Eczema, asthma, hay fever and keratoconus: what a study of over 500,000 adults found about allergy and eye rubbing

If you have keratoconus, or you're a parent watching a child with itchy eyes, eczema and a puffer in the school bag, you've probably heard that allergy and keratoconus travel together. A large new US study in the American Journal of Ophthalmology asked a more specific question: does the risk climb as the number of allergic conditions adds up? It appears to, but the authors are unusually careful about why.

What the study did

Butt and colleagues used electronic health records from the All of Us Research Program, a volunteer cohort of more than 500,000 adults across the United States. They gave each person a simple "atopic burden" score from 0 to 3, adding one point each for asthma, atopic dermatitis (eczema) and allergic rhinitis (hay fever). Allergic conjunctivitis, the itchy-eye condition most directly tied to rubbing, was looked at separately.

Two designs ran side by side. A cross-sectional analysis compared 741 people with a keratoconus diagnosis code against 507,786 without it (508,527 adults in total). A longitudinal analysis followed 283,040 people who were keratoconus-free at baseline for a median of 9.0 years and counted 498 new diagnoses. The models adjusted for age, sex, race and ethnicity, income, education, insurance, smoking, obesity and, importantly, how much contact each person had with the health system.

This was not a clinical trial and nobody was scanned: keratoconus was identified from diagnosis codes, not corneal tomography. The study received no funding; the senior author reports honoraria and research support from several ophthalmic companies.

What it found

In the fully adjusted longitudinal model, the chance of a new keratoconus diagnosis rose with each additional allergic condition. Compared with people who had none, one condition carried a hazard ratio of 1.51 (95% CI 1.14–2.01; P = 0.004) and two conditions a hazard ratio of 2.62 (95% CI 1.53–4.48; P < 0.001). The per-condition trend was a hazard ratio of 1.59 (95% CI 1.30–1.94).

A quick word on those numbers. A hazard ratio of 1.51 means the rate of new diagnoses was about one-and-a-half times higher in that group. The 95% confidence interval is the range within which the true value plausibly sits; if it stays above 1.0, the finding is unlikely to be chance alone. A P-value below 0.05 says the same thing a different way.

Only 77 people had all three conditions and just one of them developed keratoconus, so the authors say the three-condition estimate (HR 7.35; 95% CI 1.03–52.44) is unstable and should not be read as a real number.

Among adults aged 18 to 40 at baseline, the age when keratoconus usually appears, the gradient was steeper (trend HR 1.74; 95% CI 1.31–2.32), and new cases were diagnosed at a median age of 38 years. The cross-sectional data told the same story after full adjustment: a per-condition odds ratio of 1.33 (95% CI 1.21–1.47).

Allergic conjunctivitis stood out on its own, with an odds ratio of 2.81 (95% CI 2.15–3.62). And in 206 of the 335 keratoconus patients who also had atopy (61.5%), the allergy was recorded first, by a median of 4.6 years.

The catch: seeing more doctors means more diagnoses

Before adjustment, the odds ratio for three conditions was 7.12; after adjusting for healthcare contact and socioeconomic factors it fell to 2.06. People with keratoconus in this dataset had been in the health system nearly twice as long (14.5 vs 7.3 years) and had three times as many outpatient visits (224.5 vs 74.5). Someone with asthma, eczema and hay fever simply has more appointments in which a cornea might get noticed.

The authors then ran a matched analysis in the 18 to 40 age group, pairing 105 keratoconus cases with controls who had the same amount of health-system contact. In that comparison the allergy gradient all but vanished (per-condition OR 1.03; 95% CI 0.77–1.38). They are honest that this analysis was underpowered and its confidence interval still includes the main result, so it neither confirms nor rules out a genuine link. Their conclusion is that the findings are "hypothesis-generating rather than a basis for routine screening".

Where eye rubbing fits in

Eye rubbing was never recorded in these health records, and the authors say it "likely accounts for a substantial portion" of what they saw. The story is plausible: itch drives rubbing, rubbing stresses the corneal stroma, and a cornea already prone to thinning is the one that gives. The strong signal from allergic conjunctivitis, the one condition that makes eyes itch directly, fits that picture. But coded records cannot prove it.

What this means for you in Hamilton

Nothing here changes the basics, but it sharpens who should pay attention. If you or your teenager have two or more of asthma, eczema and hay fever, plus itchy eyes, that is a good reason for a proper corneal check rather than a standard glasses test. Our earlier post on spotting keratoconus early in teenagers explains why the years between 12 and 25 matter most.

The front door is a keratoconus-focused optometrist, not a surgeon. At Rose Optometry the optometrist team, including Jagrut Lallu and Jacqueline Rowe, diagnoses keratoconus with corneal tomography, repeats the maps over time to document whether the cornea is changing, and helps you manage itch so rubbing does not tip things over. If sequential scans show progression, the optometrist refers you to an ophthalmologist at the right moment for corneal cross-linking. Before and after that, vision is managed in the clinic, often with scleral lenses. You can read more about the keratoconus service at Rose Optometry or book a keratoconus assessment online.

What the studies can't tell us

• Whether allergy causes keratoconus. This is an observational study of diagnosis codes; it can show that the two travel together, not that one leads to the other.
• How much of the link is detection. The matched analysis was close to null but small (105 cases), so the question is open.
• Anything about eye rubbing directly, because it was not measured.
• Whether the corneas were truly keratoconic. No tomography was used; only 70.3% of cases had two or more codes on separate dates.
• Whether the same pattern holds in New Zealand. This is a US volunteer cohort with a mean age of 57.6 years, and it reports nothing on Māori or Pacific participants, the groups of most interest to a Hamilton clinic.
• Whether treating allergy lowers risk. The study did not test any treatment, and the numbers on dupilumab (4 keratoconus cases among 735 users) were too small to say anything.
• Absolute risk remains low: 4.4 new diagnoses per 10,000 person-years even with two conditions.

Reference

• Butt FR, Dhivagaran T, Miller T, et al. Cumulative Atopic Disease Burden and Keratoconus: Cross-Sectional and Longitudinal Associations in the All of Us Research Program. Am J Ophthalmol. 2026 (published online 5 September 2026). PMID 42700830. https://doi.org/10.1016/j.ajo.2026.09.001