FP115 : Sinsky Assisted descemet endothelium Frill formation and Edge lifting (SAFE) for DMEK

 

RANGACHARI SESSION VIDEO

Dr. PRAFULLA KUMAR MAHARANA, Dr. Pranita  Sahay,Dr. Jeewan S Titiyal

Abstract

Purpose:

To describe a simple technique of Sinsky Assisted descemetmembrane- endothelium Frill formation and Edge lifting (SAFE) for descemet membrane endothelial keratoplasty (DMEK) donor preparation.

Methods:

This experimental study was conducted with 40 human donor corneoscleral tissues. 25 tissues were used to standardize the technique and remaining 15 for establishing the final technique. A partial thickness trephination was done followed by sinsky-assisted 360 degree separation of the DM from the underlying stroma. The separation was further extended by 3-4 mm from the edge for 4-5 clock hours followed by peeling of the DM. The outcome measures were complete success (8 mm roll without peripheral edge tears) and partial success (8mm roll with peripheral edge tears).

Results:

DMEK roll was successfully peeled in 86.6% tissues (n=13/15).Complete success was obtained in 66.6% tissues while partial success was obtained in 20% tissues.

Conclusion:

SAFE is a simple technique of DMEK that does not require any sophisticated instruments.

Introduction

Introduced by Melles in 2006, descemet membrane endothelial keratoplasty (DMEK) has gained increasing popularity and interest as a method for posterior lamellar transplantation^[1].In this procedure the recipient’s diseased descemet-endothelium is replaced with the donor’s healthy descemet–endothelium complex. The major advantages of DMEK over other methods of endothelial keratoplasty is early visual rehabilitation with better visual outcomes, and a low risk of graft rejection^[2–6]. The other less discussed but often the most important advantage from the perspective of developing countries is its cost-effectiveness. It does not require sophisticated instruments like microkeratome.

Despite these advantages, DMEK is not a widely practiced surgery. The major limitations even in suitable cases aredifficult graft preparation, increased surgical manipulation and higher rates of early post- operative graft detachment.In addition, a steep learning curve leading to wastage of good quality donor tissues is a major concern in developing countries which may be a reason for lesser preference of this surgical technique amongcorneal surgeons.

Several techniques that have been described in the past require some specialized instruments such as Muraine punch, Barron vacuum block, artificial anterior chamber, curvilinear forceps with half moon shaped non-toothed anterior segment, Y-hook instrument, etc^[4–6]. In this experimental study, we describe a simple technique of Sinsky Assisted descemet endothelium Frill formation and Edge lifting(SAFE) for preparation of DMEK graft.

Methods

A total of 40 donor corneal tissues were obtained from the National Eye Bank of which 25 were used to standardize our technique. The remaining 15 tissues [nine in McCarey-Kaufman medium (MK) media and six in Cornisol] were used for establishing the final technique.

All cases were performed by a single surgeon [PKM] well versed with endothelial keratoplasty. In the initial 25 tissues, different size of trephines (9mm, 9.5mm, 10mm, and 11mm) were used to find the most appropriate size that would give us best results. It was observed that with the trephine size of > 9.5 mm, it was difficult to initiate the plane of dissection between the descemet and posterior stroma.Dense adhesion was noted which often resulted in peripheral tears of DM roll. So we concluded that 9-9.5mm is the most appropriate size for initial trephination. Several observations were made in the standardization which has been elaborated in the discussion section.

The corneoscleral rim is first placed on a Teflon block partially filled with tissue preservation media.An initial partial thickness trephination is done with a 9.5 mm manual trephine (Madhu trephines, India). At this step, it is essential not to apply undue force in order to avoid a full thickness punching. A useful sign for adequate depth of trephination is a ring formation, observed within the inner edge of trephine during this step. A broad ring is seen in the case of deep punching of the tissue while a narrow ring suggests a superficial trephination. Alternatively a guarded trephine can also be used as it would be both precise and safe. However, in our experience, manual trephine also works well, especially if the ring sign is appreciated carefully. The tissue is then stained with Trypan blue 0.06% for 3 minutes, followed by a gentle wash with tissue fluid. A 360 degree separation of the descemet-endothelium complex from the posterior stroma was obtained using a sinsky hook. The separation plane extended 2 mm inside the edge of the partial thickness trephination. The angulation of sinsky hook with reference to the tissue plane was kept at around 30- 45 degree for best results. Inside out slicing movements were made with the sinsky hook for separating the descemet endothelium complex. While making this slicing movement, it is essential to apply pressure only at stroma rather than the descemet membrane (DM). In case, there is difficulty in separating the DM roll from the underlying stroma, the stroma can be held with limbs or plain forceps at the site of partial thickness trephination and pulled outwards while proceeding with the sinsky assisted dissection of the descemet endothelium complex. This step makes the underlying tissue taut and the edge of DM roll more prominent leading to an ease in tissue dissection at the appropriate plane. Also, depressing the peripheral tissue (beyond the edge of partial thickness trephination) makes the edge of DM roll more prominent leading to ease in tissue dissection. After obtaining a 360 degree frill, the separation plane is further extended 3-4 mm from the edge to an extent of around 4-5 clock hours. This site is now placed diagonally opposite to the surgeon. The assistant supports the Teflon block and holds the tissue firmly with a toothed forceps. At every step it is essential to have a good assistance for holding the corneoscleral button in position. Bimanual peeling of the descemet-endothelium complex is initiated from the same site by holding the edge of the frill with two McPherson forceps 2 to 3 clock hours apart. Alternately a suture tying forceps can also be used. The tissue is then gently lifted up and pulled towards the surgeon leaving it attached for around 1-2 mm at the opposite end. The DM roll is then reposited back. The tissue is now trephined with an 8 mm trephine. At this step, it is essential to note that if there are any peripheral micro tears or ripped off area, then the placement of trephine should be such that these areas are avoided as far as possible in the final graft.  However, if there are no peripheral tears, then a well centred trephination should be attempted. It is important to keep the tissue wet throughout the procedure by intermittent use of tissue media. The marking of the DM roll can be performed by any of the currently available techniques of DMEK preparation^[4–9].

