Prescription Glasses and Lenses: What to Know Before Ordering

The slip you are handed after an eye test looks like code. Two rows, five or six columns, a string of plus and minus numbers, and no explanation. Yet those numbers decide everything about the pair you end up wearing. Understanding prescription glasses and lenses starts with being able to read that slip, because it tells you which lens designs are open to you and which frames will work. This guide from the Lawrence & Mayo luxury eyewear boutique decodes the prescription, then walks through what happens between the test and collection.

What You Will Learn

• What every abbreviation on your prescription means
• Which measurements are missing from the slip and why they matter
• What happens between ordering and collection
• How to check a new pair before you accept it

Prescription Glasses and Lenses: How to Read Your Prescription

According to the American Academy of Ophthalmology’s page on astigmatism, the condition is caused by an irregularly curved cornea or lens rather than any disease, which is why so many ordinary prescriptions carry a cylinder and axis value alongside the sphere. Those two columns confuse people more than any others.

Here is what each abbreviation means. The values run in increments of 0.25 dioptres, so small differences are real differences.

Term	What it means	What it affects
OD and OS	Right eye and left eye	Which lens gets which power
SPH (sphere)	Main power; minus for short sight, plus for long sight	Lens thickness and index choice
CYL (cylinder)	Power correcting astigmatism	Edge thickness in one direction
AXIS	Orientation of that correction, 1 to 180 degrees	How the lens must be oriented in the frame
ADD	Extra reading power for presbyopia	Whether you need bifocal or progressive lenses
PRISM	Correction for eye alignment	Lens thickness and which designs are possible

A worked example helps. A prescription reading OD -2.50 / -0.75 x 180 means the right eye needs 2.50 dioptres of short-sight correction plus a further 0.75 of astigmatic correction, oriented horizontally. The same eye with no entry in the cylinder column would need a simpler, thinner lens for the same sphere power.

An ADD value is the clearest signal that single vision will no longer cover your day. Our precision lens range covers progressive, bifocal and office designs, and our team can confirm which suits your numbers.

The Measurements That Are Not on the Slip

A prescription is only half the information a lab needs. The rest is taken on your face, in the frame you have chosen, and it cannot be copied from an old pair.

• Pupillary distance: the distance between your pupils in millimetres. It places the optical centre of each lens in front of each pupil. An error here introduces unwanted prism and eye strain.
• Fitting height: where your pupil sits vertically within the lens shape. Critical for progressives, where a few millimetres moves the whole corridor.
• Vertex distance: how far the lens sits from your eye. It changes the effective power on strong prescriptions.
• Pantoscopic tilt and wrap: the angle at which the frame sits. Steep angles need the lens to be compensated.

This is the reason the same prescription can produce two very different pairs. It is also why choosing a frame and taking measurements belong in the same visit, with the frame on your face. Browse our designer frames collection first, then have the measurements taken in the frame you have settled on.

What Happens Between Ordering and Collection

Once the order leaves the boutique, your lenses go through a fixed sequence. Knowing it helps you understand timelines and why some orders take longer.

• Surfacing: the back of the lens blank is ground to your exact power. Free-form designs are cut digitally at this stage.
• Coating: hard coat and anti-reflective layers are applied under vacuum. This step cannot be rushed without affecting adhesion.
• Edging: the lens is cut to the frame shape, then grooved, drilled or bevelled depending on the rim type.
• Glazing and checking: the lens is fitted and verified against the prescription before dispensing.

Two things commonly add days. A remake, where the first lens fails verification and has to be surfaced again, and a specialist tint, which is applied in batches rather than individually. Neither is a sign of a problem; both are better caught in the lab than on your face.

Simple single vision orders are usually quickest. Progressive, high-index, prism and specialist tints take longer because they are made to order rather than from stock. Timelines vary by prescription and lens type, so ask our team for a realistic date rather than assuming.

What Most People Overlook

We have found that very few people check a new pair properly at collection. Look straight ahead and confirm distance vision is clear, then read something at your usual reading distance, then walk a few steps and watch the floor. Customers most often ask us why a new pair feels fine indoors but odd on stairs, and the usual answer is fitting height or pantoscopic tilt rather than the prescription itself, both of which are adjustable. Remember also that a prescription is dated. Anything older than two years should be rechecked before you order, because you may be paying to correct eyes you no longer have.

How We Help You Get the Right Pair

Our optometrists begin with the Enhanced Precision Eye Test, which measures your vision, your working distances and how your eyes work together, then explain every number on your prescription before you choose anything. Frames from across our luxury eyewear brands are matched to your power, and all measurements are taken on your face in the chosen frame. Adjustments, fit checks and cleaning are included afterwards for as long as you wear the pair.

Verdict

Prescription glasses and lenses come together from two sources: the numbers on your slip and the measurements taken on your face. Learn to read the first, insist the second are done properly, and check the finished pair before you accept it. Book your eye test at the Lawrence & Mayo boutique and have your prescription explained in full.

FAQ

What should I know about prescription glasses and lenses before ordering?

Know what each value on your prescription means, make sure the fitting measurements are taken in your chosen frame, and check the finished pair before accepting it.

What do OD and OS mean on a prescription?

OD is the right eye and OS is the left eye, from the Latin oculus dexter and oculus sinister. OU occasionally appears and means both eyes.

What does the SPH value mean?

Sphere is the main lens power in dioptres. A minus value corrects short sight and a plus value corrects long sight.

What do CYL and AXIS correct?

Together they correct astigmatism. Cylinder is the amount of correction, and axis is the orientation in degrees that tells the lab where to place it.

What does ADD mean on a prescription?

Add is extra magnifying power for near vision, used in bifocal, progressive and reading lenses. It usually appears once presbyopia develops after about 40.

Is a higher prescription number worse for eye health?

Not in itself. A higher number means a stronger correction is needed, which is separate from whether the eye is healthy.

Why is pupillary distance measured separately?

It aligns the optical centre of each lens with each pupil. Without it, the lens introduces unwanted prism that causes strain and discomfort.

How long is a glasses prescription valid?

Most are treated as current for up to two years. Have it rechecked sooner if your vision changes or you notice strain or headaches.

Is a glasses prescription the same as a contact lens one?

No. Contact lenses sit directly on the eye, so the power differs and the prescription also needs base curve and diameter values.

What does plano or PL mean?

It means no spherical correction is needed for that eye, though cylinder, add or prism values may still apply.

How long do new lenses take to make?

Simple single vision orders are fastest. Progressive, high-index, prism and specially tinted lenses are made to order and take longer.

Why do new glasses sometimes feel odd on stairs?

Usually fitting height or frame tilt rather than the prescription. Both can be adjusted, so return the pair rather than persevering.

How should I check a new pair at collection?

Check distance vision looking straight ahead, read at your normal reading distance, then walk a few steps and watch the floor for distortion.

Can I see demonstration lenses before ordering?

Yes. You can compare indices, coatings and designs at the boutique so you understand what each option changes before you commit.

How do I book an eye test at Lawrence & Mayo?

Book an Enhanced Precision Eye Test at any boutique and an optometrist will explain every value on your prescription and recommend suitable lenses.