What Does OD and OS Mean?

The first step to understanding your spectacle prescription is knowing what "OD" and OS" mean. They are abbreviations for oculus dexter and oculus sinister, which are Latin terms for right eye and left eye.

Your spectacle prescription also may have a column labeled "OU." This is the abbreviation for the Latin term oculus uterque, which means "both eyes."

Though the use of these abbreviated Latin terms is traditional for prescriptions written for spectacles, contact lenses and eye medicines, most opticians modernize their prescriptions and use RE (right eye) and LE (left eye) instead of OD and OS.

What Do the Other Details Mean On Your Eye Prescription?

Your eyeglasses prescription contains other terms and abbreviations but what do the details actually mean?

Some of these other terms are as follows:

Sphere (SPH)

Sphere indicates the amount of lens power, measured in dioptres (D), prescribed to correct shortsightedness or longsightedness. If the number appearing under this heading has a minus sign (–), you are shortsighted; if the number has a plus sign (+) or is not preceded by a plus sign or a minus sign, you are longsighted. The term "sphere" means that the correction for short sightedness or long sightedness is "spherical," or equal in all meridians of the eye.

Cylinder (CYL)

Cylinder indicates the amount of lens power for astigmatism. If nothing appears in this column, either you have no astigmatism, or your astigmatism is so slight that it is not really necessary to correct it with your spectacle lenses. The term "cylinder" means that this lens power added to correct astigmatism is not spherical, but instead is shaped so one meridian has no added curvature, and the meridian perpendicular to this "no added power" meridian contains the maximum power and lens curvature to correct astigmatism.

The number in the cylinder column may be preceded with a minus sign (for the correction of shortsighted astigmatism) or a plus sign (for longsighted astigmatism). Cylinder power always follows sphere power in a spectacle prescription

Axis

Axis describes the lens meridian that contains no cylinder power to correct astigmatism. The axis is defined with a number from 1 to 180. The number 90 corresponds to the vertical meridian of the eye, and the number 180 corresponds to the horizontal meridian.

If a spectacle prescription includes cylinder power, it also must include an axis value, which follows the cyl power and is preceded by an "x" when written freehand. The axis is the lens meridian that is 90 degrees away from the meridian that contains the cylinder power.

Add

This is the added magnifying power applied to the bottom part of multifocal lenses to correct presbyopia. The number appearing in this section of the prescription is always a "plus" power, even if it is not preceded by a plus sign. Generally, it will range from +0.75 to +3.00 D and will be the same power for both eyes.

Prism

Prism is the amount of prismatic power, measured in prism dioptres ("p.d." or a superscript triangle when written freehand), prescribed to compensate for eye alignment problems. Only a small percentage of spectacle prescriptions include prism. When present, the amount of prism is indicated in either metric or fractional English units (0.5 or ½, for example), and the direction of the prism is indicated by noting the relative position of its "base" or thickest edge.

Four abbreviations are used for prism direction: BU = base up; BD = base down; BI = base in (toward the wearer's nose); BO = base out (toward the wearer's ear).

Sphere power, cylinder power and add power always appear in dioptres. They are in decimal form and generally are written in quarter-dioptre (0.25 D) increments. Axis values are whole numbers from 1 to 180 and signify only a meridional location, not a power. When prism dioptres are indicated in decimal form, typically only one digit appears after the decimal point (e.g., 0.5).

Additional Information on Your Eyeglasses Prescription

Your local optometrist or eye doctor might also write specific lens recommendations on your new eye glasses prescription.

Some of these recommendations may include:

• 
  
• ✓ Anti-reflective coating (anti-glare)
  
• ✓ Anti-fog coating
  
• ✓ Photochromic lenses
• ✓ Progressive lenses
• ✓ Photochromic / Transition Lenses
• ✓ Scratch-resistant lenses
• ✓ Ultraviolet treatment

Eye Glasses Prescription Example

So has all this left you feeling confused yet? Tamarind Optical will try to explain a little better by showing you an example of an eye glasses prescription and break it down as to just what the numbers and letters mean.

RE -2.00 SPH +2.00 add 0.5 p.d. BD

LE -1.00 -0.50 x 180 +2.00 add 0.5 p.d. BU

In this example prescription, your eye doctor has prescribed -2.00 D sphere for the correction of myopia in the right eye (RE, or OD). There is no astigmatism correction for this eye, so no cylinder power or axis is noted. This optician has elected to add "SPH," to confirm the right eye is being prescribed only spherical power. (Some doctors will add "DS" for "dioptres sphere;" others will leave this area blank.)

The left eye (LE, or OS) is being prescribed -1.00 D sphere for myopia plus -0.50 D cylinder for the correction of astigmatism. The cyl power has its axis at the 180 meridian, meaning the horizontal (180-degree) meridian of the eye has no added power for astigmatism and the vertical (90-degree) meridian gets the added -0.50 D.

Both eyes are being prescribed an "add power" of +2.00 D for the correction of presbyopia, and this spectacle prescription includes a prismatic correction of 0.5 prism dioptre in each eye. In the right eye, the prism is base down (BD); in the left eye, it's base up (BU).

Your Eye Glasses Prescription Is Yours

By law, your eye glasses prescription must given to you after the eye exam and must provide the basic results of the eye examination.

The Optical Consumer Complaints Service (OCCS) clarifies that "an optometrist is obliged to provide you with the written prescription following each and every eye exam. You can then choose to get your eye glasses at that particular optical services, or you can feel free to take the prescription to another place of your choice.

Schedule an Eye Exam - Get Your Eyeglasses Prescription

If you  can't see as well as you used to, if you have to squint to read a book or to look at TV, they it may be time to have your eyes tested!

Tamarind Optical Services in Sydney and Glace Bay, offer a wide range of eye-related services including Eye Exams,  Eye Screenings, Eye Treatment, Contact Lens Service, Eyeglasses Prescription, and Prescription Sunglasses for men, women, and youth, not to mention seniors.

Simply call our office to schedule a consultation appointment or book an eye exam online, and we'll address your needs from there - Sydney 902-564-5332, Glace Bay 902-842-3333