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Sphere (SPH) on an Eye Prescription: What the Number Means
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Sphere (SPH) (noun): the sphere is the first number in each eye's row of an eye prescription. It is the main lens power needed to correct short sight or long sight, measured in dioptres (D). A minus number (for example −2.50) means you are short-sighted (myopic); a plus number (for example +1.75) means you are long-sighted (hyperopic). The further the number is from zero, the stronger the lens you need. Surgeons such as Prof. Dr. Ahmet Satıcı and Op. Dr. Aysan Bayram look at the sphere first when they judge whether laser eye surgery or a lens could free you from glasses.
Sphere (SPH): key facts
- Where you see it
- In the SPH column of a glasses prescription, one row for the right eye (OD) and one for the left eye (OS)
- Unit
- Dioptres (D); American spelling "diopter". Prescriptions go up in steps of 0.25 D
- Minus sign (−)
- Short sight (myopia): distant objects look blurred, near objects stay clear
- Plus sign (+)
- Long sight (hyperopia): near vision is harder, and strong long sight can blur distance too
- "Plano", "PL" or "DS"
- No sphere power in that eye (plano), or a lens that is purely spherical with no cylinder (DS)
- Sits next to
- Cylinder (CYL) and axis for astigmatism, and ADD for reading, in the same row
- Specialist
- Ophthalmologist or optometrist; for laser and lens surgery in Istanbul, Prof. Dr. Ahmet Satıcı or Op. Dr. Aysan Bayram
What does sphere (SPH) mean on an eye prescription?
According to the American Academy of Ophthalmology (AAO), the sphere column, often written SPH, shows the lens power needed to fix your vision. A prescription usually reads like this:
| SPH | CYL | AXIS | ADD | |
|---|---|---|---|---|
| OD (right eye) | −2.50 | −0.75 | 180 | |
| OS (left eye) | −2.25 |
In this example the right eye needs 2.5 dioptres of short-sight correction plus a little astigmatism correction, and the left eye needs 2.25 dioptres of short-sight correction and none for astigmatism. OD is oculus dexter (right eye) and OS is oculus sinister (left eye), according to the AAO. The two eyes often have different numbers, which is normal.
The AAO describes the scale as a number line with zero in the middle, which needs no correction: the further you get from zero on either the minus or plus side, the stronger your prescription. Its own example, −9.00 D, means 9 dioptres of nearsightedness.
Sphere corrects the whole-eye focusing error. Cylinder, in contrast, corrects an uneven, rugby-ball-shaped surface that focuses light at more than one place. Sphere treats the eye as a round ball: it bends light by the same amount in every direction, which is why it is called spherical power. For the other columns, see Glossary: Cylinder (CYL) → and Glossary: Axis →. For a plain-English reading of a whole prescription, use Eye prescription reader (sphere, cylinder, axis, dioptres) →.
What is a dioptre?
A dioptre is the unit of lens power: one divided by the focal length in metres, so a 3 D lens focuses light at one-third of a metre. The Royal College of Ophthalmologists (RCOphth) defines it as a unit for measuring the refractive power of a lens. Sphere values change in steps of 0.25 D, so you will see numbers such as −1.00, −1.25 and −1.50.
Minus sphere vs plus sphere: short sight and long sight
A minus sphere (−) means short sight (myopia). Light from distant objects focuses in front of the retina instead of on it, so far things look blurred while close things stay clear. The AAO says this happens when the cornea is too steeply curved or the eyeball is longer than normal. The correcting lens is a minus (diverging) lens that spreads the light out before it enters the eye.
A plus sphere (+) means long sight (hyperopia). Light focuses behind the retina. EyeWiki (AAO) gives the most common cause as an eye that is too short, with a flatter cornea or a weaker lens as other causes. The NHS adds that long sight often runs in families, and that in older adults it can come from the natural lens stiffening. The correcting lens is a plus (converging) lens that bends light inward.
Plano means zero. "Plano" (PL) means no sphere power in that eye. "DS" (dioptres sphere) tells you the lens is purely spherical, with no cylinder.
A simple way to remember it: a minus is "distance is blurred, near is clear", and a plus is "near work takes extra effort". Young long-sighted people can often focus past their long sight by tightening the eye's natural lens, according to EyeWiki, so mild long sight can go unnoticed for years.
