A 66-year-old white female with chronic angle-closure glaucoma was examined 2 months after uncomplicated phacotrabeculectomy with mitomycin C in her left eye. She reported mild blurring of the vision in this eye since the removal of a releasable scleral flap suture 1 week earlier. She had no history of ocular pain, and the IOP measured 31 mm Hg in her left eye with Goldmann applanation tonometry. The anterior chamber was flat with broad contact between the IOL and corneal endothelium. A shallow but diffuse filtering bleb was present. There was no evidence of a bleb leak, the retina was attached, and there were no findings of ciliary body effusion or suprachoroidal hemorrhage.
Comments on the Treatment Options
FL: A flat anterior chamber in the presence of a diffuse filtering bleb suggests overfiltration of aqueous humor. The IOP, however, is likely to be low in such cases. A significant bleb leak is unlikely to be present if the bleb is well formed, but it might lead to a flat anterior chamber.
JGC: One possibility is that the IOP measurements were subject to artifact as a result of the IOL's juxtaposition to the corneal endothelium, which would have provided mechanical resistance to applanation. Goldmann applanation tonometry can be misleading in the presence of a flat chamber, as shown in studies on postmortem eyes.1 Gentle digital tonometry performed over the inferior sclera with the globe in upgaze suggested that, in this case, the IOP was elevated.
RNW: It would be interesting to see if any of the newer tonometers that are less affected by differences in the elastic or mechanical properties of the cornea, including the Pascal Dynamic Contour Tonometer (SMT Swiss Microtechnology AG, Port, Switzerland) or the Ocular Response Analyzer (Reichert, Inc., Depew, NY), measure IOP more accurately in eyes with flat anterior chambers than a Goldmann applanation tonometer.
Other diagnoses to consider include a pupillary block mechanism, choroidal effusion, or a suprachoroidal hemorrhage. Aqueous misdirection syndrome is a diagnosis of exclusion. The patient usually presents with a high pressure and axial shallowing of the anterior chamber in the presence of a patent iridotomy. The latter symptom is distinct from the peripheral shallowing that is observed with a pupillary block mechanism. It is important to look for a choroidal effusion, suprachoroidal hemorrhage, or any posterior mass that may be pushing the lens/iris diaphragm forward. These possibilities need to be excluded before the clinician makes a diagnosis of aqueous misdirection syndrome.
JGC: A large, patent, peripheral iridotomy (PI) was present in the affected eye, and B-scan ultrasonography revealed no evidence of choroidal detachment or suprachoroidal hemorrhage.
Four months prior to this presentation, the patient had been referred to us with a diagnosis of chronic angle-closure glaucoma. The referring ophthalmologist had performed bilateral peripheral iridectomies and initiated topical medical therapy with latanoprost, timolol, and brinzolamide. On presentation to our unit, the patient's IOPs were 23 mm Hg OD and 34 mm Hg OS. There were bilateral patent PIs, but the angle in the patient's left eye was closed with 360ยบ of peripheral anterior synechiae. There was an extensive loss of the neuroretinal rim of the left optic nerve and moderate rim loss in her right optic nerve. The axial length was 22 mm in both eyes.
The patient underwent uncomplicated combined phaco surgery and trabeculectomy with mitomycin C (0.2 mg/mL for 3 minutes) in her left eye. During the first 2 postoperative weeks, the IOP remained around 20 mm Hg OS. A releasable scleral flap suture was removed at this stage, and the patient returned 1 week later with a flat anterior chamber and a large, diffuse drainage bleb. Although her IOP was recorded with Goldmann applanation tonometry as 24 mm Hg, we felt that the findings were consistent with overfiltration. Despite reformation with intracameral Healon (Advanced Medical Optics, Inc., Santa Ana, CA), the anterior chamber again was flat upon review the following day.
We made a diagnosis of aqueous misdirection syndrome, and the patient began medical therapy with atropine, topical beta-blockers, and oral acetazolamide. The anterior chamber deepened, and the IOP decreased to the midteens. Six weeks later, her IOP had risen again. We removed another releasable scleral flap suture and had the patient discontinue the atropine. The patient presented 1 week later as described at the beginning of this article.
