The epidemiology of low vision and blindness associated with trichiasis in southern Sudan

Abstract

Background: We investigated vision status associated with trachomatous trichiasis (TT) and explored age-sex patterns of low vision and blindness associated with trichiasis in Mankien district of southern Sudan where trachoma prevention and trichiasis surgery were absent.

Methods: A population based survey was undertaken and eligible persons underwent eye examination. Visual acuity (VA) was tested using Snellen E chart and persons with TT identified. Vision status was defined using the WHO categories of visual impairment based on presenting VA: normal vision (VA > or = 6/18 in better eye); low vision (VA < 6/18 but > or = 3/60 in better eye); and blindness (VA < 3/60 in better eye). An ordinal logistic regression model was fitted and age/sex specific distribution of vision status predicted.

Results: Overall 341/3,567 persons examined had any TT. Analysis was based on 319 persons, 22 persons were excluded: 20 had both TT and cataract; and 2 had missing VA data. Of the 319 persons: 158(49.5%) had trichiasis-related corneal opacity (CO); bilateral TT and bilateral CO were found in 251(78.7%) and 110 (34.5%), respectively; 146 (45.8%) had low vision or blindness; the ratio of low vision to blindness was 3.2:1; and no sex differences were observed. In our model the predicted distribution of vision status was: normal vision, 53.9% (95% CI 50.9-56.9); low vision, 35.3% (95% CI 33.3-37.2); and blindness, 10.9% (95% CI 9.7-12.0).

Conclusion: We have reported severe trichiasis and high prevalence of vision loss among persons with trichiasis. Our survey showed that almost 1 in 20 of the entire population suffered low vision or blindness associated with trachoma. The need for trichiasis surgery, trachoma prevention services, and rehabilitation of the blind is acute.

Figure 1

Age specific prevalence of trachomatous trichiasis and corneal opacity (n = 3,567).

Figure 2

Age specific prevalence of vision loss attributable to trachoma (n = 3,567). Normal vision = presenting visual acuity of ≥ 6/18 in the better eye; Low vision = presenting visual acuity of < 6/18 to ≤ 3/60 in the better eye; Blindness = presenting visual acuity of < 3/60 in the better eye. Three children aged 0–4 years assumed to have normal vision.

Figure 3

Sample population. *Three children aged 0–4 years assumed to have normal vision. VA, visual acuity.

Figure 4

Observed and predicted distribution of vision status by age group in persons with trichiasis (n = 319). Vision status: Normal vision = presenting visual acuity of ≥ 6/18 in the better eye; Low vision = presenting visual acuity of < 6/18 to ≤ 3/60 in the better eye; Blindness = presenting visual acuity of < 3/60 in the better eye. Children aged 0–4 years assumed to have normal vision.