The term “malignant glaucoma” was first used by Albrecht von Graefe in 1869 to describe an aggressive form of postoperative glaucoma, also known as ciliary block or aqueous misdirection, characterised by shallowing of the AC with elevated IOP, resistance to treatment, and rapid evolution into blindness . Diagnosis of malignant glaucoma includes a shallow central and peripheral AC associated with increased IOP despite a patent iridotomy and a normal posterior-segment anatomy. Although the etiology of this disease is not yet fully understood, the pathophysiology involves an anterior rotation of the ciliary body with misdirection of aqueous flow, resulting in forward shifting of the iris-lens diaphragm .
Malignant glaucoma has been reported following cataract surgery with or without intraocular lens implantation, as well as following glaucoma surgery, pars plana vitrectomy, laser capsulotomy, laser cyclophotocoagulation, laser iridotomy, laser scleral flap-suture lysis, trabeculectomy bleb needling, or in association with the use of topical miotic agents . It represents a rare complication occurring more frequently after glaucoma filtering surgery, with a frequency of 0.4-6%, especially in eyes with angle-closure glaucoma . Glaucoma filtration surgery is a risk factor for malignant glaucoma reported after drainage device implantation , iridencleisis (8.9%), and trabeculectomy (4.9%) .
MIGS have been proposed as safer and less traumatic surgical procedures characterised by an ab interno approach, minimal or no traumatic manipulation of the sclera and conjunctiva, a good safety profile, and rapid recovery. MIGS are known to have a lower complication rate than glaucoma filtration surgery, though they are not free from the risk of malignant glaucoma development . Schlenker et al. reported four cases of malignant glaucoma after ab interno gelatin microstent (XENGelStent, Allergan, Inc., USA) implantation , and Montolío Marzo et al. reported a case of malignant glaucoma following phacoemulsification and XEN Gel Stent 45 implantation .
Since Grover et al. introduced GATT in the MIGS scenario, several encouraging results in terms of safety and efficacy have supported this novel technique. In their original description of the technique, Grover et al.  reported an IOP reduction from 24.7 to 15.7 mmHg at 12 months after surgery with a significant decrease in the number of medications in patients with POAG. In a longer-term study, IOP lowering results were nearly equivalent to the early ones . The same study demonstrated greater GATT efficacy in patients with secondary open-angle glaucoma (OAG) with a decrease from 30.1 to 12.9 mmHg at 12 months.
Similarly, Rahmatnejad et al. , in a retrospective chart review of PAOG patients who underwent GATT, reported an average postoperative IOP of 14.6 mmHg with a 44% decrease at 12 months after surgery. Comparably, Aktas et al.  observed a 40.1% IOP reduction at 19 months in a retrospective study conducted in PAOG patients who underwent GATT using a 6-0 prolene suture.
Sharkawi et al.  recently demonstrated that GATT safely and effectively lowers the IOP in PEXG, either when performed alone or in combination with cataract surgery.
The most common postoperative complications described in large cohorts of patients treated with GATT are transient hyphema and IOP spikes [6, 8, 9, 23, 24]. Rarer complications include panscleritis in a patient with a history of anterior uveitis , postoperative intracapsular hematoma in a pseudophakic patient , and Descemet’s membrane detachment . Recently, two cases of acute transient myopia secondary to supraciliary effusion without raised IOP have been described following GATT surgery .
To our knowledge, this is the first case of malignant glaucoma reported after an uneventful GATT procedure.
Although the exact pathogenesis of malignant glaucoma is not fully understood, different mechanisms have been proposed. Shaffer and Hoskins [29, 30] suggested misdirection of the aqueous humour backward into the vitreous cavity with secondary forward displacement of the iris-lens diaphragm. Chandler  proposed a laxity of lens zonules coupled with pressure from the vitreous humour, leading to forward lens movement, while Quigley et al. [32, 33] suggested choroidal expansion as a precipitating event that increases vitreous pressure . In the case described herein, abnormal slackness and weakness of the lens zonules, commonly seen in PEXG, may have contributed to this complication.
Despite malignant glaucoma being generally infrequent after MIGS and never described after GATT, it is essential to recognise and treat this complication early to avoid permeant vision loss.