Electron Beam Irradiated Corneal Versus Gamma-Irradiated Scleral Patch Graft Erosion Rates in Glaucoma Drainage Device Surgery

Our results show that e-beam irradiated corneal grafts were used 3.8 times more frequently relative to scleral grafts in GDD surgery at a single academic institution, yet no increase in the rate of corneal graft erosion was noted relative to scleral grafts during the mean follow-up period of 412 ± 344 days (13.7 ± 11.5 months). No erosion events were noted in either corneal or scleral patch graft GDD surgery in this study. Previous studies of erosion rates after GDD surgery reported a low 1.8% erosion rate in 169 cases with a mean follow-up time of 4.8 months, and a 3.1% erosion rate in 319 cases over a mean follow-up time of 15.4 months using gamma-irradiated corneal grafts [17, 18]. Additional studies reported a 1.9% erosion rate using glycerol-preserved corneas over a median follow-up period of 440 days (approximately 14.5 months) [6]. The same study reported a significantly higher erosion rate of 8.9% for pericardium rates over an 11-month follow-up period. Thus, our study results over a comparable postsurgical follow-up provide support that e-beam irradiated corneal grafts are a comparable and suitable option for GDD surgery.

In addition to comparable erosion rates between e-beam irradiated corneas and other graft materials, there are other safety and convenience benefits associated with the use of e-beam corneal grafts for GDD surgery. For example, fresh or glycerin-preserved tissue that can be obtained from eye banks, while screened for infectious diseases, are not sterile and carry with them a higher risk of microbial contamination than sterile grafts [19‐21]. In addition, glycerin- and alcohol-preserved grafts require additional washing and rehydration steps in the operating room that are not necessary with irradiated grafts stored in an aqueous solution.

The clarity of a corneal graft can also provide long-term benefits over an opaque material such as sclera or pericardium. A previous study reports that e-beam treated corneas retained about 90% optical clarity relative to fresh corneas even after extended storage at room temperature [15]. In situations when the device is assessible, the clear cornea offers the surgeon the ability to visualize and inspect the device placement and sutures under the grafts (Fig. 1i, ii). Improved cosmesis can also be achieved with a clear corneal graft depending on the position of the implanted drainage device (Fig. 1ii, iii).

There are several limitations in our study. First, this is a retrospective analysis with a relatively short follow-up period. Loss of follow-up and incomplete electronic health record documentation may have underestimated erosion rates in our analysis. Additionally, our follow-up period may have been too short to detect erosions as this complication can occur well past our follow-up period. However, prior studies have found erosions as early as the first postoperative month [17] and 6.4 months [18] following GDD surgery. Lastly, if an erosion event occurred but was not surgically corrected, then the erosion would not have even been captured in our study. However, this would be highly unlikely, as the standard of care for an eroded graft and exposed GDD implant is surgical correction to avoid infection and endophthalmitis. Further studies with longer follow-up periods are underway to better characterize graft erosion rates in GDD surgery. Future prospective studies investigating surgical indications, complications other than erosion, and visual acuity, among other items, will further contribute to this area of research.