Why scleral lenses are different
Hard corneal lenses rest directly on the cornea, and some, like orthokeratology lenses, are designed to reshape it. A scleral lens works differently: it arches over the cornea and rests on the white of the eye, with a layer of saline in between. A good fit clears the cornea and limbus without touching them.[8]
But “not touching” isn’t the same as “no effect.” The lens and the fluid layer under it reduce the oxygen reaching the cornea, and the cornea can respond by swelling slightly.
Swelling: small in most eyes
The cornea stays clear by constantly pumping fluid out through its innermost layer, the endothelium. When it gets less oxygen, it can take on a little water and thicken.
- Pooled evidence. A 2026 meta-analysis of 22 studies (830 eyes) found the cornea thickened by about 8 microns on average while the lens was on, and showed no significant difference after the lens came out. The authors concluded that daytime wear of modern high-oxygen lenses appears physiologically safe, with selective monitoring advisable in high-risk patients.[1]
- Keratoconus, one day. After 6 hours of wear in keratoconus eyes, the cornea thickened by about 1.8% on average, a change that fell just short of statistical significance and returned to baseline after a night without the lens.[2]
- Long-term endothelium. In keratoconus patients who had worn scleral lenses for about 5 years on average, endothelial cell measurements showed no significant change. The authors note larger studies are needed.[5]
Curvature: small changes, mostly temporary
- Short term. In the same keratoconus study, the front of the cornea flattened very slightly after 6 hours of wear, a change that wasn’t statistically significant and was back to baseline the next morning.[2]
- One year. In 65 keratoconus patients wearing 16.5 mm scleral lenses 8 hours a day for a year, measurable changes appeared in corneal thickness and in curvature in specific regions, but vision stayed stable throughout.[3]
Does wearing sclerals slow keratoconus?
There isn’t good evidence that it does. One small retrospective study compared 10 keratoconus eyes wearing scleral lenses with 14 matched eyes that weren’t, over a year. Some measures progressed less in the scleral lens group, but the authors call for larger, prospective studies before drawing conclusions.[4] Scleral lenses are a way to see better, not a treatment for the disease.
Who needs closer monitoring
Eyes with a weakened endothelium are the main exception to “small changes.” After 8 hours of wear, 12 eyes with corneal transplants swelled by an average of about 7%, more in full-thickness transplants than partial ones, and more in older grafts.[6] At one PROSE center, worsening corneal swelling was the most common reason treatment failed, and eyes with Fuchs’ dystrophy or a previous full-thickness transplant failed far more often than others.[7]
Swelling can show up as haze or blur and is confirmed by measuring corneal thickness. Reviews note that a transplanted cornea is a risk factor for swelling with scleral lens wear.[8] If you’ve had a transplant or have Fuchs’ dystrophy, ask your eye doctor how they’ll monitor your cornea, and keep your follow-up visits. For lens choices that reduce oxygen stress, see what are scleral lenses made of? and fenestrated scleral lenses. For transplant-specific information, see scleral lenses after a corneal transplant.
Common questions
Will scleral lenses fix my keratoconus?
No. They correct your vision while you wear them by covering the irregular cornea with a smooth surface and a layer of saline. They don't change the underlying condition. If your keratoconus is progressing, ask your eye doctor about corneal cross-linking, which is the treatment designed to slow it.
My glasses prescription seems different after I take my lenses out. Is that normal?
Some people notice their vision with glasses is a little different right after removing their lenses. Studies show small, temporary curvature and thickness changes after a day of wear that settle overnight. If the change is large, lasts, or is getting worse, tell your eye doctor.
Do I need special checks if I've had a corneal transplant?
Yes, usually. Transplanted corneas can swell more under a scleral lens. Your eye doctor will likely monitor corneal thickness and the health of the graft more closely, and may adjust the lens or your wearing time.