Contact Lens vs Glasses Prescription in the UK: Everything You Need to Know

Tried ordering contact lenses with your glasses prescription and got rejected? You're not alone. Your glasses prescription won't work for contact lenses. This guide explains why prescriptions differ, how to read each type, and what you need to know about UK regulations.

The Quick Answer: No, Your Prescriptions Are Different

Is contact lens prescription same as glasses? No, contact lens prescriptions and glasses prescriptions are fundamentally different. Contact lenses sit directly on your eye whilst glasses sit about 12mm away. This distance difference called vertex distance, means the power needed changes depending on where the lens is positioned. Additionally, contact lens prescriptions include measurements glasses prescriptions don't require, such as base curve and diameter.

Key Differences at a Glance

Can you use glasses prescription for contacts? No, using your glasses prescription for contact lenses results in incorrect vision correction, discomfort, and potential eye health issues.

>>> See more: How to Convert Your Glasses Prescription to Contact Lenses: Simple Conversion Guide

Why Contact Lens Prescriptions Are Different from Glasses

The Science: Vertex Distance Explained

The primary reason is contact lens prescription the same as glasses receives a "no" answer is vertex distance, the space between your eye and the corrective lens.

Glasses sit approximately 12mm in front of your cornea, whilst contact lenses rest directly on your eye's surface. Think of it like standing closer to a dartboard—the angle you need to aim changes based on where you're standing.

When vertex distance matters most: For prescriptions over ±4.00 dioptres, adjustments become significant. A -6.00 glasses prescription might require only -5.50 in contact lenses. For prescriptions under ±4.00, the adjustment is minimal but still important.

Contact Lens-Specific Measurements

• Is a contact lens prescription the same as glasses in terms of measurements? No. Contact lens prescriptions include:

• Base Curve (BC): Typically 8.3mm to 9.0mm, describing the lens back surface curvature. It must match your corneal curvature for proper fit.

• Diameter (DIA): Typically 13.8mm to 14.5mm, determining how much of your eye the lens covers. This affects comfort, stability, and oxygen transmission.

• Brand variations: Different brands use different materials and designs. Your optician specifies a brand because switching freely between brands isn't always safe, different brands may fit your eyes differently.

>>> See more: Understanding Base Curve and Diameter in Contact Lenses: A Complete Guide

Higher Prescriptions Need More Adjustment

Conversion examples:

• Glasses -2.00 → Contacts approximately -2.00 (minimal difference)

• Glasses -6.00 → Contacts approximately -5.50

• Glasses -10.00 → Contacts approximately -9.00

Important: These are estimates only. Never attempt to calculate your own contact lens prescription always see a qualified optician.

How to Read Your Prescription

Understanding Glasses Prescription Format

A typical glasses prescription includes:

• SPH (Sphere): Main corrective power. Example: -2.50 or +1.75

• CYL (Cylinder): Astigmatism correction, if needed. Example: -0.75

• Axis: Angle of astigmatism correction, 0-180 degrees. Example: 85

• ADD: Additional power for reading in bifocals. Example: +2.00

• PD (Pupillary Distance): Distance between pupils. Example: 63mm

Decoding Contact Lens Prescription Format

Is my contact lens prescription same as glasses in format? No—contact lens prescriptions include everything above (except PD) plus:

• Base Curve (BC): Example: 8.6mm. Critical for proper fit

• Diameter (DIA): Example: 14.2mm. Determines lens size

• Brand/Type: Example: "Acuvue Oasys." Often specified because parameters vary

• Expiry date: Typically valid for 2 years

>>> See more: Can You Buy Non Prescription Contacts?

UK Prescription Requirements

In the UK, contact lens prescriptions are generally valid for 2 years from examination date in England and Scotland. However, opticians may recommend annual check-ups to monitor eye health.

NHS vs private: If you're entitled to NHS sight tests (under 16, under 19 in education, over 60, pregnant, diabetic, glaucoma risk, or receiving certain benefits), your initial eye test is free. However, contact lens fittings often incur additional charges (£25-£60), as fitting is considered a separate service.

When You Can (and Can't) Use Your Glasses Prescription

Situations Where It's NOT Possible

• No current glasses prescription: Expired prescriptions cannot be used

• Astigmatism: Requires toric contact lenses with precise measurements

• First-time contact lens wearer: Fitting is legally and medically required

• Prescription over ±4.00D: Significant vertex distance adjustments needed

The Contact Lens Fitting Process

Is your contact lens prescription the same as glasses after a fitting? No—the fitting produces a completely separate prescription.

What happens:

1. Initial consultation: Lifestyle discussion and medical history review

2. Eye measurements: Corneal curvature, tear film, and eye health assessment

3. Trial lens fitting: Test sample lenses for fit, comfort, and vision

4. Training: Learn insertion, removal, and care routines

5. Follow-up: Trial lenses for home wear, check-up in 1-2 weeks

Duration: 45-60 minutes for first-time fittings Cost: £25-£60 at chain opticians, £40-£80 at independent practices

>>> See more: How to Select Your Contact Lens Material Based on Prescription?

Online Contact Lens Shopping in the UK

UK law requires online retailers to verify prescriptions before dispensing lenses. Reputable suppliers include Feel Good Contacts, Lenstore, Vision Direct, and high street optician websites.

What you'll need:

• Full contact lens prescription details (SPH, CYL, Axis, BC, DIA, brand)

• Your optician's contact details for verification

• Confirmation prescription is current

Red flags for dodgy suppliers:

• No prescription verification required

• Offering to "convert" your glasses prescription

• Not registered with the General Optical Council (GOC)

Contact lens prescriptions require vertex distance adjustments and include base curve and diameter measurements that glasses prescriptions don't have. In the UK, contact lens fittings cost £25-£80, prescriptions are valid for 2 years, and you cannot use your glasses prescription to order contact lenses. Always get a proper fitting from a qualified optician.

Common Questions Answered

1. Can I order contact lenses using my glasses prescription?

No. Contact lens and glasses prescriptions are different. Contact lens prescriptions include specific measurements such as base curve and diameter, as well as adjusted power. Using a glasses prescription can lead to rejected orders or unsafe lens fit.

2. Why do I need a separate contact lens eye test?

Because contact lenses sit directly on the eye. The test measures corneal shape, eye health, and tear quality, and determines the correct lens type, fit, and power for your eyes.

3. How much does a contact lens eye test cost in the UK?

Typically £25–£60 at chain opticians and £40–£80 at independent practices, in addition to a standard eye test. Many opticians offer combined packages.

4. Can I wear contact lenses if I have astigmatism?

Yes. Toric contact lenses correct astigmatism and require precise fitting to align properly with your eye.

5. What if my prescription is old?

If it is over two years old, you need a new eye test before ordering lenses, even if your vision seems unchanged.

6. Do I need a new test to switch contact lens brands?

Ideally, yes. Different brands vary in design and material, and the same prescription may not fit the same across brands.

7. Can I get contact lenses on the NHS?

Eye tests may be free if you are NHS-entitled, but contact lens fittings usually involve extra costs. Free lenses are only provided in specific medical cases.

8. How often should I update my contact lens prescription?

Prescriptions are legally valid for two years, but annual check-ups are recommended to monitor eye health and lens fit.