Short-sightedness

Reading your child's myopia prescription: what the numbers mean

Minus numbers, a strange axis and a word like cycloplegic. A line-by-line guide to a short-sighted child's prescription, with a made-up example, and what the numbers cannot tell you.

by Dr Chan Li Yen · MBBS, MOphth (UM), Fellowship in Paediatric Ophthalmology & Strabismus

Dr Chan Li Yen, consultant paediatric ophthalmologist, MMC 43128, NSR 132980 · Eagle Eye Centre Kuala Lumpur, Petaling Jaya

11 min read · 2,050 words

Key takeaways

A minus sign on the sphere (SPH) means short-sighted, and a bigger number means a stronger lens. The International Myopia Institute puts myopia at -0.50 D or more minus and high myopia at -6.00 D or beyond.
CYL is the extra power for astigmatism and AXIS is its direction, a number from 1 to 180 that is not a strength. Spherical equivalent is the sphere plus half the cylinder.
Measuring without cycloplegic drops tends to overestimate short-sightedness in children. In one 2025 study of 110 children the average gap was 0.72 D and the share labelled myopic fell from 62.7 to 40.9 percent with drops.
Axial length, the front to back length of the eyeball, tracks eye growth. The reference values found are European (22.36 mm at age 6, 23.10 mm at 9). No Malaysian reference curve could be found on 1 October 2026.
Keep every slip and compare like with like: date, who measured, with or without drops, spherical equivalent and axial length. The power number does not show visual sharpness or retinal health.

Many parents leave the optical shop or the clinic with a slip of paper full of abbreviations and numbers, and understand only one thing: "the power went up again". That slip actually says a lot, if you know how to read it.

This article goes through each line of a short-sightedness (myopia, rabun jauh) reading, one at a time, using an example made up for teaching. It also explains why a measurement with eye drops differs from one without, and what axial length is.

What does myopia mean on my child's prescription?

A minus sign (-) in front of the lens power means your child is short-sighted: distant things look blurred and near things look clear. The bigger the number after the minus, the stronger the lens. The unit is the dioptre (D).

Myopia happens when light from far away comes to a point in front of the retina, the light-catching layer at the back of the eye, instead of on it. For research purposes, the International Myopia Institute (IMI) sets myopia at -0.50 D or more minus, and high myopia at -6.00 D or beyond. The IMI itself notes that the -0.50 D line carries a risk of putting some children in the wrong group, so it is a guide, not a verdict.

In everyday Malaysian talk, "power 200" usually means -2.00 D, and "power 150" means -1.50 D. One thing never changes: the number tells you how strong the lens is, not how healthy the eye is.

What do SPH, CYL and AXIS mean on the slip?

SPH is the main lens power, CYL is the extra power for astigmatism (an eye curved more in one direction than another), and AXIS is the direction of that extra power. The American Academy of Ophthalmology (AAO) explains that OD is the right eye and OS the left, from Latin.

Here is an example made up for teaching. It is not a real child.

OD (right eye): SPH -2.00, CYL -0.75, AXIS 180
OS (left eye): SPH -1.75, CYL -0.50, AXIS 175

Read the first line like this: the right eye is short-sighted by 2.00 dioptres, with a little astigmatism of 0.75 dioptre. AXIS 180 is the direction of that astigmatism. The AAO says the axis is a number from 1 to 180 degrees showing which way the astigmatism lines up. It is not a strength, so a big axis number is not worse than a small one.

Astigmatism means the cornea, the clear front window of the eye, is curved more one way than the other. There is more in astigmatism in children, explained. If the CYL box is empty, there is no astigmatism to correct.

What is "spherical equivalent", and why do doctors quote it?

Spherical equivalent is one simple number for each eye: the SPH plus half of the CYL. Doctors and research papers use it because it squeezes the whole power of the eye into one figure, and that figure is what gets compared with the -0.50 D and -6.00 D lines.

In the example above, the right eye is -2.00 plus half of -0.75, which is -2.00 + (-0.375), about -2.38 D. The left eye is -1.75 + (-0.25), which is -2.00 D.