How strong is my sphere? Low, moderate and high
The strength of your sphere is the size of the number, ignoring the sign. Eye doctors group short sight and long sight into bands:
| Band | Short sight (minus sphere) | Long sight (plus sphere) |
|---|---|---|
| Low | Less than 3 D (AAO) | Up to +2.00 D (EyeWiki) |
| Moderate | 3 to 6 D (AAO) | +2.25 to +5.00 D (EyeWiki) |
| High | More than 6 D (AAO) | +5.25 D and above (EyeWiki) |
Researchers use a slightly different cut-off in studies. The International Myopia Institute (IMI) defines myopia as a spherical equivalent of −0.50 D or worse and high myopia as −6.00 D or worse, measured with the eye's focusing relaxed.
Is a sphere of −1.50 or −2.00 bad? No. A prescription measures the lens you need, not the health of your eyes. These are low myopia: you would see distance blurred without glasses, but the number does not mean your eyes are unhealthy.
Why high numbers matter. The AAO says people with high short sight have a higher risk of retinal detachment, glaucoma and cataract. EyeWiki defines high myopia as −6.00 D or more (or an eye 26.5 mm long or longer) and says stable high myopia may be followed yearly. The NHS likewise lists glaucoma, detached retina, cataracts and macular degeneration as higher risks in severe short sight. This is a reason for regular eye examinations, not for alarm.
How common is it? Very. Holden and colleagues (Ophthalmology, 2016) estimated that 28% of the world's population (about 2 billion people) were short-sighted in 2010, and projected 50% (about 5 billion) by 2050. High myopia was estimated at 4% (227 million people) in 2010 and projected at 10% (938 million) in 2050. EyeWiki puts long sight at about 10% of people in the United States (14 million).
Sphere and spherical equivalent
Many studies and some clinics reduce a whole prescription to one number called the spherical equivalent (SE). It is the sphere plus half of the cylinder. Example: a sphere of −3.00 with a cylinder of −1.00 has an SE of −3.00 + (−0.50) = −3.50 D (our own arithmetic, shown for illustration). It is the figure behind the IMI definitions above, and a handy way to compare two prescriptions that contain different amounts of astigmatism.
Plus-cylinder and minus-cylinder notation change the sphere you see. Some practices write the cylinder with a minus sign and others with a plus sign; both describe the same lens (Wikipedia, "Eyeglass prescription"). When a prescription is rewritten from one notation to the other, the sphere changes too, because the new sphere is the old sphere plus the cylinder. For example, −2.00 −1.00 × 180 and −3.00 +1.00 × 90 are the same lens. If a prescription from abroad looks unfamiliar, send it to us and we will read it for you.
Causes: why does my sphere number change?
Sphere measures how your eye focuses, so anything that changes the eye's length or the focusing power of the cornea and lens changes it.
- Growth in childhood and the teens. According to the NHS, short sight typically begins between about 6 and 13 and can get worse until about age 20. The AAO places the usual start at 8 to 12, often worsening during growth spurts.
- Genetics. Short and long sight often run in families (NHS). The AAO adds that having a short-sighted parent does not mean a child will definitely become short-sighted.
- The natural lens with age. After about 40, the lens stiffens and close focus fades (presbyopia, AAO). This is a separate problem from your sphere and is handled by the ADD column, but it means many short-sighted people need help for both distance and near.
- Other causes. Long sight can occasionally result from conditions such as diabetes or eye cancer (NHS), and EyeWiki lists cataracts among causes of hyperopia. A sudden or large change in your prescription is a reason to see an eye doctor.
The NHS says it is hard to prevent short sight. Spending more time outdoors in daylight is linked with a lower risk of myopia in children (AAO, NHS). For children whose short sight is getting worse, the AAO lists low-dose atropine eye drops and specialised contact lenses, and the NHS notes that some opticians offer myopia-control lenses or overnight orthokeratology.
Symptoms: how does an uncorrected sphere feel?
With a minus sphere (short sight):
- blurred distance vision, such as road signs or a classroom board
- squinting to see clearly
- eyestrain and headaches
- in children, holding books or screens very close and frequent eye rubbing
With a plus sphere (long sight):
- near work (reading, phone, laptop) looks fuzzy or tires the eyes
- headaches and eye fatigue after close work
- squinting at close range
The AAO, EyeWiki and NHS list these as typical. Mild cases may cause no symptoms at all. Because children often do not realise they cannot see well, the NHS advises an optician visit if a child shows signs of short sight, and notes that untreated short sight in children may lead to a squint or lazy eye.
