Chat Highlights
Non-Penetrating Glaucoma Surgery
July 25, 2001

Norma Devine, Editor

On Wednesday, July 25, 2001, Dr. Rick Wilson, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Non-Penetrating Glaucoma Surgery." 

Moderator:  Welcome, Dr. Wilson.  The topic tonight is "Non-Penetrating Glaucoma Surgery."

P:  What is non-penetrating glaucoma surgery and when is it used?

Dr. Rick Wilson:  Non-penetrating surgery is basically a large trabeculectomy with the final thin layer of Descemet's membrane left intact.  The aqueous fluid percolates through the membrane into a "lake" in a pocket of the sclera.  The fluid is absorbed into blood vessels, rather than getting to the space under the top conjunctival layer to be absorbed there.  The chance of the intraocular pressure being too low is less because there is not a complete hole through the wall of the eye.

P:  Which patients are the best candidates for non-penetrating surgery? 

Dr. Rick Wilson:  The best patients for this type of procedure are those in whom an IOP (intraocular pressure) of 17 to 18 mm Hg. would be adequate.  Mitomycin-C is not used and the IOPs are not as low as those seen with trabeculectomy.

P:  Does it matter if there are breaks in Descemet's membrane due to high pressures?

Dr. Rick Wilson:  No, because those breaks have already healed long ago.  They are also more central, and not out where this surgery is done. 

P:  Is this non-penetrating surgery always performed the same way?

Dr. Rick Wilson:  There are two variations of non-penetrating surgery.  In one, the Canal of Schlemm, into which the fluid going through the trabecular meshwork drains, is dilated by injecting a viscoelastic substance into it to encourage outflow.  In the other variation, a collagen plug maintains a space between the flap and the bed of the "lake."  As the collagen dissolves, the space is supposedly left into which the aqueous will drain and be absorbed. 

P:  Is there less chance of infection than with a trabeculectomy?

Dr. Rick Wilson:  The chances of infection are markedly reduced, unless a bleb still forms.

P:  Under what circumstances does a bleb form in that kind of surgery?

Dr. Rick Wilson:  Usually if there is a small break in the Descemet's membrane, letting too much fluid escape, and the flap was not sutured as securely as possible.

P:  Those of us with NTG  (normal-tension glaucoma) would not be candidates for this surgery?

Dr. Rick Wilson:  Right.  

P:  Can this procedure be performed after traditional trabeculectomies?

Dr. Rick Wilson:  Yes.  It is harder after the older-style cataract surgery.  But I feel that non-penetrating surgery, as it presently is, has probably passed it's zenith.  It has stimulated all of us to explore the anatomy more and think more about how to improve the surgery we do.  Dr. Steigmann (a South African) is to be congratulated for starting us down this road.

P:  About two years ago my mom had a non-penetrating procedure in Palm Springs by Dr. Milauskaus.  At that time, you said there was little evidence these procedures worked.  It looks like she has developed a bleb in one eye.  Otherwise, things have been going well.  Have you been doing the non-penetrating procedures at Wills?

Dr. Rick Wilson:  Yes, but rarely. Most of my patients have IOPs in the high teens before surgery.  As such, they are not candidates for the non-penetrating surgery.

P:  What is the percentage of success with this kind of non-penetrating surgery?

Dr. Rick Wilson:  That depends upon the criteria for success.  If the criteria for success is a 25-30% drop in IOP, in my patient population the success rate would be poor.  But in Dr. Steigmann's population, it would be quite high.  Dr. Steigmann's average preoperative IOP in South African blacks is 49 mm Hg.  If he is able to get the IOP down to 18 mm Hg, it is a terrific benefit to that patient, much more than it would be here in the U.S. for a Caucasian on medications, who is getting worse with an IOP of 24 mm Hg.

P:  What is the ideal IOP after a trab?

Dr. Rick Wilson:  Recently, national, multi-center studies found that most patients with IOPs of low to mid 20's before surgery required an IOP of 12 mm Hg. 

P:  What is normal IOP for a normal person?

Dr. Rick Wilson:  An IOP of 12 to 22 mm Hg. 

P:  If you needed glaucoma laser surgery, would you be comfortable with a general ophthalmologist performing it?

Dr. Rick Wilson:  If the ophthalmologist did a lot of them and had a large glaucoma population, yes.   The biggest mistake that general ophthalmologists make is not in doing the procedure (though most use an excessive amount of energy), but in selecting the patients who will do well with the procedure and those who should not have it.

P:  What are the chances of success using diode laser trans-scleral photocoagulation for neovascular glaucoma?

Dr. Rick Wilson:  The chance of controlling the IOP depends upon how high the IOP is originally, but is probably about 50% with the first treatment and increases with each additional treatment.  

P:  That is performed for diabetic retinopathy, isn't it ?  

Dr. Rick Wilson:  Yes.  

P:  What are the symptoms of retinal detachment? 

Dr. Rick Wilson:  The symptoms of a retinal detachment are flashing lights, lots of black or red spots in front of the eye, or a veil coming down over the vision.

Dr. Rick Wilson:  Sorry, I have to get to bed to get ready for tomorrow.  Have a good week.

End of highlights for July 25, 2001.

On August 1, Dr. Wilson discussed Systemic Factors Contributing to Glaucoma in the Chat room. Click here for highlights of that meeting.

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