Corneal topography maps the surface of the eye before a lens is fitted — but it can’t show what’s happening once the lens is actually on. That’s the gap anterior segment OCT (optical coherence tomography) fills, and it’s a technology not used in every contact lens practice and particularly valuable in complex scleral lens fitting, where the margin between a comfortable, stable fit and a problematic one can be genuinely small.

What OCT technology is, in general

Optical coherence tomography uses light waves to build a detailed cross-sectional image of tissue, similar in principle to how ultrasound uses sound waves, but with far finer resolution. OCT has been used in eye care for years to examine the retina and optic nerve, particularly in monitoring conditions like glaucoma and macular disease. Anterior segment OCT applies the same underlying technology to the front of the eye instead — the cornea, sclera, and anything sitting on top of them, including a fitted contact lens. This adaptation of an established, trusted imaging technology to a new part of the eye is part of why it integrates so naturally into a thorough assessment process.

What the Zeiss Cirrus 6000 anterior OCT does

The Zeiss Cirrus 6000 takes a cross-sectional scan through the cornea, sclera and the fitted lens itself, producing a detailed image of exactly how the lens is sitting on the eye — the depth of clearance over the cornea, the alignment of the landing zone on the sclera, and the depth of the fluid reservoir. It’s the same underlying OCT technology used to examine the retina and optic nerve, applied instead to the front of the eye.

Why this precision matters

• Objective measurement of central and limbal clearance, rather than an estimate made at the slit lamp alone
• Direct visualisation of the landing zone, so the lens edge can be adjusted to sit evenly rather than digging in or lifting
• Accurate measurement of fluid reservoir depth, which affects both comfort and oxygen delivery to the cornea
• Fewer diagnostic lens exchanges during fitting, because adjustments are guided by measured data rather than trial and error

How anterior OCT is used during a fitting

Anterior OCT imaging is typically used at several points during a scleral lens fitting: initially to assess baseline corneal and scleral shape alongside topography, then again once a diagnostic lens is on the eye to check clearance and landing zone alignment directly. If adjustments are needed, a further scan after the revised lens is fitted confirms whether the change has achieved the intended result. This iterative use of imaging is part of why complex fittings, while sometimes requiring more than one visit, tend to converge on a stable design more efficiently than relying on visual assessment alone — each scan narrows down exactly what needs to change, rather than leaving the next adjustment to guesswork.

Anterior OCT at follow-up appointments

Beyond the initial fitting, anterior OCT continues to be useful at routine reviews, particularly for patients with progressive conditions like keratoconus. Comparing a current scan against the baseline taken at fitting can reveal subtle changes in clearance or alignment before they become noticeable as discomfort or reduced vision — allowing adjustments to be made proactively rather than reactively, often before a patient would otherwise have noticed anything had changed at all.

Who benefits most from anterior OCT imaging

• Patients with more advanced or asymmetric corneal irregularity, where visual assessment alone leaves more room for uncertainty
• Patients with ocular surface disease, where confirming fluid reservoir depth and avoiding pressure on fragile areas is particularly important
• Patients who’ve had a difficult fitting experience elsewhere, where more precise measurement can help resolve a previously unstable fit
• Any patient where an especially secure, well-documented fit is valuable for long-term monitoring

The limits of anterior OCT

Anterior OCT is a genuinely valuable tool, but it’s one part of a fitting process rather than a replacement for clinical judgement or the other elements of assessment. A scan tells us precisely how a lens is positioned; it doesn’t replace listening to how a patient describes their comfort, or the broader clinical picture from topography, slit lamp examination and trial lens wear. The value of anterior OCT comes from combining it with these other elements, not from using it in isolation.

What to expect during an OCT scan

Like corneal topography, an anterior OCT scan is quick and comfortable. You’ll rest your chin on a support and look at a fixed target while the machine captures the cross-sectional image, whether or not you have a lens on the eye at the time. If the scan is being done with a diagnostic lens in place, there’s no need to remove it beforehand — the whole point of the scan at that stage is to see exactly how that lens is sitting.

Why this equipment isn’t universal in practice

Anterior segment OCT modules represent a significant equipment investment for a practice, which is part of why they’re not universally available even among practices that fit scleral lenses. Where it is available, it tends to be used most heavily for exactly the complex cases this article describes — significant corneal irregularity, ocular surface disease, or fittings that have proved difficult to stabilise using standard assessment methods alone.

If you’re being referred from elsewhere

If you’re coming to us following a difficult or unsuccessful scleral lens fitting elsewhere, anterior OCT can be particularly useful in understanding exactly what wasn’t working with the previous fit — whether that’s insufficient clearance, an uneven landing zone, or another specific, measurable issue — rather than starting again from scratch with the same trial-and-error approach.

Bringing any previous fitting notes, lens specifications or imaging you have access to is genuinely helpful in these cases, giving us a starting point to compare against rather than working entirely from a fresh assessment.

What this means for you as a patient

In practice, using anterior OCT alongside topography can help guide adjustments more precisely, which may reduce unnecessary trial-and-error during fitting. It also gives Craig an objective image to compare against at future appointments, to check the fit is still correct as your eye and lens settle over time — rather than relying on memory or a written note from a previous visit. For many patients, this translates simply into a smoother, more confidence-inspiring fitting experience overall.

Anterior OCT FAQs

Is anterior OCT the same as corneal topography?

No — topography maps the surface shape of the cornea before fitting. Anterior OCT images how the lens sits on the eye once it’s actually fitted, including clearance and the fluid reservoir. The two are complementary rather than interchangeable.

Do all scleral lens fittings use anterior OCT?

Not every practice offers it, since it requires specific equipment. At Peter Ivins Eye Care, it’s used as part of complex scleral lens fitting rather than being an optional extra.

Does anterior OCT imaging take long?

No — it’s a quick, non-contact scan, typically taking only a few minutes as part of your fitting or follow-up appointment.

Is anterior OCT imaging used for anything besides scleral lens fitting?

Yes — anterior segment OCT has broader uses in eye care, including assessing corneal thickness, monitoring certain corneal conditions, and evaluating the front of the eye before some types of surgery, though this article focuses specifically on its role in scleral lens fitting.

Will I see the OCT images from my own scan?

Yes — we’re happy to show and explain your scan results as part of discussing your fitting, since seeing the actual clearance and alignment can help make sense of any adjustments being suggested.

Does anterior OCT replace the need for a slit lamp examination?

No — anterior OCT and slit lamp examination give different, complementary information. The slit lamp allows direct visual examination of the eye and lens under magnification, while OCT provides precise cross-sectional measurement. Both remain part of a thorough scleral lens assessment, and neither is intended to substitute for the other.

Book a Scleral Lens Assessment

Call the practice on 0141 943 3300 to arrange a scleral lens consultation.