Surgical Options in Glaucoma Care
Chat Highlights
December 11, 2002

Norma Devine, Editor

On Wednesday, December 11, 2002, Dr. Rick Wilson, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Surgical Options in Glaucoma Care."

Moderator:  What are the main surgical options for glaucoma patients?

Dr. Rick Wilson:  Argon laser trabeculoplasty, followed by a trabeculectomy, followed by an aqueous shunt.  Usually, a shunt is just plumbing and can be revised to make it work.  If not, a laser or freezing cyclodestructive procedure is the last modality.

P:  When does surgery become an option?

Dr. Rick Wilson:  Surgery is usually turned to when medicine and lasers fail or it is expected they would fail.

P:  What percentage of glaucoma patients will have to have surgery of some type to control their glaucoma?

Dr. Rick Wilson:  I don't know the exact percentage, because it varies by the type of glaucoma, and the age and race of the patient.  In general, most patients are controlled by medicines and lasers.

P:  Should surgery be considered when the visual fields are stable, but the optic nerve is damaged?  

Dr. Rick Wilson:  Usually not, unless the IOP (intraocular pressure) is above the target range.

P:  How do you determine the target range?

Dr. Rick Wilson:  The target IOP has undergone a significant evolution during my time in practice.  At the start of my residency, an IOP brought into the teens was considered adequate.  Then I adopted the principle of a 25 to 30% decrease in IOP from the last level at which progression had occurred. However, a study of George Spaeth’s and my patients when we practiced under that principle showed that 7% of our patients got worse each year.  In retrospect, this made perfect sense since the indicator for us to increase medication or move to a laser or surgery was a worsening of the patient’s glaucoma. 

I then adopted Dong Shin’s 40% drop in IOP from the IOP at which progression had occurred.  Attaining that level was hard, but did result in a far greater proportion of my patients remaining stable and even improving their visual field. 

The AGIS (Advanced Glaucoma Intervention Study) data forced another reevaluation of my approach to patients with serious disc damage.  In that study, only those patients who had IOPs under 18 mm Hg one hundred percent of the time and averaged close to 12 mm Hg had their visual field stabilized over an eight-year period.  The disturbing aspect of the data was the continued progression even when IOPs averaged just under 15 mm Hg and were less than 18 mm Hg at least 75% of the time. 

P:  Do you still use percentage drops in pressure?

Dr. Rick Wilson:  I now seek target IOP ranges, rather than a percentage drop in IOP.  My target range for anyone who has shown visual field loss with IOPs in the mid 20s or lower depends upon the extent of the glaucoma damage and the risk factors involved. 

P:  What are those risk factors?

Dr. Rick Wilson:  The main risk factors I think about include family history, age, race, low systemic blood pressure, and vasospastic disease.  In general, if the damage is moderately severe or severe (that is, serious damage in both visual field hemispheres or advanced damage in one), I aim for the 12 mm Hg or less IOP, as suggested by the AGIS study.  Arcuate damage in one hemisphere puts me in the 12 to 15 mm Hg target range. 

I try to keep anyone with nerve damage and nonspecific changes on their visual field in the 16 to 18 mm Hg range.  The Normal Tension Glaucoma Treatment Trial eyes revealed that eyes with an increased susceptibility to IOP may need even lower target ranges, often in the single digits.

P:  How is a trabeculectomy different from a shunt?

Dr. Rick Wilson:  Trabeculectomy achieves lower IOPs than shunts and is a less extensive procedure.  It suffers, however, from the development of a bleb, or bubble, of conjunctiva, where the aqueous, or watery fluid, in the eye comes out. The conjunctiva can thin with time, and leaks can develop, with the possibility of infection.

P:  My son has had four trabeculectomies so far.  He is on medications for his right eye only; the left eye is doing very well, with the pressure under 10 mm Hg all the time.  Would you consider further surgery for the right eye to bring the pressure down, or stick with the eyedrops?

Dr. Rick Wilson:  I would stick with the eyedrops as long as the IOP is reasonable.

P:  When does a shunt become an option?  

Dr. Rick Wilson:  Usually a shunt becomes an option when a trabeculectomy with the use of mitomycin C fails. The indications for a shunt, rather than a trabeculectomy, are as follows:  (1) a failed, well-done, previous trabeculectomy with mitomycin C; (2) conjunctiva too scarred to elevate a conjunctival flap; (3) neovascularization in neovascular glaucoma not yet quiescent post PRP (laser photocoagulation), but IOP forces surgery; (4) recurrent episodes of serious intraocular inflammation; (5) aggressive ICE (iridocorneal endothelial) syndrome (Note:  See Chat Highlights, December 12, 2001); (6) inner ostium of shunt placed on front of anterior chamber IOL (intraocular lens) to avoid vitreous incarceration; (7) contact lens wear is essential for the patient.

P:  Can the patient feel the shunt?  

Dr. Rick Wilson:  Shunts are very rarely felt.

P:  Can a shunt be removed if it does not help or makes the person uncomfortable?

Dr. Rick Wilson:  They can be removed if they don't work out.  Usually shunts are done in eyes that have had previous surgery and have been on irritating glaucoma medications for some time.  The shunt may elevate some of the tissue overlying it and cause a mild chafe there, which is exacerbated if the eye is dry.

P:  Why is my eye still red after having a shunt surgery last February?  My IOP still goes high even though I am using two eyedrops and am back to using Diamox.

