Scleral Lens Fitting Process: Diagnostic, Vault, and Settling

What is the scleral lens fitting process?

It is a five-step diagnostic sequence: total diameter and optic zone, central and limbal clearance, landing-zone alignment, edge lift, then rotational symmetry.

That five-step framing is Eef van der Worp’s, in the open-access A Guide to Scleral Lens Fitting (Pacific University College of Optometry), and he is careful to say the order is “almost arbitrary” — many practitioners work from the periphery back to the centre, the reverse of how a corneal GP lens is read. What is not arbitrary is that all five are decided on eye, and that each one moves a value the laboratory needs.

Power is not on that list, and that is deliberate. It is settled after the lens has settled — see the last two sections.

Step 1 — what sets the starting diameter?

Diameter is chosen so the lens clears the limbus and lands on sclera, which makes corneal size, not refraction, the input.

Writing in Contact Lens Spectrum’s scleral fitting guide (October 2010), Stephen P. Byrnes describes measuring horizontal visible iris diameter in the pre-fitting examination and choosing an overall diameter that extends at least 2 mm beyond the limbal area, so that bearing falls primarily on sclera rather than cornea. In the same article Lynette K. Johns notes that she orders 0.5 mm larger or smaller than the trial lens diameter, and that changes greater than 0.5 mm produce a significantly different fit — diameter is not a free variable once the rest of the fit is set.

Diameter also decides how much scleral shape the lens has to cope with. Johns notes that toricity increases peripherally from the limbus, so the larger the lens, the more scleral toricity the landing zone will encounter. Bigger is not automatically better; it trades a wider, gentler landing for a more irregular surface to land on. What the size classes are called, and why the Scleral Lens Education Society names them by bearing rather than by millimetres, is on Scleral Lens Sizes.

Step 2 — how are central and limbal clearance established?

By putting a diagnostic lens on the eye and reading the fluid layer, then changing sagittal height until the cornea and limbus are cleared without excess.

The diagnostic lens is filled with preservative-free saline before application, and fluorescein in the bowl makes the reservoir readable at the slit lamp. Van der Worp notes that increasing the sagittal height of the lens lifts it off the eye and increases the vault; this is why many fitting sets are indexed in sagittal height rather than in radius. The clearance targets themselves, the grading scales, and how the same layer is measured on anterior segment OCT are on Scleral Lens Vault.

Two errors are worth naming here because they belong to the sequence rather than to the measurement. Judging clearance immediately after application overestimates it, because the lens has not settled. And reading central clearance without checking the limbus separately misses the region where stem cells sit — a lens can clear the corneal apex beautifully and bear at the limbus.

Step 3 — how is the landing zone aligned?

By inspecting the lens in all four quadrants for even bearing, and treating blanching of conjunctival vessels as the sign that pressure is not evenly spread.

In “Landing in the Zone” (Contact Lens Spectrum, January/February 2024), Mile Brujic describes an ideal landing zone as one that disperses the lens evenly onto the conjunctival surface all the way round, with no visible blanching in any region. He uses a foot analogy that has become the working vocabulary: the toe is the most distal part of the landing zone, the heel the most proximal. A toe-down relationship means the landing zone is steeper than the sclera and the distal edge is digging in; toe-up means it is flatter than the sclera and the distal edge is lifted, often with blanching showing at the heel instead.

Whether the landing zone needs to be toric is answered on the eye, not from corneal cylinder. Brujic’s test is to rotate the lens manually and watch: if it returns to its original position, the sclera is likely toric; if it stays where it was put, it likely is not. Diagnostic lenses carry markings in the steep meridian, the flat meridian, or both, so the meridian can be identified once rotation behaviour is known. The scleral-shape data behind all this is not marginal — Brujic cites DeNaeyer and colleagues measuring 140 eyes and finding only 5.7% spherical, with 28.6% toric-regular, 40.7% carrying asymmetric high or low points, and 26% with periodicity different from 180°.

Steps 4 and 5 — edge lift and rotational symmetry

Edge lift is judged by the shadow the lifted edge casts on the conjunctiva; rotational symmetry is the decision to stop using a spherical periphery.

Brujic gives a practical slit-lamp method for edge lift: direct the beam along the landing zone from the centre of the lens outward, and an elevated edge will cast a shadow on the conjunctiva beyond it. The greater the lift, the larger the shadow. The complementary sign is impingement — additional pressure in one region of the landing zone, visible as blanching of the vessels underneath.

Step 5 is where the fit stops being rotationally symmetrical. If the landing zone shows different bearing in different meridians, the design moves to a toric or quadrant-specific periphery. Brujic notes that most contemporary designs already use a reverse curve between the landing zone and the limbal clearance region, which is what produces the lift that clears the limbus. Named designs, laboratory nomograms and parameter grids are a manufacturer matter and are not reproduced here.

Why is a scleral lens fitted diagnostically rather than empirically?

Because the parameter that decides the fit — total sagittal height of the eye out to the landing area — cannot be calculated from keratometry.

Van der Worp puts it directly: scleral lenses are primarily fitted on sagittal depth, keratometric readings are of relatively limited use, and two eyes with identical keratometry can have completely different sagittal heights. Sagittal height depends on lens diameter, radius of curvature, corneal asphericity and the shape of the anterior sclera; the inability to measure the last of those in routine practice makes calculating it, in his words, “virtually impossible in clinical practice.” A fitting set meets the anterior surface empirically instead — the trial lens is the measuring instrument.

