What each one is
Intracorneal ring segments are small, curved implants that a surgeon places in tunnels inside the cornea, the clear front window of the eye. They flatten and reshape a cone-shaped cornea so it’s more regular. Intacs is one brand. Others include Ferrara rings, KeraRings and MyoRings, and some surgeons now use ring segments made from donor corneal tissue instead of plastic.[2]
In the US, the FDA approved Intacs for keratoconus in 2004 through a Humanitarian Device Exemption. The approval covered adults 21 and over who could no longer see adequately with contact lenses or glasses, who had a clear central cornea and enough corneal thickness (at least 450 microns at the incision site), and for whom a transplant was the only remaining option. The stated goal was to restore functional vision and possibly defer a transplant.[1]
A scleral lens is a large, rigid contact lens. It rests on the white of the eye (the sclera), arches over the cornea without touching it, and holds a layer of saline in front of it. The smooth front surface of the lens replaces the cornea’s irregular one optically. Nothing about the cornea itself changes.
Side by side
| Ring segments (Intacs and similar)[2][3] | Scleral lens[11] | |
|---|---|---|
| What it is | A surgical implant inside the cornea | A custom lens you put in each morning and take out at night |
| How it helps | Flattens and regularizes the cornea | Masks the irregular cornea with a smooth optical surface |
| Vision | Improves vision without correction and with glasses for many people. Many still need a lens afterward | Usually gives sharp corrected vision, even in advanced keratoconus |
| Reversible? | Segments can be repositioned or removed, which is a second procedure | Yes. Stop wearing it |
| Daily effort | None once healed | Insertion, removal, cleaning, and filling every day |
| Main risks | Segment migration or exposure, thinning over the segment, infection, a second procedure | Handling difficulty, fogging, infection risk shared with all contact lenses |
| Stops progression? | Not designed to. Often combined with cross-linking | No |
| Who it suits | People who can’t tolerate contact lenses and have no central scarring | Most people with keratoconus who can’t see well in glasses, including advanced cases |
What the research on ring segments shows
Vision usually improves, but results vary. A 2026 systematic review pooled 17 studies covering 544 eyes treated with Intacs for keratoconus. It found consistent improvements in vision and corneal shape, but called device-related complications “an important limitation”, including segment migration, extrusion, and the need for repositioning or removal.[3]
Long-term follow-up is small but encouraging. A Greek study followed 17 eyes of 15 people for about five years. Before surgery, all had uncorrected vision of 20/50 or worse. At the last visit, 10 of the 17 eyes (59%) saw 20/50 or better without correction, 10 eyes gained between one and eight lines of vision with glasses, and one eye lost three lines. There were no late complications in that group.[4]
Complications can be significant in some series. In a US study of a modified technique in 20 eyes with moderate to advanced keratoconus, 6 eyes developed segment exposure because the cornea thinned over the implant, one had a perforation into the front chamber of the eye, and one developed a dense corneal infiltrate.[5] A 2025 review notes that newer laser-created tunnels reduce complications compared with older mechanical methods, and that long-term serious adverse events are uncommon.[2]
Quality of life can be similar. A cross-sectional study of 67 people with moderate to severe keratoconus found similar overall vision-related quality of life in those using glasses, corneal rigid lenses, or ring segments. The ring segment group scored higher on two specific areas, social functioning and dependency, than the rigid lens group.[10] A snapshot like this can’t show cause and effect.
When people use both
Ring segments and scleral lenses aren’t always alternatives. Many people have ring segments and later wear a lens.
- After ring segments, many eyes still need a lens. In a Brazilian study of 55 eyes with advanced keratoconus, 7 of 13 eyes (53.85%) that had ring segments were later fitted with a scleral lens to improve vision. In the same study, eyes fitted with a scleral lens without surgery gained significantly more corrected vision than eyes that had ring segments.[6] It’s a small, retrospective study, so treat it as a signal rather than proof.
- Lenses can rescue a disappointing result. In a study of 19 people fitted with contact lenses after ring segments, all of whom had been contact lens intolerant before surgery, 17 achieved good or medium comfort. Two (10.5%) didn’t and went on to have a transplant.[7] In 9 eyes of 6 people unhappy with their vision after ring segments, mini-scleral lenses improved average corrected vision from 0.38 to 0.09 logMAR (roughly 20/48 to 20/25).[8]
- Scleral lens wear over ring segments looks stable. A study of 65 people with keratoconus, some with ring segments and some without, found vision stayed stable over a year of daily scleral lens wear in both groups, with small measurable changes in corneal shape.[9]
What scleral lenses offer, and where they fall short
In a study of 157 keratoconic eyes, average corrected vision improved from 0.50 logMAR in glasses (about 20/63) to 0.08 logMAR in scleral lenses (about 20/24).[11] That’s without any surgery, and the lens can be refitted if the cornea changes.
Questions to ask your eye doctor
- Is my cornea a good shape for ring segments? Is there scarring in the center?
- What vision do you expect after ring segments, with and without glasses or lenses?
- How often do your patients need a segment repositioned or removed?
- Is my keratoconus progressing? Should I have cross-linking first or at the same time?
- If I try a scleral lens first and it works, is there still a reason to have ring segments?
For more on the other options, see scleral lenses vs cross-linking, scleral lenses vs corneal transplant, and our keratoconus page.
Common questions
Can I wear a scleral lens after Intacs?
Often, yes. Because a scleral lens vaults over the cornea instead of resting on it, it can be fitted over a cornea with ring segments in it. Small studies and case reports describe good vision with scleral lenses after ring segments, including in people who couldn't tolerate other lenses. Your fitter will check clearance over the segments carefully.
Will Intacs mean I don't need contact lenses?
Some people see well enough afterward with glasses or no correction, but many don't. In one small comparison, more than half the eyes that had ring segments were later fitted with a scleral lens to improve vision further. Ask your surgeon what result is realistic for your cornea.
Can Intacs be removed?
Ring segments can be repositioned or removed if problems develop. Reviews list the need for repositioning or removal among the device-related complications. Ask your surgeon how often they see this and what happens to vision if a segment is taken out.
Do Intacs or scleral lenses stop keratoconus from getting worse?
Neither is designed to. If your keratoconus is progressing, cross-linking is the treatment aimed at stopping that. Some surgeons combine ring segments with cross-linking.
Who is a candidate for Intacs?
The original US approval was for adults 21 and over with a clear central cornea, enough corneal thickness where the segment goes in, and who could no longer see adequately with glasses or contact lenses. Your corneal surgeon will tell you whether you're a candidate.