Hypotony
Chat Highlights
October 19, 2011

On Wednesday, October 19, 2011, Dr. Anand Mantravadi, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Hypotony".

Moderator: Tonight's topic is “Hypotony.”

P: What is hypotony?

Dr. Anand Mantravadi: Ocular hypotony is a term that refers generally to a subnormal low intraocular pressure that can potentially impact the eye structurally in several ways. There are loose definitions that define hypotony as an IOP of five mmHg or less. However, one may or may not have any adverse effects at that IOP.

Subnormal low IOP can lead to decompensation of the cornea, scar formation in various parts of the eye, more rapid cataract formation, retinal swelling, and swelling in the choroidal layer of the eye.

P: How long can IOP be too low before permanent problems arise?

Dr. Anand Mantravadi: I am not sure if that is known for certain. Some of the problems resulting from low IOP are reversible and can correct as the IOP spontaneously rises with time, such as swelling in the choroidal layer of the eye called an effusion.

Other problems may be more difficult to reverse the longer they are present such as swelling in the retina in a particular location called the macula.

P: How is hypotony treated?

Dr. Anand Mantravadi: The treatment of hypotony is usually directed at the cause of hypotony (which can result from a number of conditions). For example, if hypotony is the result of inflammation, treatment would be directed at reducing inflammation. If hypotony is a consequence of surgery, the cause can be addressed with surgical revisions, or possibly medical management in some cases.

P: Can individuals do anything to help raise their IOP?

Dr. Anand Mantravadi: In the setting of post surgical or inflammatory hypotony, not really anything can be done. One generally should avoid any undue pressures on the eye that may cause hypotony to be exacerbated.

P: Will avoiding stooping, bending and lifting help raise pressure?

Dr. Anand Mantravadi: Not directly, but one is advised to avoid stooping, bending and lifting because that can result in increased venous pressure (Valsalva), which can raise the risk of bleeding in the post surgical phase.

P: Is hypotony painful?

Dr. Anand Mantravadi: It can be.

P: Is blurring of vision a consequence of hypotony?

Dr. Anand Mantravadi: When hypotony is present, blurring of the vision can occur for a number of reasons. From the front to back of the eye, one can have corneal swelling, a change in the refractive state of the eye, more rapid cataract, swelling in the retina and/or choroid that can also lead to "blurring."

P: Does hypotony cause long-term damage?

Dr. Anand Mantravadi: There are reversible consequences of long term hypotony, and then there are irreversible consequences. The reversible consequences includes corneal swelling (can be treated with surgery), cataract formation (can be treated with cataract extraction), and choroidal swelling (which can be surgically drained if required). Macular/retinal swelling is also thought of as reversible early on, but there is some suggestion that the more chronic and longstanding macular swelling persists, the less likely this will be reversible.

P: So the no bending, stooping or lifting restriction will do nothing to help with hypotony, or in the case of a trabeculectomy, heal a leak in a bleb?

Dr. Anand Mantravadi: Yes, that is correct. The avoidance of those positions is important to avoid excess valsalva/venous pressure that can then transmit to the eye, and exacerbate leaking, or rarely can raise one's risk of intraocular bleeding.

P: Are there other glaucomatous causes of hypotony besides surgery?

Dr. Anand Mantravadi: A cyclodialysis cleft is something that can result from trauma or surgery, and that can result in hypotony, where there is a separation of the ciliary body muscle from its normal position. Other glaucomatous causes of hypotony can be inflammatory glaucomas that may cause the ciliary muscle to make less fluid than it normally does thereby resulting in lower pressure.

P: Do tube shunts also make problems of hypotony?

Dr. Anand Mantravadi: There is a small risk of hypotony with tube shunt surgery.

P: Is hypotony affected by the race, age or sex of the patient?

Dr. Anand Mantravadi: Younger myopic patients tend to be at slightly higher risk of hypotony following glaucoma surgery.

P: How common is hypotony?

Dr. Anand Mantravadi: Transient hyptony is common after glaucoma surgery and is usually of no significant consequence. Long term hypotony has become more rare following many modifications to modern glaucoma surgery.