Two technologies change that arithmetic without changing the principle. Anterior segment OCT can measure the total sagittal height of the anterior eye. Scleral profilometry and impression moulding go further: Brujic describes taking a mould of the eye and having a lens produced to that scleral shape, and cites work quantifying scleral toricity so a customised periphery can be ordered directly. Neither removes the on-eye evaluation — they change which lens you start from, not whether the lens is read at the slit lamp.

This is the sharpest break with corneal GP practice, where flat K really does give a defensible first base curve and the tear lens can be calculated. That path is on RGP Contact Lens Parameters and Starting Power. It does not extend to sclerals.

How long does a scleral lens take to fit?

Long enough for the lens to settle — the fit read at application is not the fit the patient wears.

Settling is the landing zone sinking into the compressible conjunctiva and Tenon’s capsule beneath it, which flattens and tightens the fit and lowers the vault. Writing in Contact Lens Spectrum (September 2021), Ariel Cerenzie reports that the process begins immediately after application and can continue for eight or more hours, and that a seemingly aligned landing zone and optimal vault can already read as a less-than-ideal fit after 60 minutes. Kauffman and colleagues found 70% of total settling occurred within two hours; Nau and colleagues found tear clearance down by nearly half at two hours.

The chairside consequence is a waiting period rather than a number of visits. In the 2010 fitting guide, Byrnes describes allowing a lens to settle roughly 20 minutes before judging the fit; Cerenzie suggests applying the fitting characteristics after 20 to 30 minutes of settling to reduce remakes, while noting that a four-hour observation gives a more accurate representation of post-settling clearance. Because a full working day of settling cannot be waited out in the chair, designs are ordered with an allowance built in — Esen and colleagues suggest adding roughly 100 µm to the desired post-settling clearance, or about 75 µm for larger-diameter lenses, and Michaud and colleagues report that for an 18 mm lens the total settling can be estimated by doubling what settled in the first 30 minutes.

What does the sequence hand to the order?

A sagittal height, a landing geometry, and a power that comes from over-refraction through the settled lens rather than from the spectacle refraction.

Cerenzie is explicit that, unlike corneal GP lenses, it is difficult to estimate a scleral lens power empirically: base curve, reservoir depth, keratometry and the relationship between the keratometry and the back surface all interact, and the depth of the reservoir is the largest complication. So the power step is an over-refraction, and the arithmetic that turns an over-refraction into an ordered power is on the live Over-Refraction Calculator for Contact Lens Parameters. When and why re-ordering power is the wrong answer — and re-vaulting is the right one — is on Power Adjustment of Scleral Lenses After Settling.

The plane change still applies to the refraction you started from: a spectacle-plane number is not a corneal-plane number. Convert it on the Contact Lens Conversion Calculator and read why on vertex-compensated contact lens power. It is a starting value, and on a scleral lens it is further from the final order than on any other design.

Starting parameters are not a prescription

Everything above is read on eye by a licensed practitioner, and no part of it is decided from a page.

The site-wide bound is on Starting Contact Lens Parameters Are Not a Prescription. For scleral geometry, read Sagittal Depth of Contact Lenses; for what the fit is read against once the lens is on, read Scleral Lens Vault; for the parameter set as a whole, Scleral Lens Parameters.

Sources

Clinical claims on this page are attributed to the publications below.

• Eef van der Worp — A Guide to Scleral Lens Fitting(Pacific University College of Optometry, open access) — the five-step approach (diameter and optic zone, central and limbal clearance, landing-zone alignment, edge lift, rotational symmetry) and the note that the order is almost arbitrary; sclerals fitted primarily on sagittal depth with keratometry of limited use; two eyes with equal K and different sag; sagittal height as a function of diameter, radius, asphericity and anterior scleral shape; increasing sagittal height lifts the lens and increases vault.
• Contact Lens Spectrum — Scleral Contact Lens Fitting Guide(Jason Jedlicka, Lynette K. Johns and Stephen P. Byrnes, October 2010) — HVID measured pre-fitting with overall diameter at least 2 mm beyond the limbal area; ordering 0.5 mm from the trial diameter, with larger changes producing a significantly different fit; scleral toricity increasing peripherally from the limbus; allowing roughly 20 minutes of settling before judging the fit.
• Contact Lens Spectrum — Landing in the Zone(Mile Brujic, OD, FAAO; January/February 2024) — even dispersion with no blanching as the ideal landing zone; toe and heel vocabulary, toe-down and toe-up; the manual-rotation test for scleral toricity and diagnostic-lens meridian markings; the edge-lift shadow method; DeNaeyer and colleagues’ 140-eye scleral shape distribution (5.7% spherical, 28.6% toric-regular, 40.7% asymmetric, 26% non-180° periodicity); impression moulding and scleral profilometry; reverse curve between landing zone and limbal clearance region.
• Contact Lens Spectrum — Alright Folks, Let’s Settle Down(Ariel Cerenzie, OD; September 2021) — settling defined as the landing zone sinking into compressible conjunctiva and Tenon’s capsule; onset immediate and continuing eight or more hours; change already visible at 60 minutes; Kauffman et al 70% of settling within two hours; Nau et al clearance down nearly half at two hours; the 20-to-30-minute chairside recommendation and Esen et al’s four-hour observation; adding ~100 µm (or ~75 µm for larger diameters) to desired post-settling clearance; Michaud et al doubling the 30-minute settling for an 18 mm lens; the difficulty of estimating scleral lens power empirically.