Corneal blindness: a global problem

Corneal blindness is an important, yet underreported cause of avoidable visual impairment worldwide, especially in developing countries. The World Health Organisation (WHO) estimates that corneal opacities (including trachoma) accounted for 7% of the world’s blind population in 2010, making it the 3rd most common cause of blindness. Although cataracts and glaucoma (in the elderly) are more common causes of visual impairment, corneal blindness affects all age groups and is a leading cause of irreversible visual impairment. An eye blind from scarring and vascularisation of the cornea, usually remains blind for life. In this issue of Clinical and Experimental Ophthalmology, Wang et al. present findings on corneal blindness from a large, population-based study of visual impairment in rural Heilong-Jiang province, China. Although there are numerous population-based studies detailing the major causes of blindness and low vision in both the developed and developing world, few published reports have thus far attempted to detail the different causes of corneal blindness. Rapoza et al. reported corneal infections (including trachoma) to be the leading cause of unilateral and bilateral corneal blindness in Central Tanzania, followed by vitamin A deficiency and measles. Unilateral corneal opacification had similar causes, with the important addition of trauma. Bowman et al. replicated these results in a population-based study in Gambia. Wang et al. here present findings on a large sample of 10 384 participants, representative of the rural Northern Chinese population, with a high overall response rate of 88.1%. Blindness was defined according to WHO criteria as a visual acuity of less than 3/60. All respondents underwent a screening examination, including measurement of best-corrected visual acuity (BCVA). Those achieving BCVA < 6/18 were subsequently referred for a more detailed examination. Although anterior segment examination was performed with a slit-lamp biomicroscope, fundus examination was carried with a hand-held ophthalmoscope only, without pupillary dilatation. This may have resulted in misclassification of the cause of blindness in a proportion of patients. Despite this shortcoming, the study presents some important findings. First, the majority (40%) of corneal blindness in this sample was acquired in childhood. Second, trauma (an entirely avoidable) cause of corneal blindness accounted for a third of all cases. Corneal opacification is the 3rd commonest cause of childhood blindness worldwide, after non-corneal causes such as congenital cataract and glaucoma. Unlike trachomatous corneal opacification, which results from repeated episodes of trachoma infection, corneal blindness in childhood is often due to a single episode of infection, such as ophthalmia neonatarum resulting from Neisseria gonorrhoea and Chlamydia trachomatis infections acquired from the mother’s genital tract at birth. During infancy and childhood, measles is another important cause of corneal blindness in the developing world, the impact of which is mediated through multiple mechanisms, including induction of acute vitamin A deficiency, measles keratitis, secondary bacterial or herpetic keratitis as well as the use of harmful traditional medicines. The WHO has ranked trachoma, corneal opacities, as well as childhood blindness, as priority eye diseases. Blind children have a lifetime of increased morbidity ahead of them. In addition, that lifetime can be very short, with up to 60% of blind children dying within 1 year of becoming blind. In this issue, Wang et al. report trauma as the second most common cause of corneal blindness in their population. In fact, corneal ulceration in developing countries is now considered a ‘silent epidemic’. Superficial corneal injuries from agriculture or domestic incidents led to blinding corneal ulceration due to delayed presentation and treatment. Indeed, in the developing world the majority of corneal ulcerations are the result of minor trauma and foreign bodies. This highlights the importance of public health education programs, targeting highrisk populations such as males, farmers and people with lower education. These programmes need to emphasize the importance of workplace safety, and timely hospitalization for corneal ulceration. In a previous study, also from China, Zhang and Wu demonstrated a lack of knowledge and awareness