How is sphere measured?
Your sphere is measured in an eye test (a refraction) by an optometrist or ophthalmologist. They find the lens powers that give the clearest vision with your eye's focusing relaxed, which is how the IMI defines the measurement. The result is written as one row for each eye, OD and OS.
The NHS advises seeing an optician if you or your child have not had an eye test for 2 years. In the UK, NHS eye tests are free for children under 16, people over 60, people with diabetes or glaucoma, and some benefit recipients (NHS). Elsewhere, ask your optician how often you need one.
A glasses prescription is not a contact-lens prescription. The AAO says that because contact lenses sit directly on the eye, a contact-lens prescription is different and includes measurements specific to the size and brand of the lens. For strong prescriptions, the gap between lens and eye (the back vertex distance) also matters: small changes can alter the power that reaches your eye, particularly above ±4.00 D (Wikipedia, "Eyeglass prescription"). Do not order contact lenses from a glasses prescription alone.
Treatment: what can correct my sphere?
| Option | How it works | Typical sphere range | Notes |
|---|---|---|---|
| Glasses | A minus or plus lens bends light before it enters the eye | Any | Simplest option; first-line treatment per AAO and NHS |
| Contact lenses | The same correction, worn on the eye | Any (needs its own prescription) | Needs good hygiene and a lens-specific fitting |
| Laser eye surgery (LASIK, SMILE, PRK) | A laser reshapes the cornea | RCOphth: usually up to −10.00 D short sight, up to +4.00 D long sight and up to ±6.00 D astigmatism | Over 18, with a stable prescription (no change greater than 0.5 D in two years) |
| ICL (implantable contact lens) | A thin lens placed inside the eye in front of the natural lens | EyeWiki (AAO): FDA-approved for myopia from −3.0 D to −20.0 D | Often considered when laser is not suitable; FDA approval is for adults 21–45 with a prescription stable within 0.5 D for a year |
| Lens replacement (refractive lens exchange) | The natural lens is replaced with an artificial lens | Prescriptions beyond what laser treats, often with reading-vision needs | The surgeon decides after examination |
The NHS notes that laser and lens surgery are generally not available on the NHS and can be expensive. The AAO adds that LASIK cannot correct presbyopia, so for people who also have reading problems a lens option may fit better.
How your sphere shapes the choice. Your sphere, together with scans of your cornea, helps decide whether laser (up to about −10 D of short sight), an ICL (higher short sight, or when laser is not suitable) or lens replacement is the better route. The surgeon decides after measuring your eyes, never from the number alone, and laser does not stop your natural lens from ageing.
Prof. Dr. Ahmet Satıcı and Op. Dr. Aysan Bayram treat refractive errors with laser in Istanbul, and Prof. Dr. Satıcı also performs ICL and lens exchange, in a fully equipped, Ministry of Health–licensed operating theatre in Istanbul. Our prices include the pre-operative examination and scans, surgery by the named surgeon, medication, follow-up checks in Istanbul, a personal interpreter, a coordinator and remote follow-up. Hotel and airport transfers are not included; they are arranged on request for a separate charge.
When to see a doctor about your sphere
Seek urgent care (same day) if you have:
- a sudden loss or sharp change in vision
- new flashes of light, a shower of floaters or a curtain-like shadow, which can signal a retinal tear or detachment (the AAO lists retinal detachment as a higher risk in high short sight)
- a painful red eye with halos around lights, headache or nausea, which can be acute angle-closure glaucoma (EyeWiki lists it as a possible complication in long-sighted eyes)
Book a routine eye test if:
- distance or near vision is blurry, or you squint or get headaches after close work
- your glasses no longer feel right, or your prescription keeps changing
- your child shows signs of short sight, or has not had an eye test for 2 years (NHS)
- your sphere is high (about ±6 D or stronger) and you have not had a full retinal check recently
- you are thinking about laser or lens surgery and want to know whether your numbers are within range
If you already have a prescription and want a surgeon's opinion, you can send it for review before you decide anything.
