Current Concepts Chat Highlights
August 6, 2003

Norma Devine, Editor

On Wednesday, August 6, 2003, Dr. Rick Wilson, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Current Concepts."

Moderator:  Tonight we will be discussing current concepts and treatment of glaucoma.  Dr. Wilson, what are some of the questions glaucoma specialists are discussing?

Dr. Rick Wilson:  One question concerns how low IOP (intraocular pressure) needs to be or how much it should be lowered from where it is causing damage to the optic nerve. 

P:  What prompted that question?

Dr. Rick Wilson:  The Ocular Hypertension Treatment Study (OHTS) showed that a 20% drop only slowed the rate of the number of patients who converted to glaucoma from roughly 9% to half that.

P:  Before the results of the OHTS were published, was the goal to lower IOP by 20%?

Dr. Rick Wilson:  We have historically tried to lower IOP by 20 to 25%, but now know that patients who already have suffered significant damage may need pressures lowered more than that.  In some cases, the percentage of the decrease in IOP is not as important as the absolute IOP achieved being in the high single digits.

P:  When and why did the definition of glaucoma change from high IOP to damage to the optic nerve?

Dr. Rick Wilson:  When we realized that one out of every six patients with open-angle glaucoma never had IOPs above the normal range.

P:  Isn't it difficult to get a drop in IOP greater than 20%?

Dr. Rick Wilson:  With the older medications it was.  However, prostaglandins like Xalatan, Travatan and Lumigan can lower IOP by 35%.  Cosopt, as initial therapy in patients with high IOP, may lower IOP over 50%.

P:  Was there an indication that a higher percentage drop lowered conversion further?  Was it linear?

Dr. Rick Wilson:  Yes, the Advanced Glaucoma Intervention Study (AGIS) showed almost a definite decrease in progression for each mm of IOP till the average IOP was just over 12 mm Hg. 

P:  My glaucoma specialist said it is almost impossible to achieve single digits without cutting surgery. Is that correct?

Dr. Rick Wilson:  Yes.  However, I have hit single digits with laser in patients who started out with IOPs of 12 to 13 mm Hg. 

P:  What is considered to be a high IOP?  

Dr. Rick Wilson:  Greater than 35 or 40 mm Hg.

P:  Is it true that angle-closure glaucoma can be cured?  Are there any new procedures to help patients with plateau iris syndrome?  

Dr. Rick Wilson:  Acute-angle closure can be cured.  Chronic-angle closure can be greatly improved, but most patients need to continue on some medications.  There's been nothing new in the treatment of plateau iris syndrome for many years.

P:  What number defines the upper limit of normal intraocular pressure?   

Dr. Rick Wilson:  Most people would put 22 mm Hg as the top number, but some would put 21 mm Hg.

P:  I find it reassuring that even though most glaucoma patients undergoing treatment may lose some vision, they don't become blind.  

Dr. Rick Wilson:  I agree it is reassuring that although many glaucoma patients show some progression over decades, few ever go blind if they are conscientious about their treatment.  Luckily, even patients with moderately severe damage are quite functional.

P:  My IOPs are 34 and 37 mm Hg.  Why wouldn't there be damage at those high IOPs?

Dr. Rick Wilson:  It would be very unusual for someone to have those pressures for several years without damage.  Unfortunately, 30 to 40% of the optic nerve has to be killed before we can see definite glaucoma changes.  Therefore, watchful waiting should be avoided unless the patient's corneas are extremely thick.  

P:  Why does any pressure sometimes cause damage? 

Dr. Rick Wilson:  We have good evidence of why high pressure causes damage.  We are more uncertain about why glaucoma-appearing damage occurs to some optic nerves in eyes with normal intraocular pressures.

P:  What factors in a glaucomatous eye make you decide that single digits are desirable?  Do you try to reach single digits only in NTG (normal-tension glaucoma)?

Dr. Rick Wilson:  The main reason is the extent of the damage.  If the optic nerve has 90% or more damage and the visual field is very constricted, then an IOP of 12 mm Hg or under is needed.  If the patient is getting worse at an IOP of 14 mm Hg,  then an IOP in the single digits would be needed.  Low blood pressure, vasospastic disease (such as migraine headaches), and a strong family history of progression with normal IOPs make me lower the target IOP.

Moderator:  On a visual field test, what indicates advanced damage?  

Dr. Rick Wilson:  Usually one hemisphere would be almost gone, or there would be marked mid-peripheral loss in both the superior and inferior hemispheres.

P:  By the time a person with glaucoma actually notices a defect in the visual field, what would the typical cup-to-disc (C/D) ratio be? 

Dr. Rick Wilson:  I hate to tell you the answer my Dad usually gave to most of my questions when I was a child:  "It depends."  If the C/D ratio is 0.85 (which my son was born with), then it would have to be 0.97.  If there was no cup, then it might be as little as 0.3.

P:  If cutting surgery is needed to reduce IOP to single digits, what type of surgery is that?  

Dr. Rick Wilson:  Usually that would be a trabeculectomy.  Aqueous shunts usually do not get IOPs as low as trabeculectomies.

P:  Do you think doctors are starting to treat patients earlier who have pressures of 30 mm Hg?

Dr. Rick Wilson:  Yes.

P:  Are they trying to prevent damage before it happens?

Dr. Rick Wilson:  Yes.

P:  In May of 2000 Dr. Spaeth told us about the changing definition of glaucoma.  He said, "You treat only when a person is getting worse at a rate that will eventually cause enough visual functional loss that the person will become troubled."  Would most ophthalmologists today agree with him that treatment is not justified if the person is not going to develop a decrease in the quality of his or her life?

Dr. Rick Wilson:  Spaeth is philosophically correct, and probably the majority of glaucoma specialists would agree with him. General ophthalmologists, however, usually will not. Unfortunately, it is too hard to predict how long people will live.  If the doctor guesses wrong and has allowed too much damage to occur to the patient, the patient may be symptomatic and know a hungry lawyer.

P:  Can laser treatment following cataract surgery cause glaucoma?

Dr. Rick Wilson:  On average, the IOP in patients who have a capsulotomy (hole made in the opaque membrane behind the intraocular lens) sustains a 1 to 3 mm Hg rise over the next year.

P:  What was the purpose of that old keyhole surgery, where a piece was removed from the iris and the pupil looked like a keyhole? 

Dr. Rick Wilson:  It allowed a better view around a cataract for a patient.  If the cataract was being removed, it made the removal easier for the doctor. 

End of highlights for August 6, 2003.

On August 13, Dr. Wilson discussed "Pigmentary Glaucoma" in the Chat room. Click here for highlights of that meeting.

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