Outcomes of DALK After 'Big Bubble' Surgery
Outcomes of DALK After 'Big Bubble' Surgery
Aim The most popular technique for deep anterior lamellar keratoplasty (DALK) is the 'big bubble' (BB) technique wherein air is injected in the cornea to create a bubble that separates Descemet's membrane (DM) from the stroma. An attempt to create a BB often results in the cornea being filled with numerous small bubbles without the formation of a BB. Manual dissection is then required to complete the procedure. The aim of the study is to compare these two groups, successful BB versus failed bubble (FB) dissection to determine whether the clinical outcomes were different.
Methods In this retrospective comparative study, 46 patients out of 52 who underwent DALK for various corneal stromal diseases such as keratoconus, stromal dystrophy or corneal scarring (caused by different conditions) were included in the analysis. BB was achieved in 25 patients and in the remaining 21 patients a BB separation of the DM was not possible necessitating manual lamellar dissection of stroma to get as close to the DM as possible.
Results The authors compared best-corrected visual acuity, contrast sensitivity, astigmatism, interface densitometry and Scheimpflug pachymetry in the two groups. Postoperative corneal thickness was higher in the 'small bubbles' group (mean 628.9 vs 564.1 μm; p<0.0005), but there was no significant difference in best-corrected visual acuity, astigmatism, contrast sensitivity and densitometry between the groups.
Conclusions In DALK, manual lamellar dissection is a reasonable alternative when BB separation of the DM is not achieved.
Barraquer and colleagues initiated the concept of lamellar keratoplasty in the 1950s by dissecting the corneal stroma down to two-thirds of its thickness. The procedure did not gain popularity because of poor visual outcomes related to irregularity of the dissected surfaces and the risk of interface haze. However, if the plane of lamellar separation is very deep, the likelihood of 'haze' is much less. Therefore, techniques that bare Descemet's membrane (DM), such as the 'big bubble' (BB) method, have been shown to yield visual results comparable with those in penetrating keratoplasty (PK).
The technique of baring of the DM in corneal dissection started in 1970s, but the term 'deep anterior lamellar keratoplasty' (DALK), was coined in 1984 by Eduardo Archila. By the late 1990s, it was clear that DALK gave visual outcomes similar to PK without the risk of immunological rejection. Despite these positive reports, its widespread application was limited by its technical difficulty, a long learning curve and risk of DM perforation. Over the years, many variations in this technique have evolved. One is the use of automated microkeratomes to help achieve smoother planes, but even with this method a variable proportion of deeper stroma is left behind. Other techniques include use of the air injection BB technique, hydrodelamination through a sclerocorneal flap or use of a viscoelastic (sodium hyaluronate) injection. To get closer to the DM, Melles et al introduced a method of filling the anterior chamber with air to help the surgeon more accurately estimate the depth of dissection in the recipient cornea. With the introduction of the Melles and BB techniques, reliable dissection at the pre-DM level can be performed with much higher success rate. Although this method increases the precision of localising the depth of the dissection plane, it does not allow reliable baring of the DM. Recently, newer techniques combining femtosecond laser to achieve dissection at a desired depth of the cornea have claimed more predictable results. With these techniques, it is claimed that stromal interface irregularities can be eliminated because of cleavage at a plane just above the DM. This allows the donor graft (after peeling the DM and endothelium) to be laid directly onto the recipient's bare DM.
Over the years, modifications in the BB technique contributed by many surgeons have rendered the BB procedure the most popular and reliable in achieving baring of the DM with minimal risk of DM rupture. However, the main problem with the BB technique is its repeatability. Even the most experienced surgeons often cannot achieve the desired 'big bubble' and the corneal stroma is filled with numerous small bubbles without effecting a Descemet's separation. Manual lamellar dissection is then required to complete the procedure. We have termed this as the 'failed bubble' (FB) technique. With this approach, a variable thickness of deep stroma is often left behind. The objective of the present study is to compare the outcomes of DALK performed by the BB technique with those where the BB was unsuccessful enforcing the FB technique to complete the procedure.
