What is a scleral lens?
A scleral lens is a rigid gas permeable lens whose entire bearing is on the sclera, with the cornea bridged rather than touched.
The Scleral Lens Education Society nomenclature statement (June 2013) makes bearing the defining feature rather than size: a lens resting entirely on the cornea is a corneal lens, a lens resting partly on the cornea and partly on the sclera is a corneo-scleral lens, and a lens that rests entirely on the sclera is a scleral lens “no matter how large that lens is.” The society explicitly advises against classifying by diameter, because the same millimetre figure means different things on different eyes.
Two consequences follow, and they are the reason this section exists. First, the space the lens vaults fills with saline and becomes part of the optical system. Second, the surface the lens actually sits on — bulbar conjunctiva over sclera — is compressible, so the fit measured in the chair is not the fit at hour eight. Both are covered on Scleral Lens Vault.
What are the zones of a scleral lens?
Every scleral design, whatever the manufacturer, breaks down into three zones: an optic zone over the cornea, a transition zone across the limbus, and a landing zone on the conjunctiva.
Eef van der Worp’s open-access A Guide to Scleral Lens Fitting (Pacific University College of Optometry) sets out that three-zone geometry and notes that the landing zone is also called the haptic zone — from the Greek for “to fasten” or “to attach,” which is exactly what it does. The transition zone is where the lens crosses the limbus; in smaller corneo-scleral designs limbal clearance is typically absent there, because that is where the lens rests.
Each zone answers a different question. The optic zone decides how much fluid stands over the cornea and carries the power. The transition zone decides whether the limbus is cleared. The landing zone decides how the lens sits, how evenly its weight is spread, and how far it will settle. A change made in one is felt in the others, which is why a scleral order is never one number moved in isolation.
How does a scleral lens differ from a soft or corneal GP lens?
The difference is where the lens bears and what fills the gap — not comfort, and not material.
| Design | Where it bears | Fluid between lens and cornea | Parameter that decides the fit |
|---|---|---|---|
| Soft | Drapes over cornea and limbus | A tear film, not a reservoir | Base curve and diameter, from the manufacturer’s short list |
| Corneal GP | Entirely on the cornea | A thin tear lens with its own power | Back optic zone radius against flat K |
| Corneo-scleral | Shared between cornea and sclera | Limited reservoir capacity | Sagittal depth, with limbal clearance usually absent |
| Scleral | Entirely on the sclera | A standing saline reservoir in the light path | Sagittal depth over a stated chord |
The bearing and reservoir columns are van der Worp’s terminology table, condensed. The fourth column is the practical consequence: on a corneal GP lens the tear layer between lens and cornea has a power you can calculate from radius and keratometry, and that arithmetic is on RGP Contact Lens Parameters and Starting Power. On a scleral lens the reservoir is hundreds of microns deep and its depth changes as the lens settles, so the same arithmetic does not carry across. Power Adjustment of Scleral Lenses After Settling is where that boundary is written out.
Why is sagittal depth the ordering parameter, not base curve?
Because a scleral lens has to clear the cornea and reach the sclera, its height over a chord is the thing being ordered; the back radius is only one of several inputs that produce it.
Van der Worp states the clinical version plainly: scleral lenses are primarily fitted on sagittal depth, keratometric readings are of relatively limited use, and two eyes with the same keratometry can have completely different sagittal heights. He puts the total sagittal height of the fitted area of a normal eye at around 4,000 µm over a 15.0 mm chord, and notes that sag depends on lens diameter, radius of curvature, corneal asphericity and the shape of the anterior sclera — the last of which cannot be measured with a keratometer at all.
That is why many scleral fitting sets are labelled in sagittal height rather than in radius, and why a flat-K-plus-a-number rule of the kind used on soft and corneal GP lenses has no scleral equivalent. The geometry itself — the closed form, the chord dependence, and why the number is meaningless without the chord — is defined on Sagittal Depth of Contact Lenses. That page owns sagittal depth on this site; the pages below own what the sag produces once the lens is on the eye.
Which page covers which scleral parameter?