Dr. Rick Wilson:  There can be several causes.  Either the shunt reservoir area is not large enough for your case, or the scar tissue surrounding the reservoir of the shunt is getting too thick, so that the aqueous has a hard time getting through it.

P:  What is done when a tube shunt is revised?

Dr. Rick Wilson:  There are many kinds of revision.  The tube can be repositioned if scarring has moved it or blocked it.  The tube can be re-covered with a patch graft if a hole has worn in the conjunctiva overlying the tube.  A common operation is to remove the scar tissue overlying the reservoir so the aqueous can filter through the capsule more easily.

P:  Is it true that after shunts, there are no other options for glaucoma patients?

Dr. Rick Wilson:  No.  I have done a trabeculectomy after a shunt in a handful of patients.  After a shunt, however, usually the next procedure to go to is a laser or freezing destructive procedure. 

P:  In what ways do a trabeculectomy fail?  How does it cease to function?  At what point will a doctor call it a failure?

Dr. Rick Wilson:  Iris or blood can block the inside of the hole through the wall of the eye that the aqueous goes through.  The hole can gradually just get smaller and clog up.  The conjunctiva overlying the hole can seal down over the hole and close it off.  Sometimes the conjunctiva is ballooned up over the hole through the sclera, but the body scars around the ballooned up area and the aqueous still has nowhere to go.  It is usually a complete failure when medications can no longer control the IOP.

P:  What are some of the situations in a filtering procedure where you might prefer a limbal-based flap?  A fornix-based flap?  Which is easier to perform?

Dr. Rick Wilson:  The limbus is where the sclera or white of the eye meets the cornea.  A limbus-based conjunctival flap means the conjunctiva is cut circumferentially as high up under the lid as possible and hinged at the cornea.  I used to do all my flaps that way since I believed it was the best way to avoid leaks.  

Peng Khaw from England has shown that hinging the conjunctiva away from the limbus, i.e., cutting the conjunctiva at the limbus (fornix-based) and doing the surgery under the conjunctiva, then sewing the conjunctiva back down at the limbus, gives more diffuse blebs.  That is, the blebs spread out more and this type of bleb is less likely to thin and leak over time.  I have switched to that type of closure since Peng Khaw's report.

P:  Do open-angle glaucoma patients or angle-closure patients need surgery more often?  

Dr. Rick Wilson:  Angle-closure patients make up only about 15% of the patients who develop glaucoma.  I would expect that they would need surgery slightly more often than open-angle glaucoma patients, but that is just my experience.

P:  Cryotherapy changes the color of the iris.  Can the color change be reversed, or is there a contact lens that can be used? 

Dr. Rick Wilson:  What kind of cryo?  It is unusual to cryo the iris except in epithelial in-growth.  There is a contact lens with a painted pupil on it for cosmetic reasons.

P:  They froze the eye and now it's a different color.

Dr. Rick Wilson:  There could be several reasons for that.  The cornea is now cloudy, and looking through it changes the color of the iris.  Perhaps the iris is atrophic and has changed color.

P:  Can a person ever wear a contact lens over a working trabeculectomy?

Dr. Rick Wilson:  It is done, especially if the conjunctiva overlying the trabeculectomy is of normal thickness.  However, there is a risk that bacteria from the contact lens can penetrate a thin bleb into the eye.

P:  I have stopped using preservative-free dexamethazone as it was making my eye really inflamed.  Why would this drop suddenly have that effect on me?

Dr. Rick Wilson:  Do your doctors know that?  The dexamethazone should have been keeping inflammation and scarring down.

P:  Can a selective laser (SLT) procedure be effective two years after an argon laser trabeculoplasty (ALT) that was only modestly effective?

Dr. Rick Wilson:  Yes, but for how long is the question.

P:  Can someone with chronically dilated pupils wear a contact lens to make the pupils look even and not so gigantic?

Dr. Rick Wilson:  Yes.  

P:  What can be done for floaters in the eye?

Dr. Rick Wilson:  Usually floaters will sink into the bottom of the eye after a time.  The floaters can be removed surgically, but it is risky for a malady that is usually short-lived.

P:  How long, on the average, before floaters disappear?

Dr. Rick Wilson:  Months to a year or more.

P:  My vision is blurry after a trabeculectomy last week. Is that normal?  

Dr. Rick Wilson:  Yes, very normal.

P:  How many years will a trabeculectomy normally last?  

Dr. Rick Wilson:  It used to be said that trabeculectomies lasted seven years on average.  These days I think we are doing better than that.

P:  What causes a trabeculotomy to fail?   (Editor's note:  Trabeculotomy is indicated for children who have congenital glaucoma when the clear covering (cornea) over the iris is cloudy.) 

Dr. Rick Wilson:  In a trabeculotomy the iris can close off the internal opening, scarring can close off the whole opening, or it can stop working without any visible cause.

P:  Does treatment for secondary angle closure differ from treatment for primary angle closure?  Do they look different to the doctor?  

Dr. Rick Wilson:  Yes, how it looks depends on why the glaucoma is secondary, i.e., what caused it.  

P:  My IOP was 2 mm Hg after my surgery.  Is that in the danger zone?

Dr. Rick Wilson:  Yes.  I have patients over 70 years of age who could see well at that IOP,  but most people have distorted or blurred vision at that level.

End of highlights for December 11, 2002.

On December 18, Dr. Werner discussed "Coping With Glaucoma" in the Chat room. Click here for highlights of that meeting.

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