Combined-mechanism Glaucoma
Chat Highlights
November 12, 2003

Norma Devine, Editor

On Wednesday, November 12, 2003, Dr. Rick Wilson, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Combined-mechanism Glaucoma."

Moderator:  Dr. Wilson, the topic tonight is combined-mechanism glaucoma.  What is that?

Dr. Rick Wilson:  Combined-mechanism glaucoma almost always means combined open-angle and closed-angle glaucoma.  That is usually when the angle is open, except for small areas of closure.

P:  Are those small areas of closure generally visible to the ophthalmologist during a slit lamp examination?  Where are they?  

Dr. Rick Wilson:  The small areas of closure occur where the iris is stuck to the trabecular meshwork.  This can only be seen by gonioscopy. 

Moderator:  How common is combined mechanism glaucoma?   

Dr. Rick Wilson:  I think it is unusual; that is, comprising less than 1% of the glaucomas.

P:  How is combined-mechanism glaucoma treated?

Dr. Rick Wilson:  If the angle closure is caused by fluid pressure behind the iris pushing the iris toward the trabecular meshwork, then an iridectomy is required.  After a peripheral iridectomy equalizes the fluid pressure behind and in front of the iris, the patient is treated with medication, exactly as open-angle glaucoma would be treated.  

P:  In combined-mechanism glaucoma, does the eye respond to anticholinergic drugs and various medications, which are contraindicated for narrow-angle glaucoma, the same way as the eye with narrow-angle glaucoma?

Dr. Rick Wilson:  Yes.

P:  Is there a difference between mixed mechanism glaucoma and combined-mechanism glaucoma, or can the terms be used interchangeably? 

Dr. Rick Wilson:  In my experience, combined mechanism glaucoma is the combination mentioned above.  Mixed mechanism glaucoma is usually a combination of two different kinds of glaucoma, but angle closure is often not one of those two kinds.  Therefore, mixed mechanism glaucoma might be a combination of open-angle glaucoma and inflammatory glaucoma.

P:  What are some eye conditions that may predispose a person to combined-mechanism glaucoma?

Dr. Rick Wilson:  Some examples are Fuch's corneal dystrophy, Weill-Marchesani syndrome, Marfan's syndrome, spherophakia, and microspherosphakia.  

P:  Is combined-mechanism glaucoma hard to diagnose?

Dr. Rick Wilson:  Not if the examiner is good at gonioscopic examination. 

P:  Is gonioscopy part of a normal medical eye examination?

Dr. Rick Wilson:  It is for an ophthalmologist. 

P:  What are peripheral anterior synechiae (PAS)?

Dr. Rick Wilson:  Peripheral anterior synechiae are in the areas where the iris has become stuck in the trabecular meshwork.

P:  Are PAS the same as the abnormal membrane in ICE (iridio-corneal syndrome)?  

Dr. Rick Wilson:  No, PAS occur when the iris is pushed into the trabecular meshwork by the pressure of fluid behind the iris.  The ICE syndrome is caused by a membrane that either covers the trabecular meshwork or pulls the iris up over it.

P:  Is a patient with small areas of closure always considered to have combined-mechanism glaucoma?  If the area of closure enlarges, would it then be considered only closed angle glaucoma?

Dr. Rick Wilson:  If there are only a few small areas of peripheral anterior synechiae, that would be considered a straight angle glaucoma.  If there were one to two clock hours closed, then it would be a combined-mechanism glaucoma.

P:  How much is an angle closed before closed-angle glaucoma occurs?

Dr. Rick Wilson:  My take would be if the three to four o'clock angle were closed.  

P:  Does the entire chamber angle tend to close over time?

Dr. Rick Wilson:  The entire chamber angle will close in someone with a narrow angle.

P:  Are the superior angle and the inferior angle the same size?

Dr. Rick Wilson:  The superior angle is narrower than the inferior angle.

P:  After my first trabeculectomy, the doctor told me that my iris was being sucked into the meshwork.  The iris, he said, is fluid, and that can happen.  Would that be considered combined-mechanism glaucoma if I already had angle closure? 

Dr. Rick Wilson:  There are three different diagnoses.  One is open-angle glaucoma.  The second is combined-mechanism glaucoma.  The third is angle-closure glaucoma.  A person who has angle-closure glaucoma cannot move backwards and get a combined-mechanism glaucoma.

P:  How was mixed-mechanism glaucoma diagnosed before the gonioscope became available?  Or was it?

Dr. Rick Wilson:  It wasn't and isn't.  In India, now, many patients with angle-closure glaucoma are treated as if they had open-angle glaucoma, because the doctor did not gonioscope them or was unable to do so.  

P:  Could inflammation of the iris cause the iris to stick to the trabecular meshwork in a small area?  

Dr. Rick Wilson:  Only if the angle of the eye were quite narrow.

P:  Would having surgery involving the iris predispose a person to an acute angle attack?  I am thinking specifically of the full, congenital cataract extraction performed in the 1970's.  A small part of my iris had to be removed in order to remove the intact lens.   

Dr. Rick Wilson:  Certainly surgery that left no hole in the iris, but left all the jelly (vitreous) in the eye, could predispose someone to angle closure.

Dr. Rick Wilson:  It does cause inflammatory changes to the conjunctiva.  I've not seen any studies about the sclera.

P:  What is the conjunctiva?

Dr. Rick Wilson:  The conjunctiva is the clear vascular layer of tissue over the white sclera of the eye.

P:  How many of us with open-angle glaucoma actually have some small areas of closure?  

Dr. Rick Wilson:  Very few of you have any areas of angle closure.

Moderator:  Thank you, Dr. Wilson.  As always, a very informative chat.  Have a good evening and week.

Dr. Rick Wilson:  I hope you all have a wonderful week.  I look forward to seeing you here next week.

End of highlights for November 12, 2003.

On November 19, Dr. Wilson discussed "Blood Flow and Glaucoma" in the Chat room. Click here for highlights of that meeting.

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