Sir,

An overhanging bleb, a rare complication of trabeculectomy, can cause discomfort and decreased visual acuity in which case surgical removal is necessary. But, surgical removal is not free of possible risks such as leakage. We present a case in which a dissecting portion of bleb was successfully removed without leaking, with an aid of preoperative anterior segment optical coherence tomography (AS-OCT).

Case report

A 47-year-old woman visited our clinic due to visual disturbance (10/200 without correction) on her left eye. She received trabeculectomy 13 years ago. On slit-lamp examination, an overhanging filtration bleb was noted (Figure 1a). Before the surgery, AS-OCT (SL-OCT™, Heidelberg Engineering GmbH, Germany) was taken (Figure 2). The dissecting portion of the bleb over the cornea was removed with forceps and scissors. The histopathologic image of removed bleb was consistent with the imaging of AS-OCT, multiloculated cystic structures (Figure 3). One day after operation, there was no leakage around excision margin. Until 6 months after surgery (Figure 1b), the patient showed good visual acuity (20/40–20/50) and IOP (14–18 mmHg) without leaking.

Figure 1
figure 1

Preoperative slit-lamp photograph of overhanging filtering bleb (a), Slit-lamp photograph at 6 months after surgery (b).

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Figure 2
figure 2

Anterior chamber OCT images of axial view (a), schematic axial view (b), horizontal view (c), and schematic horizontal view (d) of dissecting filtering bleb. In the axial view (a and b), coarse and multiloculated cystic structure in the dissecting portion of the bleb and uniloculated main cystic bleb in the conjunctival portion of the bleb are noted, whose boundary lies at corneoscleral limbus. AC=anterior chamber; D=dissecting portion of overhanging bleb; M=main original bleb; the symbol ‘*’ signifies corneoscleral limbus.

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Figure 3
figure 3

Histopathology of excised corneal overhanging filtering bleb shows a multiloculated cystic structures (arrow) covered with flattened corneal epithelium (open arrow) and conjunctival epithelium (arrow head; original magnification × 40).

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Comment

Surgeons generally find it uncomfortable to manipulate trabeculectomy bleb due to the risk of leaking. Obtaining preoperative knowledge of bleb structures appears feasible in planning safe surgery beforehand to reduce the risk of complications from manipulation. Noninvasive approaches to examine bleb include ultrasound biomicroscopy and AS-OCT.1, 2 In our case, multiloculated bleb structure of dissecting portion apart from the main cystic bleb was confirmed by preoperative AS-OCT imaging and histological study. Previous reports of overhanging bleb3, 4, 5 stated that leaking was not a common complication even without the safety measure or suture. No leakage of aqueous humour or fast healing might be due to multicystic structures of the overhanging bleb in which the exchange of aqueous humour is suppressed.

We believe our experience with this case help readers understand the physical characteristics of overhanging blebs, as well as the feasibility of AS-OCT in planning safe surgery before bleb manipulation. However, more research and experiences should be carried out to bring up a general conclusion, which can be applied in all overhanging bleb cases.