Visual acuity in the onchocerciasis patients' cohort (n = 82) before ivermectin treatment, and at 4 years and 23 years post initial treatment (PIT).

For visual acuity an illiterate E chart (SNELEN) was used placed 6 meters away from the patient's seat. 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. *Note: At before treatment and at 4 and 23 years PIT, visual acuity was not possible to determine in 11% (n = 9), 13% (11) and 17% (19) of the patients due to lack of comprehension, respectively.