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Patient Resource

How to Read Your
Glasses Prescription

Your prescription belongs to you. Under UK law you are legally entitled to a copy after every eye test — and you can take it to any registered optician you choose. This guide explains what every number means so you can read and understand your prescription with confidence.

Your prescription, your choice. It is illegal for any optician to withhold your prescription or charge you for it. Once you have had your eye test, you are free to take your prescription to any registered optical practice — including us.

Section 01

The Prescription at a Glance

A standard optical prescription is a grid with one row for each eye and a column for every measurement your optometrist took. Here is a realistic example — hover each column header to understand what it means.

Optical Prescription

Example — Eye Love Frames, Saltash

Patient: Jane Smith  ·  DOB: 01/01/1979
Date: 03/06/2026  ·  Valid until: 02/06/2028
Optometrist: Stewart Iddon MCOptom
Eye SPH 1 CYL 2 AXIS 3 ADD 4 PRISM 5 VA 6
R (OD) –2.75 –0.50 175 +1.25 — 6/6
L (OS) –3.00 –0.75 170 +1.25 — 6/9
PD 7   R 32mm / L 31.5mm (distance)
BVD 8   Not required at this power
1
SPH — Sphere The main lens power. Minus (–) means short-sighted; plus (+) means long-sighted. In steps of 0.25.
2
CYL — Cylinder Corrects astigmatism — the uneven curvature of your cornea. Blank or "DS" means none.
3
AXIS The angle (1–180°) of the astigmatism correction. Only meaningful when CYL has a value.
4
ADD — Addition Extra near power for varifocal or reading lenses. Appears once presbyopia develops, usually from your mid-40s.
5
PRISM A correction for eye-alignment issues. Only present in a small number of prescriptions — a dash (—) means none.
6
VA — Visual Acuity How sharp your corrected vision is. 6/6 is standard; 6/9 is slightly reduced. Not needed to order glasses.
7
PD — Pupillary Distance The distance between your pupils in mm. Essential for centring the lens correctly in your frame.
8
BVD — Back Vertex Distance The gap between the lens and your cornea. Only recorded for strong prescriptions (typically above ±4.00D).

Section 02

Every Field Explained

Select any field to see a full explanation with real-world examples and what the values mean for your vision.

SPH Sphere — your primary lens power

SPH is the core refractive power your eye needs, measured in dioptres (D) in steps of 0.25D. The sign tells you everything about the type of vision error being corrected.

Minus (–) = short-sighted (myopia). Your eye is slightly too long, so light focuses in front of the retina rather than on it. You can see close-up clearly but distance vision is blurred. The higher the minus number, the more correction you need.

Plus (+) = long-sighted (hyperopia). Your eye is slightly too short, so light focuses behind the retina. You may struggle at all distances, particularly close-up, and often experience headaches or eyestrain from prolonged near work.

Plano (Pl or 0.00) means no spherical correction is needed in that eye.

–0.50
Very mild myopia
–2.75
Moderate myopia
–6.00
High myopia
+1.25
Mild hyperopia
+3.50
Moderate hyperopia
CYL Cylinder — astigmatism correction

Astigmatism means your cornea or lens is slightly curved like a rugby ball rather than a perfect sphere — so light doesn't focus to a single point, creating blurred or distorted vision at all distances.

CYL is the additional power needed on top of SPH to correct this. In the UK, most prescriptions are written in minus cylinder form. If CYL is blank, or the prescription reads "DS" (Dioptres Sphere), you have no significant astigmatism.

–0.50
Mild astigmatism
–1.25
Moderate
–2.75
Significant
DS
No astigmatism
AXIS Axis — direction of astigmatism

AXIS tells the lens manufacturer which way to orient the CYL correction — it's the angle, in degrees from 1 to 180, that describes the direction of the astigmatism in your cornea. It only has meaning when CYL has a value.

The number itself does not indicate severity — AXIS 180 is not "worse" than AXIS 45. It simply describes orientation, like a compass bearing for your prescription.

180
Horizontal (common in younger patients)
90
Vertical (more common with age)
45 / 135
Oblique — can take longer to adapt to
ADD Addition — near vision power (varifocals & reading)

ADD is extra magnifying power added to your distance prescription to enable comfortable near vision. It corrects presbyopia — the age-related gradual loss of the eye's ability to change focus between distances, which typically becomes noticeable from the mid-40s onward.

The ADD value is always positive and is usually the same for both eyes. It tells your optician whether to make reading glasses, bifocals, or varifocal (progressive) lenses.

