cataract. The red reflex could be useful for that.

One last area that I would like to talk about with the red reflex is there is something called the Bruckner test. I believe this B-R-U-C-K-N-E-R test. It is occasionally used by pediatric ophthalmologists and optmetrists who are trying to estimate a child’s refraction, see if they are nearsighted or farsighted. The theory behind it is that if you use a light and you shine it in their eye, you can kind of see where the red reflex is the strongest. If the strongest is on the bottom of the pupil, really lights up on the bottom, sometimes it’s an indicator that a child is nearsighted. If it’s strongest on top of the pupil, then the [1:00:01.5] indicate that they’re farsighted or hyperopic. If you have brightness as much brighter on one eye compared to the other, it might mean that one of the eyes is deviating outwards or inwards or it’s not lined up properly that’s why the reflex isn’t quite as intense. That’s the Bruckner test. I don’t use it that often in my practice but I figure I should mention it.
The final question, I don’t have the person’s name, they didn’t leave it on my site. It says the following: “I believe I am legally blind without my glasses. What does that mean?” We bring up a great question and we’re often asked by our patients what is legal blindness. Am I legally blind?

Legal blindness basically means that the best vision you have in your best eye, when it is corrected when you are wearing the proper glasses is 20/200 or worse. Basically, there are lots of people out there who are nearsighted, who if you didn’t check their vision with their glasses on, they’d be legally blind, they can’t see the big E in the chart. But it doesn’t matter, like I mentioned in the beginning of this talk, we don’t check people’s vision unless it is corrected because it is meaningless otherwise. Basically, if your vision in your best eye, that’s your best eye and you got proper glasses on, they’d been checked recently and they are as good as they can get, if you still can only see 20/200 or worse, then you are considered legally blind.

That’s the law in the US.

Another law that says you are legally blind is if your vision is 20 degrees or less in your best eye. We have people who have, let’s say, retinitis pigmentosa which is a genetic problem where they lose a lot of rods and they lose a lot of peripheral vision who technically have excellent 20/20 vision when they are sitting in the exam chair and read pretty good in the eye chart but their peripheral vision is so bad, it’s like looking through straws all the time. There’s really bad peripheral vision, it wouldn’t be safe to drive and they would have a hard time getting around doing things. If their visual field in their best eye at the best is 20 degrees or less, then that is also considered legal blindness. So, 20/200, 20 degrees corrected best eye is the definition of legal blindness at least in the US.

I think it about wraps things up. I hope you found this useful, I know it’s actually over one hour, I’m surprised but I hope you find this useful and if you like to see the show notes for this, you’ll find it in eyetalkradio.com. You can also go to eyebasics101.com and it will take you directly to this page, look for episode 1. I think, in our next talk, we’re going to talk about basic eye anatomy and we’ll go over some structures there but until then, thanks for listening.

Dr. Root would like to remind you that this program has been created for educational purposes. The opinion stated here should not be considered medical advice and this information is not intended to replace a direct consultation with the medical doctor. If you have an eye problem, please consult with an eye doctor.


  1. If this page looks a little strange at the moment … it’s because I’m still putting it together. Turns out, that it is harder to embed an mp3 audio file onto a page then I first imaged. However, the links above (at the top of the page) should be working just fine. Thanks!

  2. Dear Dr. Root,

    It’d be of great help if you coule let me know the link from where you got to download Dr. Smith’s lectures. I’d like to listen to them as well.

    Thank you,
    Akansha Sinha.
    3rd year Medical Student,


Please enter your comment!
Please enter your name here