This retrospective comparative study demonstrated comparable visual and refractive outcomes for both DALK and PKP procedures. Additionally, findings suggest that DALK may offer a less invasive alternative to PKP with similar functional outcomes and a reduced risk of severe complications. However, further prospective studies with larger sample sizes are needed to confirm these results and to evaluate long-term outcomes. Similar studies have demonstrated the advantages of DALK over PKP [11,12,13,14,15]. According to a meta-analysis, men undergo keratoplasty procedures more often than women do, which is consistent with our findings [16]. Keratoconus was the most common indication for both PKP and DALK in this study. Previous studies have indicated that the most common indications in high-income countries are bullous keratopathy and Fuchs’ endothelial dystrophies, whereas the most common indication in developing nations is microbial keratitis [17]. We believe that the comparatively high prevalence of keratoconus in the KSA, which is reflected in the relatively young mean age of patients receiving both types of procedures, is the cause of the differences in the indications for keratoplasty in the current study relative to other studies. Prior studies have also shown that the number of keratoconus surgeries is increasing in Saudi Arabia, primarily because of improvements in health care availability, increased graft availability, and recent population explosions [15].

In the present study, the postoperative BCVAs of the PKP and DALK patients were comparable, with no statistically significant differences detected between the total cohort and the subgroup of keratoconus patients. This finding is consistent with previous studies that reported similar visual outcomes for both PKP and DALK [16, 18]. Additionally, in a case series of macular corneal dystrophy in KSA, Al Araj et al. reported a lack of significant differences in postoperative visual outcome in terms of BCVA between PKP and DALK and that both groups of patients demonstrated improvements in BCVA after the operation [19]. However, our study findings contradict those of the systematic review by Henien et al., who reported a statistically significant difference in postoperative BCVA between the PKP group and the DALK group [20]. This difference in findings may have been due to the low to moderate quality of evidence caused by heterogeneity in the study design, outcome measures and follow-up periods. Additionally, our study revealed slightly greater myopic refraction in the DALK group postoperatively, which can be attributed to the size of the donor cornea as well as the high degree of preoperative ametropia in keratoconus patients.

Generally, PKP is considered an efficient and harmless procedure; however, graft failure is a major concern [21]. This concern was also validated in the present study, as three patients in the PKP group experienced graft failure but none in the DALK group did. In the majority of PKP cases, graft failure is attributed to immunological allograft rejection, which leads to the loss of endothelial cells [21, 22]. In DALK patients, however, corneal surface diseases such as infectious keratitis, limbal stem cell deficiency, and persistent epithelial defects have been shown to be the primary causes of graft failure [23]. Our findings are not consistent with those of Liu et al. [24], who reported similar rates of graft failure in both the PKP and DALK groups. In another study, the rate of endothelial rejection was 18.8% among PKP patients [25, 26]; PKP patients also experience a greater reduction in the number of endothelial cells [27]. This decrease in the endothelial cell count is not usually found in DALK patients because the innate endothelium is preserved during the procedure. In a long-term (5-year) study, the overall rejection rate following DALK varied from 1.7 to 13%, which is much lower than that following PKP [28]. In our investigation, 2 patients in the PKP group with endothelial rejection underwent regrafting, and all graft rejections were reversed with topical steroids. One patient who underwent DALK had to undergo regrafting due to optical failure.

Previous studies have reported a significantly greater incidence of elevated intraocular pressure (IOP) in patients undergoing PKP than in those treated with DALK [29]. In the present study, 13 patients (24.7%) who underwent PKP developed glaucoma; this percentage was much greater than the corresponding proportion in the DALK group (8%). This can be explained by the less invasive nature of DALK and the avoidance of postoperative steroid use in these patients. Other common complications reported in the current study included dry eye, loose suturing, cataracts, neovascularization, early graft edema, and keratitis in both the PKP and DALK groups. These findings are not consistent with those reported by Khattak et al., who described a greater risk of loose sutures in DALK than in PKP. However, the risk of cataracts observed in their study was similar to that reported in the present study [29]. DALK entails a more interesting and challenging technical process, but it also poses a greater risk of intraoperative complications, including the formation of a dual anterior chamber, which might be the main cause of procedure failure [30]. In the present study, DALK was associated with fewer postoperative complications, likely because DALK does not interrupt intraocular eye structures, reducing the risk of postoperative glaucoma, retinal detachment, cataract formation, and expulsive choroidal hemorrhage [19, 31]. Additionally, when the two procedures were compared for patients with keratoconus only, the DALK group had a lower incidence of complications overall.

Here, we evaluated patient satisfaction with the two procedures. 63% of the keratoconus patients in the PKP group and 48% of those in the DALK group reported that the surgical outcome met their expectations. The reports of satisfaction in our study are in line with those of a previous study, which reported similar satisfaction outcomes regarding the safety of these procedures [24]. However, our results differed from those of an earlier study conducted by Yeung et al. [32], who compared the perspectives of patients with a heterogeneous set of corneal diseases (including keratoconus, granular dystrophy, bilateral postinfectious scarring, and old interstitial keratitis) who underwent PKP in one eye and DALK in the contralateral eye. In their study, 8 out of 10 patients favored PKP in terms of vision, with a significantly different overall contentment rate than for the DALK eye (p = 0.02). Notably, there were comparable rates of preoperative and intraoperative complications between the two groups of eyes.

Owing to the retrospective nature of the study and the relative lack of documentation, it was difficult to collect topographic variables and visual quality metrics such as contrast sensitivity and endothelial cell count. While this limitation may affect the depth of analysis, it does not undermine the primary conclusion that DALK offers visual and refractive outcomes comparable to those of PKP, with a lower risk of severe complications. To provide further evidence, future studies with a prospective design and rigorous data collection protocols, including detailed topographic and visual quality assessments are essential. This will allow for a more comprehensive evaluation of long-term outcomes and potential differences between the two procedures. Additionally, differences in surgical technique among surgeons can impact outcomes, potentially confounding the results. A longer follow-up period would provide more insights into long-term outcomes and complications.