• 14 MAY 17
    • 0
    Understanding your eyeglass prescription

    Understanding your eyeglass prescription

    After your eye exam, the doctor hands you a small slip of paper covered with confusing numbers. You take it, without even looking at it, straight to your optician, who uses it to make your next pair of lenses. At no time do you understand any part of the process. Sound familiar? While you don’t really need to understand your eye prescription, in the sense that you don’t really need to understand how electricity works in order to use it…it’s definitely good to know what is going on with your eyes so you can track any changes, spot any mistakes, and understand what your prescription means to your day to day vision. Here, we’ll demystify the eyeglass prescription so you can finally know for sure what the numbers mean.

    Eyeglass prescriptions are standardized worldwide

    That’s great news if you find yourself stranded on vacation with damaged glasses – we recommend that you always carry a copy of your most current prescription in your wallet, so local opticians will be able to craft a new pair for you if necessary.

    An eyeglass prescription can contain several different numbers – no wonder it’s confusing. For a person whose prescription is -4.50                   -0.75      x 90, here is what those numbers mean:

    • The -4.50 describes the spherical refractive error, which is either farsightedness or nearsightedness. Because there is a negative sign in front of the 4.50, that means the person is nearsighted (quite nearsighted actually!). A plus sign would mean they are farsighted.
    • This second number, -0.75, indicates the person has an astigmatism, which is a distortion in the shape of the cornea that causes blurred vision. Not everyone has astigmatism, of course, so if the number wasn’t there, you’d see some letters – DS or SPH – to indicate that there is no astigmatism.
    • The last number relates back to the astigmatism. Because astigmatism causes the lens to be football- or somewhat cone-shaped as opposed to perfectly rounded, it is measured in degrees; in this case, the astigmatism has a 90-degree orientation.

    Additional numbers and letters in an eyeglass prescription

    We’ve just described what the numbers can look like for three of the most common types of refractive errors. However, some people have additional abnormalities that must be corrected to achieve perfect vision. These may be indicated by the following:

    -An additional number followed by a symbol, such as 2^, indicates prism correction. Each eye can have several prism numbers depending on the prescription

    -Near reading strength numbers for people requiring bifocals for reading. These numbers usually stay relatively low, beginning at +0.75 and ending around +3.00.

    Finally, you may be wondering what OD and OS mean. OD refers to the right eye and OS means the left eye; if you have an identical prescription in both eyes, you might see the letters OU.

    Confused after your regular eye exam?

    If you usually leave the eye doctor wondering about elements of the prescription or unsure as to what vision care options are open to you, it might be time to get a second opinion. Toronto Eye Care offers comprehensive eye exams carried out by caring and experienced eye doctors, ophthalmic technicians and assistants. Each eye examination is customized depending on your age group, medical/visual history, and personal risk factors. We’ll get to the bottom of what is causing your vision concerns and provide accurate correction so you can see clearly again. Call to book your appointment today.

    Understanding your eyeglass prescription

    After your eye exam, the doctor hands you a small slip of paper covered with confusing numbers. You take it, without even looking at it, straight to your optician, who uses it to make your next pair of lenses. At no time do you understand any part of the process. Sound familiar? While you don’t really need to understand your eye prescription, in the sense that you don’t really need to understand how electricity works in order to use it…it’s definitely good to know what is going on with your eyes so you can track any changes, spot any mistakes, and understand what your prescription means to your day to day vision. Here, we’ll demystify the eyeglass prescription so you can finally know for sure what the numbers mean.

    Eyeglass prescriptions are standardized worldwide

    That’s great news if you find yourself stranded on vacation with damaged glasses – we recommend that you always carry a copy of your most current prescription in your wallet, so local opticians will be able to craft a new pair for you if necessary.

    An eyeglass prescription can contain several different numbers – no wonder it’s confusing. For a person whose prescription is -4.50                   -0.75      x 90, here is what those numbers mean:

    • The -4.50 describes the spherical refractive error, which is either farsightedness or nearsightedness. Because there is a negative sign in front of the 4.50, that means the person is nearsighted (quite nearsighted actually!). A plus sign would mean they are farsighted.
    • This second number, -0.75, indicates the person has an astigmatism, which is a distortion in the shape of the cornea that causes blurred vision. Not everyone has astigmatism, of course, so if the number wasn’t there, you’d see some letters – DS or SPH – to indicate that there is no astigmatism.
    • The last number relates back to the astigmatism. Because astigmatism causes the lens to be football- or somewhat cone-shaped as opposed to perfectly rounded, it is measured in degrees; in this case, the astigmatism has a 90-degree orientation.

    Additional numbers and letters in an eyeglass prescription

    We’ve just described what the numbers can look like for three of the most common types of refractive errors. However, some people have additional abnormalities that must be corrected to achieve perfect vision. These may be indicated by the following:

    -An additional number followed by a symbol, such as 2^, indicates prism correction. Each eye can have several prism numbers depending on the prescription

    -Near reading strength numbers for people requiring bifocals for reading. These numbers usually stay relatively low, beginning at +0.75 and ending around +3.00.

    Finally, you may be wondering what OD and OS mean. OD refers to the right eye and OS means the left eye; if you have an identical prescription in both eyes, you might see the letters OU.

    Confused after your regular eye exam?

    If you usually leave the eye doctor wondering about elements of the prescription or unsure as to what vision care options are open to you, it might be time to get a second opinion. Toronto Eye Care offers comprehensive eye exams carried out by caring and experienced eye doctors, ophthalmic technicians and assistants. Each eye examination is customized depending on your age group, medical/visual history, and personal risk factors. We’ll get to the bottom of what is causing your vision concerns and provide accurate correction so you can see clearly again. Call to book your appointment today.

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