By Dr. Callie Sincennes · · 3 min read
Most people who end up in scleral lenses arrive having been told they were out of options. A cornea scarred by injury, distorted by keratoconus, or left irregular after surgery cannot be corrected by glasses, and being told that repeatedly is demoralising.
The reason glasses fail is simple geometry: a spectacle lens has a regular, smooth surface, and it cannot correct an irregular one. Adding more prescription does not help, because the problem is not the amount of correction. It is the shape underneath.
How a scleral lens solves it
Rather than sitting on the cornea and following its shape, a scleral lens arches over the cornea entirely without touching it, and lands on the sclera, the white of the eye.
The gap underneath fills with sterile saline before insertion. Light now passes through a smooth lens surface and a smooth fluid layer before it ever reaches your irregular cornea, so the distortion largely stops mattering. The lens, not your cornea, is doing the refracting.
Patients routinely describe the first properly fitted scleral lens as the clearest vision they have had in years. That reaction is common enough that we expect it.
Who they help
- Keratoconus at any stage, including after corneal cross-linking
- Pellucid marginal degeneration and other corneal ectasias
- Post-LASIK and post-RK corneas with irregular healing
- Corneal transplant patients, where the graft surface is rarely optically regular
- Corneal scarring from injury, infection or ulceration
- Severe dry eye, including Sjogren's syndrome and graft-versus-host disease
- High astigmatism that soft lenses cannot correct stably
- Anyone who could not tolerate smaller rigid gas permeable lenses
Why they help severe dry eye
This surprises people, because a contact lens is normally the thing that makes dry eye worse.
The difference is the fluid reservoir. The lens holds a bath of sterile saline against your cornea for the entire wearing period. Instead of a tear film that evaporates within seconds, the corneal surface sits in continuous liquid all day.
For patients with severe dry eye who have exhausted drops, plugs and prescription medication, this is frequently the intervention that finally works. It is also why sclerals are used in genuinely serious ocular surface disease, where protecting the cornea from exposure matters as much as vision.
Why bigger is more comfortable
The most common worry is that a larger lens must be less comfortable, and the anatomy explains why the opposite is true.
The cornea is one of the most densely innervated tissues in the body, which is why a speck of dust is agony. The sclera has far fewer nerve endings. A scleral lens never touches the cornea at all and lands on tissue that barely registers it.
Most patients adapt within days, and many report forgetting the lens is in.
The fitting takes several visits, honestly
I would rather set this expectation properly than have someone frustrated at visit two. This is not a one-appointment process.
Every parameter is customised: overall diameter, the vault height clearing your cornea at its steepest point, the shape of the landing zone where the lens meets the sclera, and the optics. The sclera is not spherical, it is asymmetric, and a lens that lands unevenly causes redness and discomfort no matter how good the optics are.
We start with diagnostic lenses on your eye, assess the fluid layer and the landing, then order a custom lens. Refinement across follow-up visits is normal and is part of the service rather than a sign something went wrong. Anyone promising a same-day scleral fit on a complex cornea is describing an outcome I do not recognise.
Living with them
You fill the lens with preservative-free saline before insertion, which is the main handling difference from other lenses. Most patients use a small plunger for insertion and removal, and it takes a few days to feel natural.
They are worn during waking hours and removed at night. Never sleep in them: the fluid reservoir becomes stagnant over long wear and infection risk rises considerably.
Tap water is never appropriate with these lenses, and we make sure that is understood before anyone leaves with a pair.
The short version
- A scleral lens vaults completely over the cornea and rests on the sclera, with sterile saline filling the space between.
- That fluid layer creates a smooth new optical surface, which is why sclerals work where glasses cannot.
- They are more comfortable than smaller rigid lenses, because the sclera has far fewer nerve endings than the cornea.
- The fluid reservoir also keeps the eye hydrated all day, which makes them one of the most effective treatments for severe dry eye.
- Fitting legitimately takes several visits. Anyone promising a same-day fit on a complex cornea is describing something we do not recognise.
- Never sleep in them, and never let tap water near them.
Want the full detail?
Read about scleral lensesThis article is general educational information, not medical advice or a diagnosis, and it is not a substitute for an examination. If you are experiencing sudden vision loss, eye pain or an eye injury, contact us immediately or go to an emergency room.