Abstract
Objective Big bubble (BB)-deep anterior lamellar keratoplasty (DALK) has become the reference transplantation technique for corneal stromal disorders. Type 1 BB is the desired aspect but it is not constant. We aimed to determine the predictive factors of type 1 BB success. Methods Observational cohort study including 77 consecutive eyes of 77 patients undergoing DALK by one surgeon at a single reference center without any selection. Clinical and spectral domain optical coherence tomography data were collected pre- and postoperatively. Results Stromal scars were found in 91.8% of cases and were located in the anterior (90.9%), mid (67.5%), and posterior (36.4%) stroma. Type 1 BB (49.3% of cases) was significantly associated with the absence of scars in the posterior stroma, stage 1–3 keratoconus, and deep trephination. Among eyes with posterior scars, type 1 BB was associated with higher minimal corneal thickness, maximum-minimum corneal thickness < 220 μm, and diagnosis other than keratoconus. Eyes with type 1 BB featured significantly thinner residual stromal bed (22 ± 8 µm versus 61 ± 28 µm), thinner corneas at 12, 24, and 36 months, and better visual acuity at 12 months compared with eyes with no type 1 BB. Conversely, no significant differences between both groups were observed for graft survival, visual acuity at 24 and 36 months, and endothelial cell density at 12 and 36 months. Conclusion OCT assessment before DALK is useful for choosing trephination depth that should be as deep as possible and for looking for posterior scars. The BB technique may not be the most appropriate method in keratoconus with posterior scars. Follow-up data do not support the need for conversion to penetrating keratoplasty when type 1 BB cannot be obtained nor does it support the need for performing a penetrating keratoplasty as a first-choice procedure in eyes with posterior stromal scars.
Highlights
Deep anterior lamellar keratoplasty (DALK) is nowadays the first-choice operative technique for corneal diseases not involving the endothelium because it offers advantages over penetrating keratoplasty including preservation of the recipient’s endothelium [1,2,3,4,5,6,7,8,9]
The perforated zone was localized, and no further dissection was performed in this zone. e anterior chamber was filled with air, and cautious dissection was continued outside this zone
We showed that the average thickness of the recipient’s residual stromal bed was 22 ± 8 μm in eyes with successful type 1 big bubble, which is slightly higher than combined Descemet membrane and endothelium thicknesses. is confirms that type 1 dissection must occur at the level of the predescemetic Dua’s layer [13]. e fact that we did not find any correlation between age and type 1 big bubble occurrence suggests that this predescemetic layer might not be subjected to biochemical or biomechanical changes with aging contrarily to the Descemet membrane
Summary
Deep anterior lamellar keratoplasty (DALK) is nowadays the first-choice operative technique for corneal diseases not involving the endothelium because it offers advantages over penetrating keratoplasty including preservation of the recipient’s endothelium [1,2,3,4,5,6,7,8,9]. One of the safest and most popular methods to obtain maximum depth DALK is the big bubble technique that allows cleavage at the level of a predescemetic plane, leaving only a thin layer of residual stroma (i.e., Dua’s layer) above the Descemet membrane [10, 13]. In type 1 big bubble, the desired result, air forms a well-circumscribed bubble located between Dua’s layer and the remaining stroma, up to 8.5 mm in diameter, starting at the center and expanding progressively to the periphery [13]. Type 2 big bubble is a large thin-walled bubble It starts in the peripheral cornea and enlarges very quickly centrally. It is located between Dua's layer and Descemet membrane. Further surgical steps are at high risk of perforation due to very thin posterior recipient bed
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