Regular and irregular astigmatism
Astigmatism means the eye focuses light differently in different directions, so light doesn’t come to a single point of focus. It can be regular, where the difference is even and predictable, or irregular, where the surface is uneven.[1] It can come from the cornea, the lens inside the eye, or elsewhere.[1]
Regular astigmatism is often well corrected with glasses or ordinary contact lenses. Irregular astigmatism, from conditions like keratoconus, a corneal transplant, or scarring, is much harder for glasses to correct. Our page on irregular astigmatism covers the causes in detail.
How a scleral lens corrects it
A scleral lens arches over the cornea and rests on the white of the eye, with a layer of saline filling the space between. A 2025 review describes it this way: by vaulting the cornea and resting on the sclera, scleral lenses neutralize corneal astigmatism, while providing a stable surface for the lens optics.[2] The smooth front of the lens takes over from the uneven front of the cornea.
That’s why irregular astigmatism is a main reason people are fitted. In an international survey of fitters, corneal irregularity was the reason for 87% of the fittings described.[4] In a study of 157 eyes with keratoconus, best-corrected vision was much better with scleral lenses than with glasses.[7]
When some astigmatism is left over
A scleral lens neutralizes astigmatism from the front of the cornea. It doesn’t automatically fix astigmatism from other sources. Fitters check for leftover (residual) astigmatism by testing your vision with the lens on. A review of scleral lens assessment explains that leftover astigmatism can come from inside the eye, or from the lens flexing on the eye, and the fix depends on which one it is. If it’s from inside the eye, a lens with a toric front surface (astigmatism correction built into the front) can be fitted.[3]
How common is that? In the fitter survey, 27% of lenses had toric optics and 3% had optics designed to correct more complex distortions, while 70% were spherical.[4]
A toric front surface only works if the lens stays lined up. That’s why lenses are marked so the fitter can see their orientation, and why the review advises checking rotation at every visit.[3] The shape of the edge that rests on the white of the eye matters too: in a small study of 10 healthy young adults, edges shaped to match the eye (toric landing zones) reduced both lens flexing and rotation compared with round edges.[5]
What about regular corneas?
Scleral lenses can correct regular astigmatism too, but people with regular corneas are a minority of wearers. In the fitter survey, uncomplicated refractive error was the reason for 4% of fittings.[4] In a one-year study, 77% of wearers with irregular corneas were still wearing their lenses at twelve months, compared with 58% of those with regular corneas.[6] For ordinary astigmatism, glasses, soft toric lenses, and standard rigid lenses are worth considering first.
What to ask your fitter
- “Is my astigmatism coming from the cornea, or from inside the eye too?”
- “Do I have any leftover astigmatism with the lens on?”
- “Would a toric front surface or a different edge design help?”
- “If my vision isn’t as sharp as you’d expect, what else could be causing it?”
If your vision isn’t what you hoped, see vision still not perfect with sclerals.
Common questions
Should I get scleral lenses for ordinary astigmatism?
Usually other options come first. Regular astigmatism is commonly corrected with glasses, soft toric lenses, or standard rigid lenses. Scleral lenses are mostly fitted for irregular corneas and ocular surface disease, though some people with regular eyes do wear them, often for comfort or dryness reasons. Ask your eye doctor which options suit you.
Why is my vision still slightly blurry with my scleral lens?
There may be some leftover astigmatism, the lens may be flexing or rotating, or something else may be going on, such as fogging. Tell your fitter exactly what you notice. They can measure what's left and often adjust the lens.
What are the marks on my scleral lens for?
Manufacturers often put small marks on a lens so the fitter can check its orientation on your eye. This matters most when the lens has an astigmatism correction that must line up correctly.