Corneal ring segments are small, curved inserts placed inside the cornea to flatten a keratoconic cone and make it more regular. They don't cure keratoconus and they don't stop it from progressing. What they can do, in the right eye, is improve how well you see with glasses or contact lenses, and sometimes push a corneal transplant further down the road.
This guide covers the main ring designs (Intacs, Ferrara-type and a few others), who tends to be a candidate, how rings fit with corneal cross-linking, what the published outcomes and complications look like, and what to ask before you book surgery in Colombia or anywhere else.
What corneal rings do (and what they don't)
In keratoconus the cornea thins and bulges forward into a cone. That irregular shape causes nearsightedness, astigmatism and higher-order distortions that ordinary glasses correct poorly. Ring segments go into a tunnel (a "channel") made in the mid-periphery of the cornea. Their thickness pushes the surrounding tissue apart and flattens the center, which reduces some of the steepening and irregular astigmatism.
The US Food and Drug Administration approved Intacs for keratoconus in July 2004 under a Humanitarian Device Exemption, a pathway for devices that serve small patient groups.1 The approved purpose is to reduce or eliminate myopia and astigmatism in keratoconus patients who can no longer see adequately with contact lenses or glasses. The same FDA summary is candid on two points: most patients with the inserts still needed glasses, soft toric lenses or rigid gas permeable lenses afterward, and the agency described the clinical data as not adequate to demonstrate effectiveness.1
Rings reshape the cornea. Cross-linking is the treatment aimed at slowing or stopping progression. Many keratoconus plans use both, but they solve different problems.
Intacs vs Ferrara-type rings: the design differences
All ring segments work on the same principle, but they differ in cross-section, the diameter of the ring (which sets how close it sits to the visual center), thickness and arc length. Those differences change how strongly they flatten and how likely they are to cause halos.
A 2025 narrative review in Clinical Ophthalmology summarizes the main designs.2 Intacs have a hexagonal cross-section and sit at a 7 mm optical zone, with a 6 mm version called Intacs SK. The larger zone places them in thicker peripheral cornea, which the review links to fewer halos and less glare. Ferrara rings and KeraRing segments have a triangular cross-section and sit closer to the center, with a smallest optical zone of 5 mm. A closer, triangular segment generally flattens more, which is why surgeons often choose them for steeper cones.
| Design | Cross-section | Optical zone / diameter | Thickness range | Notes |
|---|---|---|---|---|
| Intacs | Hexagonal | 7 mm | 0.21–0.55 mm | Larger zone, sits in thicker cornea |
| Intacs SK | Hexagonal | 6 mm | Varies by model | Smaller zone variant |
| Ferrara ring | Triangular | Smallest optical zone 5 mm | 0.15–0.35 mm | Arcs of 90, 120, 160 or 210 degrees; made by Mediphacos (Brazil) |
| KeraRing | Triangular | 5 mm apical diameter | 0.15–0.30 mm | Arcs of 90, 160, 210 and 355 degrees; made by Mediphacos (Brazil) |
| MyoRing | Full 360-degree ring | 5–8 mm | 0.20–0.32 mm | The only complete ring; made by Dioptex (Austria) |
| CAIRS | Donor corneal tissue | Varies | Varies | Allogenic segments, first described in 2018 |
CAIRS (corneal allogenic intrastromal ring segments) use donor corneal tissue instead of plastic. They are newer, and the evidence base is growing, including a systematic review and meta-analysis indexed on PubMed.6 If a clinic offers CAIRS, ask how many it has done and where the donor tissue comes from.
Is one type "better"?
There is no simple winner. A Cochrane review that searched for randomized trials comparing ring segments with glasses or contact lenses found none, and concluded that the effectiveness and safety of ring segments for keratoconus remain uncertain at the highest level of evidence.3 Most of what we know comes from case series and cohort studies. In practice, surgeons pick the segment type, thickness and arc length from your topography, the location of the cone and your corneal thickness. A clinic that uses one brand for every patient is worth a follow-up question.
A note on Latin America
Ferrara rings and KeraRing segments are manufactured by Mediphacos in Belo Horizonte, Brazil.2 We could not find published data on how often each ring type is used in Colombia, so we don't make claims about local volumes. Ask the clinic which brand and model it plans to use, and get that in writing.
Who is a candidate for corneal rings
Candidacy depends on disease stage, corneal thickness, central clarity and how well you do with contact lenses. The FDA labeling for Intacs is the strictest reference point. It covers patients who have progressive vision loss that prevents adequate daily vision with contact lenses or glasses, are 21 or older, have clear central corneas, have at least 450 microns of corneal thickness at the planned incision site, and for whom a transplant is the only remaining option to improve functional vision.1
Outside that label, surgeons use broader criteria. The 2025 review describes the ideal candidate as an adult who is contact lens intolerant, has reduced best-corrected vision and has no central corneal scarring.2 It also notes that the required minimum thickness depends on the segment chosen, so it has to be measured before surgery.
| Factor | What the evidence says | What to ask |
|---|---|---|
| Disease stage | Stage 4 (Amsler–Krumeich) eyes are less likely to gain much vision2 | "What stage is my eye, and what gain is realistic for that stage?" |
| Corneal thickness | FDA label: at least 450 microns at the incision site1; one study tied better outcomes to central thickness above 400 µm2 | "What is my thickness at the ring track, and what segment fits it?" |
| Central cornea | Central scarring is a contraindication2 | "Is my central cornea clear enough?" |
| Contact lens tolerance | Rings are aimed at people who can't see well or can't tolerate lenses12 | "Have scleral or specialty lenses been tried?" |
| Steepness | One study used Kmax 57 D to separate mild/moderate from advanced eyes2 | "How does my Kmax affect the plan?" |
The FDA summary lists contraindications including corneas thinner than 450 microns at the incision site, autoimmune, collagen vascular or immunodeficiency diseases, pregnancy or nursing, conditions such as recurrent corneal erosion or corneal dystrophy, and current use of isotretinoin or amiodarone.1 Bring a full medication list to your evaluation.
