The Spectrum of Ocular Diseases in the Onchocerciasis-Endemic Focus of Raga in South Sudan

Abstract

Introduction: Raga County is an onchocerciasis-endemic area in the Western Bahr El Ghazal state of South Sudan, known to have a high prevalence of blindness. The objective of this study was to determine the causes of eye disease and blindness in Raga County as well as to assess the relationship of eye diseases with other prevalent conditions like onchocerciasis and epilepsy.

Methods: We reviewed unpublished pre-community directed treatment with ivermectin (CDTI) data about eye disease and onchocerciasis in Western Bahr El Ghazal including Raga. In addition, a cross-sectional study was conducted from 21^st March to 2^nd April 2023 in 11 villages in Raga County. Participants were persons with blindness or other eye/vision problems, recruited via a community-based approach. Two senior ophthalmic clinical officers, supervised by an experienced ophthalmologist, performed the following assessments on participants: visual acuity measurement with Snellen Charts, anterior chamber examination with a loupe, and fundoscopy to assess the posterior segment with direct and indirect ophthalmoscopes.

Results: Pre-CDTI data showed that the most severe vision problems in villages with a high prevalence of O. volvulus infection were caused by onchocerciasis eye disease. During the 2023 survey, in total, 1559 persons (3,118 eyes) were examined (mean age: 47 ± 19.2 years, 58.4% male). The most frequent eye diagnosis was allergic conjunctivitis, observed in 1453 (46.6%) eyes of the participants. The main causes of blindness were onchocerciasis-related blindness (22.6%, caused by onchocerciasis chorioretinitis (9.4%), sclerosing keratitis, punctate keratitis (5.6%), and onchocerciasis optic neuropathy (7.6%)), and cataract (9.3%). A significantly higher proportion of persons with epilepsy presented with clinical signs of onchocerciasis including blindness (53.2%), compared to persons without epilepsy (32.5%) (p = 0.0007).

Conclusion: Despite years of CDTI, the main causes of blindness in Raga County remain onchocerciasis-related blindness observed in 22.6% and cataract observed in 9.3% of the study participants. The study confirmed an epidemiological association between onchocerciasis and epilepsy.

Keywords: Onchocerciasis; blindness; epilepsy; ivermectin; nodding syndrome; ocular disease.

Figure 1

(A) Location of the 6 villages surveyed for ocular disease in 1979–1984 in the Western Bahr El Ghazal area (blue rectangle on map B) (B) Map of South Sudan.