When a doctor asks "how much has the power gone up this year", the working figure is the change in spherical equivalent since the last visit. In the comparison groups of the myopia control trials reviewed by Cochrane in 2025, the median change over one year was -0.65 D. That is a figure for trial groups, not a forecast for your child. How to judge fast against slow is covered in slowing myopia down.

Why does the doctor put in drops before measuring my child's power?

Because a child's eye focuses very actively, and without drops the measurement often reads more short-sighted than the truth. The drops, called cycloplegic drops, rest the focusing muscle for a while so the eye cannot "pull" its focus during the test.

The evidence is fairly consistent. A 2025 study in India measured 110 children aged 5 to 15 twice. Without drops the average spherical equivalent was -0.54 D. With drops it was +0.18 D, an average difference of 0.72 D, and the share labelled short-sighted fell from 62.7 percent to 40.9 percent. That is one small study from one centre, but it points the same way as others. A study of 142 children found measurements without drops were more than 0.5 D more short-sighted in short-sighted eyes, and a 2015 review concluded that skipping cycloplegia slightly overestimates myopia and badly misjudges long-sightedness.

The practical lesson: if an old reading was taken without drops and a new one with drops, the new number can look as if things improved or stood still, when only the method changed. So note whether each measurement was done with or without drops. What happens when the drops go in is explained in about those eye drops at the clinic.

Optometrists and eye doctors can both measure power and advise on glasses. For a child too young to read a chart, the AAO says a retinoscope is used. If you are unsure which type of measurement was done, just ask: "Was this with drops or without?"

What is axial length, and why is it measured?

Axial length is the distance from the front to the back of the eyeball, measured in millimetres. Most childhood short-sightedness happens because the eyeball grows too long, so axial length tells you about the growth of the eye itself, not only the lens it needs.

A 2018 study by Tideman and colleagues gives reference values for European children: an average of 22.36 mm at age 6, 23.10 mm at age 9, 23.41 mm at 15 and 23.67 mm in adults. Among children whose axial length percentile rose by more than 10 between ages 6 and 9, 45.8 percent were short-sighted at 9, against 4.8 percent of the others.

An honest caveat: that is European data. A check of the published literature on 1 October 2026 found no axial length reference curve for Malaysian children. One Malaysian study measured axial length in Chinese children aged 8 to 9, but it was a small study of corneal cells, not a reference curve. So use the European values as a rough guide only, and judge a child by the change from visit to visit.

In the comparison groups of the trials in the 2025 Cochrane review, the median increase in axial length over one year was 0.33 mm. Not every eye check measures axial length, and it is not needed to make ordinary glasses. It becomes more useful when a family is weighing ways to slow myopia. Those options, and how sure the evidence is, are in atropine drops for myopia.

How do I compare one visit with the next?

Keep every slip, file them by date, and compare the same five things each time. A phone photo is enough, as long as every line can be read.

The date, and who measured (optical shop, optometrist or eye doctor).
With or without drops.
SPH and CYL for both eyes, and whether the axis moved a lot.
The spherical equivalent for each eye, worked out as above.
Axial length in millimetres, if it was measured.

Three changes are worth taking to an eye doctor. The power rising several times in a short period. One eye differing a lot from the other. Or a number heading towards -6.00 D, the line called high myopia. The AAO says severe short-sightedness raises the risk of retinal detachment, glaucoma and cataracts, which is discussed in high myopia. For a child who is not short-sighted yet but at risk, see pre-myopia.

What does the power number not tell me?

It does not tell you how sharp your child's vision is, how fast it will change, or whether the back of the eye is healthy. Those are three different things, and each is measured differently.

Visual acuity (the letter or picture chart, for example 6/6) is how clearly your child sees, with or without glasses. Power is how the eye focuses. The retina check needs the doctor to look at the back of the eye, usually after drops have widened the pupil.

So a small number does not mean "no more checks needed". The AAO says a parent with myopia raises a child's chance of it, so the family can be checked at the same visit, your own eyes included. What the first weeks in new glasses look like is in my child needs glasses.

