Single Vision Lenses: What They Correct and How to Read Your Prescription

If you've ever looked at an eyeglass prescription and felt lost in a sea of numbers, plus signs, and abbreviations, you're not alone. Most people receive their prescription at the end of an eye exam, tuck it into a pocket, and hand it over to whoever is selling them glasses without fully understanding what it says. That's a missed opportunity. Knowing what your prescription means—and what type of lens it calls for—makes you a more informed buyer and helps you avoid costly mistakes when ordering online. Single vision lenses are the most commonly prescribed lens type in the world, and they're simpler than they appear. Here's what they do, what conditions they address, and exactly how to read the numbers that determine what you need.

What Single Vision Lenses Are

A single vision lens has one focal power across the entire surface of the lens. This is in contrast to bifocal or progressive lenses, which incorporate two or more focal zones to address both distance and near vision in a single lens. Single vision lenses are prescribed for people who need correction in one focal range—either for distance, for near, or occasionally for intermediate (computer) distances. The lens is ground to a single prescription, and that prescription is consistent from edge to edge. Because of their straightforward design, single vision lenses are typically lighter, thinner, and less expensive to produce than multifocal alternatives. They are the default starting point for most first-time eyeglass wearers, and they remain the preferred choice for many experienced wearers who need separate pairs for different tasks.

What Conditions Single Vision Lenses Correct

Myopia (Nearsightedness)

Myopia is the most common refractive error globally. People with myopia can see objects up close clearly but struggle with distance—road signs, whiteboards, faces across a room. The eye is effectively too long, causing light to focus in front of the retina rather than on it. Single vision lenses prescribed for myopia have a negative power (indicated by a minus sign on your prescription) and are thicker at the edges than at the center.

Hyperopia (Farsightedness)

Hyperopia is essentially the opposite of myopia. The eye is too short, and light focuses behind the retina rather than on it. Mild hyperopia is often compensated naturally by the eye's own focusing muscles, especially in younger people, but this constant effort can cause eye strain and headaches. More significant hyperopia requires correction. Single vision lenses for hyperopia carry a positive power (a plus sign on the prescription) and are thicker at the center than at the edges.

Astigmatism

Astigmatism occurs when the cornea or lens of the eye is slightly irregular in shape—more oval than spherical. This causes light to scatter and focus at multiple points, resulting in blurred or distorted vision at any distance. Astigmatism frequently accompanies myopia or hyperopia rather than appearing on its own. Single vision lenses can fully correct astigmatism through the addition of a cylindrical power, which you'll see on your prescription under the column labeled CYL.

Presbyopia (with single vision reading glasses)

Presbyopia is the gradual loss of near focusing ability that becomes noticeable for most people in their early-to-mid forties. It happens as the natural lens of the eye becomes less flexible with age. Single vision lenses address presbyopia in the form of dedicated reading glasses—a pair worn specifically for close work. Wearers who also have distance correction often choose progressive lenses to avoid switching pairs, but single vision reading glasses remain a practical and popular option.

How to Read Your Prescription

A standard eyeglass prescription contains several fields. Here's what each one means.

OD and OS

OD stands for oculus dexter, Latin for right eye. OS stands for oculus sinister, or left eye. Some prescriptions also include OU (oculus uterque), meaning both eyes. Always check which eye each row of numbers applies to—the values are often different between eyes.

SPH (Sphere)

This is the primary lens power needed to correct your vision, measured in diopters. A negative number indicates myopia; a positive number indicates hyperopia. The further the number from zero in either direction, the stronger the prescription. A sphere of –1.00 is mild myopia; –6.00 is quite strong.

CYL (Cylinder)

This column addresses astigmatism. If this field is blank, or marked DS (diopters sphere) or SPH, you have no significant astigmatism and your lens will be purely spherical. If a number appears here, the lens needs to be ground with a cylindrical correction in addition to the spherical one. Like sphere, the number can be positive or negative depending on the convention used by your prescriber.

AXIS

The axis works in tandem with the cylinder. It specifies the orientation of the astigmatic correction, expressed as a number between 1 and 180 degrees. The axis has no meaning without a cylinder value—if CYL is blank, axis will be blank too. When ordering, both CYL and AXIS must be entered exactly as written on your prescription.

ADD

The ADD value appears on prescriptions for progressive or bifocal lenses and indicates the additional magnifying power needed for reading. If you're ordering single vision reading glasses from a standard prescription, this value tells you what to add to your distance SPH. For example, if your distance SPH is –2.00 and your ADD is +2.00, a pair of single vision reading glasses would be ground to a sphere of plano (0.00)—the two values cancel out.

PD (Pupillary Distance)

PD is the distance in millimeters between the centers of your pupils. It is critical for positioning the optical center of each lens directly in front of your eye. An incorrect PD causes misalignment that produces eyestrain, headaches, and distorted vision even if the prescription power is perfectly correct. PD may be listed as a single number (binocular PD) or as two numbers—one per eye (monocular PD). For single vision lenses, either format is acceptable.

How to Know What to Order

Once you understand the fields on your prescription, determining what to order becomes straightforward. If your prescription has an SPH value, no CYL, and no ADD—you need a simple single vision spherical lens. If your prescription includes both SPH and CYL with a corresponding AXIS, you need a single vision lens with astigmatism correction; enter all three values exactly as they appear, without rounding. If your prescription includes an ADD value and you want single vision reading glasses, add your distance SPH to the ADD value to find your reading power. Your optometrist can confirm this calculation, but the arithmetic is: Reading SPH = Distance SPH + ADD. If your prescription is more than two years old, it may no longer be accurate—an outdated prescription is the most common source of dissatisfaction with new glasses, and a current exam is always worth the investment before ordering. Finally, when ordering online you'll be asked to choose a lens index, which determines thickness. As a general rule: for prescriptions up to ±2.00, a standard 1.50 index is fine; up to ±4.00, a 1.67 index makes a meaningful difference in both weight and appearance.

The Bottom Line

Single vision lenses are the right choice for most people who need correction in a single focal range—whether for distance, reading, or computer use. They are simpler to fit, easier to adjust to, and more forgiving optically than progressive lenses. Understanding the numbers on your prescription removes the guesswork from ordering and helps ensure your new lenses deliver the clarity you're paying for. When in doubt, ask your prescribing optometrist to walk you through your prescription before you leave the exam room—they expect the question, and a few minutes of explanation can save you from a frustrating return.

 

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