Eye Prescription (Chashme Ka Number): SPH, CYL, Axis Explained

On an eye prescription, a minus SPH number means short sight, a plus means long sight, CYL and AXIS describe astigmatism, and ADD is the extra reading power most people need after about 40. A number like -0.50 is mild, and many people with it see well enough without glasses for most of the day.

If you’re holding a slip from an optician or eye doctor and wondering how bad your eyes really are, this guide decodes every box: OD and OS, SPH, CYL, AXIS, ADD, PD, visual acuity like 6/6, the eye pressure number and “fundus normal”. It also explains why two shops can give you slightly different numbers. Eyesight myths and “nazar tez” totkay are handled elsewhere, in nazar ki kamzori myths and improving eyesight naturally, so they’re not repeated here.

Eye prescription explained, box by box

A typical slip is a small grid. Rows are eyes. Columns are measurements, and sometimes there are separate rows for distance (DV) and near (NV), which is why the same slip can carry two different-looking sets of numbers for one eye.

Dioptres go up in steps of 0.25, so -0.25 is the smallest correction and -0.50, -0.75 and -1.00 follow, and the bigger the number (ignoring the sign), the stronger the lens you need. Simple.

“DS” or “sph” alone, with no CYL, means no meaningful astigmatism. A blank CYL box is normal.

Minus and plus: short sight and long sight

Minus means myopia. Short sight. You see near things clearly while far things, like road signs, the board at school or a friend’s face across a room, go soft and blurry at the edges. Plus is different. Plus means hyperopia, long sight. Young people with small plus numbers often see fine because their eye’s lens focuses hard for them, which can cause tired eyes and headaches after reading.

CYL and AXIS: astigmatism in plain words

A perfect eye is shaped like a football. An eye with astigmatism is a bit more like the back of a spoon. The CYL box says how much, and AXIS says which way, in degrees from 1 to 180. Axis 180 and axis 90 aren’t “worse” or “better”; they’re just directions. That’s why your axis number never goes on its own: without a CYL value, it means nothing.

ADD, PD and near vision

After around 40, the lens inside the eye stiffens and can’t focus up close as well. It’s called presbyopia. Everyone gets it. ADD is the extra plus power for reading, used in reading glasses, bifocals or progressive lenses. PD, the pupillary distance, is measured in millimetres and just helps the optical shop centre the lenses. It says nothing about eye health.

What is considered a high eye prescription?

There isn’t one worldwide cutoff, but eye doctors commonly group short sight roughly like this:

• Mild: up to about -3.00.
• Moderate: about -3.25 to -6.00.
• High: beyond about -6.00 (some groups draw the high line at -5.00).

So what does -0.5 eyesight mean? It’s mild. Many people with -0.50 only notice it at night, for distant signs, or on a whiteboard, and some choose glasses just for driving or class. High myopia isn’t a disease by itself either, but it does carry a higher lifelong chance of retinal problems, which is why high-number wearers are usually advised a regular dilated eye check.

Visual acuity is a different number from your prescription. 6/6 (the metric version of 20/20) means you read at 6 metres what a typical eye reads at 6 metres. 6/12 means you need to be at 6 metres to read what a typical eye reads from 12. Your acuity is often written with your glasses on and off.

Why two opticians give different numbers

Small differences are normal. Usually that’s a quarter step (0.25) in SPH or CYL, or a few degrees in axis. The test partly relies on your answers (“better with one or two?”), and those answers shift with room lighting, how tired you are, how long you stared at a screen that day, dry eyes, and whether the machine reading was taken first. A reading on a headache day, after a late night or during an eye infection, may be off.

A larger change is worth a recheck before you spend money on new glasses, and if your eyes still feel strained, swimmy or headachy after a full week of wearing a new pair, go back to the same shop or clinic and ask them to check both the prescription and how the lenses were fitted, because remakes are common and nobody should mind. Go back. Politely.

Children’s eye numbers: why drops are used

Children focus so strongly that they can “hide” long sight and even fake a bit of short sight during a normal test. That’s why children’s eyes are often tested after cycloplegic drops, which relax focusing for a few hours; the pupils stay large and near vision blurs until they wear off. Children’s numbers also change as they grow, so a yearly check (or as advised) is usual, with more frequent checks if short sight is rising fast.

1. Bring your current glasses and the last written prescription to every test.
2. Avoid testing in the first hour after waking or after 3 to 4 hours of non-stop screen use.
3. Tell the tester about headaches, diabetes, BP, pregnancy or any eye drops you use.
4. For a child’s first test or a dilated check, plan about 1 to 2 hours, and bring sunglasses for the ride home.
5. Don’t drive after dilating drops until your near and distance vision feel normal again.
6. Keep every slip, dated, so the next tester can see the trend.

Eye pressure (IOP) and “fundus normal”

Many eye checks include IOP, intraocular pressure, measured in mmHg with a puff of air or a gentle probe after numbing drops. A typical range is about 10 to 21 mmHg, but your clinic’s range and your doctor’s reading win. A single higher number isn’t glaucoma by itself; eye pressure varies with the time of day and corneal thickness, and glaucoma is judged by the optic nerve and visual field too. The kala motia (glaucoma) testing guide covers who should be checked regularly.

“Fundus normal” means the doctor looked at the back of the eye (retina, optic nerve, blood vessels) through the pupil and saw nothing wrong. It’s often done after dilating drops. “C/D ratio” is part of that check, describing how cupped the optic nerve looks.

Myth: wearing glasses makes your eyes weaker

Glasses don’t change the shape of your eye. People feel their eyes are “worse” without glasses after getting them simply because their brain has quickly got used to seeing clearly again, and the old blur that once felt normal now feels like a step backwards. In children, uncorrected blur can actually hold back how well vision develops, so a child who needs glasses should wear them as advised.

Did you know?

• A dioptre is simply 1 divided by the focal length in metres, so a -2.00 eye sees sharply up to about 50 cm without glasses.
• Time outdoors in daylight is linked with less short sight developing in children.
• The “6/6” chart was designed so each letter at the 6/6 line is sized to a very small angle of view.

Questions to ask your eye doctor

• Is my number mild, moderate or high, and has it changed since last time?
• Do I need glasses all day, only for distance, or only for reading?
• Is my eye pressure normal for me, and when should it be rechecked?
• Did you look at the back of my eye, and was it normal?
• For my child: was this tested with drops, and when is the next check?

More guides on eyes live in Eye Care.

Eye prescription questions people ask