How to Read a Contact Lens Prescription: Understanding the Key Numbers and Symbols

How to Read a Contact Lens Prescription: Understanding the Key Numbers and Symbols

 After visiting your ophthalmologist, you will receive a prescription for lenses. This includes technical acronyms that des

Read a typical prescription

cribe your specific corrective lens needs. The formula for a lens prescription describes the type of lenses needed to produce the correct refraction needed to help you see properly. Once you understand the terms and abbreviations, you will be able to read your prescription without difficulty.

 Your ophthalmologist will give you several documents, including your prescription. This looks like a table or, more rarely, a graph. While this is the standard form, the terms for the columns or axes of the graph vary depending on the doctor's preferences.

  • Be careful not to confuse your contact lens prescription with your eyeglass prescription. This will help you understand what type of lenses you will be getting. Both papers may contain similar acronyms, but the numbers may not be the same 

 All prescriptions contain basic contact information for your ophthalmologist and the patient. Your prescription should include the patient's name, exam date, prescription date, prescription expiration date, and the ophthalmologist's name, address, phone number, and fax number.
  • Lens strength information should also be on the prescription along with any special brand instructions or needs.

 Each prescription lists the correction needed for each eye. On the prescription, you may read the terms "oculus dexter" or the abbreviation "OD." "Oculus dexter" is Latin for "right eye." The term "oculus sinister" (abbreviated as "OS") means "left eye." If you have the same correction in both eyes, you will see the term "oculus uterque" or "OU," meaning the prescription is for both eyes  .
  • Most prescription terms are measured in diopters, a unit of refractive power that is equal to the reciprocal of a lens's focal length in meters. Diopter is often abbreviated with the letter D

 These numbers are often the first listed near the rows or columns containing the values ​​for OD and OS. They indicate the strength of correction for a particular eye or, if the abbreviation "OU" appears, for both eyes.
  • For example, if the field under "OD" reads -3.50 D, this means you have 3.5 diopters or nearsightedness in your right eye. If the field under "OD" reads +2.00, this means you have 2.00 diopters or farsightedness in your right eye
  • It is quite common for corrections to vary between the right and left eyes. If you find the term "PL" (for plan), it means that the eye does not require correction

 This term describes the curve the inside of the lens should follow. This is measured so that the lens fits perfectly to the shape of your cornea. Unlike most other numbers, this one is measured in millimeters.
  • This number typically ranges between 8 and 10. The lower the number in this column or row, the more curved your cornea is 

 Diameter is the measurement of a straight line that passes through the center of the lens. This helps the lens manufacturer know what diameter the lens needs to be to fit your eyes. Like BC, DIA is measured in millimeters.
  • This is a very important measurement. If it is not measured correctly, your lenses may cause irritation or abrasions to your eyes
 Typically, your ophthalmologist will give you the brand of lenses that best suits your needs. If so, your optician should give you lenses of that exact brand.
  • He may substitute a brand for a similar, more natural product or if he has his own line of lenses 

 Sometimes the prescription can be read as a simple equation. The equation should generally follow this order: +/- sphere/power +/- cylinder x axis , base curvature 'BC' = diameter DIA = number. For example: +2.25-
  • If you are unsure how to read this equation, ask your doctor to translate it for you.

Read a more detailed prescription


How to Read a Contact Lens Prescription: Understanding the Key Numbers and Symbols

 Some numbers don't always appear on the prescription. If you have astigmatism, which is common, you'll see an additional column or row for CYL. This number is a measure of how much astigmatism you have, measured in diopters. Most doctors use a positive number, but if you're given a negative value, the optician will need to convert it to a positive value.
  • It is usually caused by an irregularly shaped cornea, but can also be caused by an irregularly shaped lens.
  • A negative number indicates your nearsightedness while a negative number indicates your farsightedness 

 The axis is the measurement calculated in degrees that is needed to refract light to correct the irregular shape of the cornea. It is essentially the orientation needed to correct the cylinder.
  • This number will be higher (in the order of 090 or 160), depending on how your CYL needs to be tilted
 Sometimes your lenses are bifocal. If this is the case, your prescription should have a column or row with the term ADD, which corresponds to the correction needed for the lenses to be bifocal.
  • This term is also measured in diopters 
 Your prescription may contain the term "color." This indicates whether you need a specific type of lens to change the color of your eyes. It may also indicate a specialty lens, such as "cat's eye" lenses.
  • Specific features will vary by brand. Don't hesitate to ask your ophthalmologist any questions related to your prescription 

Advice

  • Always test a new brand of lenses before buying multiple boxes. You want to make sure they fit comfortably.
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