Chat Highlights
Hypotony - Low Eye Pressure
October 31, 2001

Moderator:  Tonight's topic is hypotony (low eye pressure).  Dr. Elliot Werner is our guest. 

P:  Dr. Werner, I certainly did have hypotony problems, but they seem to be cleared up now.

Dr. Elliot Werner:  Glad to hear it.

P:  Doctor, in hypotony, how low must intraocular pressure (IOP) be and what does it mean?  

Dr. Elliot Werner:  Too low IOP causes several distortions of the retina, lens and cornea that can degrade vision.  Hypotony is generally considered to be less than 6 mm Hg.

P:  Do more patients become hypotonic because their IOPs go lower than expected, or because their IOP targets were set too low to begin with?

Dr. Elliot Werner:  Almost by definition hypotony results from IOP going lower than expected. You would never set a target pressure in the hypotony range.

P:  Is there any way to predict which patients will have symptoms of hypotony after a trabeculectomy and which will not? (Hypothesis: perhaps those with higher episcleral venous pressures are more likely to become symptomatically hypotonic because their post-op IOPs are less "natural" for them.)

Dr. Elliot Werner:  There is no way to predict hypotony after surgery.

P: I had hypotony post trab due to a couple of bleb leaks.  That cleared up, but I have a lot of distortion in that eye now.  My glaucoma specialist and retina specialist can't see anything wrong with the retina. What else could be going on?

Dr. Elliot Werner:  Hypotony can induce changes in the orientation of the retinal cells without anything being visible on examination.  

P:  In a hypotonous eye with an IOP of  2 to 3 mm Hg., would that cause corneal folds?

Dr. Elliot Werner:  Corneal folds result because the IOP is too low to maintain the shape of the eye, and it collapses like a balloon without air.

P:  Can anything be done about those changes?

Dr. Elliot Werner:  We try to get the IOP up to a more normal level, but sometimes the changes are permanent.

P.  Yesterday my pressure was 8 mm Hg.  Might that be too low for me?

Dr. Elliot Werner:  That's hard to say. It depends on whether or not you are having complications of the low IOP.

P  Just the distortion.  Very frustrating!

Dr. Elliot Werner:  Everything about glaucoma is frustrating.

P:  Since my pressure was under 5 mm Hg for only a couple of weeks, do I probably have a good chance of the distortion clearing in time?

Dr. Elliot Werner:  That's hard to say.  Many patients show slow improvement for a long time after repair.

P:  That would be fixing the hypotony and waiting to see if the problems resolve?

Dr. Elliot Werner:  Yes.  

P:  Doctor Werner, the IOP in my left eye is down to 4 mm Hg.  I have folds in the retina.  My doctor is talking about blood injections.  When is the time to get them?

Dr. Elliot Werner:  As soon as possible. 

P:  How late is too late to fix problems resulting from hypotony?  Could they still be fixed after a couple of years?  

Dr. Elliot Werner:  Usually not after a couple of years.  Usually they should be fixed within a matter of weeks to get the best chance of recovery.  

P:  Is my IOP of 4 mm Hg the reason my vision fluctuates? 

Dr. Elliot Werner:  I don't know.  That's not uncommon in hypotony. 

P:  What's the longest a patient can have hypotony without suffering any permanent damage to his or her vision?

Dr. Elliot Werner:  It  varies, but some eyes tolerate hypotony forever without complications;   others develop complications quickly. Once complications develop, they need to be fixed as soon as possible.

Moderator:  What are the symptoms of  hypotony?

Dr. Elliot Werner:  Decreased or distorted vision.

P:  Is the distorted vision with hypotony slight or acute? 

Dr. Elliot Werner:  That varies, depending on how severely the retina is affected.

P:  What is the best way to examine the macula for changes due to hypotony?

Dr. Elliot Werner:  By direct viewing with a lens and slit lamp or by fluorescein angiography.

P:    You mentioned IOP raised to normal range.  It that anything above 6 mm Hg? 

Dr. Elliot Werner:  Generally, IOP above 6 mm Hg is safe and does not cause problems.

P:  Do you think blood injections are successful in many cases?

Dr. Elliot Werner:  About 30 to 50% of the time.

P:  How many blood injections can a patient have?

Dr. Elliot Werner: There's really no limit.  But if two don't work, most people give up.   

P:  What can be done if the injection does not work? 

Dr. Elliot Werner:  Further surgery is usually needed to close the filter.

P:  How is a bleb revised?

Dr. Elliot Werner:  An operation is carried out to partially close the filter and repair any leaks in the overlying conjunctiva. 

P:  Is intraocular pressure different from the anterior chamber level of fluid?

Dr. Elliot Werner:  No, it's the same thing.

P:  Does blood flow affect hypotony? I am not sure whether we are talking about blood or other fluids. 

Dr. Elliot Werner:  Only to the extent that poor blood flow can affect the production of fluid by the ciliary body.  People with poor blood flow to the eye often have low IOP because they don't make enough aqueous fluid.  

P:  Why do some of us get along fine with IOP under 6 mm Hg?

Dr. Elliot Werner:  I don't know.

Moderator:  Does hypotony only occur after a trabeculectomy or after other surgical procedures, too?

Dr. Elliot Werner:  Most hypotony is post surgical, but sometimes inflammation or poor blood flow can cause hypotony.  

P:  Have there been many controlled studies to determine what works and what doesn't work to raise IOP in hypotonic patients?  If so what has been learned?

Dr. Elliot Werner:  There are many studies reporting various treatments for hypotony.  The  best is surgery to close the filter, but often the IOP goes way up again. Nothing really works for ciliary body shut-down. 

