It Is Not Good to Be Shallow

CASE PRESENTATION

A 78-year-old man presents for a cataract surgery evaluation. The patient has moderately blurry vision that has worsened during the past year, does not improve with glasses, and is more severe in his left eye. Once or twice per month, he experiences a migraine, which he describes as “lightning behind my eyes.” He has no ocular pain or discomfort and no history of trauma. 

The patient’s medical history is significant for primary open-angle glaucoma. His current therapeutic regimen consists of latanoprostene bunod ophthalmic solution 0.024% (Vyzulta, Bausch + Lomb).

On examination, his BCVA is 20/40 OD with a refraction of -1.00 -4.00 x 165° and 20/30 OS with a refraction of -2.75 -2.25 x 015°. With glare testing, his visual acuity is light perception OU. The IOP is 23 mm Hg OD and 25 mm Hg OS. The patient habitually wears glasses to see at distance.

A slit-lamp examination reveals a 2+ nuclear cataract and 1+ to 2+ cortical cataract in the right eye and a 2+ to 3+ nuclear cataract and 1+ to 2+ cortical cataract in the left eye. Collarettes, scurf, telangiectatic vessels, meibomian gland dysfunction, superficial punctate keratitis, and a reduced tear film are noted in both eyes. A fundus examination finds changes in the retinal pigment epithelium, a posterior vitreous detachment, and a cup-to-disc ratio of 0.6 in each eye. There is no evidence of pseudoexfoliation (PXF). 

The patient is willing to wear glasses to read and watch TV postoperatively. After a discussion of IOL options, he chooses a toric lens with a near target in both eyes (-1.75 D OD and -2.50 D OS). MIGS is also discussed, and he elects to undergo a goniotomy bilaterally using the Omni Surgical System (Sight Sciences). 

Surgery on the first eye is uneventful. During surgery on the second eye 1 week later, the nucleus is safely removed despite a very shallow chamber. During cortical cleanup, the chamber continues to shallow, and the capsular bag bows forward. Cortical cleanup, however, is safely completed. By the end of cataract removal, the chamber is extremely shallow, and even an injection of a high-molecular-weight sodium hyaluronate OVD (Healon, Johnson & Johnson Vision) does not inflate the eye enough to allow safe IOL insertion. The patient remains comfortable throughout the procedure. 

What caused the chamber to collapse intraoperatively, and what are the associated risk factors? How would you manage the situation? In hindsight, would you have done anything differently?

— Case prepared by Neda Nikpoor, MD

BERNARDO SOARES, MD, FICO, FRANZCO 

The patient’s intraoperative course is consistent with aqueous misdirection syndrome. A diagnosis of expulsive hemorrhage is excluded by his comfort and the absence of fundal signs. Ocular risk factors for aqueous misdirection syndrome include a short axial length, nanophthalmos, a shallow anterior chamber, plateau iris configuration, anatomically narrow angles, angle-closure glaucoma, PXF, and a history of glaucoma filtration surgery. 

I would attempt to reverse the misdirection intraoperatively. I would ensure that the patient is well positioned and consider a reverse Trendelenburg orientation, particularly if he has a high body mass index or obstructive sleep apnea. 

Topical atropine 1% could be instilled to help break the ciliary block and relax the vitreous face. An intravenous (IV) injection of mannitol could be performed to provide osmotic vitreous decompression, but its delayed onset would limit the strategy’s immediate utility. A 25-gauge pars plana needle tap would allow rapid and direct vitreous decompression. If these measures are unsuccessful, a pars plana anterior vitrectomy could be performed, even if the posterior capsule has not been breached, to disrupt the anterior hyaloid face and restore aqueous dynamics. After the anterior chamber depth has been reestablished, IOL insertion and the goniotomy would proceed. 

In hindsight, a preoperative IV injection of mannitol and topical instillation of atropine, reverse Trendelenburg positioning, and preparation by the OR nursing staff for the possibility of aqueous misdirection syndrome could have reduced the risk of this complication and allowed the surgeon to be better prepared. The event, however, happened during surgery on the second rather than the first eye. Myopia, moreover, makes a short axial length less likely. These factors would have made it harder to predict aqueous misdirection as a potential intraoperative complication

P. DEE G. STEPHENSON, MD, FACS 

The scenario presented is most consistent with intraoperative aqueous misdirection syndrome (also known as acute fluid misdirection syndrome and malignant glaucoma). It is the leading cause of persistent shallowing of the anterior chamber with forward bowing of the capsular bag that fails to respond to an OVD injection during cataract surgery.¹ After removal of the nucleus, instead of flowing into the anterior chamber, aqueous or balanced salt solution is misdirected posteriorly through the zonular fibers and into or alongside the vitreous gel. This creates positive posterior pressure that pushes the capsular bag and iris-lens diaphragm forward, causing progressive shallowing of the anterior chamber. Because the underlying mechanism is posterior fluid accumulation, an OVD injection into the anterior chamber creates space only temporarily, and it is soon overcome by posterior pressure.

Other potential causes to rule out include a suprachoroidal hemorrhage (characterized by sudden pain, a loss of the red reflex, and elevated IOP) and a choroidal effusion.

Key risk factors for aqueous misdirection syndrome include hyperopia with a short (typically < 22 mm) axial length, narrow or closed angles, a shallow anterior chamber preoperatively, and female sex. PXF and a history of glaucoma surgery also increase the risk of aqueous misdirection syndrome.

I would take a stepwise approach to management. First, intensive cycloplegia (atropine 1%), aqueous suppressants (timolol or acetazolamide), and a hyperosmotic agent (IV mannitol) would be administered to reduce posterior fluid volume. If medical therapy fails, a posterior vitreous tap via the pars plana would be performed to relieve posterior pressure and deepen the anterior chamber. Should vitreous decompression also prove unsuccessful, a pars plana vitrectomy combined with an irido-zonulo-hyaloidotomy would be performed to establish a permanent communication between the vitreous cavity and anterior chamber, thereby resolving the misdirection circuit.

Once the anterior chamber has been restored, secondary IOL implantation in the capsular bag or sulcus or via scleral fixation, depending on the integrity of the capsule, could be performed at a later date. 

WHAT I DID: NEDA NIKPOOR, MD 

As the panelists describe well, the patient experienced aqueous misdirection. In this situation, it is important first to make sure that the anterior chamber is not shallow due to a suprachoroidal hemorrhage, so I ensured that he was not in pain and that the red reflex was normal. An attempt to reposition him in a reverse Trendelenburg orientation was unsuccessful. 

Next, the OR team began an IV mannitol infusion, which deepened the anterior chamber enough to allow the placement of an IOL in the bag. Of note, however, the chamber continued to shallow with irrigation to remove the OVD at the end of the case, so the following steps were taken: 

• No. 1: The flow rate and IOP settings were lowered (ie, an effect similar to lowering the bottle height);
• No. 2: A suture was placed in the main wound to avoid iris prolapse; and 
• No. 3: Bimanual irrigation and aspiration were performed to remove the OVD slowly.
• Goniotomy was deferred. If the chamber had remained shallow, a limited vitrectomy or vitreous tap would have been a reasonable next step, as would delaying secondary IOL placement to a future date. 

In the postanesthesia care unit, a fundus examination performed using an indirect ophthalmoscope confirmed that no choroidal effusion or hemorrhage was present. Oral acetazolamide 500 mg was administered, and twice-daily doses for 3 days were prescribed. The patient was closely monitored to ensure that the anterior chamber remained formed and the IOP remained within the normal range. Ultimately, his visual outcome was excellent, and he is considering whether to return for a goniotomy in the future.