Glasses by need
High Prescription Lenses
Strong prescriptions require specialist lenses — custom surfaced to your exact values. Available in all four indexes, with 1.67 and 1.74 recommended for the thinnest, lightest result.
What counts as high
Is your prescription high?
High prescription thresholds are based on your SPH and CYL values. If either value exceeds these thresholds, your prescription is considered high — and some options differ as a result.
High prescription — applies if:
SPH
Above +4.00 or below -4.00
SPH
Above +2.50 or below -2.50
Standard prescription — applies if:
SPH
Between -4.00 and +4.00
SPH
Between -2.50 and +2.50
What this means for your order
How high prescriptions affect different lens types
The impact of a high prescription varies depending on the lens type you choose. Single vision lenses are the only type affected.
Affected
Single vision
Standard single vision lenses are made from stock blanks covering common prescription ranges. High prescriptions fall outside this range and require a custom surfaced lens.
High prescription single vision lenses are sent to a specialist lab for custom surfacing before being returned and glazed into your frame. This adds approximately 5–7 working days to the lead time and an additional cost to the order.
Not affected
Varifocal
All varifocal lenses — across all packages including Occupational Office — are already custom surfaced lenses as standard. A high prescription does not change the lead time or add any extra cost.
Standard lead times and pricing apply regardless of prescription strength for all varifocal lens types.
Not affected
Bifocal
All bifocal lenses are also custom surfaced as standard. A high prescription does not affect the lead time or cost of bifocal orders.
Standard lead times and pricing apply regardless of prescription strength for all bifocal lens types.
Why surfacing is needed
What is a surfaced lens?
Stock lenses vs surfaced lenses
Standard single vision lenses are made from pre-manufactured stock blanks produced in common prescription ranges. For prescriptions within a standard range, the correct blank is selected, cut and glazed to fit the frame. High prescriptions fall outside the range of available stock blanks and must be custom ground from scratch.
What surfacing involves
Surfacing is the process of precision grinding the back surface of a lens blank to the exact curvature required by your prescription. For high prescriptions, this is performed by a specialist optical lab. The finished lens is returned and then glazed into your chosen frame. The result is a lens made precisely to your values rather than approximated from a stock range.
Why it takes longer and costs more
Surfaced lenses are sent to a specialist lab for custom grinding before being returned. This additional step adds approximately 5–7 working days to the standard single vision lead time. The extra cost reflects the specialist manufacturing involved. Varifocal and bifocal lenses are always surfaced — which is why they already have longer lead times than standard single vision.
Lens index
All four indexes available — thinner is better for high prescriptions
High prescription lenses are available in all four indexes. A higher index produces a significantly thinner, lighter lens — the difference is most noticeable at strong prescription values. We recommend 1.67 or 1.74 for the best result, but the choice is always yours.
Note: 1.74 index is not available for bifocal lenses. For bifocal with prescriptions above ±6.00, varifocal in 1.74 is the recommended alternative.
How to order
Ordering with a high prescription
1
Choose a frame
Browse our full range from £10. For high prescriptions, smaller and rounder frames tend to produce a thinner edge profile — but any frame can be fitted.
2
Select your lens type and index
All four indexes are available across all lens types. For single vision with a high prescription, we recommend 1.67 or 1.74 for the thinnest result — but you can choose any index.
3
Enter your prescription
Enter your full prescription values at checkout. High prescription single vision lenses require custom surfacing — allow an additional 5–7 working days beyond the standard lead time.
Ready to order your high prescription lenses?
All prescription strengths accepted. Available in all four indexes across single vision, varifocal and bifocal. Frames from £10. Varifocal and bifocal lead times unaffected by prescription strength.
FAQ
Frequently asked questions
How do I know if my prescription is high?
Your prescription is considered high if your SPH value is above +4.00 or below -4.00, or if your CYL value is above +2.50 or below -2.50. Either value alone is sufficient — you do not need both to exceed the threshold. Check your prescription card from your optician for these values.Why do high prescription single vision lenses cost more and take longer?
Standard single vision lenses are made from stock blanks covering common prescription ranges. High prescriptions fall outside this range and require the lens to be custom ground — a process called surfacing — by a specialist optical lab. This custom manufacturing adds both cost and time to the order. Varifocal and bifocal lenses are always surfaced, which is why high prescriptions do not add extra time or cost to those lens types.Do high prescriptions affect varifocal or bifocal orders?
No. All varifocal and bifocal lenses are custom surfaced as standard regardless of prescription strength. A high prescription does not add extra time or cost to a varifocal or bifocal order — lead times and pricing are the same as for any other prescription strength.Which lens index should I choose for a high prescription?
High prescription lenses are available in all four indexes — 1.50, 1.60, 1.67 and 1.74. We recommend 1.67 for prescriptions between ±4.00 and ±6.00, and 1.74 for prescriptions above ±6.00. Both include anti-reflective (MAR) coating as standard. Lower indexes are available but produce a noticeably thicker, heavier lens at high prescription values — a higher index makes a significant difference to both appearance and comfort.Does frame size matter with a high prescription?
Yes. Smaller frames produce a shorter distance from the optical centre to the edge of the lens — meaning less material at the edge and a thinner overall profile. Rounder frame shapes also tend to give better results than wide rectangular frames for strong prescriptions. Combining a smaller or rounder frame with a 1.67 or 1.74 index gives the best possible result for high prescriptions.