Your measurements need to reflect your real corneal shape. The 2025 review notes that contact lenses should be stopped before assessment: soft lenses for one week and rigid lenses for two weeks.2 Plan that gap before you fly, and confirm the clinic's own rule. If you're also weighing other options, our candidacy guide explains how corneas are screened before laser vision correction.
Combining rings with corneal cross-linking
Cross-linking strengthens corneal collagen and is the treatment used for progressive keratoconus.2 If your keratoconus is still progressing, a ring alone leaves the underlying problem in place. That's why many surgeons pair the two. Our guides to corneal cross-linking for keratoconus and the keratoconus cross-linking guide cover CXL itself.
The open question is order and timing. The arguments run both ways: some authors think doing CXL first stiffens the cornea and blunts the ring's flattening effect, while same-day treatment avoids a second epithelial removal.2 A meta-analysis of six studies with one-year follow-up, summarized in the review, found no significant difference in refractive astigmatism or best-corrected vision between CXL first, rings first or both on the same day.2
A 2025 retrospective study from the International Journal of Ophthalmology compared three groups over two years: rings and CXL in the same session, CXL one month after rings, and CXL three months after rings. Same-session and one-month treatment gave similar flattening, and both did better than the three-month gap.4 Same-session KeraRing plus CXL has also been reported as effective in conference coverage.5
Same-session treatment means one procedure and one recovery window. A staged plan can mean two trips or a longer stay. Ask the surgeon which sequence they recommend for your eye and why, then build the trip around it.
Outcomes: what the published data show
Results vary with stage, device and technique. A few data points give a sense of the range.
Those numbers come from one retrospective series in the FDA file.1 A separate manufacturer-sponsored European study in the same file reported moderate or severe visual symptoms such as glare, night-vision trouble or fluctuating vision in 15.8% of eyes, and removal of the inserts for dissatisfaction in 12.3%.1 After removal, eyes returned to their pre-surgery state.
Other studies in the 2025 review report refractive astigmatism falling by more than half in one series, and 70% of 55 eyes gaining three or more lines of uncorrected vision at six months after combined procedures in another.2 These are case series, not trials, so ask any clinic for its own outcomes.
Complications and long-term risks
Rings can be removed, and in the FDA file eyes returned to their pre-surgery state after removal.1 Complications still happen, and some show up years later.
- Explantation. A systematic review covering 24 years reported removal rates from 0.5% to 83.3% across studies; high-volume centers reported 0% to 1.4%.2 That spread is a strong argument for surgeon experience.
- Channel creation method. A 2022 meta-analysis found similar visual results with femtosecond laser and mechanical channels, but markedly more complications such as epithelial defects, perforation and wound gaping with mechanical dissection.2
- Late extrusion and migration. Segments can migrate or work their way toward the surface. One report describes extrusion as late as 20 years after implantation.2
- Infection. Infectious keratitis around a segment is reported and can require removal.2
- Corneal melt. Severe melt requiring removal was reported in 5 of 30 advanced eyes with one asymmetric ring design.2
- Halos, glare and foreign-body sensation. These can be enough for people to ask for removal.12
- Channel deposits. Fine deposits around segments have been described and, in one study, did not affect topography or refraction.2
Increasing pain, redness, discharge, a white spot near a segment, or a sudden drop in vision after ring surgery needs prompt examination. Don't wait for your next scheduled visit, and don't fly home with these symptoms without a doctor's clearance.
Because problems can appear years later, you need an ophthalmologist at home who will see you for routine checks and can manage a ring if something changes. Line that up before surgery, not after.
Planning ring surgery abroad
The planning around the procedure is what decides whether a trip works.
- Get current topography and tomography at home. Send scans, refraction and your contact lens history so the surgeon can judge candidacy before you book flights.
- Stop contact lenses on schedule. Use the clinic's rule; the review cites one week for soft and two weeks for rigid lenses.2
- Confirm the full plan in writing. Ring brand, model, thickness and arc; channel method; whether CXL is included and when.
- Ask how long to stay. The surgeon should give you a follow-up schedule and the earliest date they're comfortable with you leaving. Our guide to flying after eye surgery covers the general questions to raise.
- Plan vision correction afterward. Many people still need glasses or specialty lenses after rings.1 Some later have a phakic lens implant; our ICL guide explains that option.
- Arrange home follow-up. Find a cornea specialist who will take over your care.
What about cost?
We could not find reliable, citable price data for ring segments in Colombia, so we don't quote a range. Prices depend on the ring type, whether one or two segments are used, femtosecond versus mechanical channels, and whether cross-linking is bundled. Ask for an itemized written quote per eye. If you're in the US, coverage varies by insurer; some publish specific medical policies on ring segments, so check yours before comparing prices abroad.7
Questions to ask the surgeon
- What stage is my keratoconus, and is it progressing?
- Which ring brand and model, what thickness and arc length, and why that choice for my cone?
- Will you create the channel with a femtosecond laser or mechanically?
- Do you recommend cross-linking, and in the same session or later?
- How many ring procedures do you do a year, and what is your removal rate?
- What vision do you expect with and without glasses or lenses afterward?
- What happens if a segment migrates, extrudes or causes glare? Who pays for removal?
- How many days after surgery should I stay before flying?
- Will you send a written operative report with the device details for my home doctor?
For a broader list, see our questions to ask an eye surgeon abroad. When you have scans in hand, you can request provider options and compare written plans side by side.