The basic idea
A scleral lens is a large, rigid gas-permeable contact lens. Instead of resting on the cornea (the clear window at the front of the eye), it rests on the conjunctiva over the sclera, the white of the eye. It arches over the cornea and the limbus, the border where the cornea meets the white, without touching them.[1]
Before you put a scleral lens in, you fill its bowl with sterile saline. That fluid stays trapped between the lens and the cornea while you wear it. This fluid layer is what makes scleral lenses different from every other contact lens.[1]
The fluid layer does two jobs:
- It smooths out an irregular cornea. Light passes through the smooth lens and the even layer of fluid before it reaches the cornea, so bumps, scars, and cones on the cornea’s surface are largely masked.[1]
- It keeps the cornea bathed. For people with severe dry eye and other surface disease, the reservoir hydrates the cornea and shields it from the rubbing of the eyelids.[1]
The page on how scleral lenses work explains the vault, the fluid layer, and oxygen in more detail.
How big are they?
Bigger than any other contact lens. A 2018 review describes them as ranging from about 14 mm to more than 20 mm across.[1] In an international survey covering 419 eyes, the average scleral lens was 16.2 mm in diameter, with a range of 11.8 to 23.0 mm.[3]
Size alone doesn’t define a scleral lens. What matters is where the lens rests. A lens that rests partly on the cornea and partly on the white is usually called a corneo-scleral lens. A lens that rests entirely on the white is a scleral lens, and those are further divided into mini-scleral and large scleral designs.[2] The glossary explains these terms.
What are they made of?
Modern scleral lenses are made of rigid gas-permeable plastics that let oxygen pass through to the eye. They aren’t new: scleral lenses were among the first contact lenses ever made. Early versions were glass, then plastics that blocked oxygen. Today’s high-oxygen materials cut down many of the problems older scleral lenses caused.[4]
How they differ from other contact lenses
| Lens type | Where it rests | What it does well | Where it struggles |
|---|---|---|---|
| Soft lens | On the cornea, extending slightly past it | Comfortable, easy to adapt to | Can’t correct much corneal irregularity |
| Corneal rigid gas-permeable lens | On the cornea | Sharp vision on a mildly irregular cornea | Can be uncomfortable or unstable on a very irregular cornea |
| Hybrid lens | Rigid center with a soft skirt | Rigid optics with soft-lens comfort | Not suited to every corneal shape |
| Scleral lens | On the white of the eye, vaulting the cornea | Clear vision on very irregular corneas; protects a fragile surface | Takes practice to insert and remove; needs saline and daily care |
The cornea is one of the most densely innervated and sensitive tissues in the body.[5] A lens that sits on the cornea can be felt, especially on an irregular one. A scleral lens moves the load to the white of the eye instead, which is one reason many people who couldn’t tolerate smaller rigid lenses can wear them.
Who uses them
Scleral lenses are mainly a medical device. In an international survey of fitters describing 259 patients, the reasons for wearing them were:[3]
- Corneal irregularity: 87%. This includes keratoconus, corneal ectasia after LASIK, corneal transplants, scars, and other conditions that leave the cornea uneven.
- Ocular surface disease: 9%. Severe dry eye, Sjögren’s syndrome, graft-versus-host disease, Stevens-Johnson syndrome, and similar conditions.
- Uncomplicated refractive error: 4%. Ordinary prescriptions in people who don’t do well with other lenses.[3]
A separate 2020 survey of 777 experienced fitters found a similar picture: a median of 84% of their scleral lenses were fitted for corneal irregularity.[6] Browse the conditions scleral lenses are used for to see each one in detail.
What wearing them involves
Scleral lenses are a daily routine, not a one-time fix. A typical day looks like this:
- Morning: wash your hands, fill each lens with sterile saline, and insert it while looking down, usually with a small suction tool called a plunger or with your fingers.
- During the day: some people get cloudy vision as debris builds up in the fluid layer, known as midday fogging. Studies report it in 26% to 46% of wearers. The usual fix is to remove the lens, clean it, refill it, and reinsert it.[11]
- Evening: remove the lenses, clean them, and disinfect them overnight in the solution your fitter recommends. Scleral lenses are generally worn while you’re awake: a modeling study found that wearing them with the eyes closed would leave the cornea short of oxygen.[10]
The wearing guides walk through each step.
Expect a learning curve. In a one-year study of 95 new wearers, 36% could correctly put a lens in within 15 minutes at their first dispensing visit, while 13% needed more than an hour (those were people who had worn glasses, soft lenses, or nothing before). The number of attempts needed to insert and remove the lenses fell over the following year.[8] In a survey of people with keratoconus, 45% of scleral wearers said they spent 6 to 10 minutes a day handling their lenses.[7]
If these worries feel big, you’re not alone. The common worries pages take them one at a time, starting with whether scleral lenses are hard to put in.
Questions to ask if you’re considering them
- Why do you think scleral lenses suit my eyes better than the alternatives?
- What vision can I realistically expect with them?
- How many visits and lenses does a fit usually take, and what do your fees cover?
- Who teaches me to insert and remove them, and how much practice time will I get?
- Who do I call if I can’t get a lens out or my eye becomes red or painful?
Common questions
Are scleral lenses the same as hard contact lenses?
They're made of the same family of rigid gas-permeable materials as smaller hard lenses, but they behave differently. A small hard lens sits on the cornea. A scleral lens is much larger, rests on the white of the eye, and holds a layer of saline over the cornea.
Do scleral lenses touch the cornea?
They're designed not to. The lens arches over the cornea and the border around it, with saline filling the space. Your fitter checks that clearance at each visit.
Can anyone wear scleral lenses?
Most people who wear them have an irregular cornea or a severe ocular surface problem. A small share are fitted for ordinary prescriptions. Whether they suit you depends on your eyes, your other options, and whether you can learn to handle them, which is a conversation for a scleral lens fitter.
Can I sleep in scleral lenses?
Scleral lenses are generally worn during the day and removed for sleep. Modeling research suggests closed-eye wear leaves the cornea short of oxygen. A doctor may occasionally prescribe overnight wear for a specific medical reason, with close monitoring.
How long does a fitting take?
It varies. In one international survey of fitters, patients needed an average of 2.4 lenses over 3.8 visits to complete a fit.