Different techniques of deep anterior lamellar keratoplasty (DALK) have been introduced to create a uniform recipient bed, thereby reducing complications, such as interface irregularity and opacification encountered with conventional lamellar keratoplasty. The big-bubble technique provides a planned, safe, quick and consistent baring of Descemet membrane (DM) by injection of air deep into the stroma. Nevertheless, this technique has a long learning curve with a low success rate of big-bubble formation and a high rate of DM perforation when performed by surgeons in training. Different modifications to the original technique using intraoperative instruments such as corneal pachymetry, anterior segment optical coherence tomography (OCT), and femtosecond laser, have been used to increase the chances of achieving a successful DM detachment from the deep stroma by air injection. Even with these innovations, the rate of successful big-bubble formation did not reach 100%. Recently, the investigators described a modification to the original big-bubble DALK in which a 27-gauge needle was inserted into the stroma peripherally from the trephination site towards the limbus. The investigators found that air injection peripheral to the trephination can effectively and reproducibly separate the corneal stroma from the Descemet membrane (DM). This study was aimed to compare the success rate and complications of big-bubble DALK using central versus peripheral air injection performed by senior cornea fellows under the supervision of an experienced faculty member in an academic hospital.

Inclusion Criteria:

• Patients with moderate (48 D < mean keratometry < 55 D) to advanced (mean keratometry ≥ 55 D or immeasurable keratometry) keratoconus were enrolled.

Exclusion Criteria:

• History of ocular surgery, concomitant ocular pathologies, such as vernal keratoconjunctivitis, cataract, glaucoma, and retinal abnormalities.