 How do we calculate glasses for people with myopia? Myopia is when you can see things are up close very clearly, but things are very far away, very blurry. So how do we do this? The problem is when you have myopia that whatever is far away is blurred, whatever is close you can see. There is one point that we call the far point that is up to this point you can see everything clearly, further on you can't. So first step when calculating the glasses for somebody that has myopia need to ask them, okay what is your far point? So do that, they have to take their glasses off and one eye at a time they move backwards from some text or some object that they can clearly see clearly and they walk back until it starts getting blurry and then you take down that measurement. For example in my case my far point of my right eye is about 32 centimeters or 0.32 meters. Now what are my glasses doing? My glasses they create an image of the distant object that can see clearly and they create an image closer than my far point. So I need glasses, I draw the glasses here, here are my glasses. I will create an image in this case of the tree so that it is closer than my far point. Then I can see the tree clearly. So I need an image of my tree here, move the book here and then I can see it clearly. So what do I need? I have an object that is very very very very far away. So object distance is you can assume infinity, I want to see sharp at distance. What is my image distance? My image distance is the distance of the image to the eye and if I want to be able to see clearly well that needs to be closer than my far point. So 0.32 meters in my case and think about is this a virtual or real image? It's a virtual image and therefore we're going to put here a negative sign. So if I do my thin lens equation 1 over P plus 1 over Q is 1 over F or is equal to the diopters, the power of my lens then I would get 1 over infinity plus 1 over minus 0.32 is my diopters. So the diopters I need is 1 over minus 0.32 is our 0.32 3.1 negative diopters. So I need glasses for my right eye of minus 3.1 diopters. What does the negative mean? The negative means there are diverging lenses. So my lens here is actually diverging lens. One quick note, if you're trying to figure out your far point and you figure out that you can actually see clearly at all distances you cannot figure out when it gets clearly well that's normal then congratulations you have normal eyesight because if your eyesight is perfect you should be able to see clearly at objects that are very far away so the mountains at the horizon you should see them very sharply. So this only applies for people that see objects at far distance blur. So just to recap figure out how close the object has to come until you see clearly this is your far point distance. Plug that in as the image distance because that's where you want the image of the glasses you create for objects that are infinite distance away and then you get your power in diopters.