+0.75
Early presbyopia — mid 40s
+1.50
Moderate — late 40s/early 50s
+2.50
Established — mid 50s to 60s
+3.50
Maximum typical ADD — 65+
If your prescription includes an ADD, you are in the varifocal or reading glasses zone. Stewart will always discuss your lifestyle and daily tasks to recommend the most appropriate lens type for your prescription.
PRISM Prism — eye-alignment correction

Prism is used in a small number of prescriptions — most prescriptions show a dash (—) here. When it does appear, it corrects misalignment between your two eyes (binocular vision problems), which can cause double vision, persistent eyestrain, or headaches even with an otherwise correct prescription.

Prism is measured in prism dioptres (Δ) and comes with a BASE direction — where the thick edge of the wedge-shaped element is positioned: BU (base up), BD (base down), BI (base in, towards the nose), or BO (base out).

1.5Δ BI
1.5 prism dioptres, base in
0.5Δ BU
Small vertical correction
PD Pupillary Distance — lens centration measurement

PD is the distance in millimetres between the centres of your pupils. It is essential for placing the optical centre of each lens directly in front of your pupil — the wrong PD causes eyestrain and blurred vision even with a perfect prescription.

Binocular PD is a single total measurement (e.g. 64mm). Monocular PD measures each eye separately from the nose bridge centre (e.g. R 32 / L 31.5) — slightly more accurate, and important for strong prescriptions and varifocals. Facial asymmetry is common; it's perfectly normal for R and L to differ.

Section 03

Common Questions

The questions we hear most often at the dispensing table — answered plainly.

Does a bigger minus number mean my eyesight is getting worse?
Not necessarily worse — it means more correction is needed. Prescriptions naturally fluctuate, particularly in younger people, and a small change from one test to the next is entirely normal. Only a consistent, progressive increase year-on-year is clinically significant and warrants monitoring. Your optometrist will flag any concerning trend.
My left eye says Plano and DS — do I still need a lens in it?
Yes, almost always. Plano means zero spherical correction; DS (Dioptres Sphere) means no cylindrical correction. Even with no refractive power, most frames are fitted with a lens in both sides for protection, cosmetic balance, and to accommodate any coatings you've chosen such as anti-reflection or UV protection.
Can I use my glasses prescription to order contact lenses online?
No. Contact lens prescriptions are separate documents that include additional measurements — base curve, diameter, and the specific lens brand — not present on a glasses prescription. For stronger prescriptions, the power values also differ due to the different working distance. You need a valid, signed contact lens prescription to order lenses legally and safely.
What does it mean if my prescription has no AXIS value?
AXIS only appears when there is a CYL value — it describes the orientation of the astigmatism correction. If your CYL column is blank or shows DS, there is no astigmatism to correct and no AXIS is needed. This is completely normal and does not indicate a problem.
I have +1.00 for distance — why do I also need reading glasses?
Mild long-sightedness (hyperopia) in younger patients is often automatically compensated by the eye's internal focusing muscle (accommodation). As presbyopia develops through your 40s and 50s, this compensation reduces — so the distance prescription that your eye was previously correcting for itself now becomes noticeable, and a reading or varifocal prescription becomes necessary.
Can I take my prescription to any optician, or do I have to buy from where I was tested?
You can take it anywhere. Under the Opticians Act 1989, you are legally entitled to your prescription and free to use it at any registered dispensing optician or optometrist of your choice. No practice can require you to buy from them. Your NHS voucher (if applicable) can also be used at any GOS-registered practice — including us at Eye Love Frames.
What is a strong prescription — is mine strong?
There is no single threshold, but optometrists generally consider prescriptions above ±4.00D sphere or above ±2.00D cylinder to be at the higher end. Strong prescriptions benefit significantly from thinner, lighter high-index lens materials — typically index 1.6, 1.67, or 1.74 — which our team will discuss with you based on your exact values and preferred frame style.
My prescription expired last month — can I still use it?
Unfortunately not — it is a legal requirement that registered opticians cannot dispense glasses against an expired prescription. The good news is that booking a new eye test is straightforward, and with an up-to-date prescription you can have new glasses ready the same day for standard single vision lenses. Get in touch and we can arrange an appointment quickly.
My PD isn't on my prescription — can I still order glasses?
Yes — at Eye Love Frames, we measure PD as part of every dispensing appointment. If it is not on your written prescription, we will measure it ourselves before ordering your lenses. You are also entitled to go back to the practice that tested you and ask for your PD — they must provide it if it was measured during the examination.
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