Refractive and corneal imaging · London
Astigmatism assessment, refraction, keratometry and corneal topography for astigmatism.
Astigmatism means the cornea or the lens inside the eye is not perfectly round. It is very common. Assessment combines refraction, keratometry, and corneal topography. The results steer the plan — glasses, contact lenses, or refractive surgery.
Why patients choose us
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The right hands
We route you to a consultant ophthalmologist or accredited optometrist — the person doing your topography is the person deciding the plan.
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Same-week answer
Refraction, keratometry, topography and a written report typically completed inside a week.
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Independent, and free
We are paid by no clinic, so the recommendation is impartial and costs you nothing.
Key facts
The six things worth knowing about astigmatism assessment.
What the pathway is, what it settles, and the tests that anchor a modern refractive plan.
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Definition
The cornea or the lens is shaped more like a rugby ball than a football. Light lands unevenly on the retina, and vision blurs.
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Regular vs irregular
Regular astigmatism is correctable with glasses or toric lenses; irregular astigmatism usually needs rigid contact lenses or surgery.
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Topography is gold-standard
Corneal topography (Pentacam / Scheimpflug) is the gold-standard for planning refractive or cataract surgery.
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Keratometry measures curvature
K readings quantify anterior corneal curvature and axis, and anchor toric IOL calculations.
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Keratoconus screen
The pathway screens for keratoconus — irregular corneal thinning that changes the treatment plan entirely.
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Guides toric IOL and surgery
The dataset guides toric IOL selection, toric contact-lens fitting and laser refractive-surgery planning.
The diagnostic pathway
From refraction to topography — what happens, in order.
One clinician from first message to plan — typically inside a week.
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Detailed refraction
Autorefraction followed by subjective refraction to establish sphere, cylinder and axis.
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Keratometry (K readings)
Quantifies anterior corneal curvature and steep / flat meridian axis.
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Corneal topography (Pentacam)
Scheimpflug tomography maps anterior and posterior cornea, and corneal thickness across the whole surface.
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Slit-lamp examination
Rules out corneal scarring, dry eye, cataract or other structural contributors to blur.
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Rule out keratoconus
Posterior elevation, thinnest-point pachymetry and Belin/Ambrósio indices are reviewed to exclude keratoconus.
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Anterior-segment OCT (selective)
Used when epithelial mapping or corneal-layer detail is needed to explain irregular astigmatism.
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Structured optometry / ophthalmology report
A written report with refraction, K readings, topography maps and a concrete next step.
Typical end-to-end: 5–7 days. Urgent cases: same week.
What it shows
What the assessment can — and cannot — settle.
The combined refraction, keratometry and topography pathway characterises the astigmatism and flags the ectatic disease that changes the plan.
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Total astigmatism magnitude
The overall dioptric power of the cylinder — how much astigmatism you have.
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Corneal vs lenticular contribution
Distinguishes astigmatism from the cornea from that arising in the crystalline lens.
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Regular vs irregular pattern
A regular bow-tie pattern behaves predictably; an irregular pattern changes the treatment plan.
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Axis (with-the-rule, against-the-rule, oblique)
The axis of the cylinder, which anchors toric lens and IOL alignment.
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Anterior vs posterior corneal astigmatism
Posterior corneal astigmatism can shift the surgical plan — Scheimpflug tomography captures it.
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Keratoconus screen
Indices for early keratoconus, forme fruste keratoconus and post-LASIK ectasia risk.
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Corneal thickness and posterior elevation
Thinnest-point pachymetry and posterior elevation maps flag ectatic disease.
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Red flag: keratoconus indices (Belin/Ambrósio) — refer for corneal cross-linking
Progressive keratoconus needs cross-linking — a time-critical referral, not a routine review.
Next steps
Treatment options after the assessment.
The plan is a conversation between the refraction, the topography and how you actually use your eyes — not a default choice.
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Glasses with cylindrical correction
Spectacles with a cylinder correction remain the simplest and safest option for regular astigmatism.
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Toric soft contact lenses
Soft toric lenses correct regular astigmatism up to moderate cylinder powers.
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Rigid gas-permeable (RGP) lenses
The mainstay for irregular astigmatism and keratoconus — the tear film smooths the corneal surface.
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Laser refractive surgery (LASIK / SMILE)
Corrects regular astigmatism in suitable candidates with adequate corneal thickness and no ectasia risk.
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Toric intraocular lens (IOL)
Considered at the time of cataract surgery to correct pre-existing corneal astigmatism.
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Corneal cross-linking (keratoconus)
Stiffens the cornea to halt progression of keratoconus and post-LASIK ectasia.
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Intracorneal ring segments
A specialist option for keratoconus to flatten the cornea and improve contact-lens tolerance.
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Follow-up topography
Serial topography confirms stability, monitors progression and guides ongoing management.
Red flags
When astigmatism assessment needs to escalate.
