How to Read Your Glasses Prescription

Q: What does BVD mean on my prescription?

Back Vertex Distance, the distance from the back of the lens to your eye. It’s only relevant for very strong prescriptions (typically ±5.00 or higher).

How to Read Your Glasses Prescription

Reading your prescription correctly is the difference between glasses that feel right and glasses that don’t. This guide explains every value on a UK prescription in plain English, so you can copy them into our checkout with confidence.

If you’re missing your prescription, ask your optician for a copy — by law in the UK, they must give you one after your sight test.

Anatomy of a prescription

A typical UK prescription has two rows (one for each eye) and several columns. Each row begins with R or OD (right eye) and L or OS (left eye).

Abbreviation	Stands for	What it means
R / OD	Oculus Dexter	Right eye
L / OS	Oculus Sinister	Left eye
SPH	Sphere	Lens power for short- or long-sightedness. Negative (–) for short-sighted, positive (+) for long-sighted.
CYL	Cylinder	Correction for astigmatism. May be blank or zero if you don’t have any.
AXIS	Axis	Direction of the cylinder correction, given in degrees from 1–180. Required if CYL has a value.
ADD	Reading addition	Extra plus power for reading or varifocal lenses. Always positive (+).
PRISM	Prism	Correction for eye alignment. Most prescriptions don’t have this.
BASE	Base direction	Direction of the prism: Up, Down, In, or Out. Required if PRISM has a value.
PD	Pupillary Distance	Distance between your pupils in millimetres. Needed for every order.

Worked example

Suppose your prescription reads:

R   –2.50   –0.75  x 180   PD 63
L   –2.25   –0.50  x 175

This means:

Right eye: short-sighted by –2.50, with a small astigmatism correction of –0.75 at axis 180°
Left eye: short-sighted by –2.25, astigmatism –0.50 at axis 175°
Pupillary distance: 63 mm

Common mistakes to avoid

Mixing up + and – signs — the difference between +2.50 and –2.50 is the difference between reading glasses and short-sight glasses. Double-check.
Missing the AXIS value — if there’s a CYL value, the AXIS must be entered too. Without it the lens cannot be made.
Decimal vs fraction — always use the decimal form (e.g. 0.25, not ¼).
Wrong eye — enter the right-eye values into the right-eye field. Reversing them gives you blur in both eyes.
Including the ADD on a single-vision lens — the ADD only applies to reading glasses or varifocals. Don’t add it to a distance prescription.

Frequently asked questions

How long is my prescription valid?

UK opticians recommend a sight test every two years for most adults. We accept prescriptions up to two years old for online orders.

What if my prescription only has a single PD value?

That’s your binocular PD — fine for single-vision lenses. For varifocals, ask your optician for a dual PD.

What does “BVD” mean on my prescription?

Back Vertex Distance — the distance from the back of the lens to your eye. It’s only relevant for very strong prescriptions (typically ±5.00 or higher) and most lens designs assume a standard 12 mm.

My prescription has 6/6 written on it. What’s that?

That’s your visual acuity score (the UK equivalent of 20/20). It tells you how clearly you see when corrected — it’s not used to make your lenses.

Can I order glasses with someone else’s prescription?

No. Lenses are made to your specific eyes. Ordering with the wrong prescription will give you headaches and eye strain at minimum.

Still unsure? Send us a photo of your prescription via our contact form and we’ll check it for you before you order.