A Challenging Case of Aqueous Misdirection

“In glaucoma surgery, we don’t really like postoperative surprises,” said Andrew Tatham MD, as he presented a challenging case of aqueous misdirection in a patient implanted with the PreserFlo MicroShunt (Glaukos) at the 2025 ESCRS Annual Congress in Copenhagen.

The patient, 80 years old and pseudophakic, with a two-year prior glaucoma diagnosis, was also under treatment with clopidogrel due to a previous transient ischaemic attack. The patient’s intraocular pressure was 25 mmHg on maximal medical therapy, and there was evidence of progressive visual field loss. Given the severity of the glaucoma, the patient underwent a PreserFlo procedure, which Dr Tatham observed. The operation seemed to go well, with Dr Tatham noting a reasonable flow through the device at time of implantation.

However, the patient exhibited a shallow anterior chamber, 28 mmHg pressure, and slightly reduced vision the following day. Although a shallow anterior chamber can be due to over-drainage, this was clearly not the cause, given the high IOP. Dilated fundus examination and B-scan ultrasound showed a flat retina and no choroidal effusions or suprachoroidal haemorrhage, both potential causes of anterior chamber shallowing in the early postoperative period. Suprachoroidal haemorrhage also frequently causes pain and typically more severe vision loss.

The diagnosis was aqueous misdirection, also referred to as malignant glaucoma, which Dr Tatham explained as a condition resulting from a build-up of pressure in the back of the eye, leading to compression of the vitreous and reduced conduction of fluid through the vitreous from posterior to anterior, creating a vicious cycle. The pressure differential between the back and the front of the eye causes a posterior pushing force and secondary angle closure. Unlike primary angle closure, which is caused by pupil block, posterior pushing mechanisms of angle closure should not be treated with miotics like pilocarpine.

He explained the management of aqueous misdirection should follow a stepwise approach. Step one is suppressing inflammation and uveal swelling with topical steroids, attempting to deepen the anterior chamber using atropine and lowering intraocular pressure with aqueous suppressants, including oral acetazolamide. Step two involves creating a peripheral iridotomy or iridectomy to encourage fluid flow from the posterior to anterior segment, ideally with an attempt to laser the anterior hyaloid through the iridotomy. Dr Tatham recommended limited cyclodiode laser as a good option for step three, but ultimately, some patients require a more invasive surgical treatment to establish a ‘one-chamber’ eye and break the cycle.

This particular patient presented deterioration despite atropine and acetazolamide, with a worsening vision and gradually increasing intraocular pressure, prompting Dr Tatham to opt for a cyclodiode laser treatment followed by a zonular-hyaloido-vitrectomy. He added this procedure can be performed through an anterior approach, following the technique pioneered by Naomi Lois (et al).

Although an anterior approach zonular-hyaloido-vitrectomy may feel like a “crazy move”, Dr Tatham said it can be very effective and avoid the need for a retinal surgeon. There is a method in this madness: passing the anterior vitrector through the iris into anterior vitreous. Although the definitive treatment for aqueous misdirection is a complete pars plana vitrectomy, it is essential to also remove the anterior hyaloid. Sometimes retinal surgeons perform only a core vitrectomy, but this is likely insufficient. Studies have suggested similar outcomes with the anterior zonular-hyaloido-vitrectomy compared to pars plana vitrectomy.

According to Dr Tatham, this is a rare condition, but not unheard of in a patient implanted with PreserFlo.

“Think about case selection,” he said. “This kind of problem is more common in small eyes, so look at the axial length. If it is shorter than 20 mm, you should seriously consider what you want. To quote Radiohead, we want ‘no alarms and no surprises.’”

Dr Tatham presented at the 2025 ESCRS Annual Congress in Copenhagen.

Andrew Tatham MD, MBA is a consultant ophthalmic surgeon at Princess Alexandra Eye Pavilion, Edinburgh, UK. He is president of the UK and Éire Glaucoma Society. andrew.tatham@nhs.scot