Case Report

Clinical biomarker in aqueous misdirection syndrome: The pupillary snap sign

Stringa, Francesco MD*; Iqbal, Tajwar MD; Makuloluwa, Achini MD; Shankar, Vikas MD

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Journal of Cataract and Refractive Surgery Online Case Reports: January 2019 - Volume 7 - Issue 1 - p 6-8
doi: 10.1016/j.jcro.2018.08.004
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Aqueous misdirection syndrome (AMS) is a rare but well-documented sight-threatening entity. It is clinically characterized by high intraocular pressure (IOP), aqueous pooling in front of and within the anterior vitreous with forward displacement of the ciliary body, and consequent diffusely shallow anterior chamber.1 This occurs despite the existence of a patent iridotomy or iridectomy. It mainly occurs after trabeculectomy; however, it has also been reported after a broad variety of anterior segment procedures, such as cataract extraction or implantation of glaucoma drainage devices (ie, Ahmed, Molteno, Baerveldt).2–5 Moreover, it can occur after laser peripheral iridotomy, surgical peripheral iridectomy, capsulotomy, scleral flap suture lysis, cyclophotocoagulation, trabeculectomy bleb needling, and administration of topical miotics.6–12

Aims of the treatment are managing the IOP and restoring the normal anterior segment anatomy. Stepwise management is undertaken, starting with medical management, which includes cycloplegics, osmotic agents, and an aqueous suppressant. Failing this, laser and surgical options are considered.9 Disruption of the anterior hyaloid surface and decompression of the vitreous body with posterior displacement of the iris–lens diaphragm (ILD) are the endpoints of surgical interventions. These include lens extraction, neodymium:YAG (Nd:YAG) laser iridotomy with posterior capsulotomy–hyaloidotomy, transscleral cyclophotocoagulation, pars plana vitrectomy (PPV) and zonulectomy–hyaloidectomy–anterior vitrectomy (zonulo-hyaloido-vitrectomy), with or without secondary implantation of glaucoma drainage devices.13–15

The purpose of this article is to describe the management of a single case of AMS. In particular, a potentially useful clinical sign that can occur during Nd:YAG laser capsulotomy–hyaloidotomy is described. We believe that this might pinpoint the moment of aqueous misdirection reversal and confirm the presence of an uninterrupted opening from the vitreous cavity through the anterior chamber.


A 55-year-old white woman with bilateral cataract and moderate primary angle-closure glaucoma had phacoemulsification and intraocular lens (IOL) implantation in the left eye. The preoperative IOP was 19 mm Hg bilaterally, the ocular axial length measured with partial coherence interferometry (IOLMaster 500, Carl Zeiss Meditec AG) was 21.78 mm in the right eye and 21.47 mm in the left eye, and the corrected distance visual acuity (CDVA) was 20/40 and 20/100 in the right eye and left eye, respectively. The preoperative treatment included topical latanoprost. The Nd:YAG laser peripheral iridotomies were bilaterally performed approximately 20 years before the patient presented. No other concomitant ocular diseases were noted.

An intraoperative anterior extension of the capsulorhexis occurred and phacoemulsification was performed with no posterior capsule rupture. The IOL (LI61A0, Bausch & Lomb, Inc.) was inserted into the sulcus and the procedure was completed with no evidence of vitreous loss.

Postoperatively, a small piece of retained lens cortex measured 1.0 mm × 0.5 mm in the anterior chamber was observed. This was treated conservatively and topical antibiotics, steroids, and nonsteroidal antiinflammatory drugs along with oral carbonic anhydrase inhibitors were initiated.

At 4 weeks postoperatively, the CDVA in the left eye was 20/28 and the IOP was 28 mm Hg, with mild congestion, inflammatory cells reaction, and persistence of retained cortex inferiorly in the anterior chamber. The high IOP was managed medically with topical and oral carbonic anhydrase inhibitors, and the topical steroidal antiinflammatory treatment was continued. At 8 weeks postoperatively, the IOP was 22 mm Hg and the patient reported good comfort; the topical steroids were therefore gradually tapered. At 12 weeks postoperatively, despite the eye being painless and comfortable with a CDVA of 20/28, the clinical examination showed a shallow anterior chamber, patent peripheral iridotomy, and an IOP of 64 mm Hg. There was mild anterior chamber congestion because of the retained cortex, and the fundoscopy was unremarkable. The clinical picture was consistent with AMS.

The treatment was promptly commenced as follows: topical cycloplegics (atropine 1%), topical ocular antihypertensives (latanoprost, dorzolamide, and apraclonidine) and oral acetazolamide resulting in a moderate IOP reduction to 48 mm Hg after 1 hour. Despite medical treatment, the IOP was 60 mm Hg after 24 hours; therefore, the Nd:YAG capsulotomy–hyaloidotomy was performed.

After the administration of 2 peripheral single-burst laser shots at 2.2 mJ focused on the posterior capsule and anterior hyaloid, constriction and redilation of the pupil was observed (ie, the pupil snapped from approximately 6.0 mm to 4.0 mm and back to 6.0 mm within fractions of seconds). This was followed by visualization of deepening anterior chamber and vitreous prolapse into the anterior chamber. One hour after the procedure, the IOP dropped to 16 mm Hg.

