Descemet’s Membrane Endothelial Keratoplasty (DMEK) is a partial thickness corneal transplant surgery, which involves the removal of defective Descemet’s membrane and endothelium while sparing the stromal tissue layer. Because of this, DMEK offers better patient outcomes compared to other partial thickness corneal transplant methods, such as Descemet’s Stripping Endothelial Keratoplasty (DSEK), making it a preferred method in many cornea surgeon’s game-plans in tackling various corneal dystrophies and dysfunctions.
This guide will offer a comprehensive overview of DMEK for ophthalmology residents looking to expand their knowledge, including indications, surgical considerations, step-by-step guidance, and the pros and cons of the procedure.
History of DMEK
Since its emergence in 2006, DMEK has continued to grow in popularity. Accounting for nearly 44% of all endothelial keratoplasty procedures in 2019, the total number of DMEK procedures performed in the United States grew by about 38% from 2013 to 2019.1 As more and more surgeons become familiar with DMEK and surgical techniques are further standardized, this trend is likely to continue.
Indications for DMEK
The indications for DMEK are comparable to those for DSEK. These include various endothelial dystrophies, such as Fuchs’ dystrophy and posterior polymorphous dystrophy, as well as other causes of corneal endothelial dysfunction, such as pseudophakic bullous keratopathy and iridocorneal endothelial syndrome.
Fuchs’ endothelial corneal dystrophy
Fuchs’ endothelial corneal dystrophy is a progressive loss of endothelial cells which results in corneal edema and vision impairments. This disease is inherited in an autosomal dominant fashion, generally occurs bilaterally, and is noninflammatory. The degeneration of the corneal endothelium is the primary attributing factor to the resulting corneal edema.2
Posterior polymorphous corneal dystrophy
Posterior polymorphous corneal dystrophy (PPMD) is characterized by bilateral polymorphic posterior corneal surface irregularities accompanied by variable degrees of corneal decompensation. Patients with this dystrophy eventually experience a decrease in vision, which may be attributed to corneal edema.2
Pseudophakic bullous keratopathy
Pseudophakic bullous keratopathy (PBK) describes corneal stromal edema with epithelial and subepithelial bullae following cataract surgery. These findings can be attributed to cell loss and endothelial decompensation caused by trauma sustained during surgery.3
Iridocorneal endothelial syndrome
Iridocorneal endothelial (ICE) syndrome is a unilateral, noninflammatory disorder of the corneal endothelium, in which there is abnormal endothelial cell formation that may be accompanied by a proliferating membrane that can sometimes overlie the endothelium, anterior chamber angle, and iris.4 This can lead to elevated intraocular pressure, as well as visual impairment.
Surgical technique
Preparation of donor tissue
Donor tissue selection is arguably one of the most important aspects when it comes to DMEK, as it is crucial to select a graft that will favor best in each individual. When selecting graft tissue, older tissue is generally favored, as it is thicker and more resistant to wear and tear. It may also separate and unfold more easily, compared to that from a younger donor.5
Steps for preparing donor tissue
1) Prior to selecting donor tissue, the patient’s white-to-white diameter must be measured. This step ensures that the donor tissue most closely aligns with the patient’s unique anatomy, as complications may arise from donor tissue that is inappropriately sized.
2) The donor tissue is then stained, typically with Trypan Blue. This allows for the detection of any defects in the tissue, as these could attribute to a less than optimal outcome.5 Staining may be repeated as needed to ensure that no defects have been sustained secondary to manipulation of the tissue.
3) A liftable edge is then created in the selected tissue in order to remove it from the donor. There is no single way in which this is achieved, as various surgeons use their own preferred methods, all of which aim to dissect the tissue while minimizing any damage to it.
4) After a liftable edge is achieved, the donor tissue is peeled away. This may be done using the SCUBA (Submerged Corneas Using Backgrounds Away) technique, in which the donor tissue is submerged in Optisol or BSS (Balanced Saline Solution) as it is peeled away in order to minimize surface tension and allow the Descemet’s membrane to settle back on to the stroma.
