The Odds of Blindness from Glaucoma
Chat from September 1, 2010
Guest Speaker – Dr. Jonathan Myers
Steven Beck, Editor
Lorraine Miller, Editor, Chat Topic Researcher
On Wednesday, September 1, 2010, Dr. Jonathan Myers, a glaucoma specialist at Wills, and the glaucoma chat group discussed “The Odds of Blindness from Glaucoma”.
Moderator: Tonight’s topic is “The Odds of Going Blind from Glaucoma.” Our guest doctor this evening is Dr. Jonathan Myers. Doctor, would you define “blindness” for us, please?
Dr. Jonathan Myers: Great place to start. The legal definition of blindness is 20/200 or worse vision in the better eye, or, less than 20 degrees of visual field. As a reminder, 20/200 means that a person sees at 20 feet what a person with normal vision can see at 200 feet! In America, there are about 1 million people who are legally blind.
P: How many patients suffer from a blindness that is complete darkness?
Dr. Jonathan Myers: Complete blindness, or no light perception in either eye, is actually very uncommon. Perhaps less than five percent of those with legal blindness, maybe even less.
P: Can a common attribute be blamed in cases of individuals for which medical intervention seems not to affect the speed of blindness?
Dr. Jonathan Myers: The leading cause of irreversible blindness in the world in glaucoma. Cataract is another cause, but is reversible with surgery. There are many reasons for progressive vision loss in glaucoma. The most common is failure to achieve low eye pressures.
Moderator: But wouldn’t the reasons then be the reasons for failure to achieve low pressure?
Dr. Jonathan Myers: Yes, I guess that would be a reasonable way to look at it. But there are many reasons why people don’t achieve low eye pressures such as intolerance of medications, poor medication effect for that patient, poor use of eye drops by the patient, failure to diagnose the severity of the glaucoma early leading to inadequate treatment, and failure of surgery.
P: Are there some types of glaucoma that have poorer odds of retaining sight?
Dr. Jonathan Myers: Exfoliation syndrome is higher risk glaucoma. So are neovascular glaucoma, ICE syndrome, and malignant glaucoma.
P: Can narrow angle glaucoma be cured?
Dr. Jonathan Myers: Angle closure glaucoma may respond very well if caught very early, but later in its course it can be very difficult to control. Narrow angles, if treated before the IOP elevates, often do very well with excellent lifetime vision.
There are many studies on the risks of blindness, but few that are long term studies. Also, most studies focus on Primary Open Angle Glaucoma, not low tension or normal pressure glaucoma.
In the Normal Tension Glaucoma Study, patients treated aggressively, (30% IOP reduction) had an 88% chance of stability after about seven years. Those that got worse were not blind, but did show some change in their nerve or visual field.
In one major study of open angle glaucoma in Minnesota, the risk of blindness after 20 years was at least 10%. But this study was done many years ago, before a lot of the newer medications and newer surgical techniques came out.
Many studies suggest that the risk of blindness for an individual patient depends on several factors. First, how severe the glaucoma is at diagnosis (how much damage there is to the optic nerve and how much of the visual field is already lost). The worse it is when it is picked up, the greater the risk. Next, there is the issue of the patient’s age. Younger patients have more years to get worse, but older patients on average get worse more quickly, or have a greater risk of worsening.
How low we get the pressure, how consistently it is controlled, how consistently the patient takes drops are all CRITICAL.
P: Do you agree based on studies and your own experience that vision loss for patients with NTG and central vision loss tends to progress more quickly than other types of glaucoma in general?
Dr. Jonathan Myers: Patients with normal tension glaucoma are much more likely to have field loss near the center of vision, which is much more disabling. I think that some patients with normal tension glaucoma get worse more quickly, but not all, versus primary open angle glaucoma.
In one study of patients with very advanced glaucoma (“Endstage”), about 10 percent of the eyes became blind over about eight years. But these were eyes with very advanced field loss to begin with.
P: How much greater is the risk of glaucoma in a developing country than in a developed country?
Dr. Jonathan Myers: Great question. In a study in Nigeria, the prevalence of blindness was about four to six times higher than that seen here in America. In America, about one percent of adults over age 65 are legally blind. For Whites, the risk is about 0.5-0.75%. For Blacks, it’s about 2 percent.
P: If one eye has a lot of optical nerve damage at diagnosis, does that mean the other eye will also get that bad?
Dr. Jonathan Myers: If both eyes are similar (some glaucomas are known to affect only one eye), then a bad outcome in one eye increases the risk to the other eye. I sometimes think of it as that where one eye goes the other tends to follow. For me as a doctor, that means that I tend to treat the better eye more aggressively (lower pressure) if the other eye has bad glaucoma, then if the other eye was the same. However, sometimes there are reasons for one eye to be worse that are unique: prior injuries, surgical complications, and again, certain glaucomas like ICE syndrome.
P: If lack of contrast is seen as whiteness by a patient, is that blindness?
Dr. Jonathan Myers: Contrast sensitivity, the ability to discern shades of gray, is reduced in glaucoma. In very severe glaucoma, some patients may see things as “whited out” while others feel everything is too dark.
P: Does the percentage of those with unilateral blindness far exceed that of those with bilateral blindness?
Dr. Jonathan Myers: About twice as many people have blindness in one eye versus blindness in both eyes. The government, in determining disability, does not consider blindness in one eye to be significant. People with one good eye are considered legal to drive and can perform well in most jobs.
