This presumably novel study evaluated the graft survival and compared the rate of ECL along one year following both optical and therapeutic PKPs. The corneal grafts in both groups showed graft clarity in all cases after one month and remained clear till the end of the study period. The rate of ECL for both groups showed non statistically significant differences, except at the 12- months visit, where there was a statistically significant (yet clinically narrow) increase in the rate of ECL in group 2 compared to group 1.
In our two recruited groups, there was a significant difference between both groups regarding the initial ECD of the donor’s graft, where cases of group 1 had significantly higher values of ECD compared to group 2. This can be explained by the usual tendency towards selecting the better grafts for the cases of optical PKPs rather than the therapeutic PKPs, since the former are claimed to have a better prognosis. Also, the emergency nature of the therapeutic PKPs sometimes obliges surgeons to use the available grafts. Yet, we believe that this did not alter the credibility of our study results, as we mainly compared the grafts between the two groups regarding the rate of ECL rather than the ECD on its own.
In our study, we found that the rate of ECL in group 1 was 29.90% ± 2.19, 39.27%± 1.97, and 49.06% ± 2.83 at 3-, 6-, and 12-months intervals, respectively, while it was 30.77% ± 1.53, 39.29% ± 1.91, and 50.65% ± 1.59 in group 2. To the authors’ knowledge, no previous studies explored the rate of ECL for cases of therapeutic PKP. Regarding the optical PKP cases, the rate of ECL in this study is very comparable to the study by Obata et al.[9], where the determined post-operative rate of ECL reached 10.4% at 2 weeks, 16.3% at 1 month, 33.6% at 3 months, 39.4% at 6 months, and 48.2% at 12 months. This was also found in other studies conducted by Bourne et al.[10], Nishimura et al. [11], and Patel et al.[7], in which the greatest rate of ECL after optical PKP occurred during the first postoperative year, with a collective rate of 30% to 50%. Again, these documented rates of ECL after one year of performing optical PKPs are comparable to our deduced rate.
In our study, no statistically significant difference was found between both groups as regards to the rate of graft rejection. Thus, the therapeutic corneal grafts can be considered non-inferior to the optical ones regarding the viability and the prognosis of the grafts (represented in our study by the regaining of the graft clarity, the incidence of graft rejections, and the rate of ECL).
To the best of our knowledge, very few studies explored the postoperative prognosis in cases of therapeutic PKPs. Xiao et al. [12], declared that for cases of fungal keratitis and herpes simplex keratitis, the cases that performed therapeutic PKP minimally suffered from endothelial decompensation, which gradually declined in its rate along their five years of follow up. This supports our study results in declaring the good prognosis of therapeutic PKPs overtime. However, the rate of ECL was not reported in their study.
In our studied cohort of group 2, the addition of antimicrobials for 2 to 3 weeks following therapeutic PKPs did not show any detected adverse effects on the rate of ECL postoperatively. Future studies to be conducted on larger cohorts and for even longer follow up intervals may support or contradict our study results.
We excluded some patients from the statistical analysis and from further enrollment in the study. All those excluded candidates developed factors that would possibly alter the rate of ECL. Discarding those participants gives more credibility to the present study.
In conclusion, our study results declared that therapeutic PKP can be considered non-inferior to optical PKP regarding the rate of graft rejection, the graft viability, and the rate of ECL along a follow up interval of one year. Hence, it can be considered as a safe alternative for cases with infected corneal ulcers which are resistant to the conventional medical therapies. Further long-term longitudinal studies are needed to validate or contradict our study results and to determine whether the clinically narrow change that was detected in the rate of ECL at the 12 months interval in cases of therapeutic PKP is an ongoing process that may progressively affect the graft survival or it is a stationary loss rate.