 Hey everybody, Dr. O here and this is where we're going to cover visual acuity. So here you see a snel and eye chart which is used to test your visual acuity. So normal vision or maybe quote unquote perfect vision is rated as 20-20. So if you can't see that well then you're either going to be farsight or nearsighted which we'll cover. So nearsightedness is called myopia and farsightedness is called hyperopia. Normal refractive status or normal visual acuity is called hematropia so 20-20 vision. So 2200 at the top of the chart here that would be legally blind. So if you can't see that with correction then you are legally blind. But then I also want you to note that this so what does this mean 2200 means that let's say let's say you do have 2200 vision you'd have to be 20 feet away from something to see it. Let's say a stop sign whereas someone with 20-20 vision could be 200 feet away from it and see it as well as you. So 2200 is pretty bad. I have really bad eyes though so thankfully I can use contacts and glasses. But I have 2900 vision which means if you have 20-20 vision I would have to be 20 feet away from something to see it clearly. You could be 900 feet away from it and see it just as clearly as me. So that's what these 20 whatever numbers mean. So 2200 is legally blind and then there is what's called I guess better than perfect vision. There are people that have vision that's 2015 or 2010 a lot of athletes like I know of some professional baseball players that have vision that's 2015 or 2010. That means that they can see better than someone that has normal or perfect vision. Alright so that's visual acuity and how we measure it. So we already said if your eyes are normal that's called emitropia. Let's go ahead and look at myopia and hyperopia. So here we see nearsightedness or myopia. So you can see things up close but you can't see things far away. And this is one that generally gets worse as you go on in life. It has to do with the shape of the eye. So either they would say the eye is too long or too deep or else the lenses are too curved too rounded and there's too much refraction because what's happening is you can see from the middle of that image the image is being focused in front of the retina not on the retina where you can see it. So thankfully this is what corrective lenses would fix. So you can correct this with what's called a diverging lens or a concave lens or a minus lens that actually refocuses that image on the retina so you can see it clearly. So that's nearsightedness or myopia. Then we have on the opposite end we have hyperopia or farsightedness where you can see things that are far away but you can't see things that are near away. So you would say here the eyeball is actually too short or too shallow because notice that the image is being focused behind the retina not on the retina. This is usually a present birth it's not something that just slowly progressively gets worse but it can be corrected so you notice here the lens is called a converging lens or a convex lens or I guess you call it a plus lens. So either way nearsighted or farsighted thankfully you can use glasses or contacts or things that will move the focal point of an image to the retina so you and your brain can see it. Alright that's normal visual acuity and then nearsightedness and farsightedness. I hope this helps. Have a wonderful day. Be blessed.