Cross-linking in children, teenagers and adults: what a five-year US study found

If you or your child have been told the words "progressive keratoconus", one of the first questions is usually about cross-linking: does it work, does it last, and does it matter whether you are 14 or 34 when you have it? A new five-year study from a United States eye hospital looks at that mix of ages. This article is based on the published abstract only; full-text details such as attrition, the numbers behind each result, funding and the authors' stated limitations were not available to us.

What the study looked at

Chen and colleagues at a tertiary care ophthalmology centre in the United States reviewed the records of patients who had standard epithelium-off corneal cross-linking (CXL) for progressive keratoconus between January 2017 and May 2023. To be included, a patient needed a diagnosis of progressive keratoconus and at least 12 months of follow-up. The analysis covered 243 eyes from 193 patients, and 80 of those eyes (32.9%) belonged to paediatric patients younger than 18 years. The remainder were adolescents and adults; the abstract does not say how many were in each group or how the groups were defined.

Four things were measured before surgery and at 12-month intervals out to 60 months: corrected distance visual acuity (CDVA, your best vision with glasses or contact lenses), maximum keratometry (Kmax, the steepest point on the corneal map), minimum central corneal thickness (CCTmin) and wavefront aberrations, a measure of how irregular the eye's optics are.

We have written before about what cross-linking is and who it is for. If you are new to the topic, start with our post on corneal cross-linking for keratoconus in New Zealand.

What the abstract reports

The authors describe cross-linking as being associated with "significant and sustained" improvements. Taking each measure in turn:

• Vision (CDVA): mean corrected vision improved from baseline and remained improved through 60 months (P < .05).
• Corneal steepness (Kmax): the greatest mean flattening occurred within the first two years, with stability maintained through 48 months (P < .05).
• Corneal thickness (CCTmin): the thinnest point of the cornea was thinner after treatment than before, then showed a trend of gradual rethickening after 24 months (attributed to stromal remodelling) while remaining below baseline (P < .05).
• Wavefront aberrations: remained stable.
• Safety: adverse events were described as minimal, with no counts given in the abstract.

A quick word on "P < .05". A P-value is the probability that a difference at least as large as the one observed would turn up by chance alone if there were really no change. A P-value below 0.05 means that chance is less than one in twenty, which is the conventional threshold for calling a result "statistically significant". It tells you the change is unlikely to be noise; it does not tell you how big the change was. The abstract gives no mean values, standard deviations or 95% confidence intervals, so we cannot say how many letters of vision were gained or how many dioptres the cornea flattened.

Why the age mix matters

Much of the cross-linking evidence comes from adults, and keratoconus in children and teenagers tends to behave differently: it is often diagnosed at a steeper stage and can progress faster. That is why our earlier piece on early detection in teenagers matters so much. This study is useful because roughly a third of the treated eyes were in under-18s, and the authors' overall conclusion is that the improvements were sustained "across pediatric, adolescent, and adult patients".

What the abstract does not do, though, is give us the results broken down by age group. We cannot tell from it whether the children flattened more or less than the adults, or whether they were more likely to need a second treatment. If the full paper contains those comparisons, we will update this post when we can access it.

What the studies can't tell us

This is a retrospective, uncontrolled study from a single tertiary centre. That design has real limits:

• No comparison group. Every result is a change from each eye's own pre-treatment baseline. Without untreated eyes to compare against, we cannot separate the effect of cross-linking from the natural tendency of some keratoconus to slow down on its own, particularly in older adults.
• Unknown drop-out. Patients only needed 12 months of follow-up to be included, so the number of eyes actually contributing data at 48 and 60 months is not stated in the abstract. Five-year figures built on a subset of the original 243 eyes are less reliable than they look.
• No effect sizes. "Significant" here means statistically significant. We do not have the size of the vision or Kmax change, so we cannot judge whether the improvement is something a patient would notice.
• Unmasked, retrospective measurements collected during routine care rather than under a research protocol.
• Funding and conflicts are not visible in the abstract.
• Generalisability. This is a US tertiary-referral population. New Zealand has a high burden of keratoconus, especially among Māori and Pasifika communities, and the age at presentation and severity may differ from this cohort.

None of this means the findings are wrong; they sit alongside the broader cross-linking literature, which generally shows slowing of progression rather than a cure. But "was associated with sustained improvement" is the honest phrasing, and a five-year abstract is not a promise of a stable cornea for life.

What this means for you in Hamilton

The most useful message in this study is the word in front of the surgery: progressive. Every eye in this cohort was treated because progression had been documented. That documentation is the job of a keratoconus-focused optometrist, and it happens before anyone books a theatre slot.

At Rose Optometry, the optometrist team (Jagrut Lallu, Jacqueline Rowe and colleagues) diagnose keratoconus, map the cornea with sequential tomography so that change over time can be measured rather than guessed, and refer to an ophthalmologist for cross-linking when the maps show the cornea is actually steepening. Cross-linking is performed by an ophthalmologist, but the decision about whether and when it is needed rests on that sequence of maps, which is why we emphasise advanced corneal imaging and keratoconus monitoring. After cross-linking, the same team continues the monitoring and fits scleral or other specialty lenses if your vision needs more than glasses can give.

If you have keratoconus, or a teenager in the family keeps needing a new prescription, you can read more about the keratoconus service at Rose Optometry or book a keratoconus assessment in Hamilton. Whatever your age, the first step is a baseline map, not a referral letter.

Reference

• Chen KM et al. Long-term outcomes of corneal crosslinking for keratoconus across pediatric, adolescent, and adult populations in a diverse U.S. population. J Cataract Refract Surg. 2026;52(9):872-878. PMID 41774470. https://doi.org/10.1097/j.jcrs.0000000000001932