Blindness

Causes in the Developing World

A cataract is an opacity in the lens of the eye that can have many causes but is most often age related. It is the most common cause of world blindness, treatable or otherwise, accounting for almost 50 percent of cases. Cataract surgery, which involves surgical removal of the lens usually followed by the implantation of a synthetic intraocular lens, is extremely cost-ef-fective. A number of medical centers and temporary camps in developing countries perform affordable, high-volume cataract surgery to address the substantial backlog of affected individuals. However, despite these efforts, the number of cataract blind is anticipated [Page 269]to double in the next 20 years as the population increases in both size and age.

Glaucoma is a group of diseases characterized by damage to the optic nerve of the eye, usually associated with elevated pressure within the eye. Affecting an estimated 12 million individuals worldwide, glaucoma is the second most common cause of world blindness, as well as the leading cause of blindness among African Americans. The goal of glaucoma treatment is to prevent damage to the optic nerve through the use of medications and surgical interventions that decrease the pressure within the eye.

Trachoma is the most common infectious cause of blindness in the world, and is most prevalent in developing countries where crowding, poor hygiene, and limited access to water are particularly problematic. The causative bacterium, C. trachomatis, is spread through contact with eye discharge from infected individuals, typically carried by flies. Repeated episodes of trachoma cause scarring of the conjunctiva and eyelid deformities, which in turn lead to corneal scarring, ulceration, and eventual blindness. Trachoma can be effectively treated with antibiotic therapy consisting of oral azithromycin or tetracycline eye ointment. Because infection tends to recur, current public health efforts are focused on prevention through improving facial hygiene and access to clean water.

Onchocerciasis is also known as “river blindness” because the blackfly that transmits the parasitic worm Onchocerca volvulus is most abundant near fast-flowing rivers. Upon biting its human host, the infected blackfly transmits larvae that mature into adult worms; these in turn produce larvae that migrate to the skin and ocular tissues where they cause a locally damaging immune response to the skin and eyes upon dying. The blinding complications of onchocerciasis are effectively prevented with the antiparasitic agent ivermectin. Additional public health efforts have promoted the use of insect repellents, protective clothing, and insecticidal spraying.

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