Results:

DMEK roll was successfully peeled in 86.6% tissues (n=13/15). Complete success (8 mm DMEK roll with no peripheral edge tears) was obtained in 66.6% tissues. While, partial success (8 mm DMEK roll with peripheral edge tears/ripped off area) was obtained in 20% tissues. The medianage of the donor tissue was 45 years. The donor age of the tissues, from which DMEK roll could not be obtained (n=2/15) was 15 days and 18 years.The three tissues which had peripheral edgetear/rip off, the extent of the defect was less than 1x1mm after final trephination with an 8 mm trephine. Nine tissues were preserved in MK medium while, six were in Cornisol. The details of the donor tissues have been described in Table-1. Regression analysis was attempted to know the impact of individual factors such as age, sex, DET and preservation media on the success rate of donor tissue preparation, however due to the relatively small number of tissues in the failure group, it could not be done.

Discussion

We describe a technique that can be easily mastered and performed with the use of routinely used keratoplasty instruments without the need for any specialized or expensive instruments. The initial attempts for standardization of the technique provided us some valuable observations. Some of our observations reinforce the earlier findings by Kruse et al^[5,10], Tenkman et al^[6] and Schlotzer-Schrehardt et al^[11].

• The adhesion between descemet and stroma is apparently more towards the periphery which increases the chances of rip off of DM in the periphery. Thus the use of a trephine size of 9-9.5mm may reduce the chances of DM tear while peeling it off.
• Thechances of tear are high at the edges of trephination. When 360 degree edge of DM was made free with the assistance of a sinsky hook, the instance of DM tear was almost negligible. Thus creating a 360 degree frill of free DM to the extent of 1-2 mm is an important step in achieving successful DM roll.
• While creating the frill with sinsky hook, it is important to apply a pushing down force at the DM-stroma junction at an angle of 30-45 degree. However, at this step it is important to remember not to apply direct force to the DM as it would lead to DM tear.
• Additionally, it is better to re stain the DM after partial trephination so that the edge of trephination becomes clearly visible, thereby facilitating the step of frill formation and edge lifting.
• It is important to do an initial superficial trephination only, as deep trephination would lead to difficulty in initiating the process of DM separation. The “ring sign” as described in result section is extremely helpful in this regard. A thin ring suggests shallow while a broad ring suggests a deeper plane of trephination.
• After a 360 degree frill separation, the DM roll was separated for 3-4mm towards the centre for an extent of 4-5 clock hours.
• We recommend the beginners to go for peeling at a slow speed. As per Newton’s rule F = ma (f=force, m= mass, a= acceleration). Assuming that the mass of DM remains constant, the force (or in other words the traction at DM stroma junction) is directly proportional to the acceleration (which is the speed of peeling in this scenario). Thus the surgeon must always remember “Go steady, Go slow”. Any sudden jerky movement or too fast peeling can lead to excessive traction at the stroma-DM junction with consequent DM tear and hence must be avoided.
• Keeping a safe margin of around 1.5 mm (initial trephine 9.5 mm, final trephination 8 mm) allows for exclusion of any torn or ripped off areas of DM at the time of final trephination.

The success rate of our technique is relatively less compared to other studies reporting success rate as high as 99%^[6]. This is largely due to the inclusion of young donors. If young donors are excluded then our success rate would be nearly 100%. Most experts recommend donor age to be > 55 years^[5]. During the course of standardization of our technique, we realized that though it is not impossible to peel a young donor, the primary difficulty with young donors is a tight DM roll. A tight roll will be extremely difficult, at least for the beginners, to unroll inside the eye. It is better for the beginners to select a donor corneal tissue of age between 55-70 years initially.

