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Rare aqueous misdirection requires quick diagnosis, relief, physician says
The rare complication of surgery in eyes with narrow angles may be managed with medical or surgical strategies.
Aqueous misdirection, also called malignant glaucoma, is a relatively rare complication of intraocular surgery that can be vision-threatening if not treated immediately, according to a glaucoma specialist.
Most surgeons will go their entire career without ever seeing a case of aqueous misdirection, said Ronald L. Gross, MD. He sees only about one case per year, from his own patient base or referral, but he advises clinicians to keep the diagnosis in mind for its rare appearance.
He shared some pointers for recognizing and treating aqueous misdirection at the Ocular Surgery News Symposium, Glaucoma: Improving Your Odds, in Las Vegas.
Diagnosis
| Slit-lamp photos show clinical presentations of aqueous misdirection. Photos courtesy of Ronald L. Gross, MD. | ||
Aqueous misdirection has been reported to occur after 0.4% to 6% of surgical cases for angle-closure glaucoma, Dr. Gross said. It is generally seen 1 to 3 days postoperatively, although it can occur or reoccur months or years later. It is not related to preoperative IOP level, he said.
Predisposing conditions for aqueous misdirection include hyperopia, eyes with angle closure or narrow angles, and fellow eyes of eyes with these conditions, Dr. Gross said. It is also seen rarely secondary to cases of traumatic and inflammatory glaucoma.
Aqueous misdirection may occur with the cessation of cycloplegia or the introduction of miotics after surgery. Ophthalmologists may notice the onset of aqueous misdirection immediately after instituting miotics, Dr. Gross said.
Aqueous misdirection is characterized by a uniform shallowing of the central and peripheral anterior chamber. Upon examination, the ophthalmologist will observe a low bleb or no bleb, a patent peripheral iridectomy and either marked or modestly elevated IOP.
The pathophysiology of aqueous misdirection is the redirection posteriorly of the normal anterior flow of aqueous. With misdirection of the aqueous into the posterior chamber, the lens-iris diaphragm will be uniformly pushed forward, with decreased outflow of aqueous fluid and increase of IOP, Dr. Gross said. The anterior chamber will be shallow, he added.
Differential diagnosis of aqueous misdirection includes pupillary block and choroidal detachment, Dr. Gross said. In pupillary block, however, there may not be a patent peripheral iridotomy and the central anterior chamber will be deeper than the peripheral. In choroidal detachment a serous detachment should be visibly identifiable, and IOP is usually low. A hemorrhagic detachment would also be visible. B-scan ultrasound would help to distinguish a detachment from aqueous misdirection, he said.
Medical management
When aqueous misdirection is identified, Dr. Gross suggested beginning a medication routine if no rapid resolution is seen.
“Because of the high pressure and shallow chamber we need a rapid response – within 8 to 24 hours,” he said.
Medical management is generally attempted first to attempt to control the flow of aqueous fluid posteriorly. Dr. Gross recommended strong cycloplegia to try to pull the lens-iris diaphragm posterior and re-establish the normal flow of fluid. He said atropine 1% may help re-establish the flow anteriorly, but it may need to be continued indefinitely.
Aqueous suppressants may also be helpful, Dr. Gross said, to decrease the production of fluid. He said a beta-blocker, an alpha-agonists or a carbonic anhydrase inhibitors would serve to decrease production of aqueous fluid.
Hyperosmotics, such as mannitol and glycerol, can also be used to decrease the vitreous volume, he said.
Surgical management
If response to medical management is inadequate, with little improvement in 24 hours, surgical intervention may be necessary, Dr. Gross said.
In pseudophakic eyes, he advised using transpupillary Nd:YAG laser to disrupt the anterior hyaloid face. Pars plana vitrectomy is also an option, he said.
In phakic eyes, he advised performing pars plana vitrectomy with an attempt to disrupt the anterior hyaloid face. Lens extraction could also be performed at this time, Dr. Gross said.
For a surgeon encountering his first case of aqueous misdirection, Dr. Gross said that if the lens is still present a referral to a glaucoma or retinal specialist might be appropriate.
Other surgical methods that have been described but are not generally used include transpupillary argon laser to the ciliary processes and disruption of the anterior hyaloid through the peripheral iridotomy.
“These are not generally used because of potential risks to adjacent structures, including the lens,” Dr. Gross said.
Theories
Several theories have been proposed to explain the mechanism of aqueous misdirection. One is that aqueous accumulates behind the posterior vitreous face, resulting in the anterior movement of all intraocular contents. The aqueous could form pocket in the vitreous in this scenario, Dr. Gross said.
Another is that breaks in the anterior hyaloid form a one-way valve directing aqueous posteriorly or preventing the anterior flow of trapped aqueous. Another is that lens zonules become slack allowing aqueous fluid to seep into the posterior chamber. However, Dr. Gross said, it is likely that the cause of aqueous misdirection is multifactorial.
For Your Information:
- Ronald L. Gross, MD, can be reached at Baylor Eye Consultants, Smith Tower, 6550 Fannin, Suite 1401, Houston, TX 77030; 713-798-6100; fax: 713-798-4082/3782; e-mail: rgross@bcm.tmc.edu.
- OSN Staff Writer Kim Norton writes on cataract and refractive topics.