Four pages: the fitting sequence, the vault, the size classes, and power after settling.
| Page | What it covers | When to open it |
|---|---|---|
| Scleral Lens Fitting Process | The five parameter decisions in order, and why the first lens is a diagnostic one | You want the sequence, start to order |
| Scleral Lens Vault | Central and limbal clearance, the landing zone, settling, and how each is measured | You are reading a fit at the slit lamp or on OCT |
| Scleral Lens Sizes | Corneoscleral, mini-scleral and large scleral as bearing classes, not shopping sizes | A report or a fitting set names a class and you need the definition |
| Power Adjustment After Settling | Why a settled lens is re-powered from an over-refraction rather than re-converted | The fit is right and the vision is not |
Where do this site’s calculators stop on a scleral lens?
They stop at power at the corneal plane. No calculator here produces a sagittal depth, a landing-zone geometry, or a scleral lens order.
What still transfers is the plane change. A refraction written at the spectacle plane is not the power a lens on the eye needs, and that arithmetic is the same whatever the lens is made of — convert it on the Contact Lens Conversion Calculator, or read why on vertex-compensated contact lens power. What does not transfer is the idea that the converted number is the number you order. On a scleral lens the reservoir stands between the lens and the cornea, so the ordered power is settled by over-refraction through the diagnostic lens.
This section also declines several things on purpose. It publishes no laboratory design tables, no parameter grids by brand, and no fitting nomogram cloned from a manufacturer’s guide. It is manufacturer-agnostic, as the rest of the site is, and a scleral lens is a fitting decision made with a practitioner.
Starting scleral parameters are not a prescription
A scleral lens is selected diagnostically and verified on eye, and every value on these pages is a starting value until that has happened.
The bound that applies across this site is written up on Starting Contact Lens Parameters Are Not a Prescription, and it is tighter here than anywhere else on the site: the lens seals a fluid reservoir against a cornea it is bridging, so fit errors are physiological, not just optical. Convert power. Fit sag and landing on eye. Verify with over-refraction after the lens has settled.
Patient aside (Grade 8–9)
A scleral lens is bigger than a normal contact lens and rests on the white of the eye instead of on the cornea. The space it leaves over the cornea is filled with sterile saline. Because of that, the lens cannot be chosen from your glasses prescription — it is measured and tried on your eye by a practitioner who fits them.
One thing on this page is not about numbers. If your eye hurts, if your vision dropped suddenly, or if things are still blurry with the lens out, take the lens out and call your eye doctor today. A scleral lens sits sealed over its own reservoir, so a quiet, comfortable lens is not evidence of a quiet eye. Numbers can wait a day. That cannot.
Related reading on this site: Sagittal Depth of Contact Lenses for the geometry, GP Contact Lens Design for the rigid-lens parameter spine, and Irregular Cornea for how corneal shape narrows the lens class.
Sources
Clinical claims on this page are attributed to the publications below.
- Scleral Lens Education Society — Scleral Lens Nomenclature(June 2013) — bearing, not diameter, is the defining feature; corneal, corneo-scleral and scleral definitions; the society’s advice against diameter-based classification.
- Eef van der Worp — A Guide to Scleral Lens Fitting(Pacific University College of Optometry, open access) — the three-zone geometry; landing zone as haptic zone and the Greek derivation; terminology table of bearing and tear reservoir by class; sclerals fitted primarily on sagittal depth with keratometry of limited use; two eyes with equal K and different sag; total sagittal height of a normal fitted area around 4,000 µm over a 15.0 mm chord.
- Contact Lens Spectrum — Scleral Contact Lens Fitting Guide(Jason Jedlicka, Lynette K. Johns and Stephen P. Byrnes, October 2010) — scleral lenses as large-diameter GP lenses that cover the cornea entirely and extend onto the sclera.
- University of Iowa, EyeRounds Ophthalmic Atlas — Appropriate Scleral Lens Sagittal Depth(Tressa Larson, OD, FAAO) — steeper base curve deepens sag, flatter reduces it; larger-diameter sclerals have deeper sag.
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