The first anterior lamellar keratoplasty was performed by Anton Elschnig in 1914.1 By the mid-20th century, the advantages of lamellar keratoplasty transplantation were already known, but clinical results were still far behind those obtained with penetrating keratoplasty.2 Both the irregularity and the thickness of the stromal bed of the host were the main problems in obtaining a good visual result. Therefore, there was a need to look for a deeper and smoother plane during surgery. The evolution of surgical techniques progressed from manual dissection to Malbran's peeling off, air-assisted manual dissection and from the spatula technique by Melles et al. until, the big-bubble technique that was a consistent way to obtain what was assumed to be as the bare Descemet membrane (DM) described by Anwar and Teichmann.3–6
Later, when Dua et al. described the corneal Dua layer (DL), surgeons not only had to differentiate the presence of the big bubble but also, if possible, identify the corneal layers that made up its walls.7 This is not always an easy step during surgery because of the poor visualization of the anterior chamber caused by corneal emphysema. In this study, we describe a new tool, corneal transillumination, which did not require any instruments other than a vitreoretinal endoilluminator.
After marking the center of the cornea and the position for a future side port, a partial-thickness trephination is made with a manual trephine blade (8 mm, Katena) to a depth of approximately 80% of the corneal thickness. Then, a crescent blade (2 mm, Surgistar) is used to perform an anterior stromal keratectomy. Similar to the technique by Anwar and Teichmann, air is injected into the deep stroma with a bent 30-gauge needle while maintaining the bevel facedown. Careful observation of the cornea is needed during the injection of air to accurately identify a big bubble.
Type 1 big bubble, where there is air separation between DL and the deep stroma, starts as a silvery circle that expands from the center of the cornea to the periphery, not exceeding 7 to 8 mm in diameter. Type 2 big bubble, where there is air separation between the DL and the DM, starts in the periphery and enlarges centrally; it could be bigger than type 1 big bubble. Type 3 big bubble is a conjunction of type 1 and type 2 big bubbles.
Sometimes assessment for big bubble is not easy because of poor visualization of the anterior chamber and the corneal structure itself. This mostly occurs because the injected stromal air causes corneal emphysema.
Our technique involves using a vitreoretinal endoilluminator (23-gauge endoilluminator, Alcon Laboratories, Inc.) to assess the cornea postair injection. After injecting air into the stroma, the microscope and operating room lights are turned off. Then, a vitreoretinal endoilluminator is placed against the periphery of the cornea. In case of a big bubble, the light will reflect off the bubble wall, imparting information on its limits or boundaries and on its size and location. The movement of the vitreoretinal endoilluminator across the bubble is in the opposite direction to the movement of the reflected light. Once the bubble collapses, the same movement of light can help discern the limits but without the inverse light movement. The image created by the total internal reflection of the light in the presence of a centered and rounded type 1 big bubble was called “full moon” (Figure 1). If a decentered and irregular shine is observed, it might be indicative of a type 2 big bubble (Figure 2), called the “waning moon.”
In the case of an absent big bubble, the light will only show local emphysema (Figure 3) under the light probe. After this, further air injections are performed, and a manual deep anterior lamellar keratoplasty is performed if no big bubble appears. In addition, if the waning moon bubble is observed, the surgery should be continued using a manual technique because of the elevated risk of DM rupture in type 2 big bubble. The known location of the bubble can be used to avoid puncturing it in case a side port is made. At any sign of a full moon bubble, a side port is made to decompress the anterior chamber, and an incision is made to open the bubble roof with a 15-degree knife (Surgistar). Careful removal of the stromal side of the bubble is performed with blunt scissors until the margins of the initial trephination are reached. When the DL does not have remnant stroma over it, the donor cornea is trephined, and the endothelium is removed with a soft-cell PVA surgical spear (OASIS Medical). Finally, it is placed over the DL and sutured. The corneal transillumination technique and signs can be seen in Video 1 (available at http://links.lww.com/JRS/A162).
A total of 270 keratoplasties were performed from 2010 to 2019 with the big-bubble technique where corneal transillumination was used. Type 1 big bubble was diagnosed in 183 patients (67.77%), type 2 in 46 patients (17.03%), and type 3 in 1 patient (0.37%). However, in 2 cases (0.74%), the type of the big bubble could not be determined. In 38 patients (14.07%), big bubble could not be achieved after several air injections and, hence, underwent manual surgery. Lamellar keratoplasty was performed in 256 cases (94.81%), whereas in 14 cases (5.18%), the surgery was converted to penetrating keratoplasty.
Although it is associated with increased technical difficulty, deep anterior lamellar keratoplasty has become a common surgical technique for treating corneal pathologies in patients with a healthy corneal endothelium. Introduced by Anwar in 2002, the big-bubble technique allows the achievement of a clear separation between DL and either the stroma or the DM. Because no residual stroma is left during the surgery, the visual outcomes are similar, if not equal, to penetrating keratoplasty with the added advantage of no endothelial rejection, deeper wound, lesser glaucoma risk, and lower dose of steroids in the short and long terms. Making a correct diagnosis of the presence and type of big bubble during surgery is crucial for overall success of the procedure and for deciding on the next steps.
In 2007, Tan described the small-bubble technique that is useful in confirming the presence of big bubble.8 It consists of injecting a small amount of air in the anterior chamber. If this new bubble stays on the periphery, it can be deduced that the center of the chamber is occupied by the big bubble. In 2013, Burkhart et al. described the use of a handheld slitlamp for illuminating big bubbles; the aforementioned inverse light movement was observed in the presence of a bubble.9
Corneal transillumination is a new tool for surgeons for big-bubble diagnosis. Apart from being a simple technique, it is also advantageous in its ability to be used under conditions of poor anterior chamber visualization where other techniques are impractical.
WHAT WAS KNOWN
- The presence of a big bubble is difficult to discern in a white emphysematous cornea.
WHAT THIS PAPER ADDS
- Presence of big bubble and its boundaries and type were diagnosed in a complete emphysematous cornea using the corneal transillumination technique.
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