VISUAL-FIELD CONSTRICTION AS A CAUSE OF BLINDNESS OR VISUAL IMPAIRMENT

Reported are the results of a study of onchocerciasis in communities m esoendemic for savanna onchocerciasis in Kaduna State, northern Nigeri a. The study involved 6831 individuals aged greater than or equal to 5 years who underwent an extensive screening examination for visual fun ction including Friedmann field analysis. A total of 185 (2.7%) were b ilaterally blind by acuity and an additional 28 (0.4%) were blind by v isual field constriction. Also 118 (1.7%) individuals were visually im paired by acuity criteria. No criteria for visual impairment by field constriction have been established and we therefore investigated three potential criteria. As a result, a further 60 (0.9%) individuals were identified with significant visual impairment due to field loss by th e various definitions. Small islands of remaining peripheral field occ urred in 50 individuals, while 40 individuals had marked reduction of binocular visual field below the horizontal meridian. Concentric visua l field constriction to <20 degrees was found in seven individuals. Th e WHO definition of blindness currently includes visual field damage c riteria for blindness but not for visual impairment. Visual field loss is recognized as a major disability. We hope that these findings stim ulate international discussion leading to the development of satisfact ory definitions for visual impairment by visual field constriction.