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Up Front | Jul 2006

Corneal Blindness

A look at its leading causes and treatment success.

Diseases of the cornea are a major cause of blindness, second only to cataract.1 Infectious and inflammatory eye conditions affect the transparency of the cornea and cause corneal blindness. They add burden to the community and health care resources. Corneal blindness patients are usually younger compared with those suffering from cataract. Hence, the impact of corneal blindness (ie, total blind years) is greater.

EPIDEMIOLOGY
Using the World Health Organization's (WHO; Geneva, Switzerland) blindness definition,1 45 million people worldwide are bilaterally blind, of which 6 to 8 million are blind due to corneal disease. In some African areas, nearly 90% of the total blindness is due to corneal pathology.2 The prevalence of corneal disease varies from country to country and even from one population to another depending on factors including availability and general standards of eye care.3

In India, there are approximately 6.8 million people who have corneal blindness with vision <6/60 in at least one eye, and of these, about 1 million have bilateral corneal blindness.4 If the present trend continues, it is expected that the number of corneally blind individuals in India will increase to 8.4 million in 2010 and 10.6 million by 2020.5

COMMON CAUSES
Cataract is responsible for nearly 20 million of the 45 million blind people in the world, and the next major cause is trachoma, which is responsible for blindness in 4.9 million people, mainly due to corneal scarring and vascularization. Ocular trauma and corneal ulceration are also causes of corneal blindness and may be responsible for 1.5 to 2.0 million new cases of uniocular blindness every year. Infectious conditions (eg, trachoma and corneal ulcer) are common in the developing world, whereas noninfectious entities (eg, corneal dystrophies and pseudophakic bullous keratopathy) are more common causes in developed countries.6-9

Trachoma is the world's leading preventable and infectious cause of blindness and the foremost cause of ocular morbidity.10 At present, there are 146 million people worldwide with trachoma; 10 million suffer from trichiasis and need surgery to prevent corneal blindness, and another 4.9 million are totally blind from trachomatous corneal scarring.4,11

INFECTIOUS KERATITIS
Infectious keratitis is one of the most common causes of ocular morbidity in the developing world (Figure 1). Most of these ulcers follow minor farming-related agricultural injuries. Although herpes virus is the most common cause of corneal ulcer in developed countries, bacterial and fungal infections are more common in developing countries. Gonzales et al12 found that the annual incidence of corneal ulceration in the Madurai District in South India was 113 per 100,000 people, 10 times the annual incidence of 11 per 100,000 reported from Olmsted County, Minnesota, in the United States.13 By applying the 1993 corneal ulcer incidence rate in Madurai District to all of India, approximately 840,000 people develop corneal ulcers per year. This figure is 30 times the number of corneal ulcers seen in the United States.12 The rampant and unjustified use of topical steroids in cases of red eye leading to corneal superinfection14 is an important factor for the high prevalence of corneal blindness in developing countries.

Ocular trauma has been reported to be the most important cause of the unilateral loss of vision in developing countries, and up to 5% of all bilateral blindness has been attributed to direct ocular trauma.15 Corneal and corneoscleral perforation and subsequent scarring due to ocular trauma may result in a variable amount of blindness.

The use of traditional eye medicines (eg, dried plant materials crushed into powder and dissolved in an aqueous medium; animal/human products such as breast milk, saliva or urine) is an important risk factor for corneal ulceration and blindness in many developing countries. Twenty-six percent of childhood blindness in Malawi was associated with the use of traditional eye medicines, and 25% of corneal ulcers in the United Republic of Tanzania were associated with its use.17

Corneal dystrophies and bullous keratopathy represent other major causes of corneal blindness and are more significant in the developed world. In children, the causes of corneal blindness include keratomalacia,18 ophthalmia neonatorum, accidental ocular trauma19 that may be mechanical or chemical,20 and less frequently, ocular diseases such as herpes simplex virus infections and vernal keratoconjunctivitis.21

