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Sir,

Needling of the glaucoma filtration bleb is increasingly used in the immediate and late post-operative management of glaucoma filtration surgery. Bleb needling has been shown to be effective in both these situations in improving aqueous drainage and lowering intraocular pressure (IOP) with a low complication rate.1,2,3,4

Although a relatively safe procedure that can be performed in the outpatient setting, it is not without risk of serious complications. Reported adverse events include hypotony with serous choroidal detachment,5 bleb leak, corneal abrasion, hyphaema, iris incarceration into the sclerostomy, and endophthalmitis.6

We describe aqueous misdirection following the needling of a filtration bleb. This is a previously unreported and potentially serious complication of a needling procedure.

Case report

A 70-year-old African-Caribbean lady with advanced refractory open angle glaucoma (highest IOPs right −32mmHg, left −34mmHg) on maximal medical therapy underwent left trabeculectomy augmented with mitomycin-C (0.2 mg/ml). Surgery was uncomplicated with a fornix-based conjunctival flap and two releasable scleral flap sutures. Ten years previously she had undergone uncomplicated extracapsular cataract surgery with a 7.00 mm optic size rigid posterior chamber intraocular lens implant.

On day 1 post-operatively, the anterior chamber (AC) was deep with a formed bleb and the IOP was 10mmHg. At 1 week following surgery the IOP was 23 mmHg and both releasable sutures were removed sequentially over 2 weeks. Despite this intervention, progressive bleb encystment occurred with reduced drainage, bleb injection, and loss of microcysts. At 4 weeks following the surgery the IOP had risen to 26 mmHg.

A needling procedure was performed at the slit-lamp using a 27G needle. The bleb increased in size and the IOP decreased to 4 mmHg. The AC depth was noted to shallow by 50%. The peripheral iridotomy (PI) was clearly patent and peripheral enough to prevent pupil block. On review the following day the AC was almost flat; however, no corneal-lens implant touch was noted. The IOP remained low at 5 mmHg but the filtration bleb was noted to have decreased in size. Intensive dilation and cycloplegia with G Cyclopentolate 1%, G Phenylepherine 10%, and G Atropine 1% had no effect on AC depth although the IOP rose to 8 mmHg over the next 5 days.

Although the IOP remained stable, subacute aqueous misdirection was suspected. Peripheral capsulo-hyaloidotomy was performed with Nd:YAG laser through the surgical PI. The Nd:YAG aiming beam was focused at and behind the zonules adjacent to the ciliary processes. Sequestered soft lens matter (SLM) from previous extracapsular cataract surgery was visible in the PI. An immediate flow of fluid from the vitreous cavity to the anterior chamber could be seen by observing the movement of particles of sequestered SLM carried in the stream of fluid. The AC deepened within 30 min and had returned to its normal depth the following day. Over the next 2 weeks the IOP rose to 28 mmHg. A further needling procedure was successfully performed in the operating theatre. The IOP remained stable below 18 mmHg during 4 months of follow-up.

Comment

Aqueous misdirection has been associated with most types of intraocular procedure. To our knowledge this has not been previously reported in association with needling of trabeculectomy blebs. Aqueous misdirection should be suspected in cases with shallow AC even before an increase in IOP occurs. It has also been shown that the assessment of IOP in eyes with flat anterior chambers can be inaccurate.7

This patient had several risk factors for aqueous misdirection: (1) a short axial length at 21.8 mm; (2) sequestered SLM in the capsular bag obstructing the surgical peripheral iridotomy performed at the time of trabeculectomy; (3) reduction in AC depth from initial transient over drainage following the first needling procedure. These factors led to progressive shallowing of the AC as a result of aqueous misdirection. A reversal of this process was successfully achieved by Nd:YAG laser capsulo-hyaloidotomy.8

Although a relatively safe procedure, clinicians should be aware that bleb needling can lead to potentially serious complications including aqueous misdirection, which has not previously been reported.