C3R (corneal collagen cross-linking) is right for you if you have a progressive corneal condition like keratoconus or corneal ectasia, meet specific medical criteria, and want to halt further vision loss.
Eligibility is based on your diagnosis, corneal thickness, age, and overall eye health, so a thorough evaluation by an eye specialist is essential.
If you’re considering C3R and want to know if you qualify, this guide will walk you through who benefits most, what doctors look for, and important factors to weigh before making a decision.
What Is C3R and How Does It Work?
C3R, or corneal collagen cross-linking, is a minimally invasive treatment that aims to strengthen and stabilise the cornea. It’s primarily used to treat progressive corneal diseases like keratoconus and corneal ectasia.
The procedure involves applying riboflavin (vitamin B2) eye drops to the cornea and then activating them with ultraviolet A (UVA) light. This process creates new chemical bonds between collagen fibers, increasing the cornea’s rigidity and helping to halt further deformation.
Who Is Eligible for C3R? Key Criteria
Primary Candidates
- Keratoconus patients: C3R is most commonly recommended for people diagnosed with keratoconus, a condition where the cornea thins and bulges outward, distorting vision.
- Progressive corneal ectasia: Individuals experiencing progressive thinning and bulging of the cornea, whether from keratoconus or post-refractive surgery complications (like post-LASIK ectasia), are strong candidates.
- Post-LASIK or PRK ectasia: If you’ve developed corneal instability after laser vision correction, C3R can help stabilise your cornea and prevent further deterioration.
Age Requirements
Most guidelines recommend C3R for patients aged 14 years and older. Younger patients may be considered if the disease is progressing rapidly, but careful monitoring and individualised assessment are important.
Corneal Thickness
- Minimum corneal thickness: Standard C3R requires ≥ 400 µm stroma after epithelial removal; some clinics use modified “epi‑on” or contact-lens-assisted protocols for thinner corneas. This is crucial to protect the deeper layers of the eye from UVA exposure and prevent complications.
- If your cornea is thinner, special “epithelium-on” or customised protocols may be considered, but these are less common and require expert evaluation.
Disease Progression
C3R is generally reserved for patients with evidence of progression, such as:
- Worsening vision or prescription
- Increasing corneal curvature (steepening)
- Changes in corneal topography or tomography
Doctors may recommend close observation for mild, stable cases, especially in children or those with good vision in one eye.
Exclusion Criteria
C3R may not be suitable if you have:
- Corneal thickness less than 400 microns (for standard protocols)
- Active or recent herpes simplex keratitis
- Ongoing eye infection, severe scarring, or opacification
- Poor epithelial wound healing or severe ocular surface disease
- Autoimmune disorders or uncontrolled systemic disease
What Are the Goals and Benefits of C3R?
Main Objectives
- Stop progression: The primary goal is to halt or slow the progression of corneal thinning and bulging, preserving vision and delaying or avoiding the need for corneal transplantation.
- Increase corneal stiffness: Cross-linking boosts the biomechanical stability of the cornea, helping it resist further bulging.
- Maintain or slightly improve vision: C3R primarily prevents further loss. Some patients notice modest vision improvement over time, especially when combined with contact lenses or procedures like Intacs.
Long-Term Outcomes
Clinical studies show that C3R is effective in halting disease progression for most patients, with benefits lasting several years. Some may require repeat treatment if progression resumes, especially in younger or high-risk individuals.
What to Expect? The C3R Procedure and Recovery
How does the Procedure work?
- The eye is numbed with anaesthetic drops, and the epithelium—the thin outer layer of the cornea—is gently removed to allow riboflavin absorption.
- Riboflavin (vitamin B2) drops are applied for about 30 minutes to fully saturate the corneal tissue.
- The cornea is exposed to UVA light for another 30 minutes, activating the cross-linking process.
- A soft bandage contact lens is placed to aid healing, usually removed after 5 days.
Recovery and Risks
- Most patients have mild discomfort, increased light sensitivity, and blurry vision for a few days.
- Serious complications are rare, but can include delayed healing, infection, transient haze, or corneal damage, especially if eligibility criteria are not strictly followed.
- An alternative version called “epithelium-on” (transepithelial) C3R leaves the surface layer intact. It’s more comfortable and has a shorter recovery, but its effectiveness is still debated and may be lower, especially in progressive cases.
Special Considerations Before Choosing C3R
Individual Assessment
C3R isn’t right for everyone. Your eye doctor will evaluate:
- Corneal thickness and shape (via topography and pachymetry)
- Rate and pattern of disease progression
- Overall eye and systemic health
- History of eye infections or surgeries
Pediatric and High-Risk Cases
Children and teens with fast-progressing keratoconus may benefit from early C3R, but they need regular follow-ups and sometimes retreatment. High-risk eyes (very thin or steep corneas) may need alternative protocols or additional procedures.
Repeat or Combined Treatments
If keratoconus progresses after initial C3R, repeat cross-linking may be considered. C3R can also be combined with other treatments like Intacs, corneal rings, or specialty contact lenses for better vision outcomes.
C3R Eligibility at a Glance
| Eligibility Factor | Standard C3R Criteria | Notes |
| Age | 14 years and older | Younger patients may qualify if disease is progressing rapidly |
| Diagnosis | Keratoconus, corneal ectasia | Includes post-LASIK or PRK ectasia |
| Corneal Thickness | >400 microns (after epithelium removal) | Modified protocols available for thinner corneas |
| Disease Progression | Documented progression | Based on topography, vision changes, or prescription shift |
| Exclusions | Active infection, thin cornea, HSV, severe scarring, poor healing, autoimmune disease | These conditions may increase risk or limit effectiveness |
Recap and Next Steps
C3R is a proven, safe, and effective treatment for halting progressive corneal diseases like keratoconus and ectasia—if you meet the right criteria.
If you or a loved one has been diagnosed with a corneal condition, consult a corneal specialist for a detailed evaluation. With early intervention and proper selection, C3R can help preserve vision and delay or avoid more invasive surgery. Book an appointment with your eye doctor to discuss your options and ensure the best path for your long-term eye health.
Frequently Asked Questions About C3R Eligibility
Can I have C3R if my cornea is thinner than 400 microns?
Standard C3R is not recommended for corneas thinner than 400 microns due to safety concerns. Some centres offer modified protocols, but these are considered on a case-by-case basis by corneal specialists.
Is C3R painful?
Most patients describe mild discomfort, watering, and light sensitivity for a few days after the procedure. Pain is usually well-managed with medications and improves as the cornea heals.
Will my vision improve after C3R?
C3R’s main goal is to stop further vision loss. Some patients notice a slight improvement in vision or corneal shape, but significant vision recovery is not typical unless combined with other treatments.
How soon can I return to normal activities after C3R?
Most people return to work and daily activities within a week. Avoid rubbing your eyes and follow your doctor’s instructions for drops and follow-up visits.