STRATEGIES TO REDUCE CORNEAL BLINDNESS
Preventative. Public health prevention programs are the most cost-effective means of decreasing the global burden of corneal blindness, because it is difficult to treat once it occurs. The prompt diagnosis and appropriate treatment of corneal ulceration and the easy availability of antibiotics and antifungals, even in rural areas, should be the aim of community health programs. The failure to implement standard management protocol for infectious keratitis at first contact is a major factor contributing to ocular morbidity in developing countries.22

Hygiene. Ocular and personal hygiene plays an important role in reducing the prevalence of preventable corneal blindness. The SAFE strategy of prevention of trachoma blindness includes (S) surgery for trichiasis, (A) antibiotic treatment of clinically active chlamydial infection, the promotion of (F) facial cleanliness, and the improvement of (E) environmental conditions.23

Protective. Safety in workplaces has to be improved to reduce trauma causing corneal blindness. The use of protective devices and headgear for appropriate eye protection for people performing high-risk industrial work as well as agricultural labor can reduce the risk of corneal injuries.

Educational. Educating ophthalmologists at primary health centers and district hospitals regarding the avoidance of injudicious use of steroids in red eye can help prevent the occurrence of corneal blindness. Properly educating traditional medicine users and eliciting their cooperation in directing patients to appropriate health care facilities is essential in preventing complications that lead to blindness from the use of traditional medicines. Also, parents' awareness in preventing children from playing with sharp objects,19 firecrackers (Figure 2) and lime packets20 might be helpful. Prevention programs in children include widespread immunizations, the regular distribution of high-dose vitamin A capsules to children at risk, prophylaxis to reduce ophthalmia neonatorum,24 nutritional education for families, and dietary fortification for populations with poor nutrition.

Curative. Once a corneal scar develops, surgical management remains the only option for visual rehabilitation. Corneal transplantation is the definitive treatment for a corneal scar, however, only 40% of bilateral corneal blindness is treatable.25 The pathology for corneal disease is the main determinant of the success of keratoplasty. Although success rates for corneal transplantation surgery are high in the developed world, they are very low in developing countries (46.5%).26

Adding to the existing prevalence of corneal blindness in developing countries is the high rate of failed corneal grafts as well as the low availability of good-quality donor corneas. In India, nearly 3.5 million good-quality donor corneas are required to restore vision in all the eyes that can be treated with keratoplasty. Approx-imately 20,000 corneas or eyes are collected annually, while every year, approximately 40,000 new cases of corneal blindness are added to the existing backlog.

Optical sector iridectomy in cases of corneal opacities is an alternative to corneal transplant that is a simple and safe procedure to improve visual outcomes and provide ambulatory vision to patients, particularly in eyes with poor prognosis for penetrating keratoplasty.27

Corneal blindness may result from a wide variety of causes, depending upon the community and strata of the population. Prompt measures to prevent and appropriately manage the clinical condition can limit any associated disability.

As the majority of corneal blindness is avoidable, health-promotion strategies have to be developed and implemented to raise awareness about the causes and prevention of corneal blindness, particularly in developing countries.

Rasik B. Vajpayee, FRCS(Ed), MBBS, MS, is professor of ophthalmology at the Rajendra Prasad Centre for Ophthalmic Sciences in the All India Institute of Medical Sciences, in New Delhi, India. Dr. Vajpayee may be reached at rasikvajpayee@rediffmail.com or +91-11-26593192.

Rajesh Sinha, MD, FRCS, is senior research associate of ophthalmology at the Rajendra Prasad Centre for Ophthalmic Sciences in the All India Institute of Medical Sciences, in New Delhi, India. Dr. Sinha may be reached at sinharaj1@rediffmail.com or+91-11-26593192.

Namrata Sharma, MD, is assistant professor of ophthalmology at the Rajendra Prasad Centre for Ophthalmic Sciences in the All India Institute of Medical Sciences, in New Delhi, India. Dr. Sharma may be reached at namrata103@hotmail.com or +91-11-26593144.


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