Chronic Angle Closure
Chat Highlights
June 3, 2009

On Wednesday, June 3, 2009, Dr. Michael Pro, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Chronic Angle Closure".

Moderator: Welcome back Dr Pro. Our topic this evening is Chronic Angle Closure. What is chronic angle-closure glaucoma and how does it differ from acute angle-closure glaucoma?

Dr. Pro: Great; let's talk about the basics. Angle closure glaucoma is straightforward in that the mechanism is understood. It is unlike open angle glaucoma in this respect. In angle closure there is not enough space between the iris and the cornea. As you know from earlier chats, the drainage system in the eye (the trabecular meshwork or TM) is located here. If the iris and the cornea are touching then the aqueous may not be able to exit the eye. In an acute attack, the angle suddenly closes and the drain suddenly closes off; the IOP gets very high the eye can be in extreme pain. This is a dangerous situation where high IOP can cause nerve damage in a very short time frame (hours to days). In chronic angle closure the process is much more gradual. The same anatomical feature exists with the iris close to the cornea, but we see a gradual rise in the IOP over time (much like open angle glaucoma or POAG). We understand this to be due to gradual scarring over of the TM. Although the end result can be the same as POAG, the mechanism of chronic angle closure glaucoma (CACG or PACG) is different.

P: People with open angle glaucoma are not susceptible to these attacks, right?

Dr. Pro: True.

P: How is it diagnosed?

Dr. Pro: Narrow angles are diagnosed during routine ophthalmologic examination by gonioscopy. CACG is diagnosed by noting narrow angles, scarring in the trabecular meshwork, and the sequelae of glaucoma such as optic nerve damage, visual field changes, and often high IOP, sometimes resistant to therapy.

P: Does an individual first need a diagnosis of acute angle-closure and subsequently the glaucoma changes to chronic angle-closure?

Dr. Pro: No, it is more common to develop CACG and never have had an acute attack. Acute attacks are rare, whereas CACG may represent up to 20 percent of glaucoma in the U.S. and as much as 50 percent in Asian populations. Persons who have acute attacks can wind up with CACG though.

P: Is there pain as associated with chronic angle-closure glaucoma?

Dr. Pro: No, the IOP is not usually acutely elevated (like in an acute attack). It's more like POAG, where patients never know that they have it.

P: When is it warranted to perform a laser peripheral irdotomy?

Dr. Pro: That is nearly always as the first step in starting treatment for CACG. You want to know if opening the angle more can help control the IOP. You would not do a PI when there is total scarring shut of the angle and you know that a laser PI would be ineffective in opening this permanently closed angle.

P: Is this a more difficult form of glaucoma to treat? Does it respond to drops, laser trabeculoplasty, or surgery differently than POAG?

Dr. Pro: Yes, it often is. It is often resistant to treatment and it does respond differently to all of the above.

First, drops—some drops are less effective, particularly those that facilitate aqueous outflow, when the angle is completely scarred shut.

Laser trabeculoplasty is not effective for most CACG because you cannot see the TM to treat it with the laser.

Surgery can behave differently, too. Sometimes the anterior chamber can be so shallow that there is not enough space to do a trab or especially a tube. This can affect the success of surgery and you often have to do cataract surgery first, or at the time of surgery, to make more room in the anterior chamber.

P: Is there a greater chance of blindness with this glaucoma compared to the other forms of glaucoma?

Dr. Pro: Unfortunately statistics on blindness does not normally discriminate between types of glaucoma, so I don't know the answer.

P: Is this seen in those under 40 years of age or children?

Dr. Pro: Forms of angle closure are seen in kids, but they are due to inherited ocular malformations and represent a different process than I described earlier. You can see it in young adults, but like POAG it is usually a disease related to aging.

P: What is the relationship between angle closure and plateau iris?

Dr. Pro: Plateau iris is an anatomical condition where the iris is pushed forward from behind. It can lead to chronic angle closure glaucoma if not properly addressed.

P: I read there are five types of chronic angle closure: (1) peripheral anterior synechia formation (PAS), (2) combined mechanism, (3) mixed mechanism, (4) plateau iris, and (5) miotic-induced angle-closure glaucoma. Could you tell us about each and what makes them different? What is the most common to least common of chronic angle-closure glaucomas?

Dr. Pro: (1) PAS simply refers to the scar tissue that develops between the iris and the cornea, I discussed this above;
(2) and (3) are difficult to answer because there is no agreement on these terms. I usually use mixed mechanism to refer to patients when have narrow angles;
(4) They undergo a PI and the angle opens up, but still go on to develop glaucoma (basically open angle glaucoma);
(5) Miotic induced—basically pilocarpine can cause a forward rotation of the lens-iris diaphragm and can exacerbate angle closure in certain patients.

P: Dr., I had problems with angle closure and was on atropine for many years to keep the angle open just enough to keep my pressure down. Can you explain why one would need atropine?

Dr. Pro: Think of atropine as the opposite of pilocarpine. It causes dilation (which you usually do not want in angle closure because the iris folds back into the angle) but it also causes backwards rotation of the lens-iris diaphragm and can actually cause a deepening of the anterior chamber. This would not usually be done in a CACG patient, but everyone's anatomy can be different and perhaps the doctor saw a big improvement on the atropine.

P: Dr., my angles closed over a long period of time and they tried lasers, trabs and then I had an acute attack post trab and needed vitrectomy with a lens implant. Is this something that can occur when the angle closes over a period of time?

Dr. Pro: An attack after a trab suggests a rare condition called aqueous misdirection, where the aqueous is trapped in the back of the eye, forcing the iris and lens forward. It can be relieved by a laser, but often needs a vitrectomy.

P: How often should gonioscopy be performed on a patient with acute angle closure that has been treated and stabilized?

Dr. Pro: Often I recommend cataract surgery on patients who had attacks of acute ACG. Then the angle opens up and we don't need to worry about the angle any more. But if for some reason cataract surgery is not performed, and the attack is broken with a PI, then I would probably check the gonio every six months for a few years and back off to once a year after that as long as the angle looked unchanged.

Moderator: Dr. Pro, we are out of time. This has been an informative and interesting chat. Thank you for taking the time with us.

Dr. Pro: You're welcome. Good night everyone.

On July 1, Dr. Pro discussed "Vision Imperfections" in the Chat room. Click here for highlights of that meeting.

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