How to Read Your Eye Prescription
On an eye prescription, SPH is the main lens power (minus for short-sight, plus for long-sight), CYL and AXIS correct astigmatism, ADD is extra reading power and PD is the distance between your pupils.
What each value means, and why a prescription is not an eye health check
An eye prescription gives the lens power for each eye: SPH is the main correction (minus for short-sight, plus for long-sight), CYL and AXIS correct astigmatism and its direction, ADD is extra reading power usually needed after about 40, and PD is the distance between your pupils. For example, -2.00 means short-sight needing a minus 2 dioptre lens. A prescription does not measure eye health: glaucoma, cataract and retinal disease need a full eye examination.
Last updated: 26 October 2026
After an eye exam, your doctor hands you a piece of paper filled with numbers and abbreviations that can seem confusing. But understanding your eye prescription is not difficult once you know what each symbol represents. In this comprehensive guide, we explain every part of your prescription in simple, clear language, helping you understand your eye condition and available treatment options.
Example of a typical prescription:
| Eye | SPH | CYL | AXIS | ADD |
|---|---|---|---|---|
| Right (OD) | -2.50 | -1.25 | 180 | +2.00 |
| Left (OS) | -3.00 | -0.75 | 90 | +2.00 |
PD: 64mm
What Do the Numbers Mean?
Sphere
The sphere value indicates the lens power needed to correct your vision. A negative (-) number means you are nearsighted (myopic) — you see close objects clearly but distant ones are blurry. A positive (+) number means you are farsighted (hyperopic) — distant objects may be clear but close-up work is difficult. The number is measured in diopters (D). For example, -2.50 means moderate myopia, while +1.75 means mild hyperopia.
Cylinder
The cylinder value corrects astigmatism, which occurs when the cornea or lens has an irregular shape — more like a rugby ball than a perfectly round basketball. This causes light to focus at multiple points instead of one, creating blurred or distorted vision at all distances. If this box is empty, you have no or negligible astigmatism. CYL values can be negative or positive. For example, -1.25 indicates moderate astigmatism.
Axis
The axis is a number between 1 and 180 that indicates the orientation (angle) of astigmatism in your eye. It tells the optician exactly where to position the cylindrical correction in your lenses. The axis is always paired with a CYL value — if there is no CYL, there is no axis. For example, an axis of 90 means the astigmatism is oriented vertically, while 180 means it is horizontal.
Addition
The ADD value is the additional magnifying power added to the bottom part of multifocal or bifocal lenses to help with close-up vision. It is almost always a positive number, typically ranging from +0.75 to +3.00. This value is needed for people with presbyopia — the age-related loss of near focusing ability that usually begins after age 40. Both eyes typically have the same ADD value.
Pupillary Distance
PD measures the distance in millimeters between the centers of your pupils. It ensures the optical center of each lens aligns precisely with your eyes. An incorrect PD can cause eye strain, headaches, and blurred vision even with the correct prescription. PD may be given as a single number (binocular PD, e.g., 63mm) or as two numbers (monocular PD, e.g., 31/32mm) if your face is slightly asymmetrical.
Common Refractive Conditions
Myopia (Nearsightedness)
SPH: -0.25 to -20.00+
Myopia occurs when the eyeball is too long or the cornea is too curved, causing light to focus in front of the retina instead of on it. Distant objects appear blurry while close objects remain clear. It is the most common refractive error worldwide and has been increasing rapidly, particularly among young people who spend more time on screens and less time outdoors. Myopia usually develops in childhood and may worsen until the early twenties.
Hyperopia (Farsightedness)
SPH: +0.25 to +10.00+
Hyperopia occurs when the eyeball is too short or the cornea is too flat, causing light to focus behind the retina. While people often think farsightedness means only close vision is affected, moderate to high hyperopia can blur vision at all distances. The eye's natural focusing ability (accommodation) can compensate for mild hyperopia in young people, which is why it may go undetected. However, this extra focusing effort leads to eye strain and headaches.
Astigmatism
CYL: -0.25 to -6.00+
Astigmatism results from an irregularly shaped cornea or lens. Instead of being perfectly spherical like a basketball, the eye is shaped more like a rugby ball, with one meridian being more curved than the other. This causes light to refract unevenly, creating multiple focus points and resulting in blurred or distorted vision at all distances. Most people have some degree of astigmatism. It commonly occurs alongside myopia or hyperopia.
