| Live births 1984–1988, n = 168 475 | Live births 1989–1993, n = 179 181 | Live births 1994–1998, n = 172 584 | p Trend‡ | ||||
| n (%) | CI† (95% CI) | n (%) | CI† (95% CI) | n (%) | CI† (95% CI) | ||
| Severity | |||||||
| VI¶ | 131 (47.1) | 7.8 (6.5 to 9.2) | 135 (55.8) | 7.5 (6.3 to 8.9) | 102 (59.6) | 5.9 (4.8 to 7.2) | 0.04 |
| SVI/BL§ | 147 (52.9) | 8.7 (7.4 to 10.3) | 107 (44.2) | 6.0 (4.9 to 7.2) | 69 (40.4) | 4.0 (3.1 to 5.1) | <0.001 |
| Gestational age | |||||||
| ⩽28 weeks | 24 (8.6) | 640.0 (414.3 to 937.3) | 24 (9.9) | 361.4 (232.9 to 533.0) | 15 (8.8) | 182.5 (102.5 to 299.1) | <0.001 |
| 29–32 weeks | 22 (7.9) | 153.0 (96.1 to 230.7) | 19 (7.9) | 102.2 (61.6 to 159.1) | 7 (4.1) | 37.1 (14.9 to 76.2) | 0.001 |
| 33–36 weeks | 33 (11.9) | 43.5 (30.0 to 61.1) | 26 (10.7) | 30.1 (19.7 to 44.0) | 24 (14.0) | 27.0 (17.3 to 40.1) | 0.07 |
| ⩾37 weeks | 199 (71.6) | 12.5 (10.9 to 14.4) | 173 (71.5) | 10.3 (8.8 to 11.9) | 125 (73.1) | 7.8 (6.5 to 9.4) | <0.001 |
| Birth weight** | |||||||
| <1000 g | 16 (5.8) | 345.6 (198.8 to 555.1) | 18 (7.4) | 329.7 (196.5 to 516.0) | 7 (4.1) | 100.3 (40.4 to 205.5) | 0.004 |
| 1000–1499 g | 23 (8.3) | 231.9 (147.5 to 345.9) | 16 (6.6) | 153.0 (87.7 to 247.2) | 12 (7.1) | 105.9 (54.8 to 184.3) | 0.02 |
| 1500–1999 g | 21 (7.5) | 100.7 (62.5 to 153.5) | 17 (7.0) | 75.8 (44.2 to 121.0) | 12 (7.1) | 51.4 (26.6 to 89.6.0) | 0.06 |
| 2000–2499 g | 29 (10.4) | 39.3 (26.3 to 56.4) | 33 (13.7) | 43.5 (29.7 to 61.3) | 13 (7.7) | 17.2 (9.2 to 29.4) | 0.02 |
| 2500–3499 g | 126 (45.3) | 13.4 (11.2 to 16.0) | 93 (38.4) | 10.1 (8.1 to 12.4) | 80 (47.4) | 9.0 (7.2 to 11.2) | 0.004 |
| ⩾3500 g | 63 (22.7) | 10.0 (7.6 to 12.7) | 65 (26.9) | 9.3 (7.2 to 11.9) | 45 (26.6) | 6.4 (4.6 to 8.5) | 0.001 |
| Sex | |||||||
| Female | 124 (44.6) | 15.1 (12.6 to 18.0) | 84 (34.7) | 9.6 (7.7 to 11.9) | 68 (39.8) | 8.1 (6.3 to 10.2) | <0.001 |
| Male | 154 (55.4) | 17.8 (15.1 to 20.9) | 158 (65.3) | 17.2 (14.6 to 20.0) | 103 (60.2) | 11.7 (9.5 to 14.1) | 0.001 |
| Plurality | |||||||
| Singletons | 264 (95.0) | 16.0 (14.1 to 18.1) | 236 (97.5) | 13.5 (11.8 to 15.4) | 156 (91.2) | 9.3 (7.9 to 10.9) | <0.001 |
| Multiples | 14 (5.0) | 38.9 (21.3 to 65.3) | 6 (2.5) | 13.1 (4.8 to 28.6) | 15 (8.8) | 29.6 (16.6 to 48.8) | 0.54 |
| Total | 278 (100.0) | 16.5 (14.6 to 18.6) | 242 (100.0) | 13.5 (11.9 to 15.3) | 171 (100.0) | 9.9 (8.5 to 11.5) | <0.001 |
*Category specific denominators were used to calculated individual rates; †CI, cumulative incidence per 10 000 live births; ‡p value for the test for trend over time; ¶VI, visual impairment defined as a corrected visual acuity in the better eye of 6/18 to 6/60; §SVI/BL, severe visual impairment/blindness defined as a corrected visual acuity in the better eye of less than 6/60 or no useful vision; **birth weight was missing for 2 children born in 1994–1998.