Eye Diseases and Disorders

Eye disease affects more than 10 million North-Americans who suffer from loss of visual function, over 500,000 of whom are legally blind. Eye disease includes cataracts, glaucoma, age-related maculopathy and diseases of the retina and choroid. Animal models have been of critical importance to surgeons and researchers. The development of laser techniques, as well as transplant and other surgical procedures, has been dependent on the use of animals to educate and instruct medical professionals.

Today, corneal transplants restore sight to thousands of people annually. Transplantation centers have provided surgical tissue to ophthalmic surgeons for corneal transplants to more than 10,000 blind or visually-impaired patients over the past 30 years. None of the very early work to develop the precision tools and sew in tissue from a deceased eye donor could have been confidently attempted on humans without the use of animal trials first. The first human corneal transplant was performed in 1957. Some forty years later, the recipient of this transplant continues to see clearly with transplanted corneas in both eyes.

The drug Ivermectin, originally developed for dogs as a heartworm preventive, was found to be helpful in defeating a parasitic disease in humans called onchocerciasis or "river blindness", which affects up to 40 million people in tropical countries and is the leading cause of blindness in the developing world. Until the discovery of this breakthrough drug, public health authorities had little success in fighting river blindness.

Experiments on animal models have also given researchers new surgical techniques for eye surgery. One example is a new surgical procedure to correct for cataracts, a condition in which the clear lens of the eye becomes so cloudy that vision is impaired. Vision can only be restored by surgical removal of the cataract. With the new procedure, a surgeon does not have to suture, or stitch, the incision. Instead, the eye's normal internal pressure pushes the edges of the severed tissue together and the incision heals naturally, a dramatic improvement over conventional cataract surgery, in which a surgeon had to make seven to 10 sutures to close an incision. Approximately one million cataract operations are performed each year in the United States.

Animal models are the key to present and future breakthroughs in research on eye diseases. Lasers, for example, which have been successfully used in rabbits to treat eye tumors, are beginning to undergo human trials in order to remove eye tumors without cutting into the eye. Lasers are also being studied as instruments to reshape the cornea without scarring. Such a technique could potentially free millions of people from the need to wear corrective lenses.

Experimental retinal transplants, thus far only achieved using animals, raise the prospect of one day restoring sight to people who are currently considered "permanently" blind. Retinal transplants, currently being performed on mice and other small animals, will soon be tried in primates, whose visual systems are similar to those of humans. If the primate model is successful, researchers hope that the surgical techniques developed will restore sight to blind people; in particular, those suffering from retinitis pigmentosa and other degenerative retinal diseases.

Vision is perhaps the one of the five senses on which we rely most. Humane and responsible biomedical research using animals offers hope for a better quality of life for all visually-impaired children and adults.