Two different jobs
Keratoconus causes two separate problems. The cornea, the clear front window of the eye, weakens and changes shape over time, and its irregular shape blurs and distorts vision. Cross-linking and scleral lenses each address one of those problems.
Corneal cross-linking is a procedure. Riboflavin (vitamin B2) drops are applied to the cornea, which is then treated with ultraviolet light. The aim is to stiffen the cornea so it stops bulging further. The FDA approved the first cross-linking system in the US in 2016, for progressive keratoconus and for corneal ectasia after refractive surgery.[2]
A scleral lens is a vision correction. It rests on the white of the eye, arches over the cornea, and holds a layer of saline against it. The smooth front of the lens replaces the cone’s irregular surface, so light focuses properly. It doesn’t change the cornea’s strength or the course of the disease.
Side by side
| Corneal cross-linking | Scleral lens | |
|---|---|---|
| What it is | A procedure done in the clinic, with a recovery period | A custom contact lens you wear daily |
| Rests on / acts on | Acts on the tissue of the cornea itself | Rests on the white of the eye (sclera) |
| Touches the cornea | Yes. Treats the cornea directly | No. Vaults the cornea over a layer of saline |
| Irregular corneas | Stabilizes the cornea. Flattening is usually small | Corrects the vision problem the irregularity causes |
| Dry eye | Dry eye was among the reported side effects in the US trials[2] | Keeps the cornea bathed in saline while worn |
| Comfort | Pain and discomfort during healing, then no daily device | Daily wear. Often comfortable once fitted |
| Handling | Nothing to handle after recovery | Daily insertion, removal, and cleaning |
| Cost drivers | Procedure fee, coverage for the procedure, follow-up visits | Custom fitting, number of lenses and visits, replacement lenses, care products |
| Who it suits | People whose keratoconus is getting worse | Anyone whose vision isn’t good enough in glasses, whether or not the disease is progressing |
What cross-linking does, according to the trials
It stops progression in most young patients. The KERALINK trial in the UK randomized 60 people aged 10 to 16 with progressive keratoconus to cross-linking or standard care with glasses or contact lenses. After 18 months, keratoconus had progressed in 7% of those who had cross-linking, compared with 43% of those who received standard care.[1] Corrected and uncorrected vision were also better in the cross-linking group.[1]
It flattens the cornea only a little. In the trials behind the US approval, the steepest part of the cornea flattened by an average of 1.4 diopters in one study and 1.7 diopters in another at 12 months, while untreated eyes steepened slightly.[2] That’s a meaningful sign the cornea has stabilized, but it’s small compared with the distortion most people with keratoconus have. That’s why most people still need specialty lenses afterward.
It may reduce the need for transplants. After cross-linking was introduced across the Netherlands, about 25% fewer corneal transplants were performed for keratoconus over the next three years than in a comparable period before.[3] That’s an observational finding, and other changes over the same period may have contributed.
It has side effects, mostly temporary. In the US trials, the most common effects in treated keratoconus eyes included corneal haze, damage to the corneal surface that needed to heal, eye pain, and blurred or reduced vision. Dry eye was also reported. Most resolved in the first month, though haze could take up to 12 months. In 1% to 2% of patients, some findings, including haze and scarring, were still present at 12 months.[2] The FDA label also notes that safety and effectiveness have not been established in children under 14.[2]
What scleral lenses do, and don’t do
They restore vision, often dramatically. In a study of 157 keratoconic eyes, average vision improved from 0.50 logMAR in glasses (about 20/63) to 0.08 logMAR in scleral lenses (about 20/24).[4] In a study of 89 eyes fitted with mini-scleral lenses, vision and patients’ ratings of their everyday visual function both improved significantly.[7]
They can delay or avoid a transplant in advanced disease. A Belgian clinic found that 40 of 51 eyes with severe keratoconus, which would otherwise have been referred for transplant, were still wearing scleral lenses after about two and a half years on average.[6]
They don’t stop the disease. In that 157-eye study, 14.6% of eyes lost some of their best scleral lens vision during the study period, all because the keratoconus progressed.[4] A lens can be refitted as the cornea changes, but it can’t keep the cornea from changing.
How they work together
For someone with progressive keratoconus, the usual sequence is: confirm the disease is progressing, have cross-linking to stabilize it, then fit or refit lenses for the best vision once the eye has healed. Many people wear glasses or lenses before cross-linking too.
A small study followed 23 eyes of 21 people who had cross-linking and then wore scleral lenses for at least a year. Lenses were prescribed an average of 6.75 months after cross-linking, with wide variation. Over the first year of lens wear, the corneas stayed stable and vision with scleral lenses was significantly better than with the patients’ previous correction.[5] It’s a small, retrospective study, but it matches what fitters see: the two treatments sit comfortably together.
Questions to ask your eye doctor
- Is my keratoconus progressing? How are you measuring that?
- Am I a candidate for cross-linking, and which technique do you use?
- Should I stop wearing my lenses before scans or before the procedure? For how long?
- How long after cross-linking should I wait before a scleral lens fitting or refit?
- Will my lens need to be refitted after cross-linking changes my cornea?
For more on lens options, see scleral lenses vs corneal transplant and our keratoconus page.
Common questions
If I have cross-linking, will I still need contact lenses?
Usually, yes. Cross-linking aims to stop the cornea from getting worse, and in the trials behind the US approval the cornea flattened only slightly on average. Most people still need glasses or specialty lenses to see clearly, and many wear scleral lenses.
Can scleral lenses stop my keratoconus from progressing?
No. A scleral lens changes how light enters your eye. It doesn't strengthen the cornea. In a study of keratoconic eyes wearing scleral lenses, some lost lens-corrected vision over time because the keratoconus progressed.
How soon after cross-linking can I be fitted for scleral lenses?
Your surgeon and fitter will decide based on how your eye heals. In one small study, lenses were prescribed on average a little under seven months after cross-linking, with wide variation between patients.
Do I need cross-linking if my keratoconus is stable?
Cross-linking is aimed at keratoconus that is progressing. Whether yours is progressing is a question for your eye doctor, who will compare corneal scans over time.
Can I keep wearing my lenses until cross-linking?
Often, but ask your surgeon. Some ask you to stop wearing contact lenses for a period before measurements or the procedure, so the scans reflect your cornea's true shape.