Table 4 Five-year incidence of best corrected visual impairment and blindness stratified by age at baseline in participants.

Age at baseline (years)	Incidence of visual impairment			Incidence of blindness
Age at baseline (years)	N	n	% (CI)	N	n	% (CI)
United States Criterion*
< 40	31	1	3.2 (0.5, 22.2)	35	3	8.6 (2.9, 25.3)
40–49	83	20	24.0 (16.4, 35.3)	94	7	7.4 (3.7, 15.2)
50–59	145	26	17.9 (12.7, 25.4)	179	20	11.2 (7.4, 16.9)
60–69	74	14	18.9 (11.8, 30.3)	82	7	8.5 (4.2, 17.3)
70 +	2	0	NA	3	0	NA
			p = 0.51			p = 0.82
Crude Overall	335	61	18.2 (14.5, 22.8)	393	37	9.4 (6.9, 12.8)
WHO Criterion^φ
< 40	34	3	8.8 (3.0, 26.0)	36	3	8.3 (2.8, 24.6)
40–49	88	8	9.0 (4.7, 17.6)	99	5	5.0 (2.1, 11.9)
50–59	167	26	15.6 (11.0, 22.2)	184	12	6.5 (3.8, 11.3)
60–69	77	11	14.3 (8.3, 24.7)	87	3	3.4 (1.1, 10.5)
70 +	2	0	NA	3	0	NA
			p = 0.24			p = 0.82
Crude overall	368	48	13.0 (10.0, 17.0)	409	23	5.6 (3.8, 8.4)

N = number at risk at baseline; n = incident cases; % (CI) = prevalence and 95 percent confidence interval. p value calculated using test of trend; Number of observations = 424.
U.S. Criterion* Incidence of visual impairment: Person with Baseline best corrected visual acuity (BCVA) of 6/12 or better in better seeing-eye, and follow-up BCVA worse than 6/12 but better than 6/60 (not including 6/12 or 6/60) in better seeing-eye. Incidence of Blindness: Persons with Baseline BCVA better than 6/60 in the better Seeing Eye and follow-up BCVA 6/60 or worse (including 6/60).
W.H.O. Criterion^φ Incidence of visual impairment: Persons with Baseline BCVA 6/18 or better in better seeing-eye and follow-up BCVA worse than 6/18 but better than or equal to 3/60 (not including 6/18 but including 3/60) in the better seeing-eye. Incidence of Blindness: Persons with Baseline BCVA 3/60 or better in better seeing-eye and follow-up BCVA worse 3/60 (not including 3/60) in better seeing-eye.
NA no incident cases.

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