To conclude, the SAFE technique for DMEK donor preparation is a simple, easy to learn and a cost effective technique that can be performed with the help of few commonly used keratoplasty instruments. It combines the different lessons that have been learned over the decades by different researchers.

Performing an electron microscopy on the peeled DM could have provided us with useful information, but it couldn’t be performed due to lack of facilities for the same. In addition, we couldn’t evaluate the endothelial cell loss since it was an experimental study and DMEK rolls were not used in any patients of endothelial dysfunction. It may be argued that the usefulness of this technique can be verified only after its use in human subjects, however, we believe that the DMEK roll preparation is the most challenging step of DMEK surgery and our work describes this in a simple technique with the help of common but often ignored concepts of physics.

References

1. Melles GRJ, Ong TS, Ververs B, van der Wees J. Descemet membrane endothelial keratoplasty (DMEK). Cornea 2006;25(8):987–90.
2. Tong CM, Melles GRJ. Where is endothelial keratoplasty going: from Descemet stripping (automated) endothelial keratoplasty to Descemet membrane endothelial keratoplasty to Descemet membrane endothelial transfer? Can J Ophthalmol J Can Ophtalmol 2012;47(3):197–200.
3. Hamzaoglu EC, Straiko MD, Mayko ZM, Sáles CS, Terry MA. The First 100 Eyes of Standardized Descemet Stripping Automated Endothelial Keratoplasty versus Standardized Descemet Membrane Endothelial Keratoplasty. Ophthalmology 2015;122(11):2193–9.
4. Droutsas K, Lazaridis A, Papaconstantinou D, Brouzas D, Moschos MM, Schulze S, et al. Visual Outcomes After Descemet Membrane Endothelial Keratoplasty Versus Descemet Stripping Automated Endothelial Keratoplasty-Comparison of Specific Matched Pairs. Cornea 2016;35(6):765–71.
5. Kruse FE, Schrehardt US, Tourtas T. Optimizing outcomes with Descemet’s membrane endothelial keratoplasty. Curr Opin Ophthalmol 2014;25(4):325–34.
6. Tenkman LR, Price FW, Price MO. Descemet membrane endothelial keratoplasty donor preparation: navigating challenges and improving efficiency. Cornea 2014;33(3):319–25.
7. Ruzza A, Parekh M, Salvalaio G, Ferrari S, Camposampiero D, Amoureux M-C, et al. Bubble technique for Descemet membrane endothelial keratoplasty tissue preparation in an eye bank: air or liquid? Acta Ophthalmol (Copenh) 2015;93(2):e129-134.
8. Muraine M, He Z, Toubeau D, Gueudry J, Thuret G, Lefevre S, et al. Validation of a novel device to easy the preparation of endothelial graft for DMEK. Acta Ophthalmol (Copenh) 2014;92:0–0.
9. Price FW, Price MO. Descemet’s stripping with endothelial keratoplasty in 50 eyes: a refractive neutral corneal transplant. J Refract Surg Thorofare NJ 1995 2005;21(4):339–45.
10. Kruse FE, Laaser K, Cursiefen C, Heindl LM, Schlötzer-Schrehardt U, Riss S, et al. A stepwise approach to donor preparation and insertion increases safety and outcome of Descemet membrane endothelial keratoplasty. Cornea 2011;30(5):580–7.
11. Schlötzer-Schrehardt U, Bachmann BO, Laaser K, Cursiefen C, Kruse FE. Characterization of the cleavage plane in DESCemet’s membrane endothelial keratoplasty. Ophthalmology 2011;118(10):1950–7.

Table Legends

Table-1:Details of the donor tissues used for the Sinsky assisted descemet endothelium frill formation and edge lifting technique.

Sl no	Age in years	Preservation Media	Pre-op Specular count	DET in hours	Outcome
1	55	MK	NA	13	Complete success*
2	54	MK	NA	7	Complete success
3	45	MK	1669	3	Partial success**
4	18	Optisol	2506	12	Complete success
5	18	Optisol	2435	6	Partial success
6	65	MK	NA	5	Complete success
7	46	MK	NA	4	Complete success
8	32	Optisol	2257	6	Complete success
9	37	Optisol	2033	12	Complete success
10	37	MK	1828	1	Partial success
11	40	MK	2024	8	Complete success
12	60	MK	1742	1	Complete success
13	64	MK	NA	5	Complete success
14	64	MK	1975	3	Failure
15	15 days	Optisol	NA	6	Failure

Footnotes:

MK- Mc Carey Kaufman; DET: Death enucleation time

*Complete success- DMEK scroll with no peripheral edge tears; Partial success (8 mm DMEK scroll with peripheral edge tears/ripped of area)