Two very different lenses
An implantable collamer lens (ICL) is an artificial lens permanently implanted inside the eye. It sits behind the iris and in front of your own natural lens, which stays in place. It bends light so it focuses on the retina, correcting nearsightedness, and the toric version also corrects astigmatism.[1]
A scleral lens is a large rigid contact lens that rests on the white of the eye and vaults over the cornea, with a layer of saline underneath. You put it in each morning and take it out at night. Because the fluid fills in the gaps between the lens and an irregular cornea, it can correct blur that glasses can’t.
The key difference: an ICL corrects a focusing error. A scleral lens can also correct an irregular front surface of the eye.
Who an ICL is approved for
In the US, the current EVO and EVO+ Visian ICL and toric ICL were approved by the FDA in 2022.[1] The FDA-approved labeling says they’re indicated for people aged 21 to 45 who are nearsighted, within set prescription ranges, with a stable prescription for a year before surgery and enough depth in the front chamber of the eye.[2]
The FDA says they should not be used in people who:[1]
- are pregnant or nursing
- are younger than 21
- have moderate to severe glaucoma
- have a front chamber of the eye that’s too shallow, or a drainage angle that’s too narrow
- don’t have enough endothelial cells, the single layer of cells on the inside of the cornea that keeps it clear
The labeling also says safety and effectiveness haven’t been established in people with unstable or worsening nearsightedness, a history of previous eye surgery, or a progressive sight-threatening disease other than nearsightedness.[2] That last group can include progressive keratoconus.
ICL risks to know about
The FDA-approved patient booklet lists risks including:[3]
- Cataract. The risk of a cataract continues to rise with each year the lens is in the eye, and is higher with older age and stronger nearsightedness.
- Loss of corneal endothelial cells beyond normal aging, which in severe cases can lead to corneal swelling that may need a transplant.
- Raised eye pressure and glaucoma.
- Glare and halos, especially in dim light.
- Further surgery to remove, replace, or reposition the lens.
Regular eye exams for as long as the lens is in place are part of having an ICL.[3]
ICL and keratoconus
Because an ICL doesn’t reshape the cornea, its role in keratoconus is narrower than in ordinary nearsightedness. Surgeons have used ICLs and other phakic implants in stable keratoconus, outside the FDA-approved uses:
- A 2024 review found no randomized trials, only retrospective and prospective case series. It concluded that phakic implants are a valid option in stable keratoconus with moderate to high prescriptions and regular or mildly irregular astigmatism, and suitable for eyes without advanced keratoconus or highly irregular astigmatism.[5]
- A 2025 meta-analysis of 16 observational studies (397 eyes) found that ICLs significantly improved uncorrected vision and reduced prescription, but did not significantly improve best-corrected vision. The authors noted the evidence was limited by observational designs and short follow-up.[4]
Put simply, an ICL can reduce how much someone with stable keratoconus depends on glasses, but it doesn’t remove the distortion an irregular cornea causes. That distortion is what scleral lenses are designed to correct. In one study of 157 keratoconus eyes that wore scleral lenses successfully for at least a year, average best-corrected vision improved significantly compared with glasses.[6]
Side by side
| ICL | Scleral lens | |
|---|---|---|
| What it is | Lens implanted inside the eye | Large contact lens on the eye’s surface |
| Surgery | Yes | No |
| Corrects | Nearsightedness, regular astigmatism | Most prescriptions, plus an irregular cornea |
| Irregular cornea (keratoconus, transplant) | Doesn’t correct the irregularity; used off-label in some stable keratoconus | A main use |
| Dry eye or surface disease | Doesn’t treat | Can protect the surface |
| Daily routine | None once healed | Insert, remove, clean every day |
| Age | FDA-approved for 21 to 45 | Children to older adults |
| Main risks | Surgical risks, cataract, endothelial cell loss, raised eye pressure | Infection, especially with poor care; handling problems |
| Reversible | Removable with further surgery | Stop wearing at any time |
Who each tends to suit
An ICL may suit a nearsighted adult with a regular cornea, a stable prescription, and an eye that meets the measurements, who wants to stop wearing glasses or contacts.
Scleral lenses may suit someone whose cornea is irregular from keratoconus, a transplant, previous refractive surgery, or scarring; someone with severe dry eye or surface disease; or someone who wants to avoid eye surgery. They require daily handling, which not everyone manages. See am I a candidate for scleral lenses?
Some people with stable keratoconus are offered combinations, such as cross-linking first, then an implant. See scleral lenses vs cross-linking and scleral lenses vs Intacs.
What to ask
Your surgeon:
- Is my cornea regular enough that an ICL would give me clear vision?
- Is my prescription, and my keratoconus if I have it, stable?
- Do my eye measurements and endothelial cell count meet the requirements?
- What follow-up will I need, and for how long?
Your scleral lens fitter:
- Is the blur I have from my prescription or from my cornea’s shape?
- Would I still need a scleral lens after an ICL?
Common questions
I have keratoconus. Could an ICL replace my scleral lenses?
For some people with stable, milder keratoconus, an ICL can reduce how much they rely on glasses or contact lenses, and it's been studied in that setting. It doesn't fix the irregular cornea itself, so people whose vision is limited by irregularity may still need a scleral lens. This use is outside the FDA-approved indications. Ask a cornea or refractive surgeon who treats keratoconus.
Can I have an ICL and still wear scleral lenses?
Some people do use both, with the ICL handling the prescription and a scleral lens handling an irregular surface or dry eye. Whether that makes sense for you is a question for your surgeon and fitter together.
Is an ICL permanent?
It's designed to stay in the eye, but it can be removed or replaced in another operation. The FDA-approved patient labeling says another surgery may be needed to take out, replace, or reposition the lens, or if a cataract develops.
I had a corneal transplant. Can I get an ICL?
The FDA labeling says the safety and effectiveness of the ICL haven't been established in people with a history of previous eye surgery. That doesn't rule it out for every patient, but it's a specialist decision. Scleral lenses are one option after a transplant: see our corneal transplant condition page.
Which is safer?
They carry different kinds of risk. An ICL carries surgical risks and longer-term risks inside the eye, such as cataract and loss of corneal endothelial cells. A scleral lens carries daily-wear risks, such as infection, especially with poor lens care. A surgeon and fitter can weigh them for your eye.