Aqueous misdirection syndrome
Description, Causes and Risk Factors:
Alternative Name: Aqueous misdiretion glaucoma.
Aqueous misdirection glaucoma is now known to have a broad clinical spectrum. It occurs after routine cataract surgery, after the administration of miotics in eyes with or without a prior surgical history, after ciliary body swelling, or even spontaneously. It may be difficult to make an accurate diagnosis, particularly in the early stages.
Aqueous misdirection glaucoma has been reported to occur in 2-4% of patients who undergo surgery for angle-closure glaucoma (ACG), especially if some of the angle is closed preoperatively. If the angle is open or has been opened prophylactically via a laser iridectomy before the development of an angle-closure attack, aqueous misdirection seems less likely to occur after subsequent surgery. This condition also may occur spontaneously or after the cessation of topical cycloplegic therapy, the initiation of topical miotic therapy, laser iridotomy, laser capsulotomy, laser cyclophotocoagulation, cataract extraction, seton implantation, central retinal vein occlusion, or argon laser suture lysis, or in eyes that have hyperopia, short axial lengths, or nanophthalmos.
The pathogenesis of aqueous misdirection glaucoma is thought to involve posterior misdirection of aqueous flow by a relative pupillary block into or behind the vitreous body; the subsequent increase in vitreous volume results in a shallower anterior chamber and an increase in intraocular pressure
(IOP). Events that incite such a pupillary blockage include a small, crowded anterior segment; angle closure; swelling and inflammation of the ciliary processes; and anterior rotation of the ciliary body.
Axial hyperopia and a history of angle closure are risk factors that predispose a patient to aqueous misdirection. The risk is present whether there is partial or total closure of the anterior chamber angle and regardless of whether there is a patent iridectomy or iridotomy. Furthermore, aqueous misdirection can rarely develop in eyes without any known risk factors.
Symptoms may include redness, eye pain, and decreasing vision (especially in patients with an ocular history of angle closure, eye procedures/surgeries, inflammation or infection).
The diagnosis of aqueous misdirection is based clinically on the previously mentioned ocular manifestations, and it is made only after ruling out pupillary block, suprachoroidal hemorrhage, serous choroidal effusions, or other causes of a flat anterior chamber. High-resolution ultrasound biomicroscopy can be useful to confirm the diagnosis.It reveals anterior rotation of the ciliary body against the peripheral iris and forward displacement of the posterior chamber intraocular lens, as well as a shallow central anterior chamber, all of which are reversible.
B-scan ultrasonography can help to exclude choroidal detachments and suprachoroidal hemorrhage, which are two important differential diagnoses. B-scan is particularly helpful in cases where corneal clouding precludes direct retinal examination.
- Ultrasound biomicroscopy (UBM) also can also be used to image the anterior chamber angle, iris configuration, and lens configuration. UBM can help supplement history and physical exam.
- Anterior segment optical coherence tomography (OCT) can be used to measure anterior chamber depth and configuration in cases where the cornea is sufficiently clear.
The first line of therapy is medical and involves the use of cycloplegics and mydriatics, such as atropine 1% four times a day and phenylephrine 2.5% four times a day to move the lens-iris diaphragm back and relax the ciliary muscle. To decrease aqueous production, topical ß-blockers, oral or topical carbonic anhydrase inhibitors, and a-agonists are used. Isosorbide orally or mannitol intravenously over a 45-minute period can be used to shrink the vitreous volume. No oral foods or liquids should be given 2 hours before and after the administration of a hyperosmotic agent to avoid reduction in the osmotic effect. The patient is maintained on atropine for a prolonged period with a very slow taper because of the high risk of recurrence. Miotic agents are contraindicated, as they may cause or contribute to aqueous misdirection.
The second line of treatment is laser therapy. Neodymium: yttrium-aluminum-garnet (YAG) laser may be used in aphakic and pseudophakic patients to create a large peripheral iridectomy and anterior hyaloid rupture to release the trapped aqueous from the vitreous and reestablish normal aqueous flow. Several openings are made peripherally — that is, not directly behind the optic — because the optic may continue to block the egress of fluid, and the treatment will fail.
While the anterior chamber reforms after medical or laser therapy, corneal and lenticular contact may occur, with the risk of corneal decompensation; therefore, the chamber should be reformed by the injection of a viscoelastic substance via a 30-gauge cannula through the original paracentesis at the slit lamp.
When medical or laser therapy fails, or in phakic eyes for which laser treatment is not a good option, pars plana vitrectomy may be used to debulk the vitreous and possibly also to disrupt the anterior hyaloid face.
If a narrow angle is present in the fellow eye, a laser peripheral iridectomy (PI) is performed before any surgical procedures. The risk of aqueous misdirection may be reduced in the fellow eye after iridectomy if the angle remains open and the IOP is normal; failure to provide prompt therapy to the fellow eye has been reported to result in bilateral blindness.
Medical therapy is successful in approximately 50% of cases within 4-5 days. Laser or surgical intervention may be required before the 4-5 days of medical therapy is completed to avoid corneal decompensation because of lenticular-corneal touch or optic nerve damage from markedly elevated IOPs. Vitrectomy has been shown to effectively relieve aqueous misdirection when medical and laser therapies fail, especially in pseudophakic patients in whom access to the anterior hyaloid, lens capsule and zonules is direct. A high rate (30-50%) of persistent aqueous misdirection and postoperative cataract formation has been reported in phakic eyes after vitrectomy without lensectomy. In general, a vitrectomy alone is considered first; however, lensectomy may be considered in eyes that have substantial corneal edema or dense cataract, or when the anterior chamber does not deepen during vitrectomy.
NOTE: The above information is for processing purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.
DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.