**4. Bleb-associated postoperative infectious endophthalmitis**

Endophthalmitis is a sight-threatening rare complication of glaucoma surgery. Mostly delayed in onset. The rates of endophthalmitis associated with glaucoma filtering surgeries vary with surgical technique and use of antimetabolite agents. A study based on 5-year, retrospective data showed a 0.55% risk of blebitis and 0.45–1.3% risk of endophthalmitis after glaucoma filtering surgery [21]. The tube versus trabeculectomy study (TVT) reported endophthalmitis developed in 1 of 107 in the tube group and 5 of 105 in the trabeculectomy group over five years [22].

Early bleb-associated postoperative endophthalmitis is rare with a reported incidence of 0.1% [22]. Majority of bleb-associated postoperative endophthalmitis occurs months to years after the original procedure.

There are multiple reported risk factors under this entity. Among these are; cystic bleb, which may create direct access of pathogens to the eye either by the high permeability of the cystic wall or by the relatively frequent coexistence of a conjunctival leak [23]. Use of antimetabolites, such as mitomycin C and 5-fluorouracil, changes the thickness, cellularity, and vascularity of the overlying conjunctiva, which increases the risk of developing endophthalmitis. Furthermore, the use of these agents weakens the barrier against the migration of bacteria across the bleb wall. Patients with recurrent or persistent bleb leak are more at risk of developing endophthalmitis [24]. Hence, screening for bleb leakage following each visit is recommended among patients with trabeculectomy surgery. Finally, an inferiorly located bleb is more likely to lead to endophthalmitis than a superiorly located one probably due more to exposure of the bleb to the bacteria-rich tear film [23].

Patients with bleb-associated postoperative endophthalmitis may present with a drop in vision, redness, and eye discharges. It is often preceded by the accelerated prodromal syndrome of brow ache, ocular pain, and headache, which progress rapidly over a short period of few hours [3].

Clinically, the visual acuity is significantly reduced and anterior segment evaluation may reveal discoloration or mucopurulent discharge within the bleb described as a "white on red" appearance against conjunctival erythema. The anterior chamber may show the cellular reaction of cells, flare, and/or hypopyon. Seidel test may identify early bleb leak. Posterior segment evaluation may show vitreous cells and filaments, however, if dense vitritis, fundus view might be obscured, and hence, the B-scan ultrasonography is indicated to confirm vitreous involvement and rule out complications, such as retinal detachment.

True bleb-associated postoperative endophthalmitis must be differentiated from blebitis. In blebitis, there is a chalky white bleb surrounded by conjunctival injection and might be associated with a bleb leak and mild anterior chamber cellular reaction without significant vitritis. The diagnosis is based on a clinical exam and confirmed by standard adequate vitreous or aqueous sample for culture and sensitivity.

The array of organisms associated with bleb-related endophthalmitis differs from those associated with cataract surgery. Bleb-related endophthalmitis is mostly preceded by bleb infection, therefore, clinicians must be more aggressive in the treatment of blebitis. This includes oral and hourly topical fourth-generation antibiotics and daily monitoring for signs of progression, which includes assessment of the bleb, anterior chamber, and anterior vitreous face until a positive response to therapy is observed [25].

Intravitreal antibiotics, the combination of vancomycin (for gram-positive coverage) and ceftazidime (for gram-negative coverage) commonly administered during vitreous

tap & inject. Intravitreal amphotericin B and voriconazole are considered if a fungal infection is suspected and/or confirmed. The use of corticosteroids is controversial since their effect on the visual outcome is not yet known [26].

Following the endophthalmitis vitrectomy study (EVS) guidelines; patients presented with hand motion or better vision may be treated with tap and inject; on the other hand, patients with light perception or worse should be considered for immediate pars plana vitrectomy (PPV) and intravitreal antibiotics. However; the population EVS study did not include patients with post-glaucoma surgery endophthalmitis. Therefore, it might be fair to consider early vitrectomy in patients with more virulent organisms, and it has been shown that vitrectomy in such cases may produce more favorable outcomes [24, 26].

Although bleb-associated endophthalmitis carries a poor visual prognosis; early recognition and treatment are necessary for optimizing the outcome of filtering surgery. Therefore, it is important to inspect the bleb or tube at each visit for any evidence of leak or erosion and if endophthalmitis is suspected, immediate aggressive and appropriate treatment is initiated.
