What are the Odds of Going Blind from Glaucoma?
Chat Highlights
May 2, 2007

On Wednesday, May 2, 2007, Dr. Michael James Pro, a glaucoma specialist at Wills, and the glaucoma chat group discussed "What are the Odds of Going Blind from Glaucoma?"

Moderator:  Tonight's topic is "What Are the Odds of Going Blind from Glaucoma?” Is there an answer other than "It depends"?

Dr. Pro:  Actually, I hate to say it, but it’s true. It depends on how advanced the glaucoma is at diagnosis.

Moderator:  Dr. Pro, do you have some points you would like to discuss?

Dr. Pro:  Yes, in fact, I prepared a few points for discussion. For instance, available data on the incidence of glaucoma blindness and prevalence are weak and rely on blindness registries. These registries lack standardization.

The Model Reporting Area (MRA) study came out in the 70’s and used data from 16 states. The study reported a glaucoma blindness prevalence of 8.8 per 100,000 persons for whites and 131 per 100,000 for non-whites in the age group of 45 to 64 years.

A study from Israel was more sobering and demonstrated the inadequacy of blindness registries. The study found that only 22% of the blind patients from a large glaucoma clinic were registered.

Moderator:  Are there any other recent studies you would like to tell us about?

Dr. Pro:  The Advanced Glaucoma Intervention Study (AGIS) and Collaborative Initial Glaucoma Treatment Study (CIGTS) studies are recent large glaucoma studies, and we are still learning from the results. Both studies seem to demonstrate the importance of setting a "target pressure" and achieving that goal either by drops, laser, or surgery. Patients in the studies who demonstrated progression were those with generally higher pressures or less robust reductions in pressure. That was important in patients with advanced glaucoma from the outset.

The AGIS is interesting. The study followed patients for 10 years, and strict treatment guidelines and goals had been set. At 10 years, approximately 12 to 15 percent of black patients and 8 to 10 percent of white patients were legally blind in one eye.

The AGIS found that treated patients also went blind. However, those patients who did poorly were generally from the subset that began the study with more advanced disease or failed treatment outcomes; they did not have robust intraocular pressure reduction.

Moderator:  What is the legal standard for blindness in the United States?

Dr. Pro:  The standard definition for legal blindness in the U.S. is (1) visual acuity of 20/200 or worse in the better eye with corrective lenses. The figure 20/200 means that a person must be 20 feet from an eye chart to see what a person with normal vision can see at 200 feet. (2) The visual field is restricted to 20 degrees diameter or less (tunnel vision) in the better eye.

P:  Don’t glaucoma patients usually fall into the "20 degrees from fixation" category of blindness? That still leaves a lot of functioning vision compared to "no light perception" blindness, doesn’t it?

Dr. Pro:  Absolutely.

P:  How many new cases of blindness from glaucoma occur every year?

Dr. Pro:  An estimate based on the MRA study and a large population study (Baltimore Eye Survey) estimated 12,000 new cases of blindness from glaucoma in the U.S. every year.
I’m grateful to Dr. Rick Wilson for the following data from his lectures to residents. Half of the 2.5-million Americans with glaucoma are unaware they have it. Approximately 130,000 Americans are blind (best-corrected visual acuity less than or equal to 20/200 or visual field less than 20º in diameter) from primary glaucoma.

Glaucoma recently surpassed trachoma as the second leading cause of blindness overall, and is in the top three causes in any country in the world. Angle-closure glaucoma is two to three times as likely to cause blindness as open-angle glaucoma.

If the effect of the Asian population is considered, angle-closure glaucoma causes more blindness than open-angle glaucoma. Open-angle glaucoma is the number one cause of blindness in African-Americans, who are four times more likely to have the disease, and six times more likely to be blind from it. They are, however, half as likely to be treated for it.
African-Americans are usually diagnosed 10 years earlier than whites and are 14 to 17 times more likely to go blind from glaucoma between the ages of 45 and 65 than Caucasians.

Worldwide, five to seven million people are blind from all types of glaucoma. For example, in Nigeria, 10% of the population has glaucoma. Of that 10%, 91% are unilaterally blind (one eye), and 34% are bilaterally blind (both eyes).

P:  What's trachoma?

Dr. Pro:  Trachoma is a disease caused by the bacteria chlamydia (most frequently reported sexually transmitted disease). In third-world countries, a specific strain causes scarring on the eyelids, which leads to corneal scarring and eventual blindness. Chlamydia is completely treatable.

P:  What percentage of blindness is caused by glaucoma?

Dr. Pro:  I don't know the exact percentage. As I said, the data are somewhat inadequate, but generally glaucoma is the second or third leading cause of blindness in the U.S.

P:  Are those percentages for untreated glaucoma?

Dr. Pro:  No, the percentages also include people whose glaucoma has been treated.

P:  Are the estimates for people who have been treated broken down by type of glaucoma?

Dr. Pro:  No. The U.S. and global estimates generally do not specify the type of glaucoma. We know that certain types of glaucoma are more common in certain groups. For instance, angle-closure glaucoma is more common in Asians.

P:  Is advanced glaucoma the level of damage?

Dr. Pro:  Yes, that is generally demonstrated by the amount of visual field loss.

P:  What is the definition of advanced glaucoma?

Dr. Pro:  There is no strict definition. Most specialists will label patients as "advanced" if the visual field shows dense defects and if the optic nerve is deeply "cupped". Finally, patients with advanced glaucoma are often aware of their visual field limitations or have reduced central visual acuity.

P:  Is there a way I could figure out my odds of going blind?

Dr. Pro:  Well, that’s a tough one. As I mentioned, it is important to know how advanced your glaucoma is. Then it helps to know the amount of IOP reduction achieved once treatment began and what the target IOP is. If you have reached the target, the chance of going blind is reduced.

P:  Do glaucoma specialists keep records of how many patients in their practice are blind? It seems that there is a blind patient in my specialist's office every time I'm there.

Dr. Pro:  I don’t know of anyone who keeps that data. You see blind patients in glaucoma specialists’ offices because patients with advanced disease are eventually sent to one of us!

P:  Is there a certain sequence when you start going blind from glaucoma, like decreased acuity, color loss, etc.

Dr. Pro:  Acuity and color loss usually occur later in the disease. Very subtle defects in functional testing show up early, but most patients aren't aware of them. That is why many patients are diagnosed so late.

Moderator:  Thank you, Dr. Pro. Your time and expertise are most appreciated.

Dr. Pro:  Nice chat. Thanks to everyone for the great questions. Also, thanks to Steve for moderating.

On June 6 , Dr. Richard Lee discussed "Pseudoexfoliation Glaucoma" in the Chat room. Click here for highlights of that meeting.

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