Table 5 Ten-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	34	4	11.8 (4.7, 29.5)	40	6	15 (7.2, 31.4)
40–49	91	17	18.7 (12.2, 28.7)	103	15	14.6 (7.2, 18.6)
50–59	164	28	17.1 (12.2, 23.9)	191	26	13.6 (9.5, 19.5)
60–69	81	16	19.8 (13.7, 30.6)	87	8	9.2 (4.8, 17.8)
70 +	3	1	33.3 (6.7, 165.1)	4	0	NA
			p = 0.39			p = 0.22
Crude overall	373	66	17.7 (14.2, 22.0)	425	55	12.9 (9.5, 15.6)
WHO Criterion^φ
< 40	38	4	10.5 (4.2, 26.6)	41	3	7.3 (2.5, 21.8)
40–49	98	13	13.3 (8.0, 22.0)	107	8	7.5 (3.8, 14.6)
50–59	181	21	11.6 (7.8, 17.3)	196	16	8.2 (5.1, 13.0)
60–69	85	7	8.2 (4.0, 16.7)	93	7	7.5 (3.7, 15.3)
70 +	3	0	NA	4	0	NA
			p = 0.40			p = 0.96
Crude overall	405	45	11.1 (8.4, 14.6)	441	34	7.7 (5.6, 10.6)

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 = 455.
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: 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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