What the vault is
A scleral lens is shaped like a shallow dome. It lands on the white of your eye and arches over the cornea without touching it. The space underneath is filled with saline when you put the lens in. The depth of that space is the vault, also called clearance, the fluid reservoir, or the post-lens fluid layer.
Fitters care most about the center, but they also check the middle and edges of the cornea and the limbus, the border where the cornea meets the white of the eye. A good fit clears the whole cornea and limbus with no contact, while landing evenly on the white of the eye without pressing into it.[1]
Why it matters
Too little vault. The lens sinks a little during the first hours of wear. If the vault starts thin, it can end up touching the cornea, which risks mechanical irritation over time.[1] Some authors suggest dispensing a little extra vault for progressive conditions like keratoconus, to allow for the cornea changing shape.[1]
Too much vault. The saline layer is itself a barrier to oxygen. One review notes the fluid has an oxygen permeability of about 80, lower than the high-permeability lens materials used today, so a thick reservoir adds to the barrier the lens already creates.[3] Excessive vault can contribute to corneal swelling in people whose corneal endothelium is weakened.[1] Vault can also change vision: in a pilot study of 15 healthy eyes, fitting lenses with deeper vaults shifted the prescription toward nearsightedness and increased some optical distortions.[4]
What the targets are
There’s no single agreed number, and you’ll see different ranges:
- One review reports that manufacturers tend to suggest 100 to 200 microns of central vault after the lens has stabilized.[1]
- Another review gives 100 to 300 microns as the ideal central clearance range.[2]
- Theoretical studies suggest corneal swelling may be avoided with a fluid layer no thicker than 200 microns, though many lenses in use exceed that.[1]
The same 2022 review concludes that the best vault is one that gives good vision and comfortable wear without disturbing the health of the eye’s surface.[1] In other words, the numbers are a starting point, not a pass-fail line.
The vault changes during the day
The vault is thickest just after you put the lens in and thins as the lens settles. In 22 keratoconus eyes, the central vault dropped by an average of about 63 microns over 8 hours, with most of that in the first 4 hours.[5] In a larger study of 75 people, the fluid layer thinned by about 149 microns at the center over 4 hours, most rapidly in the first 2 hours.[6] That’s why fitters often judge the vault after a period of wear rather than right after insertion. For more, see what is scleral lens settling?
What you can do
You can’t adjust the vault yourself, but you can help your fitter judge it:
- Wear your lenses for a few hours before follow-up visits if your fitter asks you to, so they see the settled fit.
- Report blur that develops over the day, discomfort, or redness, and when it starts.
- Keep follow-up visits even when you feel fine, since corneal swelling may not cause symptoms you’d notice.
Common questions
Can I see or feel my vault?
No. The fluid layer is far too thin to notice. Your fitter checks it at the slit lamp, sometimes with a yellow dye in the saline, or with an imaging scan. What you may notice are the effects of a vault that's off, such as blur, discomfort, or a lens that seems to touch.
Why did my fitter say my vault was fine when the lens first went in, then change it?
The vault shrinks over the first few hours as the lens settles into the tissue on the white of the eye. A vault that looks generous on insertion can be much thinner by the afternoon, so fitters often re-check after the lens has settled before deciding.
Is a high vault dangerous?
Not in itself, but a very thick fluid layer reduces the oxygen reaching the cornea and can affect vision. That matters most for corneas that already swell easily, such as after a transplant. Your fitter balances vault against those effects for your eye.