Why glasses stop being enough
Keratoconus makes the cornea, the clear front window of the eye, thin and bulge into a cone. That creates two kinds of focusing problem. One is the familiar kind: nearsightedness and regular astigmatism, which glasses correct well. The other is irregular astigmatism, where the surface is uneven in ways a spectacle lens can’t match. That’s what causes the ghosting, smearing and halos many people describe.
A rigid contact lens, including a scleral lens, corrects irregular astigmatism because its smooth front surface takes over the job of the uneven cornea. A scleral lens does this while resting on the white of the eye, vaulting over the cornea with a layer of saline underneath.
Side by side
| Glasses[2] | Scleral lens[1] | |
|---|---|---|
| How it corrects | A lens in front of the eye. Corrects regular focusing errors | Replaces the cornea’s irregular surface optically |
| Vision in keratoconus | Often good in early disease. Gets worse as the cornea becomes more irregular | Usually sharp, even in advanced disease |
| Touches the eye | No | Rests on the white of the eye, not the cornea |
| Handling | Put them on | Daily insertion, removal, cleaning, and filling with saline |
| Infection risk | None from the glasses themselves | Small, as with all contact lenses |
| Fitting | A standard eye test | Custom lens, often several visits |
| Stops progression? | No | No |
| Who it suits | Milder keratoconus, or anyone as a backup | People whose vision isn’t good enough in glasses |
How much difference a lens makes
In scleral lens studies, the gain is large. In a study of 157 keratoconic eyes fitted with scleral lenses, average corrected vision improved from 0.50 logMAR in glasses (about 20/63) to 0.08 logMAR in scleral lenses (about 20/24).[1] In a study of 89 eyes of 50 people, vision improved significantly with mini-scleral lenses, and people’s own ratings of their everyday visual functioning improved too.[3]
Across all lens types, the pattern is the same. At a US academic eye clinic, people with keratoconus seen in 2020 had average vision of 0.35 logMAR in glasses with their best-corrected prescription (about 20/45), improving to 0.13 logMAR (about 20/27) in contact lenses. Scleral lenses were prescribed for the people with the most advanced disease, and still gave good vision.[2]
Rigid lenses also help both eyes work together. A study comparing glasses with corneal rigid lenses in adults with keratoconus found better distance and near vision, and better depth perception, with the lenses.[5]
When glasses are enough
Vision isn’t the only thing that matters. A cross-sectional study of 67 people with moderate to severe keratoconus found no significant difference in overall vision-related quality of life between people using glasses, corneal rigid lenses, or ring segment implants.[4] A snapshot like this can’t tell you whether those people would have done better if they’d switched, but it’s a reminder that some people are happy in glasses.
In the large CLEK study of 1,209 people with keratoconus, 65% wore rigid gas permeable lenses at the start of the study, and most of those (73%) said their lenses were comfortable.[8] Lenses are common, but they aren’t compulsory. Glasses remain a reasonable choice when they give you the vision you need for driving, work and reading.
Glasses prescriptions may be improvable. In a study of 37 eyes with keratoconus, a prescription calculated from measurements of the eye’s optical errors gave better vision than a standard eye test in 68% of eyes, and 32% gained more than one line on the chart.[6] Another research team found that experimental spectacle lenses designed for irregular astigmatism improved vision in 14 of 23 eyes (61%).[7] Neither approach is widely available yet.
Questions to ask your eye doctor
- How much better would I see in a rigid or scleral lens than in my glasses?
- Is my keratoconus stable, or is it progressing?
- Would a corneal rigid lens, a hybrid lens, or a soft specialty lens work for me before going to a scleral lens?
- Can my glasses prescription be refined to give me better vision?
- If I try lenses and can’t manage them, what are my other options?
See also scleral vs RGP lenses, scleral vs soft lenses, scleral lenses vs cross-linking, and our keratoconus page.
Common questions
Why can't glasses fix my keratoconus vision?
Glasses correct regular focusing errors, where the eye's curvature is even. Keratoconus makes the cornea irregular, so different parts of it bend light differently. A spectacle lens sits away from the eye and can't follow those irregularities. A rigid contact lens can, because it replaces the cornea's surface optically.
Should I still have glasses if I wear scleral lenses?
Yes. You'll need something to see with before the lenses go in, after they come out, and on days you can't wear them. Ask your eye doctor for an up-to-date glasses prescription, even if it isn't as sharp as your lenses.
Will wearing glasses make my keratoconus worse?
Glasses don't touch or reshape the cornea. Neither glasses nor contact lenses are a treatment for the disease itself. Cross-linking is the treatment designed to slow or stop progression.
Can a better glasses prescription help?
Sometimes. Research teams have shown that prescriptions calculated from detailed measurements of how the eye bends light can give some people with keratoconus sharper vision in glasses than a standard eye test does. These methods are not yet widely available. Ask your eye doctor whether your prescription could be refined.