P: Is there a correlation between the age of diagnosis and blindness?
Dr. Jonathan Myers: The younger the age of diagnosis, the greater the risk over a lifetime of blindness. Since we can’t change our age at diagnosis, race, or severity at diagnosis, it is best to focus on consistent control of eye pressure.
P: Can any of the tests performed on glaucoma patients predict glaucoma loss?
Dr. Jonathan Myers: Testing is helpful. In the Ocular Hypertension Treatment Study, a worse HRT result (Optic nerve imaging instrument) at the beginning was found to predict a greater risk of worsening. However, to some extent this is the same as saying that people who looked worse at the beginning were more likely to get worse.
P: What constitutes a worse HRT result?
Dr. Jonathan Myers: The HRT, or Heidelberg Retina Tomograph, measures the shape of the optic nerve head. In glaucoma the optic nerve undergoes “cupping” which is the progressive loss of tissue in the nerve head, from the inside out, similar to a bagel or doughnut being eaten from the inside out. A worse HRT result is a larger “cup”. The HRT can also, over time (with repeated tests), help the clinician identify worsening (a larger cup).
P: Based on what you said above then, non-compliance with the treatment regimen becomes a major risk factor for blindness?
Dr. Jonathan Myers: Yes. Many patients may get “off the wagon” and off their drops. This is a major cause for progressive loss, as is a break in regular check ups. This issue is very widespread. In studies at Wills Eye Institute, patients who were told that their drop use was going to be monitored took less than 80 percent of their drops on average!
It’s worth noting that for patients who have trouble taking drops, laser trabeculoplasty may be worth considering as a way to reduce the need for drops.
P: After many years of faithful annual eye exams with my ophthalmologist (who also did my LASIK surgery), at one point he indicated I was a glaucoma suspect but my vision kept getting worse and I sought out a glaucoma specialist who diagnosed advanced glaucoma! How can this happen?
Dr. Jonathan Myers: Early glaucoma can be very hard to pick up. In normal tension glaucoma, there is no high pressure to tip the doctor off. In near sighted people, the optic nerve may be anomalous, or atypically shaped, in a way that may mimic glaucoma or may hide its early signs. So, it is not uncommon for normal tension glaucoma in a near sighted person to be picked up relatively later.
P: So how do Visual Field Tests help if HRTs seem to show the progression accurately?
Dr. Jonathan Myers: Studies show that worsening glaucoma may be picked up by either fields or HRTs. However, each test will miss some of the people who get worse. Studies have not shown one to be clearly superior, so we continue to rely on both field testing and optic nerve analysis, such as the HRT.
P: Is there a crude formula someone could use to figure out my personal odds of going blind?
Dr. Jonathan Myers: Unlike heart disease, in which we have very good risk calculators for the risk of heart attack or death, so far we don’t have all the information to do a risk calculator for blindness. In the Ocular Hypertension Treatment study, they created a risk calculator for the odds of getting worse over a five year period in patients with ocular hypertension (high pressure, no definite glaucoma damage).
The key factors were 1) age, 2) IOP, 3) corneal thickness, 4) Optic nerve cup to disc ratio (size of doughnut hole), and 5) visual field status. Untreated, the overall risk of worsening was 9.5% over five years; with treatment, 4.4 % (for ocular hypertension).
A tricky aspect in reviewing the risk of worsening is that different studies define this differently. Blindness has a more clear definition, which is better, but there are far fewer studies, and most are not long term. These studies are hard to do, since they are long term, and since, thankfully, the vast majority of patients will never go blind.
P: Is there any hope at all as far as stem cell research and possible optic nerve regeneration as a result? If so, how far away is this?
Dr. Jonathan Myers: There is currently research on regenerating optic nerves with stem cells. The research is still in its early stages. It is similar to research on spinal cord injuries as the nerves are similar. So far, we don’t have treatments for people, but there are some hopeful animal results. In some parts of the world, there are centers that advertise stem cell treatments for glaucoma. There is no evidence that these centers are actually doing anything other than profiting on selling false hope.
The day will come, but sadly we are not there yet. Hopefully the United States will take a leadership role in this field, as we have been leaders in so much of medical research, but that will take funding and a concerted effort as the issues are many and complex.
P: What is on the horizon as far as optic nerve cell “neuro cell protection?”
Dr. Jonathan Myers: Neuroprotection refers to glaucoma treatments that protect the nerve. IOP reduction does that, but the term neuroprotection is used to connote treatments other than IOP lowering. So far we have no approved neuroprotective drugs for glaucoma. There have been some trials, but no clear positive results. We know that factors other than pressure play a role in the development and progression of glaucoma, but we don’t yet have drugs that clearly work on these, or at least well enough to show an effect in human trials. Some animal trials have had positive results and there is a lot of research on this currently.
P: Through the chat you have mentioned advanced glaucoma and severe damage. Could you define those terms better for us?
Dr. Jonathan Myers: Glaucoma damage is a spectrum from undetectable to complete vision loss. Most of us consider glaucoma advanced when the damage leads to significant visual field changes, such as the loss of the top half of the field of vision. There’s no strict definition, but, in general a high cup to disc ratio (e.g. 0.9) or a lot of field loss (black on the field print out) are the very rough descriptors.
Moderator: Thank you Dr. Myers for taking the time to be with us. Your answers were very helpful and educational.
Dr. Jonathan Myers: This was great. Thanks to everyone for some very insightful questions, and thank you to the Moderators for their help as well. Good evening to everyone.