Abstract and Introduction
Abstract
Aim The most popular technique for deep anterior lamellar keratoplasty (DALK) is the 'big bubble' (BB) technique wherein air is injected in the cornea to create a bubble that separates Descemet's membrane (DM) from the stroma. An attempt to create a BB often results in the cornea being filled with numerous small bubbles without the formation of a BB. Manual dissection is then required to complete the procedure. The aim of the study is to compare these two groups, successful BB versus failed bubble (FB) dissection to determine whether the clinical outcomes were different.
Methods In this retrospective comparative study, 46 patients out of 52 who underwent DALK for various corneal stromal diseases such as keratoconus, stromal dystrophy or corneal scarring (caused by different conditions) were included in the analysis. BB was achieved in 25 patients and in the remaining 21 patients a BB separation of the DM was not possible necessitating manual lamellar dissection of stroma to get as close to the DM as possible.
Results The authors compared best-corrected visual acuity, contrast sensitivity, astigmatism, interface densitometry and Scheimpflug pachymetry in the two groups. Postoperative corneal thickness was higher in the 'small bubbles' group (mean 628.9 vs 564.1 μm; p<0.0005), but there was no significant difference in best-corrected visual acuity, astigmatism, contrast sensitivity and densitometry between the groups.
Conclusions In DALK, manual lamellar dissection is a reasonable alternative when BB separation of the DM is not achieved.
Introduction
Barraquer and colleagues initiated the concept of lamellar keratoplasty in the 1950s by dissecting the corneal stroma down to two-thirds of its thickness. The procedure did not gain popularity because of poor visual outcomes related to irregularity of the dissected surfaces and the risk of interface haze. However, if the plane of lamellar separation is very deep, the likelihood of 'haze' is much less. Therefore, techniques that bare Descemet's membrane (DM), such as the 'big bubble' (BB) method, have been shown to yield visual results comparable with those in penetrating keratoplasty (PK).
The technique of baring of the DM in corneal dissection started in 1970s, but the term 'deep anterior lamellar keratoplasty' (DALK), was coined in 1984 by Eduardo Archila. By the late 1990s, it was clear that DALK gave visual outcomes similar to PK without the risk of immunological rejection. Despite these positive reports, its widespread application was limited by its technical difficulty, a long learning curve and risk of DM perforation. Over the years, many variations in this technique have evolved. One is the use of automated microkeratomes to help achieve smoother planes, but even with this method a variable proportion of deeper stroma is left behind. Other techniques include use of the air injection BB technique, hydrodelamination through a sclerocorneal flap or use of a viscoelastic (sodium hyaluronate) injection. To get closer to the DM, Melles et al introduced a method of filling the anterior chamber with air to help the surgeon more accurately estimate the depth of dissection in the recipient cornea. With the introduction of the Melles and BB techniques, reliable dissection at the pre-DM level can be performed with much higher success rate. Although this method increases the precision of localising the depth of the dissection plane, it does not allow reliable baring of the DM. Recently, newer techniques combining femtosecond laser to achieve dissection at a desired depth of the cornea have claimed more predictable results. With these techniques, it is claimed that stromal interface irregularities can be eliminated because of cleavage at a plane just above the DM. This allows the donor graft (after peeling the DM and endothelium) to be laid directly onto the recipient's bare DM.
Over the years, modifications in the BB technique contributed by many surgeons have rendered the BB procedure the most popular and reliable in achieving baring of the DM with minimal risk of DM rupture. However, the main problem with the BB technique is its repeatability. Even the most experienced surgeons often cannot achieve the desired 'big bubble' and the corneal stroma is filled with numerous small bubbles without effecting a Descemet's separation. Manual lamellar dissection is then required to complete the procedure. We have termed this as the 'failed bubble' (FB) technique. With this approach, a variable thickness of deep stroma is often left behind. The objective of the present study is to compare the outcomes of DALK performed by the BB technique with those where the BB was unsuccessful enforcing the FB technique to complete the procedure.
