During the late 1950s, Harold Dickson and his teenage son, Howard, went to a shooting range to test their marksmanship on clay pigeons. “I would sight the birds, and then just as I was about to shoot, they would disappear,” recalls Dickson, 83, a retired dentist from St. Thomas, Ont. The experience prompted Dickson to see an eye specialist. The ophthalmologist diagnosed glaucoma, a disease that attacks the optic nerve and can cause progressive loss of vision. Following an eye operation during the 1970s, hemorrhaging developed and Dickson lost the use of one eye; later, the vision in his other eye deteriorated until Dickson became clinically blind. His son Howard, now 51 and associate dean of research at Halifax’s Dalhousie University, also has glaucoma, which was diagnosed when he was 25. So far, his condition has been effectively treated with eye medication and he has suffered no loss of vision. “I’m concerned,” says Dickson. “But if things progress the way they are, I don’t expect any serious deterioration in my vision.”
The Dicksons’ experiences illustrate the importance of early diagnosis—and the strides that have been made in treating glaucoma, a baffling cluster of diseases that are often inherited and afflict more than 134,000 Canadians. Glaucoma can take confusingly different forms, and scientists admit that they do not understand some of the basic mechanisms underlying the disease. Despite that, doctors using modern drugs and surgical techniques increasingly are able to save the vision of many glaucoma victims. Now, American and Canadian specialists may be paving the way for more effective early diagnosis and treatment of some forms of glaucoma. By identifying the flawed gene, or genes,
that cause glaucoma, scientists say that they might someday even find a cure.
In September, a team of Ontario and Quebec specialists will travel to the village of Grande-Vallée, 560 km northeast of Quebec City in the province’s Gaspé region, to collect blood samples from members of an extended family in which glaucoma strikes frequently. The 525-member Glaucoma Research Society of Ontario is seeking to raise $600,000 for the startup costs involved in analysing genetic material taken from the blood of family members and searching for telltale “markers” to determine exactly which gene is involved.
A U.S. team has already taken a lead in the same search. In May, University of Iowa scientists announced that after analysing genetic material from a large family in the American Midwest with a high incidence of glaucoma, they had established a link between the first chromosome and the disease in that family. Edwin Stone, the ophthalmologist and molecular biologist in charge of the Iowa team, says that researchers will now try to pin down the precise gene responsible for the family’s glaucoma.
The Canadian team plans to begin its search by examining the same region of the first chromosome in its study of the Gaspé family. But it may turn out that some forms of glaucoma are related to different genes. Brenda Gallie, a Toronto ocular geneticist who is helping to co-ordinate research into the Quebec family, says: “The different kinds of glaucoma, the differing degrees of severity and different ages of onset, suggest that there could be as many as 10 genetic mutations involved, and they could be on different genes.”
Though causes may different, problem in most glaucoma cases is the same. It begins with the fluid inside the eyeball that nourishes and protects the optical system. Normally, excess fluid drains through a grid of tissue at the front of the eye known as the trabecular meshwork. Sometimes, the meshwork becomes blocked and increased fluid pressure begins to exert force on the optic nerve, damaging it in the process.
For many glaucoma patients, drugs administered as eyedrops can keep fluid pressures within safe limits. One of the most effective family of drugs is the so-called beta-blockers, which were used originally to control high blood pressure. When taken by glaucoma patients, beta-blockers help reduce the production of fluid inside the eye. When drugs no longer work, doctors use laser beams to stretch and reopen the drainage system, and, as a last resort, perform eye surgery to cut a new drainage system.
Despite the rapid progress in treating glaucoma, early diagnosis remains crucial. According to Graham Trope, chairman of the University of Toronto’s department of ophthalmology, by the time some victims begin losing their vision and see a doctor, “about 50 per cent of the optic nerve will have been destroyed.” Once scientists begin zeroing in on the genetic causes of glaucoma, improved treatments and even cures for the disease may be possible. But “the first spinoff,” adds Trope, will be in simple genetic tests to determine which members of families with a history of glaucoma have inherited the disease. With that knowledge, victims will stand a good chance of remaining safe from the dire consequences of a potentially devastating disease.
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