Understanding Eye Prescriptions

Last updated on April 6th, 2017 at 05:13 pm

So, you’ve simply had an eye exam and your optometrist or ophthalmologist has offered you a spectacles prescription. She or he probably discussed that you are nearsighted or farsighted, or possibly that you have astigmatism.

But what do all those numbers on your spectacles prescription indicate? And what about all those abbreviated terms, such as OD, OS, SPH and CYL?

Understanding Eye Prescriptions

This article will assist you understand all parts of your prescription and discuss it knowledgeably with an optician when you’re purchasing eyeglasses.

The prescription you get might be a chart with headings that are filled out, or it may just be written out. In any case, it is composed in a specific order, with the results for each eye noted first.

What OD And OS Mean

The first step to comprehending your glasses 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 glasses prescription also may have a column identified “OU.” This is the abbreviation for the Latin term oculus uterque, which means “both eyes.”

Though the use of these shortened Latin terms is traditional for prescriptions written for eyeglasses, contact lenses and eye medicines, some medical professionals and centers have chosen to modernize their prescriptions and use RE (right eye) and LE (left eye) rather of OD and OS.

On your glasses prescription, the details for your right eye (OD) comes prior to the details for your left eye (OS). Eye doctors compose prescriptions by doing this due to the fact that when they face you, they see your right eye on their left (first) and your left eye on their right (2nd).

Other Terms On Your Eyeglass Prescription

Your eyeglass prescription consists of other terms and abbreviations as well. These consist of:

Sphere (SPH). This indicates the amount of lens power, determined in diopters (D), prescribed to correct nearsightedness or farsightedness. If the number appearing under this heading has a minus sign (–), you are nearsighted; if the number has a plus sign (+) or is not preceded by a plus sign or a minus sign, you are farsighted.

The term “sphere” means that the correction for nearsightedness or farsightedness is “spherical,” or equal in all meridians of the eye.

Cylinder (CYL). This indicates the amount of lens power for astigmatism. If absolutely nothing appears in this column, either you have no astigmatism, or your astigmatism is so slight that it is not actually needed to fix it with your eyeglass lenses.

The term “cylinder” implies that this lens power contributed to remedy astigmatism is not spherical, however instead is formed so one meridian has no added curvature, and the meridian perpendicular to this “no added power” meridian contains the optimal power and lens curvature to remedy astigmatism.

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

Understanding Eye Prescriptions

Axis. This describes the lens meridian that contains no cylinder power to correct astigmatism. The axis is specified 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 an eyeglass prescription includes cylinder power, it also needs to 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 far from the meridian which contains the cylinder power.

Include. This is the included amplifying power used 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. Typically, it will range from +0.75 to +3.00 D and will be the exact same power for both eyes.

Prism. This is the quantity of prismatic power, determined in prism diopters (” p.d.” or a superscript triangle when written freehand), recommended to make up for eye alignment problems. Just a little percentage of eyeglass prescriptions consist of prism.

When present, the amount of prism is indicated in either metric or fractional English units (0.5 or 1/2, for example), and the instructions of the prism is shown by keeping in mind 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 user’s ear).

Sphere power, cylinder power and add power always appear in diopters. They are in decimal kind and normally are composed in quarter-diopter (0.25 D) increments. Axis values are entire numbers from 1 to 180 and symbolize only a meridional place, not a power. When prism diopters are indicated in decimal kind, usually just one digit appears after the period (e.g., 0.5).

An Example Of An Eyeglass Prescription

Baffled? Let’s use an example to clear things up. (Pun planned.)

Here is a sample glasses prescription:

OD -2.00 SPH +2.00 include 0.5 p.d. BD
OS -1.00 -0.50 x 180 +2.00 add 0.5 p.d. BU

In this case, the eye doctor has recommended -2.00 D sphere for the correction of myopia in the right eye (OD). There is no astigmatism correction for this eye, so no cylinder power or axis is kept in mind. This doctor has chosen to add “SPH,” to confirm the right eye is being prescribed only spherical power. (Some physicians will include “DS” for “diopters sphere;” others will leave this area blank.).

The left eye (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, implying the horizontal (180-degree) meridian of the eye has no additional power for astigmatism and the vertical (90-degree) meridian gets the included -0.50 D.

Both eyes are being recommended an “include power” of +2.00 D for the correction of presbyopia, and this spectacles prescription includes a prismatic correction of 0.5 prism diopter in each eye. In the right eye, the prism is base down (BD); in the left eye, it’s base up (BU).

An Eyeglass Prescription Is Not A Contact Lens Prescription

Glasses and contact lens prescriptions aren’t the same. An eyeglass prescription is for the purchase of eyeglasses only. It does not contain particular details that is important to a contact lens prescription which can be gotten only during a contact lens consultation and fitting.

In addition to the details in an eyeglass prescription, a contact lens prescription must specify the base (central) curve of the back surface of the contact lens, the lens diameter, and the specific maker and brand name of the lens.

Likewise, the power of an eyeglass prescription often is customized when figuring out the best contact lens power. One factor is that glasses lenses are worn some distance (normally about 12 millimeters) from the surface of the eye, whereas contact lenses rest directly on the cornea.

A precise contact lens prescription can be composed just after a contact lens fitting has been performed and the recommending doctor has assessed your eyes’ reaction to the lenses and to call lens wear in basic.

Your Eyeglass Prescription: It’s Yours To Keep

The Federal Trade Commission is the United States federal government’s customer defense company, and in 1980 the FTC’s Prescription Release Rule ended up being law. The guideline requires optometrist (both optometrists and eye doctors) to offer patients a copy of their spectacles prescription at the end of an eye exam that includes a refraction.

The guideline is meant to safeguard the “portability” of your eyeglass prescription, allowing you to use it to buy glasses from the vendor of your option.

Your optometrist should give you a copy of the prescription whether or not you ask for it. Eye doctors might not condition the release of your prescription on your arrangement to purchase glasses from them, nor might they charge you an additional fee to launch your prescription. They also may not disclaim liability for the accuracy of the prescription if you buy spectacles elsewhere.

The FTC enforces the Prescription Release Guideline, and eye doctors who violate the rule go through a civil penalty of $10,000.

Alik Muradov (Eyexan Team Member) / author of the article
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