Pigment Dispersion Syndrome and Pigmentary Glaucoma
Chat Highlights
May 3, 2006

On Wednesday, May 3, 2006, Dr. Tricia Thomas, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Pigment Dispersion Syndrome and Pigmentary Glaucoma."

Moderator:  We'd like to give a big, warm welcome tonight to Dr. Tricia Lennox Thomas.  Dr. Thomas graduated cum laude (Molecular Biology) from Princeton University, served a fellowship with Dr. Ritch at NYE&E before her residency at Wills, and joined the staff at Wills last January.  Thank you so much for being here tonight.

Dr. Tricia Thomas:    Thank you. I’m glad to be able to be here.

Moderator:   Our topic tonight is Pigment Dispersion Syndrome (PDS) and Pigmentary Glaucoma (PG).  Dr. Thomas, since you served a fellowship with Dr. Robert Ritch, you know his Rule #1:  "Anyone with open-angle glaucoma under the age of 50 has pigmentary glaucoma until proved otherwise."  Why is that his Rule #1?

Dr. Tricia Thomas:   Dr. Ritch believes PDS is missed frequently clinically.  The typical triad for PDS is pigmentation on the cornea (called Krukenberg spindles), transillumination defects, and dense pigmentation in the trabecular meshwork.  You won’t see all of these signs in many patients unless you look carefully.

P:    I thought it was easy to see the pigment in the trabecular meshwork.

Dr. Tricia Thomas:   It is easy to see the pigmentation.  However, you have to perform gonioscopy.

Moderator:   Isn't that part of a standard examination?

Dr. Tricia Thomas:   It is not part of a standard eye exam, but should be performed on anyone who is suspicious for glaucoma.

P:   What does gonioscopy involve?

Dr. Tricia Thomas:   In gonioscopy, a special lens is used to look at the drainage structure of the eye.

P:   What are the risk factors for pigmentary glaucoma?

Dr. Tricia Thomas:   That type of glaucoma is hereditary and is more common in myopic (near-sighted) individuals.

P:   Some glaucoma patients say they have both primary open-angle glaucoma and PG. Isn't PG one of the many types of open-angle glaucoma?

Dr. Tricia Thomas:   PG is a type of open-angle glaucoma.

Moderator:   Does PDS always lead to PG?

Dr. Tricia Thomas:   No, not all individuals with PDS get PG.

P:   What other secondary glaucomas could be mistaken for PG?

Dr. Tricia Thomas:   PDS is characterized by a disruption of the iris pigment epithelium. That deposits the pigment in various parts of the front of the eye, including the drainage structure, which can make the eye pressure go up.

P:   When is the pigment released?

Dr. Tricia Thomas:   It’s released early in the process, from age 20 to 40.  As we get older, however, we do not make as much pigment and the pigment can be absorbed, making it look more like open-angle glaucoma.  The optic nerve shows damage.

P:   Is the treatment different for pigmentary glaucoma than it is for open-angle glaucoma?

Dr. Tricia Thomas:   Often the treatment is the same for PDS/PG and other open-angle glaucomas.

P:   Would it be fairly easy for an ophthalmologist to originally diagnose pigmentary and then, a few months later, decide it is open-angle glaucoma? (That happened to me.)

Dr. Tricia Thomas:   Yes, that could happen. In fact, I saw someone today who was diagnosed years ago with PDS and was then recently told it was open-angle glaucoma.

P:   Why is pigment normally released?

Dr. Tricia Thomas:   Pigment is not normally released. In this condition, the iris is bowed posteriorly and rubs on the zonules, which are small fibers attached to the lens.

P. Are there anatomical differences in the angles of patients with PDS and PG?

Dr. Tricia Thomas:   PDS and PG patients have a larger iris than normal individuals, and the insertion of the iris is more posterior (located further back in the eye).  This anatomical difference allows the iris to rub on the zonules.

P:   Why do we make less pigment as we get older? Is it like graying hair?  And at about the same age (say 50's)?

Dr. Tricia Thomas:   As the iris rubs, pigment is dispersed.  As we get older, the lens of the eye gets larger, so there is less room for the iris to rub.  In addition, when we are young, the iris curves backward during accommodation (near vision).  As we get older, however, we are not able to accommodate as well.

