16 Endothelial Keratoplasty in Glaucoma

Endothelial keratoplasty (EK) has become the most frequently performed type of corneal transplant in the United States, with the most prevalent EK technique being Descemet stripping endothelial keratoplasty (DSEK).¹ EK is now used for over 90% of cases of endothelial failure, so it is not surprising that EK surgeries are being done in eyes with preexisting glaucoma. Moreover, we know that the long-term use of topical corticosteroids to prevent keratoplasty rejection often leads to the development of glaucoma. We have found that approximately one-third of patients without a preexisting history of glaucoma will develop increased intraocular pressure (IOP) during the first year after DSEK with a prednisolone acetate 1% dosing regimen of four times a day for 4 months, then tapering to three times a day for 1 month, twice a day for 1 month, and once a day through 1 year.² The percentage of eyes developing increased IOP can be higher with higher steroid dosing or lower if the dosing is decreased. Either way, glaucoma and keratoplasty are inextricably intertwined.

When examining 5-year DSEK survival rates, we as well as others have found that the most significant risk factor for graft failure is previous glaucoma filtration surgery, with tubes being associated with a higher rate of graft failure than trabeculectomies.^3,4,5 These findings have important implications when setting appropriate patient expectations for surgery. Patients who have a tube should be cautioned that the graft will likely need to be replaced within 5 years. Compared with penetrating keratoplasty (PK), an EK graft is much easier and less traumatic to replace. EK also provides quicker visual recovery than a full-thickness graft, which requires multiple sutures, each of which causes some scarring to the recipient cornea.

Why do grafts fail sooner in eyes with prior glaucoma filtration surgery? Whenever performing keratoplasty on an eye with a tube, we trim the tube at the time of transplant surgery, or we reposition the tube a month ahead of time so that no tubes touch the cornea. So the increased risk of graft failure in these eyes is not attributable to the tube contacting the cornea. We have sampled anterior chamber fluid from eyes with tubes and trabeculectomies and found that eyes with tubes (both valved and nonvalved) have on average a 10-fold higher protein concentration in the aqueous humor, and eyes with a trabeculectomy have a 5-fold higher protein concentration than eyes undergoing routine cataract surgery in the absence of prior glaucoma surgery (► Fig. 16.1).⁶ We believe that glaucoma filtration surgery produces an unhealthy aqueous environment for the corneal endothelium.

Early graft failure after tubes and trabeculectomies is an important demographic issue. In reviewing our PK cases performed between 1982 and 1996, we found that eyes with a history of prior glaucoma surgery accounted for only 3% of the pseudophakic corneal edema cases, whereas in our DSEK series performed between 2003 and 2005, eyes with prior glaucoma surgery accounted for 33% of the pseudophakic corneal edema cases.^3,7 Thus pseudophakic corneal edema is increasingly associated with prior glaucoma surgery. If the grafts in these eyes only last about 5 years on average, then we will see a large number of regrafts being performed for these problems. This will be aggravated by a switch that is occurring in the United States to make tubes the primary surgical procedure for glaucoma instead of trabeculectomies.

To put all this into prospective, our analysis of DSEK graft survival showed that the 5-year survival rate was 95% in eyes without a preexisting history of glaucoma and 90% in eyes with medically managed glaucoma, which was not a significant difference. However, the 5-year survival rate dropped to 59% in eyes with a prior trabeculectomy and was only 25% in those with a prior aqueous shunt (► Fig. 16.2).³ When we analyzed graft survival in eyes with a previous failed PK that was treated with DSEK, we were surprised to find that the number of previous failed PKs and corneal neovascularization were not risk factors for graft failure—the only significant risk factor was a prior tube.⁸ The 4-year survival rate of EK under a failed PK was 96% in eyes without a glaucoma filter but only 22% in eyes with a filter.⁸ Filters are going to lead to many regrafts. They will also cause of lot of secondary corneal decompensation in virgin corneas. Tubes may become the most common cause for grafting corneas.

Fig. 16.1 The protein concentration of the aqueous humor is significantly elevated in eyes that have undergone glaucoma filtration surgery, such as Express or standard trabeculectomy, or implantation of an Ahmed or Baerveldt aqueous shunt, as compared with eyes without prior surgery (controls). In the box plots, the diamond shows the mean value, the horizontal line shows the median, the bottom and top of the boxes represent the 25th and 75th percentiles, respectively, and the vertical lines extend to the minimum and maximum sampled values.

Fig. 16.2 Kaplan–Meier survival curves for Descemet stripping endothelial keratoplasty (DSEK) performed in eyes without any previous diagnosis of glaucoma, eyes with glaucoma managed with eyedrops, eyes with a previous trabeculectomy, and eyes with a previous aqueous shunt. EK, endothelial keratoplasty; trab, trabeculectomy.

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