Aqueous misdirection is a challenging and often refractory form of glaucoma initially described as malignant glaucoma in 1869 by von Graefe. Aqueous misdirection occurs with iridotrabecular apposition, a shallow central anterior chamber in the presence of a patent iridotomy and typically follows some type of intervention although it has been documented to occur spontaneously. Aqueous misdirection has been reported after routine cataract surgery, trabeculectomy, laser iridotomy and capsulotomy, intravitreal injection and can also follow the cessation of topical cycloplegic drops. The intraocular pressure is markedly elevated and may be nonresponsive to aggressive topical therapy, however in rare cases the pressure may be closer to the normal range. Chronic angle closure glaucoma and a short axial length are risk factors.
It is not well understood why malignant glaucoma occurs, however it is clear that aqueous humor is unable to get from the ciliary processes across the vitreous cavity, through the zonules/lens capsule, and around the iris to access the trabecular meshwork. This may occur because the vitreous face does not allow the passage of aqueous through (low conductance) or because of ciliochoroidal swelling which rotates the ciliary processes forward (present in some but not all cases).
The treatment of aqueous misdirection begins with topical IOP lowering agent with the exception of the miotic class. Cycloplegic agents are used to bring the lens-iris diaphragm posteriorly and can be effective, as can oral or intravenous carbonic anhydrase inhibitors or hyperosmotics. If no iridotomy is present, one should be placed. If the patient is pseudophakic or if there is a large iridotomy, YAG laser to the zonules/hyaloid face or in the pseudophakic eye, the posterior capsule, can occasionally resolve aqueous misdirection resulting in chamber deepening and pressure lowering. Surgical treatment of aqueous misdirection addresses the inability of aqueous to access the trabecular meshwork by creating a unicameral eye, i.e., with one chamber. The procedure is called irido-zonulo-hyaloido-vitrectomy and involves the passage of a vitrector through iris, peripheral capsule and/or zonules, through the anterior hyaloid face and into the vitreous cavity where a vitrectomy is performed. While aqueous misdirection can be challenging to diagnose and manage, proper attention and treatment can result in resolution of this unique form of glaucoma.
Nathan Radcliffe, MD, a glaucoma specialist, is an assistant professor of ophthalmology and director of the Glaucoma Service at Weill Cornell Medical College and New York-Presbyterian Hospital in New York.