P:   If I understand this form of glaucoma correctly, wouldn't ALT (argon laser trabeculoplasty) or SLT (selective laser trabeculoplasty) be effective for patients with PG under age 50?

Dr. Tricia Thomas:   The treatment for PDS and PG is glaucoma drops first.  However, ALT and SLT are also effective.

P:   My pigmentary glaucoma is being treated with Xalatan.  I have a problem, not so much with my individual treatment, as with the paradigm of treating the symptom but not the cause, i.e., lowering the pressure, but not addressing the shedding of pigment.  Since I have retinal problems that put me at risk for retinal detachment, I wouldn't consider a miotic such as pilocarpine.  I've seen papers from European researchers indicating the use of Dapiprazole, a miotic that acts only on the iris dilator muscle, causing miosis without traction on the retina.  Since that sounds like such an intuitive approach, why haven't more researchers picked up on it?  My clinician thinks there's not enough experience with Dapiprazole over the long term, although the people publishing what little data exist say it's well tolerated. Your thoughts, please.

Dr. Tricia Thomas:   Dapiprazole is used in Europe and is effective at straightening the iris to make it flat and not release more pigment.  This medicine constricts the pupil and pulls the peripheral iris away from the zonules. The problem is that it is poorly tolerated due to burning and redness.

P:   The reason I'd prefer to address the shedding of pigment is the fear that even once pigment release has abated, the trabecular meshwork has been irreparably damaged, so that even in the absence of further pigment release, there is lifelong dysfunction of the trabecular meshwork.  Doesn't that occur frequently?

Dr. Tricia Thomas:   The peripheral laser iridotomy is likely to be more effective early in the disease process before a lot of the pigment has been dispersed.  Once the optic nerve is damaged, the iridotomy will not be as effective.

P:   Do you think that head movement in certain types of exercise is what causes the associated pigment showers, or could it be due to the elevation of the ocular pulse, irrespective of movement?  I saw a paper once that documented pigment release in response to exercise on stationary bikes.  The researchers postulated that it was the latter (elevated ocular pulse) that resulted in pigment release, either from pupillary block, or reverse pupillary block.  Obviously, everybody else in the literature says jarring head movements must be avoided.  How do you counsel your PG patients regarding exercise?

Dr. Tricia Thomas:   Some patients with PDS or PG have pigment release during exercise and will have blurry vision or elevated eye pressure.  I have not read the article on elevated ocular pulse.  However, it is more likely due to the reverse pupillary block (from the posteriorly bowed iris). In patients with this problem, a drop of pilocarpine before exercise can relieve that, as pilocarpine is a miotic, constricts the pupil, and eliminates the pupillary block.

P:   What indicates that PDS or PG is "burned out" or almost resolved?

Dr. Tricia Thomas:   There is a regression phase when pigment is no longer released, the corneal pigmentation clears, transillumination defects in the iris can disappear, and the pigmentation in the drain clears first in the inferior drain.

P:   Do blue-eyed people have fewer problems with pigmentary glaucoma?

Dr. Tricia Thomas:   Actually, it is the iris pigment epithelium behind the blue part of the iris that is disrupted and deposited throughout the eye. It is easier to see this condition in blue-eyed individuals.

P:   So the epithelial cells get rubbed off and drain into the trabecular meshwork, where everything dissolves but the pigment?

Dr. Tricia Thomas:   Correct.  The drain gets clogged with this pigment.  Think of it as throwing coffee grounds into the sink.  If there is too much, the sink won't drain.

P:   We have not had a chat about PG and PDS since 2004.  Have there been long-term clinical trials since then showing that iridotomy will prevent the eventual increase of IOP in patients with PDS?

Dr. Tricia Thomas:   We still need a long-term study.  The American Glaucoma Society published one study, in which all glaucoma specialists were asked to submit results from their patients. Only 60 were submitted, which was not enough to determine if it was really effective.

Moderator:   Dr. Thomas, we've really enjoyed having you here tonight.  Thanks so much.  Your answers have been helpful and informative.  We hope you will come again.

On May 10, Dr. Werner discussed "Glaucoma Terminology" in the Chat room. Click here for highlights of that meeting.

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