Missed type 2 big bubble as an under-recognized cause of post-deep anterior lamellar keratoplasty double anterior chamber: A case report

INTRODUCTION

Deep anterior lamellar keratoplasty (DALK) is preferred for corneal ectasias and stromal pathologies that spare Descemet membrane (DM). It preserves the host endothelium and prevents endothelial rejection, offering longer graft survival than penetrating keratoplasty. Among DALK techniques, the big-bubble (BB) method described by Anwar and Teichmann creates a smooth dissection plane by injecting air into the deep stroma to separate it from the DM.

Two distinct BB types are recognized. Type 1 BB forms between deep stroma and the preDescemet (Dua’s) layer – centrally located, opaque, and feathery-margined. Type 2 BB, however, forms between Dua’s layer and true DM – thin, transparent, peripheral, and fragile.^[1-3] Type 2 BBs are rare but more rupture-prone, especially in advanced keratoconus.

A post-operative double anterior chamber (AC) is a known early complication of DALK, most often due to DM microperforation. However, it may also occur after an apparently uneventful surgery, secondary to residual viscoelastic, incomplete adhesion, or undetected type 2 bubble formation.^[4-6] We present a case where a missed type 2 BB caused early post-operative double AC – an overlooked mechanism not widely recognized in the literature.

CASE REPORT

A 16-year-old girl presented with bilateral advanced keratoconus. The right eye had best-corrected visual acuity of 20/200 and severe corneal thinning on anterior segment optical coherence tomography (AS-OCT). DALK was performed under peribulbar anesthesia using the BB technique.

After trephination to 70% depth, air was injected with a bent 30-gauge needle. The first attempt failed to produce a bubble. A second injection caused diffuse stromal whitening with numerous intrastromal microbubbles, suggesting intrastromal emphysema. No definite BB was visualized, so the surgeon proceeded with manual dissection to bare deep stroma. The donor lenticule was sutured with 10–0 nylon without intraoperative perforation.

On day 1, slit-lamp examination revealed a clear graft with a double AC [Figure 1]. AS-OCT confirmed complete DM detachment with fluid at the graft–host interface. Retrospective surgical video review revealed a fleeting, thin, central bubble during the second injection – consistent with a type 2 BB. Its transparency and the corneal whitening from superficial trephination likely obscured it intraoperatively.

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Figure 1: Postoperative day 1 showing double anterior chamber. (a) Slit-lamp photograph showing a double anterior chamber. (b) Anterior segment optical coherence tomography demonstrating descemet membrane detachment with interface fluid.

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By day 3, partial resorption of the interface air unmasked a central DM tear [Figure 2]. The patient underwent intracameral air descemetopexy, filling two-thirds of the chamber. Because the detachment was large and central with a DM tear and shallow chamber, a transcorneal suture (10–0 nylon) was added across the tear to ensure firm apposition and prevent re-detachment [Figure 3]. This approach was chosen based on prior reports demonstrating that transcorneal suturing provides mechanical support in refractory or extensive DM detachments when air or SF₆ alone is insufficient.^[7]

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Figure 2: Day 3 showing partial resorption of interface air with central Descemet membrane tear. (a) Slit-lamp photograph on postoperative day 3. (b) Anterior segment optical coherence tomography showing central descemet membrane tear and persistent detachment.

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Figure 3: Intraoperative image showing transcorneal suture placement across the Descemet membrane tear after descemetopexy.

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By the next day, complete reattachment of DM and a single AC was confirmed [Figure 4]. One-month follow-up showed a clear cornea and uncorrected visual acuity of 20/40.

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Figure 4: Post-procedure confirmation of reattachment. (a) Slit-lamp photograph showing reattached Descemet membrane and clear cornea. (b) Anterior segment optical coherence tomography confirming reattachment of descemet membrane with restoration of a single anterior chamber. OD: Oculus dexter (right eye).

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DISCUSSION

Double AC formation occurs in 5–20% of DALK cases, mostly due to microperforation or incomplete DM adhesion.^[4,5] In this case, a missed intraoperative type 2 BB was the cause. Such bubbles form in the deep potential space between Dua’s layer and DM and are easily overlooked because of their extreme thinness and transparency. Their rupture allows aqueous ingress into the interface, producing a secondary DM detachment.

This report is among the few to document post-operative double AC due to an unrecognized type 2 BB, confirmed retrospectively from the surgical video. The case reinforces that even in the absence of visible perforation, type 2 BB formation must be considered when unexplained DM detachment occurs.

Type 2 bubbles occur more often in advanced keratoconus with extremely thin corneas, where altered cleavage planes promote deeper dissection.^[3,8] Preventive measures include injecting a small air bubble into the AC before dissection to detect unintended DM separation, avoiding complete corneal whitening by limiting intrastromal air, and keeping the periphery clear to observe any AC movement.^[9]

If missed, type 2 BBs can lead to spontaneous DM tear, pupillary block from trapped air, or interface scarring if left untreated.

Management depends on the extent and integrity of DM. Spontaneous reattachment may occur in minor cases,^[10]but large or central detachments with DM tears require prompt air descemetopexy. When the chamber is shallow or tear extensive, adding a transcorneal suture stabilizes DM, prevents recurrence, and avoids pupillary block.^[7]

Early recognition, careful intraoperative visualization, and awareness of type 2 BB behavior are crucial to avoid this complication and achieve good visual outcomes.

CONCLUSION

A missed intraoperative type 2 big bubble is an important and likely under-recognized cause of early postoperative double anterior chamber after DALK. Careful intraoperative observation, especially in advanced keratoconus with very thin corneas, is essential to identify this fragile and easily overlooked bubble. Prompt recognition and timely management with intracameral air, with or without transcorneal suturing depending on the extent of Descemet membrane tear and detachment, can lead to successful anatomical reattachment and good visual recovery.