The exact incidence is unknown, but can be higher with anti-metabolite use in glaucoma surgery. However, the advantages of using an anti-metabolite during glaucoma surgery and improvement in overall surgical success are fairly clear.

P: Can the eye become less rigid and therefore more unstable with this?

Dr. Anand Mantravadi: With lower pressures, the eye does become less rigid. "Unstable" will depend on if there are actually any structural changes that can result from hypotony as I have listed earlier.

P: Are there other glaucomatous causes of hypotony besides surgery?

Dr. Anand Mantravadi: There are many causes of hypotony. Post surgical hyptony, traumatic causes, a cyclodialysis cleft as mentioned earlier, inflammation or ischemia (insufficient oxygen perfusion), pharmacologic, or even due to some systemic causes are all causes.

P: Can fluid intake affect hypotony?

Dr. Anand Mantravadi: There is some suggestion that depending on the cause of hypotony, fluid intake can improve aqueous humor production, which would be a good thing in trying to treat hypotony.

P: What is the lowest "safe" pressure that a glaucomatous eye should be, Doctor, or does that really vary by case? Is 10 mmHg, as a standard, the lowest IOP should go?

Dr. Anand Mantravadi: You hit the nail on the head as it varies case by case. For one individual, if there are signs of worsening at a low pressure, say 14, then perhaps less than 10 is needed for that individual. For another individual who shows no signs of changing at pressure of 22, that person does not need that low of a pressure. Individualizing treatment goals and plans based on each person’s stage of disease is the key factor here.

P: Can you give an example of an anti-metabolite?

Dr. Anand Mantravadi: Examples of anti-metabolites used in glaucoma surgery are 5-Fluorouracil and Mitomycin-C.

P: Are retina wrinkles after hypotony reversible a long time after they appear?

Dr. Anand Mantravadi: That is less clear. It is generally felt that the longer the macular folds persist, the less likely one will have total recovery of vision.

P: From what I understand, hypotony indicates a pressure of five mmHg or lower. So in some cases a pressure of five mmHg can be "safe" for a severe glaucoma case?

Dr. Anand Mantravadi: Yes, although five mmHg has been loosely associated with the definition of hypotony, there are people with that pressure that do not have any of the structural consequences that can result from very low pressures and maybe the severity of that person's case may require very low pressures to halt the process.

P: After my trab, my pressure was as low as three and slowly came back.

Dr. Anand Mantravadi: That's very common, and as I stated earlier, transient hypotony following glaucoma surgery is common and often of no real long term consequence.

P: Can the sleep position of the patient have any effect on hypotony?

Dr. Anand Mantravadi: I would recommend avoiding positions that put excess pressure on the eye. In the post surgical period, we often recommend an eye shield during sleep or naps.

P: If a leak is going to heal, how quickly can healing occur?

Dr. Anand Mantravadi: It depends on the individual. Some leaks heal quickly and some take longer. It depends on that individual's propensity to heal.

P: How often are office visits for patients suffering from hypotony?

Dr. Anand Mantravadi: It depends on the severity, and the nature of the structural changes, that are a result of the hyptony. Some patients with hypotony require very close follow-up and others may not. Therefore it depends on the discretion of your physician.

P: Can a patient fly in an airplane while suffering from hypotony?

Dr. Anand Mantravadi: Yes, unless one has a gas placed in the eye due to recent retinal surgery, then one should not fly.

P: Should swimming be avoided?

Dr. Anand Mantravadi: If people have had a trabeculectomy in the past, we generally recommend avoiding possible causes for infection, like lake water, pool water, etc. If one swims, proper fitting goggles that don't place pressure on the eye, can be used to help minimize risk.

P: Will hypotony cause blindness?

Dr. Anand Mantravadi: The risks of hyptony after glaucoma surgery are low. The risks of blindness from untreated glaucoma are high. Therefore, although hyptony can in some instances cause severe visual loss, the benefits of glaucoma surgery often outweigh the risks for this disorder.

Moderator: Dr. Mantravadi, there are no more questions.

Dr. Anand Mantravadi: Thanks everyone. It's always a pleasure to be here. Good night.

Moderator: Thanks, Dr. Mantravadi. We'll see you next time.

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