Table 3. Causes of bilateral visual impairment and blindness in the onchocerciasis patients' cohort (n = 82) before ivermectin treatment, and at 4 years and 23 years post initial treatment (PIT).

Bilateral visual impairment and blindness	before ivermectin	4 years PIT	23 years PIT
Visual Acuity: ≥1/20 and <3/10	n (%)	n (%)	n (%)
Impaired by non onchocerciasis cataract	2 (2.4)	1 (1.2)	2 (2.4)
Impaired by onchocerciasis	3 (3.6)	4 (4.8)	5 (6.0)
Impaired by glaucoma	0	0	2 (2.4)
Impaired by other causes	0	3 (3.6)	1 (1.2)
Total with impaired vision	5 (6.0)	8 (9.6)	10 (12.0)
Visual Acuity: (<1/20 or <3/60)
Blindness by non onchocerciasis cataract	0	1 (1.2)	2 (2.4)
Blindness by onchocerciasis	0	0	6 (7.3)
Blindness by onchocerciasis & other causes	0	0	3 (3.6)
Blindness by glaucoma	0	0	1 (1.2)
Blindness by other causes	0	0	2 (2.4)
Total of blindness	0	1 (1.2)	14 (16.9)

The patients' visual acuity was graded according to WHO criteria; blind were those with a visual acuity on the right (RE) or left eye (LE) or both eyes (RLE) of less than 1/20 (3/60 or unable to count fingers at 3 meters); impaired vision had those with a visual acuity between 1/20 (3/60) and less than 3/10 (6/18); good vision had those with a visual acuity equal or greater than 3/10.