Glaucoma Around the World
Chat Highlights
February 12, 2003

Norma Devine, Editor

On Wednesday, February 2, 2003, Dr. Rick Wilson, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Glaucoma Around the World."

Moderator:  Dr. Rick, we have in the chat room tonight glaucoma patients living in Brazil, England, various provinces in Canada, as well as northern, southern, eastern, western and middle western states.

Dr. Rick Wilson:  Welcome to all.

Moderator:  I think we've all heard that different races are affected by different types of glaucoma.  What are the most significant differences around the world?

Dr. Rick Wilson:  In the United States, most glaucoma is primary open-angle glaucoma (POAG) (cause unknown).  The prevalence of angle-closure glaucoma, about 15%, is much greater among Alaskan Eskimos than among Caucasians.  In China, the proportions are almost the opposite, with far more angle-closure glaucoma than POAG, while in Japan there's more normal-tension glaucoma (NTG) than POAG. 

P:  World-wide, which type of glaucoma causes the most blindness?

Dr. Rick Wilson:  Because angle-closure glaucoma has two to three times the chance of resulting in blindness than POAG, and because the number of Chinese with angle-closure glaucoma stack the deck, closed-angle glaucoma probably causes more blindness than POAG.  

P:  What accounts for the differences? Genetics?  Diet?  Culture?  

Dr. Rick Wilson:  Genetic difference seems to determine the proportions of the anterior chamber of the eye and the shape of the iris.

P:  What about in Europe, South Africa, and South America?  

Dr. Rick Wilson:  The prevalence in Europe is similar to that in the U.S.  Hispanics have twice the prevalence of glaucoma after age 70.  African-Americans are four times as likely to get glaucoma as Caucasians; six times as likely to go blind from it.  Unfortunately, African-Americans are only half as likely to get treated for glaucoma.  They have thinner corneas, on average, so that the Goldmann applanation tonometer underestimates their intraocular pressure (IOP).  They also have larger optic nerve cups, on average.

P:  Can't the difference in the proportions of glaucoma world-wide be used to search for its cause?

Dr. Rick Wilson:  It does help research causes. 

P:  So, worldwide, is there more angle-closure glaucoma than other kinds?  

Dr. Rick Wilson:  No.  There's more open-angle glaucoma, but there may be slightly more blindness due to angle-closure glaucoma, because angle-closure glaucoma results in blindness two to three times more frequently.

P:  Do Africans in Africa have the same prevalence of glaucoma as African-Americans?  And do Chinese in North America have the same rates and types of glaucoma as those in China?

Dr. Rick Wilson:  Pure African-Americans (who are quite hard to find) have the same prevalence of glaucoma as the Africans where their genes originated.  The same is true for the Chinese Americans.  It seems to be nature, not nurture.  I never saw a case of angle-closure glaucoma in Kenya (East Africa) when I worked there for five weeks, but I saw quite a bit of silent angle-closure glaucoma in Ghana (West Africa).

P:  Do African-Americans develop glaucoma sooner than Caucasians?  

Dr. Rick Wilson:  Although African-Americans may develop glaucoma 10 years younger than comparable Caucasians, they are usually diagnosed later in the course of disease.  

P:  In the Ocular Hypertension Treatment Study (OHTS), corneal thickness, not racial differences, predicted glaucoma.  African-Americans do tend to have thinner corneas, though. 

Dr. Rick Wilson:  In the OHTS, corneal thickness was a risk factor for developing glaucoma.  We don't know whether corneal thickness only related to how accurately the pressures were obtained or whether there was also a factor of the support of the optic nerve maybe being thinner in patients with thin corneas.  

P:  Is there a difference in types of glaucoma that prevail in Northern Europeans and Southern Europeans?  

Dr. Rick Wilson:  There is a significant difference between the prevalence of pseudoexfoliative glaucoma in Scandinavian countries and that in countries south of them. 

P:  Is normal-tension glaucoma prevalent elsewhere, besides Japan?  What about India?

Dr. Rick Wilson:  Open-angle and closed-angle glaucoma are the prevalent forms in India.

P:  Is treatment of glaucoma around the world similar, or do countries differ in their modes of treatment?

Dr. Rick Wilson:  That depends completely upon their sophistication and access to medications.  In Kenya, most of the patients I treated could not afford, and did not have access to, glaucoma medications.  It was, therefore, a surgical disease.  In most cases, I did not even take the eye pressure.  If there was glaucoma damage, even very early damage, I operated.  If there was no damage, I didn't.

P:  I thought open-angle glaucoma could be normal-tension glaucoma.  Is normal IOP, by itself, diagnostic of glaucoma? 

Dr. Rick Wilson:  Normal-tension glaucoma is a subgroup of the open-angle glaucoma group.  The normal eye maintains an internal pressure of between 12 and 22 mm Hg.  "Normal" intraocular pressure, however, is only a statistical average.   If someone gets progressive glaucoma damage with IOPs that are consistently within this range, then they would be said to have NTG.  Some patients have elevated IOP and no glaucoma; others may have normal intraocular pressure and have glaucoma.  An intraocular pressure test alone is a poor indicator of whether or not a patient has glaucoma.

P:  Are there good glaucoma specialists all over the world?

Dr. Rick Wilson:  They are usually proportionate to the sophistication of the country.  Europe has been held back to some extent by the tendency in many academic centers to have subspecialists still responsible for treating types of eye disease other than they were trained in.  The chiefs of most ophthalmology programs in Europe have in the recent past been fairly autocratic and rarely admitted that they could not do everything.

P:  Many thanks, Dr. Rick, for helping us understand a difficult and important subject.

Dr. Rick Wilson:  Tonight's chat was a little more scholarly than usual, so it was nice to have an attentive audience.  Have a great week everyone.  

End of highlights for February 12, 2003.

On February 19, Dr. Henderer discussed "Visual Fields" in the Chat room. Click here for highlights of that meeting.

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