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Study indicates lens removal an unnecessary precaution when performing DMEK

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Performing Descemet’s membrane endothelial keratoplasty (DMEK) without removal of the natural lens will produce a better visual outcome than will a combination procedure, with no additional risk to the graft, said Jack Parker MD, at the 17th ESCRS Winter Meeting. “Phacoemulsification after DMEK can be performed with minimal risk of graft dislocation and can provide good refractive and visual outcomes with an acceptable decrease in endothelial cell density,” said Dr Parker, Netherlands Institute for Innovative Ocular Surgery in Rotterdam.

Dr Parker presented the results of a study that involved a consecutive series of 106 phakic eyes that underwent DMEK for Fuchs' endothelial dystrophy or bullous keratopathy. Six to nine months after their keratoplasty procedures, five patients developed cataracts and underwent phacoemulsification. None of the other graft recipients developed cataracts throughout a follow-up period of 22 months. Among the patients who developed cataracts, all phacoemulsification surgeries were uneventful and there were no dislocations or detachments of the DMEK graft. Furthermore, six to 12 months after the cataract procedures all eyes achieved a best-corrected visual acuity of 20/30 or better and were within 0.5 D of the predicted refraction. Moreover, mean endothelial cell density remained within safe limits, decreasing from 1535 cells/mm2 before, to 1158 cells/mm2. In addition, all corneas remained clear throughout the study period and there were no significant changes in pachymetry values during a follow-up period ranging from six to 12 months. The performance of the DMEK procedures involved first stripping a 9.5mm flap of Descemet’s membrane with its layer of endothelium from the posterior stroma of a prepared donor corneal buttons and storing the flaps in organ culture. Then, through a 3.0mm tunnel incision in the limbus of the graft recipient’s eye a circular portion of Descemet’s membrane, 9.0mm in diameter, is excised with an inverted Sinskey hook. After placing the graft into the anterior chamber, the graft is manipulated onto the iris with air and liquid. Then a bubble of air is injected beneath the graft to lift it up against the recipient’s stroma. The anterior chamber is then filled completely with air for 45 to 60 minutes, and afterwards air–liquid exchange is used to pressurise the eye. Combined procedures based on misguided principle Dr Parker noted that many surgeons who perform endothelial grafts will commonly combine the procedure with lens removal in order to avoid the need for a second procedure later on, should they accidentally induce a cataract during the keratoplasty procedure. The theory is that a subsequent cataract procedure might compromise the graft. However, the combined procedures can actually result in a poorer visual outcome than DMEK grafts alone.

“While combined procedures may be possible, they may not be desirable. Specifically the past data seems to suggest that patients do better after DMEK if the natural lens is left in place. They can see more letters on the eye chart. Visual rehabilitation is faster and they are subjectively more pleased with their vision because they retain the ability to accommodate. All of these findings are well reported and established,” he said. He cited a study he and his associates carried out which compared two age-matched groups of Descemet’s membrane endothelial graft recipients. One of the groups included 53 patients who had undergone a combined procedure and were pseudophakic, the other group included 52 patients who underwent DMEK alone, retaining their natural lenses. At six months’ follow-up, there was no statistically significant difference between the corrected distance visual acuities of the two groups, although the highest visual acuities occurred among the phakic eyes (Parker et al, J Cataract Refract Surg, 2012; 38: 871-877). He noted that the results of the current study take the argument a step further by showing that the fears that some may have regarding cataract surgery subsequent to a DMEK procedure may be unfounded. For example, the cataract surgery did not appear to compromise vision in the graft recipients. All had visual acuity of at least 0.6 and four had a visual acuity of 0.8 or better. Neither was visual rehabilitation after cataract surgery delayed among the graft recipients, as the cornea remained clear through surgery and follow-up. Most importantly, there were no instances of the endothelial graft becoming sucked off the posterior corneal surface, as some have imagined might occur during phacoemulsification. Instead, all grafts remained completely adherent to the stroma. Furthermore, the rate of endothelial cell loss increased only slightly after the cataract procedure. "The first key point to remember is that phakic eyes do better than pseudophakic eyes after DMEK, even if they later have to undergo a subsequent phaco procedure. Therefore we should not engage in combined procedures as a matter of course. When we operate on phakic eyes we should leave them phakic and if they subsequently develop a cataract, that's okay. We can deal with that well and safely in a subsequent procedure,” Dr Parker concluded.

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