5) After the donor tissue is peeled away, it is then marked to ensure that is oriented correctly when injected into the recipient’s eye, as malalignment of the graft could lead to primary graft failure.5 A mark is typically made using a letter that is easily recognizable if upside-down (i.e, “F” or “S”).
6) Once marked, the donor tissue is then punched out using a trephine.
Fortunately, many eye banks can often prepare the donor tissue beforehand, allowing for a more streamlined process prior to surgery.
Descemetorrhexis
Before the prepared donor tissue is implanted, the diseased Descemet’s membrane and endothelium must be removed from the recipient.6 Incisions are made in the patient’s cornea, and the anterior chamber is inflated with balanced saline solution (BSS) and/or viscoelastic in order to maintain its integrity. The diseased Descemet’s membrane and endothelium are then stripped away, leaving the stromal layer exposed.
A note on LPI
As this procedure involves injecting air into the anterior chamber, there is a risk of pupillary block. Therefore, most surgeons opt to create a laser or surgical peripheral iridotomy (PI) either right before or at the time of surgery. The PI is generally made in the inferior iris, so that when the patient is sitting upright, the air bubble does not block its opening.
Implantation
Once the interior corneal surface is readied, the donor tissue is implanted. Most surgeons will gently irrigate the graft using BSS in order to create a double scroll configuration. This is then inserted into the anterior chamber. This may be done with a variety of devices, including special glass pipettes, intraocular lens cartridges, or a modified Jones tube.6 If viscoelastic was used at any time prior to graft insertion, it is imperative that it is removed in toto, usually with the assistance of an irrigation/aspiration probe.
The graft is then assessed to make sure that is correctly oriented. If it needs to be repositioned, this may be done by giving a quick flush of BSS. Once adjusted, the tissue is then unfolded within the anterior chamber and moved into place.
Positioning
It is important that the graft is positioned and maintains the correct orientation following surgery. In order to accomplish this, the graft is manipulated externally using a tapping technique until optimal positioning is achieved. An air bubble (room air or SF6 gas) is then injected into the anterior chamber behind the graft tissue to hold it in place.6
Post-operative care
Following DMEK, patients must remain supine as much as possible, aside from eating and using the restroom, for as long as the air bubble is present. It is important that they are kept and monitored for about one hour following the procedure to ensure that the graft remains well seated. Bubble size, pupil size, and intraocular pressure should also be checked at this time. The patient is started on topical antibiotics and steroids, in order to minimize the risk of infection or graft rejection. These are gradually tapered.6
Special considerations for DMEK
Aside from deeming DMEK medically necessary in treating a patient’s specific condition, it is important to also take into consideration any other conditions or individual concerns that they may have. Some may find lying flat for extended periods of time difficult or have trouble tolerating the procedure in general, therefore, care should be taken to tailor treatment to the specific individual. Patients unable to maintain positioning may be better candidates for full-thickness penetrating keratoplasty instead of DMEK.
Complications and benefits of DMEK
Complications of DMEK can include:
- Graft detachment
- Graft failure
- Immune rejection
- Intraocular pressure elevation
- Cystoid macular edema
- Endothelial cell loss
Most commonly, grafts may only partially detach, although they are able to reattach spontaneously without affecting visual outcomes.7 Complications associated with DMEK negatively correlate with surgeon experience levels. Thus, as one becomes better acquainted with the procedure, they may begin to see better results in their patients.
The benefits of DMEK include shorter recovery times compared to full-thickness corneal transplants, improved visual outcomes compared to other partial-thickness corneal transplants, and ultimately the ability to restore the cornea to near-anatomical condition.8 DMEK’s increase in popularity over the years may be attributed to these reasons.
