Prism treatment corrects binocular double vision by incorporating a prism into your glasses that shifts the image in the misaligned eye until it lines up with the other, restoring single vision. It begins with a specialist orthoptic and ophthalmic assessment (from £250) to measure the misalignment and identify its cause. Small, stable deviations are corrected with Fresnel or ground-in prisms; larger or changing deviations may need botulinum toxin or squint surgery. Prisms are non-surgical, reversible and can be trialled the same day.
What is double vision (diplopia)?
Diplopia means seeing two images of a single object. Binocular diplopia — the type prisms treat — disappears when either eye is covered, because the problem is that the two eyes are not aligned. Monocular diplopia, which persists in one eye even with the other covered, is caused by something within that eye (such as a cataract or dry eye) and is not treated with prisms.
Binocular double vision has many causes, and a careful assessment is essential to identify which applies to you:
- Decompensating phoria — a long-standing latent eye imbalance that the brain can no longer control
- Cranial nerve palsy — a weakness of one of the nerves that move the eye (fourth, sixth or third nerve)
- Thyroid eye disease — swelling and tethering of the eye muscles
- Adult squint (strabismus) — a manifest turn of one eye
- After trauma or eye-muscle surgery
Sudden, new double vision — especially with headache, drooping eyelid, unequal pupils or weakness — needs urgent assessment to rule out a serious cause. Where the picture suggests a neurological origin, our neuro-ophthalmology service investigates further.
Seeing double? A specialist orthoptic assessment measures the misalignment precisely and pinpoints the cause before any treatment.
Book a diplopia assessmentTreatment options for double vision
The right treatment depends on the size of the misalignment, whether it is stable, and its cause. Prisms are the mainstay for small, steady deviations; larger or evolving ones may need muscle treatment. Your consultant and orthoptist will guide you.
Where the deviation is too large for a prism, or is caused by an underactive muscle, adult squint (strabismus) surgery can realign the eyes. Diplopia from thyroid eye disease is managed as part of that condition, sometimes needing orbital decompression before the squint is corrected. In children, alignment and any associated lazy eye are handled through our paediatric squint service.
How prism treatment works
A prism is a wedge of lens that bends light towards its thicker edge. By placing a prism of the correct strength and orientation in front of the misaligned eye, the incoming image is shifted so that it falls on the same point of both retinas — and the brain fuses the two pictures into one.
- An orthoptist measures the deviation in every direction of gaze, for distance and near, using a cover test and prism bars.
- The consultant ophthalmologist examines your eyes and eye movements to establish the cause and check nothing more serious is present.
- A Fresnel (stick-on) prism of the measured strength is applied to your glasses so you can experience single vision immediately and confirm it works.
- Once the measurement is stable over a few weeks, the prism can be ground permanently into new spectacle lenses.
- If the deviation is too large or unstable for a prism, the team plans botulinum toxin or squint surgery instead.
Adapting to prism glasses
Prisms are not surgery, so there is no recovery period — but there is a short settling-in phase while your eyes and brain adjust.
Same day
A Fresnel prism is fitted in clinic and most people see a single image straight away. A stick-on prism can look slightly blurred or have faint lines — this is normal and improves.
First 1-2 weeks
You adapt to the prism during everyday tasks. The orthoptist may fine-tune the strength if the double vision is not fully corrected in all positions.
Weeks 4-8
Once the measurement is steady, the prism is ground into new glasses for clearer, more durable vision. Some deviations continue to change and need review.
Ongoing
Diplopia from nerve palsies often recovers over months, so the prism may be reduced or removed. Persistent, stable diplopia can be corrected long-term with prisms or, if preferred, surgery.
Cost of diplopia treatment
Treatment begins with a specialist assessment; onward costs depend on which treatment you need.
- Specialist orthoptic & ophthalmic assessment: from £250, including measurement of the deviation and a same-day Fresnel prism trial.
- Prism glasses: the prism is added to a standard spectacle prescription; Fresnel prisms are a low-cost stick-on option.
- Squint surgery / botulinum: where prisms are not suitable — see our adult squint surgery cost guide.
- Insurance: recognised by Bupa, AXA, Aviva, Vitality, Cigna and WPA where diplopia is medically investigated.