Therapeutic lamellar keratoplasty, an alternative technique to PKP, has become a popular technique for the management of corneal diseases with an intact corneal endothelium1,9,10. It has several advantages over the PKP technique. Moreover, the DLKP procedure has some advantages and disadvantages in patients with medically uncontrolled infectious keratitis. DLKP is an extraocular surgical procedure, which reduces the risk of infection into the anterior chamber and endophthalmitis, but is unable to completely remove the infectious organisms, which may lead to recurrence of infection compared to PKP, where the entire cornea is replaced.
Xie et al 11 have reported higher recurrence rates following DLKP for fungal keratitis. One study showed that recurrence of infection occurred in 15.3% of patients in the DLKP group, and 12% of patients in the PKP group, but the infection did not recur after the modified Anwar big-bubble DLKP technique, which entails removal of the entire corneal stroma1. The data from the current study showed that the rate of recurrence was 18.8% (3/16) in the DLKP group and 19.4% in the PKP group. Therapeutic DLKP with complete removal of the infected stroma down to the DM can be more effective compared to PKP for managing corneal infections and improving BCVA and visual acuity1,9. The higher recurrence was attributed to the presence of keratitis with corneal perforations. We did not observe any case of endophthalmitis in the DLKP group. Only one eye developed endophthalmitis in the PKP group.
The main advantage of DLKP is that is maintains the integrity of the patient’s endothelium, thus eliminating the risk of endothelial immunological allograft rejection and endothelial failure. We found that the frequency of graft rejection was 12.5% in the DALK group, while 42.9% of patients developed graft rejection in the PKP group. Studies have shown that the rate of graft rejection following PKP depends on the patient’s condition and related risk factors1,2. Corneal neovascularization (CNV) is one of the factors responsible for graft rejection, CNV is characterized by the outgrowth of blood vessels from the limbus, which causes loss of corneal transparency and even graft failure2,12,13.
Manual techniques for lamellar keratoplasty are usually associated with worse visual outcomes than those with PKP due to the inability to consistently perform complete lamellar dissection down to the DM layer.1. Studies have reported that incomplete removal of the posterior stroma and residual infectious keratitis in the deep stroma following DALK resulted in higher rates of recurrence compared to that following PKP for fungal or acanthamoeba keratitis1,11.
This study did not find significant differences in the BCVA improvements between the DLPK and PKP groups. The average increment in the number of Snellen lines was 6.8 in the DLKP group and 4.2 in the PKP group, and the difference between the two was statistically significant (p = 0.03). Another study showed a trend toward better visual acuity outcomes following DLKP compared to PKP, although the difference was not statistically significant1. Several studies have reported variable visual acuity changes after DLKP and PKP9,11,14,15.
Graft survival is closely related to the size of the graft, quality of the donor graft, severity of the preoperative and postoperative infections, surgical technique used, and postoperative complications such as CNV13,16,17. In our study, the graft survival rates at the one-year follow-up were significantly higher in the DLKP group than those in the PKP group ( p = 0.033). Anshu et al.1 reported similar outcomes with 90% graft survival rates after DALK and 78.4% after PKP, although the difference lacked statistical significance owing to the small sample size. They also showed that nonperforated ulcers exhibited better graft survival rates than those of perforated ulcers. Corneal perforation is considered to be amongst the important high-risk factors for graft survival18. Previous studies have demonstrated that DLKP is a safe surgical procedure for the treatment of corneal perforation resulting from keratoconus and hereditary dystrophies to severe corneal infection and corneal perforation8,19. Graft failures mainly consisted of the recurrence of primary infection, CNV, postoperative DM detachment, endothelial failure, and endophthalmitis.
DLKP has several advantages over PKP, including the reduced incidence of secondary cataract and glaucoma. One study showed that the elevation of intraocular pressure (IOP) following DLKP is a transient condition, which is related to a low incidence of secondary glaucoma. 20 The use of topical steroids is one of the risk factors for IOP. Higher IOP and secondary glaucoma are common sequelae of the PKP procedure14. Postoperative complications after therapeutic keratoplasty require early recognition and adequate management.
Bandage contact lenses are widely used for the postoperative management of persistent corneal epithelial defects. A previous study noted that fitting epidermal growth factor-treated bandage contact lens onto the damaged eye may aid in the regrowth of the corneal epithelium in patients with delayed wound healing21. However, another recent prospective study demonstrated that 29.8% of these contact lenses were contaminated22. Frequent replacement of these lenses could decrease incidence of contamination and hypoxia-related complications.
This study had some limitations. This investigation was a clinical retrospective cohort study, in which statistical comparisons were not performed for the risk factors, size of infiltration and severity of corneal infections of each surgical group. The number of patients with advanced infectious keratitis, with respect to the donor graft size and cases of perforation, in the PKP group was obviously higher than that in the DLKP group.