Frequently asked questions
SPH stands for sphere. It is the main lens power, in dioptres, that corrects short sight (minus) or long sight (plus). It is the first number in each eye's row, before cylinder (CYL) and axis.
A minus sphere (−) corrects short sight: distance is blurred, near is clear. A plus sphere (+) corrects long sight: near vision is harder, and strong long sight can blur distance as well. The larger the number, the stronger the correction.
Plano (PL) means zero sphere power: that eye needs no correction for short or long sight. It may still have a cylinder for astigmatism. "DS" means the lens is purely spherical.
By the AAO's grouping, −3.00 D sits at the border between low and moderate short sight (low is less than 3 D, moderate is 3 to 6 D). Without glasses, distant objects look blurred, but your eyes are not unhealthy because of the number.
Sphere corrects short or long sight, which affects focus equally in all directions. Cylinder corrects astigmatism, where the eye is shaped more like a rugby ball than a football and focuses light at more than one place (NHS). Axis, in degrees from 1 to 180, tells you the direction of the astigmatism (AAO). Many people have both.
It is common for the two eyes to have different spheres. Each eye is measured separately (OD for right, OS for left). If the difference is large, ask your eye doctor whether it needs any special attention, particularly in children.
It can often reduce it a great deal, within limits. According to the RCOphth, laser is usually suitable up to −10.00 D of short sight and +4.00 D of long sight if you are over 18 and your prescription has been stable (no change greater than 0.5 D in two years). Outside that range an ICL or lens exchange may suit you better. Laser does not stop your natural lens from ageing, so you may still need reading glasses later.
For many people short sight settles around age 20 (NHS), but a prescription can change at any age, for example with the natural lens changes after 40 or with conditions such as cataract or diabetes. That is why a stable prescription is required before surgery.
No. A contact-lens prescription is different and includes details such as lens size and brand (AAO). Ask your optician for a separate contact-lens fitting.
Sources for the facts on this page
- American Academy of Ophthalmology (AAO). How to Read Your Eyeglasses Prescription. https://www.aao.org/eye-health/glasses-contacts/how-to-read-eyeglasses-prescription
- AAO. Myopia (Nearsightedness): What Is Myopia? https://www.aao.org/eye-health/diseases/myopia-nearsightedness
- AAO. What Is Presbyopia? https://www.aao.org/eye-health/diseases/what-is-presbyopia
- AAO. LASIK Laser Eye Surgery. https://www.aao.org/eye-health/treatments/lasik
- EyeWiki (AAO). Hyperopia. https://eyewiki.org/Hyperopia
- EyeWiki (AAO). Myopia. https://eyewiki.org/Myopia
- EyeWiki (AAO). Pathologic Myopia (Myopic Degeneration). https://eyewiki.org/Pathologic_Myopia_(Myopic_Degeneration)
- EyeWiki (AAO). Implantable Collamer Lens. https://eyewiki.org/Implantable_Collamer_Lens
- NHS. Short-sightedness (myopia). https://www.nhs.uk/conditions/short-sightedness/
- NHS. Long-sightedness. https://www.nhs.uk/conditions/long-sightedness/
- NHS. Astigmatism. https://www.nhs.uk/conditions/astigmatism/
- Flitcroft DI, et al. IMI: Defining and Classifying Myopia. Invest Ophthalmol Vis Sci 2019;60:M20–M30. https://pmc.ncbi.nlm.nih.gov/articles/PMC6735818
- Holden BA, et al. Global Prevalence of Myopia and High Myopia and Temporal Trends from 2000 through 2050. Ophthalmology 2016;123(5):1036–42, as summarised in Community Eye Health: https://pmc.ncbi.nlm.nih.gov/articles/PMC6688420/
- The Royal College of Ophthalmologists. Laser Vision Correction: Patient Information (2024), including its glossary. https://www.rcophth.ac.uk/guidance-resources/laser-vision-correction/
- Wikipedia. Eyeglass prescription (plano, DS, plus and minus cylinder notation, back vertex distance). https://en.wikipedia.org/wiki/Eyeglass_prescription
Not sure what your sphere means for laser or lens surgery?
Send us your prescription and any eye scans you have. Prof. Dr. Ahmet Satıcı or Op. Dr. Aysan Bayram will review them and tell you which treatments may suit your eyes, with no obligation.
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