Evaluation of the risk factors associated with conversion of intended deep anterior lamellar keratoplasty to penetrating keratoplasty

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Abstract

Background/aims

To identify and evaluate risk factors associated with the need to convert intended deep anterior lamellar keratoplasty (DALK) to penetrating keratoplasty (PK).

Methods

Retrospective institutional cohort study including all consecutive eyes undergoing intended DALK between May 2015 and October 2018 at ‘Villa Igea’ Hospital (Forli, Italy). The indications for surgery were categorised as (1) keratoconus without scarring; (2) keratoconus with scarring; (3) non-keratoconus without scarring; and (4) non-keratoconus with scarring. Multivariate binary logistic regression analysis was performed, introducing, as independent variables, those that reached a significance level of less than 0.05 in univariate analysis. The main outcome measure was whether or not conversion to a PK occurred.

Results

705 eyes were included, with conversion to PK occurring in 16.2% (n=114) of cases. The factors that remained significant in multivariate analysis were corneal scarring (OR=3.52, p<0.001), manual dissection (OR=42.66, p<0.001), type 2 bubble (OR=90.65, p<0.001) and surgeon inexperience (OR=10.86, p<0.001). A receiver operating characteristic (ROC) curve based on the factors significant in the multivariate binary logistic regression analysis achieved a sensitivity of 89.5% (95% CI 82.3% to 94.4%) and a specificity of 80.2% (95% CI 76.8% to 83.3%) with an area under the ROC curve of 0.91 (95% CI 0.88 to 0.93) (p<0.001)

Conclusion

Occurrence of a type 2 bubble, the need for manual dissection, the presence of scarring and surgeon inexperience are independent risk factors for the need to convert intended DALK to PK. Correct identification and management of the type of bubble achieved during pneumatic dissection is instrumental in minimising the rate of conversion to PK.

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Most cited references 14

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Big-bubble technique to bare descemet’s membrane in anterior lamellar keratoplasty

Mohammed Anwar, Klaus Teichmann (2002)

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Deep Anterior Lamellar Keratoplasty for Keratoconus: Multisurgeon Results

Kunal Gadhvi, Vito Romano, Luis Fernández-Vega Cueto … (2019)

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Differentiating type 1 from type 2 big bubbles in deep anterior lamellar keratoplasty

Harminder Dua, Tarek Katamish, Dalia Said … (2015)

Dear editor We read with interest the paper by Anwar et al.1 The authors have described a technique to bare Descemet’s membrane (DM) by multiple lamellar dissection of the deep corneal stroma when stromal injection of air fails to achieve a big bubble (BB) in deep anterior lamellar keratoplasty (DALK). The technique is a variation of the principle of exploiting “microdetachments” of DM dissecting successive layers of the deep stroma until the desired residual thickness is achieved. The text and the video illustrate the technique well and we agree that this is a useful option when there is a failure to obtain a BB in DALK. However, we suggest that the conclusions they have drawn both in the text and the narration of the video are incorrect. It is well known now that when air is injected into the corneal stroma three types of BB can be achieved.2 1) Type 1 BB where the air separates Dua’s layer (DL) from the deep stroma creating a large central bubble of around 8 to 9 mm in diameter. This is the preferred type of bubble in DALK, as DL confers additional strength to the recipient cornea as the authors have stated. After excising the recipient stroma, the complex of host DL and DM and endothelial cells is retained. 2) Type 2 BB wherein the DM is separated from the posterior surface of DL by the air bubble. This BB is larger with a thinner wall and more susceptible to tears and bursting. 3) Mixed BB when the above two coexist, usually type 1 is complete and type 2 is partial but both can be complete. In our experience during DALK surgery, about 80%–85% of the BB is type 1 and 15%–20% is type 2 or mixed. It has recently come to light that the plane of cleavage between DL and deep stroma can be accessed by fungi in corneal infections and even mechanically by blunt dissection (Dua HS et al and Hardik P et al, unpublished data, 2015) during DALK or preparation of tissue for pre-Descemet’s endothelial keratoplasty.3,4 When the plane is mechanically accessed during DALK, the host’s retained tissue complex is as described above with a type 1 BB. The surface of this tissue complex gives a rough appearance (Figure 1A) related to broken strands or fibers of collagen that are stretched when DL is separated from the deep stroma. These strands or fibers can be seen to extend between the posterior surface of the deep stroma and the anterior surface of DL during mechanical dissection and have to be severed or cut. In comparison the surface of the DM (type 2 BB) appears very smooth and featureless (Figure 1B). In the images and video provided by Anwar et al, they have in fact reached and nicely dissected in the plane between DL and stroma and not bared the DM. The appearance of the surface of the host’s retained deep tissue is like that in Figure 1A. Moreover, in the video at several places and especially when the last quadrant is being excised, the strands or fibers between DL and deep stroma are clearly visible. These facts strongly suggest that they were dissecting in the plane analogous to a type 1 BB. Moreover, the formation of a type 1 BB commences with the appearance of small pockets of air between DL and deep stroma which become confluent to produce the full BB.2 In Figure 6B, Anwar et al have illustrated with arrows the microdetachment of the DM. Careful examination of the microdetachment reveals a layer, Dua’s layer, of eosinophilic stained tissue anterior to the darkly stained DM. This is a small pocket of air between DL and deep stroma and not a microdetachment of DM. Such a pocket can be accessed and allow cleavage in that plane by blunt dissection as the authors have very clearly demonstrated. We congratulate the authors for developing and sharing this technique, but we suggest that they present this technique as one that preserves DL and hence is more akin to a type 1 BB with all the advantages especially adding strength to the transplanted eye.5 Theoretically, it is possible to find the plane between DL and DM by mechanical dissection but carries a much greater risk of DM tear or rupture. Disclosure The authors have no conflicts of interest to disclose.