EK eclipsing PK

Endothelial keratoplasty (EK), particularly Descemetâ's membrane EK (DMEK), offers significant safety and visual advantages over penetrating keratoplasty (PK), with similar three- to five-year graft survival rates at large centres, and superior five-year endothelial cell density preservation, according to a review by the Cornea Research Foundation of America, Indianapolis, USA.

Results from several long-term studies also show that EK graft failure rates are higher early in the surgical learning curve, and prompt replacement of failed grafts improves visual outcomes, Marianne O Price PhD, MBA told the 6th EuCornea Congress in Barcelona, Spain.

The biggest risk factor for late EK failure is prior glaucoma surgery, while the lower rejection risk of DMEK permits reduced steroid use, which in turn reduces the risk of intraocular pressure (IOP) spikes after surgery, added Dr Price, Executive Director, Cornea Research Foundation of America.

Registry reports show EK volume exceeded PK in the USA since 2012, while in the UK more than three-quarters of Fuchs endothelial dystrophy and 70 per cent of pseudophakic corneal oedema cases were treated with EK in 2013 – not surprising given the safety advantage of a smaller incision, and quicker and better visual recovery that EK offers, Dr Price said.

UK registry data also show more failures of EK at two years for both Fuchs and corneal oedema, and failure rates are much higher for surgeons with 15 or fewer EK procedures (Greenrod et al. Am J Ophthalmol 2014; 158;957-66).

A similar EK learning curve was observed at Dr Price’s large referral centre, with six out of the first 100 Descemet’s stripping EK (DSEK) cases failed but only one of the second 100 (Price and Price. J Cataract Refract Surg 2006;32:411-8), and seven of the first 75 DMEK cases failed but only two of the second 75 (Guerra, Price et al. Ophthalmology 2011;118:2368-73).

Re-operate DMEK failures early

Replacing a failed DMEK graft promptly results in visual outcomes equal to primary DMEK surgery, Dr Price said (Price et al. Ophthalmology 2015;122:1639-44). If the graft doesn’t clear after a procedure involving surgical trauma, it should be replaced promptly. After routine surgery, wait one month because sometimes it can take several weeks for a successful DMEK graft to clear, she advised.

Quickly replacing failed grafts minimises oedema and pain, as well as anterior stromal changes or scarring that can degrade outcomes, Dr Price added. After successful clearing, the five-year survival rates for DMEK, DSEK and PK for Fuchs are similar at Dr Price’s centre, running at about 95 per cent.

Similarly, the Singapore National Eye Centre reports three-year graft survival for Descemet’s stripping automated EK (DSAEK) at 87 per cent and PK at 85 per cent (Ang et al. Ophthalmology 2012;119:2239-44). The somewhat lower surivval rate is likely due to more complications in a population with 70 per cent corneal oedema, Dr Price noted.

Long-term failure risks

At five years, only 59 per cent of DSEK grafts survived in patients with a prior trabeculectomy and just 25 per cent in patients with a prior shunt, compared with 90 per cent for medically managed glaucoma patients and 96 per cent for patients with no prior glaucoma, Dr Price said (Anshu et al. Ophthalmology 2012;119:1982-7).

The differences may be due to increased plasma proteins found in the aqueous of eyes with glaucoma shunts, suggesting a breach in the blood-aqueous barrier, Dr Price said. Increased oxidative, apoptotic and inflammatory proteins may accelerate endothelial cell damage. Protein concentrations are up to 10 times higher in eyes with tubes and five times higher in eyes with Express shunts or trabs than control eyes without glaucoma surgery (Rosenfeld et al. Mol Vision 2015;21:911-8).

But that does not mean glaucoma surgery should be avoided, Dr Price said. Rather, set realistic expectations. Her centre counsels patients that glaucoma surgery is important because the optic nerve can’t be replaced, and while a corneal transplant may fail sooner because of a glaucoma procedure, the graft can be replaced. After the initial cell loss associated with the surgical procedure, PK eyes lose endothelial cell density at a higher rate than EK eyes so that five years out, EK eyes have higher mean endothelial cell density, Dr Price noted (Price et al. Ophthalmology 2011;118:725-9. Ophthalmology 2013;120:246-51).

PK also has higher incidence of rejection episodes, with 18 per cent at two years vs 12 per cent for DSEK and less than one per cent for DMEK at a centre with similar patient demographics for all three procedures, Dr Price said (Anshu et al. Ophthalmology 2012;119:636-40). The rejection rate may be related to the number of layers transplanted, she said. DMEK has such a low rejection rate it allows reduced steroid strength after surgery, she said.

Marianne O Price:

marianneprice@cornea.org