Presbyopia
ADD: +0.75 to +3.00
Presbyopia is the gradual loss of the eye's ability to focus on nearby objects. It is a natural part of aging that usually becomes noticeable in the early to mid-40s. The lens inside the eye becomes less flexible over time, making it harder to shift focus from distant to close objects. You may notice you need to hold your phone or book further away to read. Everyone eventually develops presbyopia, regardless of other refractive errors.
Prescription Range & Treatment Options
The right option depends on your prescription and overall eye health. The table below is general guidance only, not a substitute for an examination:
| Range | Values | Options that may be discussed |
|---|---|---|
| Mild Myopia | -0.25 to -3.00 D | Glasses, contact lenses, or LASIK |
| Moderate Myopia | -3.25 to -6.00 D | Glasses, contact lenses, LASIK, or PRK |
| High Myopia | -6.25 D and above | Glasses, contact lenses, ICL, or a lens-based option |
| Mild Hyperopia | +0.25 to +2.00 D | Glasses or contact lenses (may not need correction in youth) |
| Moderate Hyperopia | +2.25 to +5.00 D | Glasses, contact lenses, or LASIK |
| Severe Hyperopia | +5.25 D and above | Glasses, contact lenses, or a lens-based option |
| Mild Astigmatism | 0.25 to 1.00 D | Often no correction needed; glasses if symptomatic |
| Moderate Astigmatism | 1.25 to 2.00 D | Glasses, toric contact lenses, or LASIK |
| Severe Astigmatism | 2.25 D and above | Glasses, toric contacts, LASIK, or toric ICL |
Can Laser Surgery or Other Treatment Correct My Prescription?
Laser surgery (such as Femto-LASIK, PRK or CLEAR) can correct many refractive errors, but it is surgery with risks and does not suit everyone. Limits depend on the technique, corneal thickness and eye health. As a rough guide, LASIK can generally correct:
- ✓Myopia (nearsightedness) up to -10.00 D
- ✓Hyperopia (farsightedness) up to +6.00 D
- ✓Astigmatism up to 6.00 D
If your prescription is beyond the laser range, an ICL lens implant may be discussed, or, over about 45 to 50, lens-based options similar to cataract surgery. Well-fitted glasses or contact lenses remain a safe choice. A suitability assessment decides which option, if any, fits.
Does a New Prescription Mean My Eyes Are Healthy?
Not necessarily. A sight test sets lens power; a comprehensive eye examination also checks eye pressure, the lens, the retina and the optic nerve. Several conditions start without symptoms or first show up as a change in vision:
How Often Should You Update Your Prescription?
Children & Teens
Every 6-12 months
Eyes change rapidly during growth. Early detection of myopia progression allows for myopia management interventions.
Adults (20-40)
Every 1-2 years
Prescriptions typically stabilize but can still change. Regular exams also screen for emerging conditions.
Adults (40+)
Every year
Presbyopia progresses, and risk for glaucoma, cataracts, and macular degeneration increases with age.
Frequently Asked Questions
What does a negative number on my prescription mean?
A negative number in the SPH box means you have myopia (nearsightedness). The larger the negative number (e.g., -5.00 vs -1.00), the stronger the myopia. This means you see close objects clearly but distant objects appear blurry.
Can my eye prescription change over time?
Yes, your eye prescription can change over time. In children and young adults, myopia may gradually increase until stabilizing in the early twenties. After age 40, most people begin needing reading glasses due to presbyopia. This is why updating your exam every 1-2 years is recommended.
Can laser eye surgery correct my prescription?
Laser surgery can correct many levels of short-sight, long-sight and astigmatism, but the limits depend on the technique, your corneal thickness and eye health, so the prescription alone cannot tell you. High prescriptions or thin corneas may suit an ICL lens instead, and over about 45 to 50 lens-based options may be discussed. A suitability assessment decides what, if anything, fits.
What is the difference between glasses and contact lens prescriptions?
A contact lens prescription differs from a glasses prescription because contacts sit directly on the eye while glasses are about 12mm away. Contact lens prescriptions include additional information like lens diameter and base curve. You cannot use a glasses prescription to purchase contact lenses directly.
What does PD mean on my prescription?
PD stands for Pupillary Distance — the distance between the centers of your pupils, measured in millimeters. This measurement is essential for manufacturing glasses accurately so the optical center of the lenses aligns with your pupils. The average adult PD ranges from 54-74mm. Without the correct PD, glasses can cause eye strain or headaches.
Need Help Understanding Your Prescription?
Ophthalmologists at Finland Eye Center can explain your prescription, check the health of your eyes and discuss the options that suit you.
Finland Eye Center — Branches in Muscat, Sohar, Nizwa, and Salalah