Prognosis
The prognosis for patients undergoing DMEK seems to be better than those undergoing alternative procedures, such as DSEK, for similar corneal disorders. Regarding recovery time, visual outcome, and rate of graft rejection, DMEK appears to be superior.9
Coding and billing for DMEK
DMEK is billed in the same manner as DSEK, sharing the same billing codes. It is generally covered by Medicare, Medicaid, or private insurance companies when deemed medically necessary. This includes treatment for disorders of the corneal endothelium, such as those mentioned earlier, or failure of a previous corneal transplant.10
Conclusions
For many patients suffering from corneal dystrophies or other corneal dysfunctions, DMEK can be a sound surgical solution, allowing for life-changing improvements in visual acuity. Due to its advantages over other corneal transplants, it is no surprise that DMEK continues to grow in popularity as more and more cornea surgeons continue to add it into their practice. It can be expected that DMEK will continue to evolve as time progresses, thus it is important for ophthalmology residents to stay up-to-date on this topic to ensure that they are able to provide the best care for their patients.
References
- Weisenthal RW, Yin HY, Jarstad AR, Wang D, Verdier DD. Long-term Outcomes in Fellow Eyes Comparing DSAEK and DMEK for Treatment of Fuchs Corneal Dystrophy. American Journal of Ophthalmology. 2022;233:216-226. doi:10.1016/j.ajo.2021.06.013
- Yanoff M, Duker JS, Rosado-Adames N, Afshari NA. Diseases of the Corneal Endothelium. In: Ophthalmology. 5th ed. Edinburgh: Elsevier; 2019. https://www-clinicalkey-com.arktos.nyit.edu/#!/content/book/3-s2.0-B9780323528191002693?scrollTo=%23top. Accessed February 24, 2022.
- Pricopie S, Istrate S, Voinea L, Leasu C, Paun V, Radu C. Pseudophakic bullous keratopathy. Rom J Ophthalmol. 2017;61(2):90-94. doi:10.22336/rjo.2017.17
- Mannis MJ, Holland EJ, Carpel EF. Iridocorneal Endothelial Syndrome. In: Cornea. 5th ed. London: Elsevier; 2022. https://www-clinicalkey-com.arktos.nyit.edu/#!/content/book/3-s2.0-B9780323672405000743. Accessed February 24, 2022.
- Prafulla MK, Pranita S, Deepali S, Namrata S, Jeewan TS. Donor Preparation in Descemet Membrane Endothelial Keratoplasty. New Frontiers in Ophthalmology. 2019;5(1). doi:10.15761/NFO.1000227
- Stuart A. Performing DMEK: A Step-by-Step Guide. American Academy of Ophthalmology. https://www.aao.org/eyenet/article/performing-dmek-stepbystep-guide. Published August 8, 2017. Accessed February 24, 2022.
- Maltry AC, Greiner MA. Descemet's Membrane Endothelial Keratoplasty (DMEK) for Fuchs' Endothelial Dystrophy. https://webeye.ophth.uiowa.edu/eyeforum/cases/182-DMEK.htm. Published November 6, 2013. Accessed February 24, 2022.
- Donaghy CL, Vislisel JM, Greiner MA. Descemet Membrane Endothelial Keratoplasty (DMEK). https://webeye.ophth.uiowa.edu/eyeforum/tutorials/cornea-transplant-intro/5-DMEK.htm. Published May 21, 2015. Accessed February 24, 2022.
- Deng SX, Lee WB, Hammersmith KM, et al. Descemet Membrane Endothelial Keratoplasty: Safety and Outcomes. Ophthalmology. 2017;125(2):295-310. doi:10.1016/j.ophtha.2017.08.015
- Farid M, Rhee MK, Akpek EK, et al. Corneal edema and opacification PPP - 2018. American Academy of Ophthalmology. https://www.aao.org/preferred-practice-pattern/corneal-edema-and-opacification-ppp-2018. Published November 2018. Accessed February 24, 2022.
