Eyeglass Prescription Explained

Most of us have the tendency to avoid a visit to the optometrist, for the fear of being diagnosed with an eye number, or some other eye problem, and the need to wear eyeglasses. However, it is advisable that the sooner you discover a problem with your vision, by visiting an optometrist, the easier it will be for you to correct the problem.

Now, though an optometrist will explain whether you are nearsighted or farsighted, there are several other terms on an eyeglass prescription, that are usually beyond comprehension, and which you tend not to ask your optometrist either. For this you have to simply try and understand the implication of each term and the figure it represents.

There are specific terms that are used by optometrists to describe each eye on a prescription for eyeglasses. These terms have been explained here.

• Oculus Dexter (OD): Latin for right eye, also referred to as R.E by some doctors.

• Oculus Sinister (OS): Latin for left eye, also referred to as L.E by some doctors.
• Oculus Uterque: Latin for both eyes

The prescription for each eye may vary depending on the condition, and is explained in terms of cylinder, sphere, axis, and in some cases, prism correction and bifocal power.

Sphere indicates the nearsightedness (myopia) or farsightedness (hyperopia) of the affected person. This number is indicated by the abbreviation SPH on a prescription, and describes what we call the power in each eye. The power is indicative of diopter, that measures the refractive strength of a lens, or that of an eye.

The range for sphere powers varies from +/- 0.25 diopters to about +/-15.00 diopters. Anything above 15.00 will require the use of special contact lenses to correct it. The (+) sign is an indicator of farsightedness, whereas the (-) sign is an indicator of nearsightedness. Whether positive or negative, a higher number is indicative of a stronger power, and therefore, the use of a stronger lens.

A cylindrical number refers to any irregularities in the shape of the cornea, and therefore the presence of astigmatism.

A cornea without a cylindrical power is the shape of a baseball, but the presence of a cylindrical number or astigmatism, means the cornea may be football-shaped. When you notice a cylindrical number in your eyeglass prescription, it refers to the amount of astigmatism you may have.

Some optometrists may represent a cylindrical number in the (+) range (traditional method of representation), while some may represent them in the (-) range. In any case, they mean the same. The range for a cylindrical number can vary from +/-0.25 diopters to +/-5.00 diopters. Any figure above +/-2.00, may require the use of special lenses for vision correction.

Axis in an eyeglass prescription is represented in relation to the cylindrical number. It refers to the angle of the prescription lens that is placed in the frame, for the purpose of correcting astigmatism.

It is represented by means of an angle, that may range from 1-180 degrees. In most cases, the axis may be either 90 degrees, or 180 degrees. It is possible to have a cylindrical number and axis without a spherical number.

The presence of any figure under this section known as 'Addition' (additional power), may refer to the need to use bifocals or, what are commonly known as reading glasses. The number in this field is positive, and the higher the number, the higher will be the power of the lens used for reading.

Usually, this is common for those above the age of 40, and corrective lenses with bifocal power are used to treat a condition called presbyopia. It is not the same as being farsighted, and even if you have never had an eyeglass number, it is a condition you may have to face as you grow older.

That's all there is to an eyeglass prescription. Perform the basics of eye care, to avoid the need to wear eyeglasses and any further problems of the eyes.