Background To investigate the difference in clinical outcomes between large-diameter deep anterior lamellar keratoplasty (L-DALK) and standard DALK (S-DALK) for the treatment of keratoconus.

Methods 132 patients (132 eyes) from the Zhongshan Ophthalmic Center with a clinical diagnosis of keratoconus were enrolled. The participants were featured by the intolerance to rigid gas-permeable contact lenses or unsuccessful fitting of contact lenses. Using stratified blocked randomisation, eligible eyes were allocated into the L-DALK group or the S-DALK group (66 eyes, respectively). Postoperative uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), refractive sphere, manifest cylinder and spherical equivalent refractive error were tested at 6, 12, 18 and 24 months after surgery.

Results After surgery, the L-DALK group had better UCVA and BSCVA than the S-DALK group (p=0.000 and 0.021, respectively). At 24 months, mean BSCVA was 0.17±0.10 logarithm of the minimum angle of resolution (logMAR) (Snellen equivalent, 20/25) in the L-DALK group vs 0.22±0.10 logMAR (Snellen equivalent, 20/32) in the S-DALK group. Differences were observed between the L-DALK group and the S-DALK group in terms of refractive sphere (p=0.015), manifest cylinder (p=0.014) and spherical equivalent refractive error (p=0.034) at any time interval postoperatively. At 24 months, the mean spherical equivalent refractive error was −3.5±3.2 D and −5.2±2.6 D in the L-DALK and S-DALK groups, respectively.

Conclusions L-DALK can reduce the degree of postoperative myopia and manifest astigmatism and improve visual acuity outcomes in keratoconus compared with S-DALK.

Trial registration number Chinese Clinical Trial Registry (TRC-13003122).