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Red reflex-guided big-bubble DALK technique enhances control of dissection depth
A modified technique using red reflex guidance may assist corneal surgeons regarding current limitations associated with deep anterior lamellar keratoplasty.
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A modified big-bubble technique guided by intraoperative red reflex may allow for better control of depth at which a cannula is inserted during deep anterior lamellar keratoplasty, according to a study.
The big-bubble technique has been established to overcome the limitations associated with DALK, but it still has a challenging learning curve and poor standardization caused by the difficulty of inserting the cannula into the stroma. If insertion is too shallow, it can result in failure of the bubble formation and diffuse corneal emphysema, whereas too deep of an insertion can lead to Descemet’s membrane perforation.
The red reflex technique uses lines seen in the red reflex of the microscope light source as a reference to guide the insertion of a blunt probe down to a pre-Descemetic plane, the study said.
“Using an intraoperative visual reference, rather than just ‘feeling’ the tissue resistance to the probe or cannula advancement, as in the standard procedure, may allow a safer and closer approach to the deepest corneal layers, with the major benefits of increasing the rate of successful bubble formation and minimizing the risk of perforation,” study author Vincenzo Scorcia, MD, told Ocular Surgery News.
Red reflex-guided method
The retrospective, noncomparative interventional case series, reported in Cornea, evaluated 132 consecutive keratoconic eyes that underwent DALK using the intraoperative red reflex to visualize the amount of residual stroma beneath the inserted cannula.
Shortly before the procedure, a single drop of tropicamide 1% is instilled into the inferior fornix to obtain a bright red reflex, similar to that present during routine phacoemulsification.
An 8- to 8.5-mm circular incision is then made in the recipient cornea, which is approximately 80% of the thinnest measurement of the peripheral corneal thickness. Next, a blunt dissection spatula is used to enter the stroma at the base of the corneal incision and advanced 2 mm to 3 mm centripetally, Scorcia said.
At this stage of the procedure, a dark line is noted ahead of the spatula tip, marking the interface between the endothelium and the aqueous. The width of the red zone between the spatula tip and the line corresponds to the thickness of the residual non-dissected stromal bed.
Next, the cannula is slowly advanced deeper, progressively reducing the width of the red zone up to its disappearance or when the intended depth is reached. Lastly, air is injected until the big bubble is formed and surgery is continued per the conventional technique, Scorcia said.
Technique success
Overall, a big bubble was achieved in 118 eyes.
The mean residual stromal thickness was 63.3 ± 19.2 µm in those with successful bubble formation.
Of the 14 eyes without a bubble, 11 eyes underwent completion via layer-by-layer manual dissection and three eyes were converted to penetrating keratoplasty after the bubble burst while trying to enlarge it.
Corneal perforation did not occur in any cases during the initial insertion of the spatula or tunnel dissection.
“In several studies the authors describe that the initial success rate in the bubble formation does not exceed 50%,” Scorcia said. “I believe that this technique may be very helpful in flattening the learning curve by reducing the risk of intraoperative perforation.”
To prove its value, Scorcia would like fellows or inexperienced corneal surgeons to challenge the technique to demonstrate whether and how much their learning curve can benefit from red reflex guidance.
“As the modification is a very simple one, I strongly believe that it can only help any corneal surgeon, even those who have just approached DALK,” he said. – by Kristie L. Kahl
- Reference:
- Scorcia V, et al. Cornea. 2015;doi:10.1097/ICO.0000000000000497.
- For more information:
- Vincenzo Scorcia, MD, can be reached at Department of Ophthalmology, University of Magna Graecia, Via dei Crociati 40, 88100 Catanzaro, Italy; email: vscorcia@libero.it.
Disclosure: Scorcia reports no relevant financial disclosures.