See an eye doctor sooner if…

The power has risen several times within a short period.
One eye is much more short-sighted than the other.
The number is heading towards -6.00 D.
Your child's vision drops suddenly in one eye.
Flashes of light, a new shower of floaters or a curtain over part of the vision: same-day care.

Common questions

What does -2.00 mean on my child's glasses prescription?

It means your child is short-sighted by 2.00 dioptres. In everyday Malaysian talk this is often called power 200. The number says how strong the lens must be, not how healthy the eye is.

What do SPH, CYL and AXIS mean?

SPH is the main lens power, CYL is the extra power for astigmatism, and AXIS is the direction of that astigmatism, a number from 1 to 180 degrees according to the American Academy of Ophthalmology. AXIS is not a strength, so a high axis number is not worse than a low one.

What is spherical equivalent and how do I work it out?

Spherical equivalent is the sphere plus half the cylinder. For SPH -2.00 and CYL -0.75, it is -2.00 + (-0.375), about -2.38 D. Doctors use it to compare an eye with the -0.50 D and -6.00 D myopia lines and to track change between visits.

Why does my child need eye drops before the power is measured?

Children focus hard, and without cycloplegic drops the measurement tends to read more short-sighted than it really is. In a 2025 study of 110 children, the average spherical equivalent was -0.54 D without drops and +0.18 D with them. Drops rest the focusing muscle so the reading is steadier.

What is axial length in myopia?

Axial length is the front to back length of the eyeball in millimetres. Most childhood short-sightedness comes from an eyeball that grows too long. European reference values average 22.36 mm at age 6 and 23.10 mm at age 9, and no Malaysian reference curve could be found on 1 October 2026.

My child's reading is -1.50. Is that bad?

A reading of -1.50 D is still far from the high myopia line (-6.00 D), and what matters more is how fast it changes from visit to visit. Compare readings taken the same way, with or without drops, and ask an eye doctor if the power keeps rising.

Can I compare readings from different shops or clinics?

You can, but only with care. Check whether each reading was taken with or without drops, because that alone can shift the number by about 0.7 D in one study. Keep all slips and take them with you to the next visit.

Does a small number mean my child's eyes are healthy?

No. The power number says nothing about how sharp the vision is or how the back of the eye looks. A short-sighted child still needs regular eye checks, and the American Academy of Ophthalmology notes that severe short-sightedness raises the risk of retinal detachment, glaucoma and cataracts.

References

American Academy of Ophthalmology · How to read an eyeglasses prescription · www.aao.org
Investigative Ophthalmology & Visual Science · IMI, Defining and classifying myopia (2019) · pubmed.ncbi.nlm.nih.gov
Cureus · Comparison of cycloplegic and non-cycloplegic refraction in school-aged children (2025) · pubmed.ncbi.nlm.nih.gov
Acta Ophthalmologica · Cycloplegic refraction is the gold standard for epidemiological studies (2015) · pubmed.ncbi.nlm.nih.gov
Acta Ophthalmologica · Axial length growth and the risk of developing myopia in European children (2018) · pubmed.ncbi.nlm.nih.gov
Cochrane Database of Systematic Reviews · Interventions for myopia control in children (2025) · pubmed.ncbi.nlm.nih.gov
Journal of Ophthalmology · Cutoff values of noncycloplegic spherical equivalent refraction for myopia detection in southwestern Chinese children (2025) · pmc.ncbi.nlm.nih.gov
American Academy of Ophthalmology · Nearsightedness (myopia) · www.aao.org
Clinical Ophthalmology · Manifest refractions, cycloplegic refractions and retinoscopy on an autorefractometer in children aged 3 to 15 (2009) · pubmed.ncbi.nlm.nih.gov
F1000Research · Corneal endothelial morphology of healthy myopic Malaysian children of Chinese ethnicity aged 8-9 years and its association with axial length (2022) · pubmed.ncbi.nlm.nih.gov

By Dr Chan Li Yen. General information only. It does not replace a consultation. If you are worried about your child's eyes or vision, please see an eye doctor.