P:  If surgery is used to close the filter, can't a new one be created?  Would the success rate be higher the second time around?

Dr. Elliot Werner:  You're usually dealing with a patient with real bad problems, and it is very difficult to predict.  Success with second operations is never as good as with first. 

P:  Is the distorted vision with hypotony slight or acute?  I have had a vision change.

Monitor:  But you have not had a trab and your IOPs are not 5 mm Hg.  

P:  True, I have not had a trab, but my IOPs may have gone down from 10 mm Hg.  

Monitor:  From medication? 

Dr. Elliot Werner:  Symptomatic hypotony from medications alone is almost unheard of.

P:  Good.  Glad to hear that. 

P:  If  you have macular puckers and many wrinkles in your retina due to hypotony, is that called  hypotony?  

Dr. Elliot Werner:  Hypotony is defined by the level of  IOP. It is usually below 6 mm Hg.   If it is no longer low, you do not have hypotony, but you may have persistent damage from the complication.  

P:    You mentioned IOP raised to normal range.  It that anything above 6 mm Hg? 

Dr. Elliot Werner:  Generally, IOP above 6 mm Hg is safe and does not cause problems.

P:  How is the eye affected by hypotony.  

Dr. Elliot Werner:  Hypotony distorts the retina, causes cataracts,  corneal distortion, and edema.

P:  My pressures are 10 mm Hg OU (both eyes).  But my eyes don't like it.  They are painful and I have lost more vision then I care to admit.   If I wanted that hole closed up a little, would that be too risky?  

Dr. Elliot Werner:  The hole is generally either open or closed; you can't titrate it.

P:  What is titration?  I don't know that word.

Dr. Elliot Werner:  It means to adjust something to control its response.

P:  If  the hypotony goes away, can it return?  

Dr. Elliot Werner:  Yes, if the filter is still working.

P:  Does hypotony ever occur after or during a vitrectomy?

Dr. Elliot Werner:  Yes, but it is unusual.

Monitor:  In 1993,  Drs. Wilson, Moster and Schmidt published a paper about hypotony maculopathy following the use of mitomycin-C.  Has there been a significant reduction in the number of  those occurrences?  

Dr. Elliot Werner:  Yes, because we are generally using lower doses of mitomycin-C since the early 90's. 

Monitor: Who are the best candidates for the use of  mitomycin-C? 

Dr. Elliot Werner:  Anyone with a high risk of filtration failure.  There's a long list of indications.  

P:  After my second trabeculectomy in the left eye about 12 years ago, I guess I had hypotony.  About a week later, the doctor had to operate to rebuild the chamber.  I've had nothing but trouble in that eye ever since.  How is the chamber rebuilt?  

Dr. Elliot Werner:  Usually you fill the chamber with air or a very thick fluid called viscoelastic and hope the chamber does not collapse again.  Hypotony is much harder to treat than elevated IOP. 

Moderator:  Are females more prone to hypotony?

Dr. Elliot Werner:  I've never heard that.

P:  Does cataract surgery tend to help or hinder hypotony?  

Dr. Elliot Werner:  It sometimes helps by causing postoperative inflammation and partially closing the filter.

P:  What is the probability of a third blood injection working when the other two failed after one year each?  

Dr. Elliot Werner:  I don't know.  There are no studies on that, but my experience is if two don't work,  then persisting in blood injections is useless. 

Moderator:  Do you see many patients with hypotony?

Dr. Elliot Werner:  Fortunately, not too many.  But  the ones you do see take a lot of time and effort and that can be very frustrating.

P:  Are there no pharmacological treatments for raising IOP other then steroids, even as a side effect of a drug?

Dr. Elliot Werner:  I don't know of any drugs that effectively raise IOP in hypotonous eyes.

P:  Well, I am having a fourth blood injection on Saturday.  I am a risk taker. 

Dr. Elliot Werner:  Why not have your filter revised?

P:  That will be discussed.  I may go that route.  I want my pressure up and the pain gone. 

P:  Is a revision the same as titrate?

Dr. Elliot Werner:  No, revise means to alter or change something partially, such as to revise a manuscript.  Titrate means to adjust something, usually something that has a number attached  to it, such as temperature or salt concentration.

P:  The subtlety of revision versus titration is somehow lost on me.  If, as you say, the filter can be "partially closed," why can't the IOP be raised in a controlled manner?

Dr. Elliot Werner:  Because the result depends on the healing response of the patient, and that varies from person to person and cannot be controlled.

P:  Drinking large amounts of water throughout the day can increase IOP and would seem to be a relatively safe intervention for most people.  Is this a possible therapy for hypotony?

Dr. Elliot Werner:  The problem is it doesn't work.

Moderator:  Have you ever encountered patients with hypotony post cataract surgery?

Dr. Elliot Werner:  Yes, if they have a wound leak or develop some serious problem, such as carotid artery occlusions.

P:  What are carotid artery occlusions?

Dr. Elliot Werner:  A blockage in the large artery in the neck that reduces blood flow to the eye.

P:  Is pain a symptom of hypotony?

Dr. Elliot Werner:  Often, yes.  Eyes with low IOP are often inflamed and painful.

P:  If one has hypotony without pain or inflammation is that generally a hopeful sign?

Dr. Elliot Werner:  Possibly, because it usually means there is no inflammation or hemorrhage in the eye.

End of highlights for October 31, 2001.

On November 5, Dr. Henderer met with the Monday night support group.  Click here for highlights of that meeting.

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