Some presentations need urgent specialist review rather than a routine refractive slot. These are the ones we look for first.
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Keratoconus
Progressive corneal thinning and steepening — needs specialist review and consideration of cross-linking.
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Post-LASIK ectasia
Corneal thinning and irregular astigmatism after refractive surgery — an urgent referral.
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Sudden change in refraction
A rapid shift in prescription can signal cataract, keratoconus progression or systemic disease.
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Corneal scarring
Scarring from infection, trauma or dystrophy can produce irregular astigmatism that spectacles cannot correct.
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Pellucid marginal degeneration
A related ectatic disorder with an inferior crescent of thinning — needs the same escalation as keratoconus.
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Following ocular surgery / trauma
Post-surgical or post-traumatic astigmatism warrants specialist assessment before refitting.
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Rapid progression of astigmatism
A steepening K reading over months is the signature of active keratoconus.
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Amblyopia in children
Untreated childhood astigmatism can cause lazy eye — the pathway prompts early paediatric ophthalmology review.
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Contact-lens intolerance
New or worsening intolerance can be the first sign of an ectatic disorder — do not ignore it.
Sources
The guidance that anchors this page.
Reviewed on 2026-07-30. Next scheduled review 2027-07-30.
Recognised by major UK insurers
Cover depends on your policy and clinic; we confirm with your insurer before booking.
Frequently asked
Everything we get asked about astigmatism assessment.
Quick answers on regular vs irregular astigmatism, topography, toric IOLs, LASIK screening and keratoconus.
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What is astigmatism?
Astigmatism is a common refractive error where the cornea or lens is not perfectly round — it is shaped more like a rugby ball than a football. Light focuses at more than one point on the retina, so vision is blurred or distorted at all distances.
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What is the difference between regular and irregular astigmatism?
Regular astigmatism has two clear principal meridians at 90° to each other and is correctable with spectacles or toric contact lenses. Irregular astigmatism — often from keratoconus, scarring or post-surgical change — has no such symmetry and usually needs rigid gas-permeable lenses or surgical treatment.
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Why do I need corneal topography and not just a glasses test?
Refraction tells us the total optical error; topography tells us the shape of the cornea, distinguishes corneal from lenticular contribution, screens for keratoconus and — critically — plans toric IOL or refractive surgery. Refraction alone cannot do that.
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Do I need a Pentacam scan for LASIK?
Yes. Modern refractive surgeons require Scheimpflug tomography (Pentacam or equivalent) before LASIK or SMILE to screen for keratoconus and post-LASIK ectasia risk. Screening is the reason modern refractive surgery is as safe as it is.
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Can astigmatism be corrected at the time of cataract surgery?
Yes. A toric intraocular lens implanted during cataract surgery can correct pre-existing corneal astigmatism — the pre-operative keratometry and topography drive the lens choice and alignment axis.
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What happens if the pathway finds keratoconus?
Progressive keratoconus is treated with corneal cross-linking to halt progression, alongside specialist contact-lens fitting or, in advanced cases, intracorneal ring segments. Cross-linking is time-critical — earlier treatment preserves more vision.
Related
Looking for a different test or procedure?
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Cataract surgery
Lens replacement — with a toric IOL option to correct astigmatism.
Learn more -
Optometry
Refraction, spectacles and contact-lens fitting.
Learn more -
Corneal cross-linking
Stiffens the cornea to halt keratoconus progression.
Learn more -
All tests
Browse every test and procedure we arrange.
Learn more -
Cataracts
Related condition guide.
Learn more -
Glaucoma
Related condition guide.
Learn more -
Cornea Transplant
Related treatment option.
Learn more -
Corneal Crosslinking
Related treatment option.
Learn more
In practice, in London
Why private astigmatism assessment moves differently in London
With astigmatism assessment, the London question is usually about report turnaround and the radiologist reading it — not whether the scan is available. On the NHS, astigmatism assessment typically sits behind a triage step and a wait that can stretch from a few weeks into months. In London’s private sector, the same appointment often lands within days. That speed matters when symptoms are disrupting work, sleep, or a plan you’d already committed to — and it’s the single most common reason people call us in the first place.
A typical private booking for astigmatism assessment in London starts with a consultant conversation — sometimes in person on Harley Street or Marylebone, sometimes on video if that suits better. Any imaging or diagnostics happen at a nearby CQC-registered facility, and reports usually land within 24 to 72 hours. The whole loop, from first call to written report, is often done inside a fortnight. For astigmatism assessment specifically, the difference between a routine report and a sub-speciality read is where private care earns its keep.
Fit matters more than people expect. For astigmatism assessment, the right consultant depends on what you actually need — a second opinion, a definitive diagnosis, a bridge into treatment, or reassurance that nothing’s being missed. We match on that, not on who has the biggest brochure. If a test isn’t the right next step, we’ll say so before you book anything.