Glasses Prescription Explained How to read your prescription for glasses

Hey, Eyes and Shine. Dr. Allan here, and today we're going to walk you through how to read your glasses prescription, meaning all the cool numbers that are on this device here and what those numbers mean on your physical hard copy paper glasses prescription. It sounds like basic thing, but it's actually pretty important and kind of fascinating. So, let's get to it. Okay, so printed off copy of my own eyeglasses prescription so we can walk through it together. At the top, you may see just your name, date of birth, and other identifying information, but below that should be your true glasses prescription. On the far left side, you may see the letters OD and OS. OD stands for Oculus Dexter and is your right eye, and OS stands for Oculus Sinister, which is your left eye. Sometimes it may just read right eye and left eye, but in case you see the OD and OS, now you know what they mean. The next column over is for the sphere power. sphere lens is the most basic, simple type of eyeglasses lens that can be made. Below that, you'll see power numbers that range anywhere from zero and go up or down in quarter-diopter steps. In front of those numbers, you should see either minus sign or plus sign, and those signs are really important. If you see plus sign in front of these numbers, that means that lens has to be made with magnifying power to help someone correct for farsightedness or hypermetropia. If you see minus sign in front of these numbers, like you see on my prescription, that means it corrects for somebody who has myopia or nearsightedness. Just sort of fun side note: if somebody does have high plus power in their glasses, you can sometimes tell because when you look at them, their eye can look magnified and really big. Conversely, if somebody has strong nearsighted prescription in their glasses, it can do just the opposite and make their eyes look small through those lenses. Now, the next column over is the cylinder lens. Cylinder lenses are kind of unique. If hold it up here, you can imagine line going straight across, and in that line, there would be zero power in that lens. But going perpendicular to that line, up and down, there is power. cylinder lens is used to correct for astigmatism. If you've ever heard of that term before and you're not fully sure what it means, that's okay. I've done previous videos on that topic, and I'll put links to those videos in the description below so you can learn little bit more. Otherwise, if you're someone who doesn't have astigmatism, you may just see either blank spot here, or it'll read DS for dioptric sphere, basically meaning there's no correction for astigmatism needed. But if you do see some numbers in this column here, like you see on mine, that means that the glasses do correct for astigmatism. One thing that can be little confusing about the cylinder power for astigmatism is the sign in front of it. It should usually have either plus or minus sign. Most doctors will probably write this with minus sign in front of the cylinder power because that's how glasses are manufactured in what we call minus cylinder form. Occasionally, though, doctors will write the glasses prescription with plus symbol in front of the cylinder power. There's nothing wrong with that, and for most people, it's not going to make difference. Opticians or whoever's making your glasses, if they see plus cylinder sign, they will do some simple math to convert it back to minus cylinder form. If you really want to nerd out with me toward the end of the video, I'll show you what that calculation looks like. But again, for most people, unless you're making glasses, wouldn't worry about that plus or minus symbol in the cylinder power. Moving on to the next column, we have the axis. The axis still refers to that cylinder lens correcting for astigmatism, but the axis really just tells us at what angle this part of the cylinder lens needs to be oriented. This will be three numbers ranging from 000 to 180. The accuracy of this axis can be really important, especially if you have high powers of astigmatism correction, because the way your glasses are sitting on your face, if the lenses are rotated, your vision through that lens is not going to be correct, and your vision will be blurry. In fact, in the industry, there are accuracy standards about how exact this axis is manufactured in the glasses compared to what's written on the prescription. Now, moving on to the next column here, it says ADD, which stands for additional lens. An additional lens, or an ADD, is used to describe the power of magnification needed in glasses that require bifocal, progressive, or sometimes also known as varifocal lens. As you see in my prescription, there's nothing there because personally don't require an ADD in my glasses prescription yet. But if you are somebody who requires bifocal or progressive lens, then you probably will see some numbers there, going anywhere from plus one all the way up to maybe plus 2.50 and sometimes even higher, depending on what someone's demand is for reading up close. Next on my prescription are just the expiration dates for the prescription, but there are often few other categories that doctors will write in on prescription. One of those categories is lens called prism. Not everyone requires prism correction in their glasses, but prism lens, if you do see that, is special lens that helps shift the image of whatever you're looking at to different angle. This is usually prescribed to help people who have muscle imbalance or poor coordination with their eye muscles. Doctors will often prescribe prism values if somebody has problems with double vision, for example. Prism powers can usually go from being very little to very high, but what's important is more of what direction these prisms are oriented at. You should see some letters starting with which stands for base, and then another letter which stands for either BD for base down, BU for base up, BI for base in, or BO for base out. The prism power can be in front of just one eye alone, but sometimes if it's higher amount, it can also be split between the two eyes. The final two things you may see on glasses prescription are either additional notes, such as directions that the glasses are meant for distance vision only or perhaps they're written for near vision only for people just to see up close, or they could be written for multifocal lens or special computer type of glasses prescription. One thing you may not see on my prescription here is PD, or pupillary distance. pupillary distance is measurement between one pupil and the other, and this is important for orienting the glasses correctly on your face. The challenge is that most electronic software for writing glasses prescription often does not have an area for pupillary distance. This instead is measurement that's often taken by an optician or whoever is fitting you to purchase glasses at local store. Sometimes this can be challenge if you're choosing to purchase glasses online, for example, and that's why lot of online retailers will have their own guide on how to check your pupillary distance. There are even phone apps available now that are pretty accurate at checking your pupillary distance. recommend doing them two or three times and taking an average to make sure it's just right. Alright, so there you have it. That's how you read and understand your glasses prescription. Now, the one extra bonus thing want to throw in here at the end is how to transpose minus cylinder form glasses prescription to plus cylinder form and vice versa. Again, this is probably something that other eye doctors or someone who works in an eye clinic may want to know about. Otherwise, if you maybe have an older glasses prescription that was written in plus cylinder form and your new one is in minus cylinder, you may want to be able to compare back and forth. That's where this information might be useful. To transpose my prescription from minus cylinder to plus cylinder, first look at the cylinder power, including the sign in front of it. So, have -1.50. I'm going to add this cylinder power to the sphere power. So, -5.50 for my right eye for the sphere plus the -1.50 equals total of -7.00 for the sphere. Now, moving back to the cylinder, keep the same power: still have 1.50 diopters of power, but change the sign from minus sign to plus sign. Then, moving over to the axis, because we've changed the power of the lens, the axis now has to rotate 90 degrees. So, you can add 90 degrees to the 102 and get 192. The only thing is that we don't ever describe it being higher than 180 degrees, so you can eliminate the 180 from the 192 and you end up with 12 or 012 for the axis because saying axis 12 is equivalent to saying axis 192 and vice versa. To convert plus cylinder back to minus cylinder, it's the same steps: you add the plus cylinder to the sphere power, change the cylinder sign from plus to minus, and change the axis by adding another 90 degrees. hope this all makes sense. know this is just little extra credit, but if you have any other questions about this math or any part of glasses prescription, let me know in the comment section below. Otherwise, thank you so much for sticking around. Keep an eye on it, and we'll see you in the next video. Peace.