One week later, the IOP increased to 47 mm Hg. Gonioscopy showed peripheral anterior synechiae (PAS) over 270 degrees. Subsequently, the patient had anterior vitrectomy, goniosynechiolysis, lens matter removal, and zonulo-hyaloido-vitrectomy via pars plana.

Five days after the procedure, the IOP increased back to 50 mm Hg, requiring an aqueous shunt procedure in the left eye. A Baerveldt tube was implanted. Subsequently, the patient had transient hypotony, which responded to conservative management. Six months after the shunt procedure, the IOP stabilized to 18 mm Hg, the optic cup-to-disc ratio was 0.4 and CDVA was 20/20.


In 1869, Graefe1 documented a case of a postoperative complication characterized by flattening of the anterior chamber and elevated IOP. Because of its poor reaction to conventional treatment, it was named malignant glaucoma, subsequently known as AMS.

Although not clearly understood, it has been postulated that patients with AMS have an abnormal anatomical relationship between the ciliary processes, the ILD, zonular fibers, and the anterior hyaloid face. Possible risks factors include a narrow iridocorneal angle, plateau iris configuration, hyperopia, zonula laxity, spherophakia, and postoperative sclerocorneal wound leak.7,9,16–20

The most commonly held pathophysiology theory involves anterior rotation of the ciliary processes causing forward movement of the ILD and misdirected flow of aqueous that accumulate in the vitreous or adjacent to it in the Berger space. Further aqueous production elicits a vicious circle that causes further displacement of the anterior vitreous with apposition of the anterior hyaloid face against the lens and ciliary body.13,21 In addition, the vitreous gel has limited fluid conductivity and it is prone to trap pockets of aqueous within and behind its substance, especially as the pressure gradient increases.22

Therefore, principles of the treatment are evacuating vitreous and aqueous humor from the vitreous cavity and establishing a communication with the anterior chamber, thus, braking the vicious mechanism that eventually leads to an increase in IOP.

Although medical treatment is a viable option to temporally stabilize the IOP, it does not address the underlying pressure imbalance and the relapse rate is reported to be as high as 100%.9 Pars plana vitrectomy has been reported to be the treatment of choice for pseudophakic AMS. Nevertheless, relapse after PPV has been reported to be as high as 66% unless an zonulectomy was added to the procedure. A total vitrectomy combined with zonulectomy, iridectomy, and capsulectomy has been described to be 100% effective in relatively larger groups of patients, and therefore, it is considered to be the most exhaustive treatment. However, rhegmatogenous retinal detachment, IOL subluxation/dislocation, and vitreous hemorrhage from trauma to the ciliary body are potential complications of this procedure.8,9 In addition, it has been hypothesized that during conventional vitrectomy peripheral vitreous could not be completely removed, hence the relapse of AMS can occur.17

An Nd:YAG laser capsulotomy–hyaloidotomy is a useful method of managing AMS in pseudophakic eyes because it has been proven to be effective and minimally invasive.13 It can be performed at short notice with relatively little preparation compared with intraocular surgery, and, in some cases, it can be the definitive treatment with normalization of the anterior chamber's anatomy.23 However, the procedure might have a short-term effect with a high recurrence rate of 75%, presumably because the amount of vitreous and aqueous humor released might not be enough to counteract the mechanism of misdirection.9

A previous study24 described a rush of aqueous anteriorly associated with deepening of the anterior chamber at the point of success, but this might be subtle and difficult to recognize while performing the Nd:YAG laser capsulotomy–hyaloidotomy procedure.

In this case report, we describe a brief pulse of constriction and dilatation of the pupil followed by vitreous prolapse into the anterior chamber. This snap of the pupil might be a more overt manifestation of pressure release than the rush of aqueous. The mechanism behind the pupillary snap is essentially a release of pressure from the posterior chamber and the onward movement of vitreous and aqueous toward the anterior chamber. The moment of pressure release allows posterior repositioning of the ILD and this sudden movement causes the pupillary snap that was observed in our case.

As previously described in another case report by Halkias et al.,25 retained lens matter in our case could have elicited inflammation of the ciliary body causing adhesions between the ciliary processes and the vitreous, or surgical trauma could have resulted in disengagement of the vitreous from the pars plana, thus misdirection of aqueous consequentially.

In the case we presented, the IOP increased after 1 week from the Nd:YAG laser capsulotomy–hyaloidotomy. This could have been related to the fact that the vitreous release was not sufficient to reverse the misdirection mechanism, and/or to the underlying PAS formation. In addition, the subsequent zonulo-hyaloido-vitrectomy was not effective in steadily lowering the IOP. We believe that this might be linked to the persistence of peripheral vitreous and/or PAS.

In conclusion, although AMS has been well known for a relatively long time, it represents a real challenge for the ophthalmologist, and the management of it is still an object of debate. Effective use of capsulotomy–hyaloidotomy can remove the immediate threat to sight of high pressures in aqueous misdirection, and allows more time to plan for definitive correction, if necessary. We postulate that the pupillary snap might be a good indicator of the point when the anatomical and physiological abnormality has been reversed.


None of the authors has a financial or proprietary interest in any material or method mentioned.


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