Author: Claude (AI), from PubMed abstracts · Reviewed by: Dr Mina Abdelmseih · Reviewed: 2026-11-15 · Review due: 2027-11-15

Educational content only. Not personalised medical advice. Clinical decisions remain the responsibility of the treating clinician.

Keratoconus and corneal cross-linking

Keratoconus is a lifelong, sight-threatening corneal ectasia that usually begins in the second to fourth decade of life and causes vision loss through thinning, irregular astigmatism and scarring [S4] [S2]. Corneal collagen cross-linking (CXL) with riboflavin and ultraviolet A light is the only treatment shown to slow progression [S4]. Progression is fastest in young patients and steep corneas, so early detection matters [S2].

Key points - Untreated keratoconus steepened by a mean of 0.7 D in Kmax over 12 months in a meta-analysis of 11 529 eyes; younger age and Kmax above 55 D predicted more progression [S2]. - Eye rubbing is consistently associated with keratoconus (pooled OR 6.46), although causality is unproven [S3]. - There is no unified definition of progression; Kmax change is the most common criterion [S10]. - Epithelium-off CXL is the reference technique; no alternative (transepithelial or accelerated) has been shown to be better at halting progression [S4] [S9]. - In children, pooled progression after epithelium-off CXL was about 10% [S6].

Evidence last checked: 2026-10-17 (PubMed abstracts).

Red flags

• A young patient (under 17 years) or Kmax steeper than 55 D: higher risk of progression; closer follow-up and a lower threshold for CXL are advised [S2].
• Vision that can no longer be fully corrected with glasses in a young person: consider keratoconus [S7].
• Refractive surgery candidates. Missed keratoconus before refractive surgery can lead to ectasia [S7].
• Pain, redness or an infiltrate in the days after CXL. Infectious keratitis after epithelium-off CXL is uncommon but presented at a mean of 4.8 days, mostly bacterial [S5].
• Corneal perforation or scarring can occur in keratoconus [S4].

Recognise it

• Frequency. Reported as about 1 in 2000 people [S1] or 86 in 100 000 [S2].
• Risk factors. Eye rubbing (pooled OR 6.46 from six case-control studies) [S3].
• Symptoms. Gradual increase in corneal curvature and decrease in visual acuity, with impact on quality of life [S1].

Confirm it

• Diagnosis is based on clinical examination and corneal imaging; early cases without clinical signs depend on topography or tomography interpreted by trained specialists [S7].
• AI tools. A Cochrane review of 63 studies found summary sensitivity 98.6% and specificity 98.3% for manifest keratoconus, and 90.0% and 95.5% for subclinical keratoconus, but the evidence was low to very low certainty [S7].
• Defining progression. Of 221 studies, 85.5% used Kmax, and most assessed progression over 6 to 12 months; criteria are not unified [S10].

Manage it

Before acting on this section, check the national and local guidelines, product information and regulatory approvals that apply where you practise. See the medical disclaimer.

Tier A (primary care / no specialist)

• Advise patients not to rub their eyes [S3].
• Refer young people whose vision is no longer fully corrected by glasses for corneal imaging [S7] (see "Refer when").

Tier B (general eye clinic)

• Refract, examine and arrange topography or tomography where available [S7].
• Monitor for progression, most commonly by Kmax change over 6 to 12 months [S10]; follow younger patients and steep corneas more closely [S2].
• Spectacles and contact lenses are not covered by these abstracts.

Tier C (specialist centre)

1. CXL for progressive disease. A Cochrane review (2015) of 3 RCTs (219 eyes analysed) found treated eyes about 2 D less steep and with about 2 lines better uncorrected vision at 12 months, but evidence was very low quality [S1]. Adverse effects were not uncommon but mostly transient [S1].
2. Epithelium-on versus epithelium-off. A Cochrane review of 13 RCTs found no clear difference in Kmax at 12 months or later (very low certainty); epithelium-off CXL caused slightly more haze or scarring (moderate certainty). It remains unknown whether any approach is better than epithelium-off [S4].
3. Accelerated versus conventional. A meta-analysis of 14 RCTs found conventional CXL gave greater flattening and a deeper demarcation line, whereas accelerated CXL caused less thinning; visual outcomes did not differ [S9].
4. Thin corneas (under 400 µm). In 29 mostly retrospective studies (470 eyes), modified CXL protocols flattened Kmax by 1.4 D at 12 months without reported major complications [S12].
5. Children. In 35 studies (2186 eyes) most CXL protocols achieved stabilisation above 80% [S11]; pooled progression after epithelium-off CXL was 9.9% [S6].
6. After CXL. Postoperative steroids and bandage contact lenses, and atopic or herpetic disease, were associated with infection; prophylactic antivirals are advised where appropriate [S5].
7. Visual rehabilitation. A network meta-analysis suggests combinations of phakic intraocular lenses, intracorneal ring segments and CXL for regular corneas up to stage 3, and surface ablation with ring segments and CXL for irregular corneas [S8]. This is a complex synthesis and should be applied by specialists.

Refer when

Pitfalls

• Waiting for progression in a child; younger patients progress faster [S2].
• Assuming transepithelial or accelerated CXL is equivalent in every respect [S4] [S9].
• Using a single Kmax reading as the only progression criterion [S10].
• Missing early keratoconus before refractive surgery [S7].

Evidence notes

• The Cochrane CXL trials were at high risk of performance, detection and attrition bias and enrolled only adults [S1].
• The two prevalence estimates differ (1 in 2000 vs 86 in 100 000) [S1] [S2].
• Paediatric and thin-cornea data are largely observational with high heterogeneity [S6] [S12].
• Most AI studies were case-control designs at high risk of bias [S7].
• Not covered by these sources: spectacle and contact lens fitting, keratoplasty outcomes for keratoconus, cost and access to CXL in low-resource settings.

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• Contact lens complications and safe wear

References

See the numbered source list below. Each marker [S#] links to its PubMed and DOI record.