PURPOSE: To describe the annual incidence rate of keratoconus in Denmark 1995-2015 and prevalence of keratoconus in the National Danish Patient Register 1977-2015.

METHODS: All patients diagnosed with keratoconus in the National Danish Patient Register 1977-2015 were included in the study. The annual incidence rates and the overall prevalence of diagnosed keratoconus in the register were calculated using life tables from the general Danish population. A sub-analysis excluding immigrants and descendants was performed.

RESULTS: An increase in the annual incidence rate was seen from 1.24 per 100 000 person-years in 2003 to 3.83 per 100 000 in 2011. The average incidence rate 2011-2015 was 3.60 per 100 000 person-years. A survey of primary-sector ophthalmologists supported that the register data could be considered complete from 2011. The prevalence of diagnosed keratoconus in the National Patient Register 1977-2015 was 44 per 100 000 persons. Excluding immigrants and descendants yielded an average incidence rate 2011-2015 of 2.89 per 100 000 person-years and a prevalence of diagnosed keratoconus in the National Patient Register 1977-2015 of 40 per 100 000 persons.

CONCLUSION: The present incidence rate (based on 2011-2015 data) has increased 2-3-fold during the last 10-15 years. The increase is possibly largely a consequence of more complete data due to the availability of corneal cross-linking, which has changed the referral pattern from the primary sector. Other factors such as better diagnostic tools and immigration may also play a role.