Comments on Pathogenesis
RNW: The initial events that lead to aqueous misdirection syndrome are not well understood. One feature that may provide some insight into the condition's pathogenesis is that the problem appears to arise less commonly after laser PI than after surgical iridectomy. The shallowing of the anterior chamber that may occur during surgical iridectomy, but not laser PI, could be an initiating event that leads to a juxtaposition of the anterior hyaloid face and ciliary body. Subsequently, the permeability of the anterior hyaloid face decreases and prevents the passage of aqueous humor, which accumulates in the vitreous, pushes the lens/iris diaphragm forward, and increases the IOP.
JGC: One week prior to both episodes of aqueous misdirection, this patient had a releasable scleral flap suture removed. It may have contributed to the onset of aqueous misdirection syndrome in this patient, although immediate shallowing of the anterior chamber after each suture's removal was not documented at the time.
Comments on Management
FL: I would treat the patient medically in the first instance and restart the aqueous suppressants and topical atropine. Drug therapy might lead to a deepening of the anterior chamber and lower the IOP, as it did following the earlier presentation. Other approaches would include Nd:YAG laser disruption of the posterior capsule and hyaloid face. The surgeon might also use an argon laser to shrink the ciliary processes if they were visible through the PI. If medical and/or laser treatment failed, the anterior vitreous and anterior hyaloid face might also be disrupted with a vitrector or needling technique2 via a transcorneal approach through the PI. Alternatively, the surgeon could employ a pars plana vitrectomy. It might be necessary to disrupt the posterior capsule during pars plana vitrectomy, because an intact posterior capsule has been associated with reduced success.3
JGC: We elected to perform a central Nd:YAG laser capsulotomy and anterior hyaloidotomy (Figure 1). This procedure led to a rapid reformation of the anterior chamber, although there was no immediate change in the IOP. The patient resumed atropine 1% t.i.d. and aqueous suppressants. Upon examination 1 week later, the patient's IOP remained elevated at 22 mm Hg in her left eye, but the anterior chamber was deep. We performed laser suture lysis to the remaining scleral flap suture. The IOP decreased to 13 mm Hg, and the anterior chamber remained deep. One month later, the IOP in the patient's left eye was 9 mm Hg with a visual acuity of 20/60.
Figure 1. Upon presentation, the patient's anterior chamber was flat, and the IOL's optic was in contact with the corneal endothelium (left). One hour after hyaloidotomy and capsulotomy, the anterior chamber had reformed (center). The capsulotomy was clearly visible (arrow, right).
Conclusion
Aqueous humor misdirection is more common in eyes with short axial lengths and a previous diagnosis of angle closure. Clinicians should be cautious in their interpretation of IOP measurements in eyes with flat anterior chambers. A disruption of the anterior vitreous face with a laser or in conjunction with vitrectomy may be required in cases of aqueous misdirection that do not respond to medical therapy.
The authors acknowledged no financial interest in the products or companies mentioned herein.
Section editor Jonathan G. Crowston, MD, PhD, is Professor and Director of Glaucoma Research, Department of Ophthalmology, University of Melbourne, Victoria. Robert N. Weinreb, MD, is Distinguished Professor of Ophthalmology and Director of the Hamilton Glaucoma Center, University of California, San Diego. Dr. Crowston may be reached at crowston@unimelb.edu.au. Dr. Weinreb may be reached at weinreb@eyecenter.ucsd.edu.
Franklin Li, MD, is an ophthalmology resident at the University of California, San Diego.
1. Wright MM, Grajewski AL. Measurement of intraocular pressure with a flat anterior chamber. Ophthalmology. 1991;98:1854-1857.
2. Francis BA, Wong RM, Minckler DS. Slit-lamp needle revision for aqueous misdirection after trabeculectomy. J Glaucoma. 2002;11:183-188.
3. Tsai JC, Barton KA, Miller MH, et al. Surgical results in malignant glaucoma refractory to medical or laser therapy. Eye. 1997;11:677-681.
