How to Read Your Eyeglass Prescription: SPH, CYL, Axis, ADD & PD

Handed a slip of paper covered in abbreviations after an eye test, most people just fold it up and trust the optician to sort out the rest. But once you start ordering glasses online, understanding your own prescription becomes genuinely useful — it helps you catch data-entry mistakes, compare lens options, and know what your eyes actually need. Here is a plain-language breakdown of every number you will see.

SPH — the sphere power

SPH tells you the main strength of correction your eye needs, measured in diopters. A minus number (like -2.50) means you are nearsighted (myopic) and have trouble seeing distant objects clearly. A plus number (like +1.75) means you are farsighted (hyperopic) and may struggle more with close-up focus. The higher the number, ignoring the sign, the stronger the correction.

CYL and axis — for astigmatism

If your eye's cornea is slightly oval rather than perfectly round, you have astigmatism, which is recorded as a CYL (cylinder) value. This number, always paired with an axis reading between 0 and 180 degrees, tells the lab exactly which direction the extra correction needs to be oriented on the lens. If your prescription has no CYL or axis listed, it simply means you have little to no astigmatism.

Why axis matters so much

A CYL value with the wrong axis is almost as unhelpful as no CYL correction at all — even a 10-15 degree error can cause noticeable blur or eye strain. This is one reason it is worth double-checking these fields carefully when entering your prescription online.

ADD — for reading and near vision

ADD power appears on prescriptions for people over roughly 40 who need extra magnification for close-up tasks, a natural age-related change called presbyopia. It is always a plus number and is added on top of your distance prescription in bifocal or progressive lenses. If you are new to this part of your prescription, our guide on single vision vs bifocal vs progressive lenses explains how ADD power is actually used in each lens type.

PD — pupillary distance

PD is the distance in millimeters between the centers of your two pupils, and it is arguably the most commonly missing number on prescriptions from routine eye exams, since it matters more for lens fabrication than for diagnosing your vision. Getting PD right ensures the optical center of each lens lines up with your eye, which matters more as your prescription strength increases. If your prescription does not include it, see our guide on measuring PD at home.

Putting it all together: reading a sample prescription

• OD refers to your right eye, OS to your left eye
• A line like "OD: -3.00 -0.75 x 90" means -3.00 SPH, -0.75 CYL, at a 90-degree axis
• "ADD +2.00" means an extra +2.00 diopters of near-vision correction, on top of the distance prescription
• "PD: 62" means your pupils are 62mm apart total (sometimes split as 31/31 for each eye)

Why getting this right matters when buying online

Whether you are picking men's eyeglasses, women's eyeglasses, or a lightweight rimless frame, the frame is only half the equation — the lens has to be cut precisely to your prescription and PD to give you clear, comfortable vision. Our full walkthrough on buying prescription eyeglasses online in Pakistan covers the ordering process end to end.

If any abbreviation on your slip still looks unfamiliar after reading this, Eyeglass.pk's support team can walk through it with you before your order is processed, so nothing gets misread at checkout.

Other notes you might see on a prescription

Some prescriptions also list a "prism" value, used to correct specific alignment issues between the two eyes, and an expiry date, since eye prescriptions are generally considered valid for one to two years. The NHS notes that regular eye tests are important even without noticeable symptoms, since some changes in vision happen gradually enough to go unnoticed without a formal check. If your prescription includes a prism value or looks unusually complex, it is worth asking your optometrist to walk through it directly rather than guessing from a general guide.

Double-checking your entries before you order

A simple way to avoid mistakes is to read every field back from your printed prescription slip rather than from memory, and to enter the right values under the right eye — OD for right, OS for left — since transposing them is one of the most common ordering errors. Taking an extra thirty seconds to compare your typed entries against the original slip before submitting an order is a small habit that prevents a frustrating and avoidable remake.

Frequently asked questions

What does a negative SPH number mean?

A negative SPH value means you are nearsighted, and the further from zero the number is, the stronger your prescription. For example, -5.00 is a considerably stronger correction than -1.25.

Do I always need a CYL and axis value?

No — many people have little to no astigmatism, in which case these fields are left blank or shown as zero. Only enter a CYL and axis if your prescription slip explicitly lists them.

Can I order glasses without a PD listed on my prescription?

Yes, PD is not always included by default, and many opticians will give it to you on request or you can measure it yourself accurately at home. According to the American Optometric Association, PD is a standard measurement any eye care provider can supply during a routine exam.