Table 1

Characteristics of keratoconus patients and age-matched/sex-matched control group of the Achmea Health Database

CharacteristicsKeratoconus casesControlsTotal
No. of enrollees (%)2051 (14.3)12 306 (85.7)14 357
Years of enrolment in plan, no. (%)
 1 year45 (2.2)973 (7.9)1018 (7.1)
 2 years101 (4.9)956 (7.8)1057 (7.4)
 3 years183 (8.9)1217 (9.9)1400 (9.8)
 4 years218 (10.6)1304 (10.6)1522 (10.6)
 5 years205 (10.0)1146 (9.3)1351 (9.4)
 6 years1299 (63.3)6710 (54.5)8009 (55.8)
Age in years, mean (SD)29.7 (6.5)29.8 (6.4)29.8 (6.5)
Sex, no. (%)
 Male1289 (62.8)7734 (62.8)9023 (62.8)
 Female762 (37.2)4572 (37.2)5534 (37.2)
Socioeconomic status, no. (%)
 Below average688 (33.5)3227 (26.2)3915 (27.3)
 Average1038 (50.6)6824 (55.5)7863 (54.8)
 Above average277 (13.5)1708 (13.9)1985 (13.8)
 Unknown48 (2.3)1546 (4.4)594 (4.1)
Urbanisation status, no. (%)
 Urban1635 (79.7)8790 (71.4)10 425 (72.6)
 Rural378 (18.4)3050 (24.8)3428 (23.9)
 Unknown38 (1.9)466 (3.8)504 (3.5)
  • Data are no. (%) or mean (SD).

  • Socioeconomic status and urbanisation status are based on ‘postal codes’-related data from the Statistics Netherlands.14 Socioeconomic status is determined by a neighbourhood’s average income, level of unemployment, percentage of low-income households, and percentage of people with a low level of education. Urban and rural areas are defined as ≥1000 and <1000 households per km2, respectively.