visual outcomes after successful versus failed big-bubble deep anterior lamellar keratoplasty in keratoconus

purpose: to compare visual outcomes after deep anterior lamellar keratoplasty (dalk) between eyes with and without successful big-bubble formation. methods: in this retrospective comparative study, a total of 290 consecutive eyes from 257 keratoconus-affected patients underwent dalk with the big-bubble technique were enrolled. in cases where the big bubble could not be accomplished, manual stromal dissection down to dm was progressively performed using a crescent knife. the rate of successful big-bubble formation was determined. visual acuity and refractive outcomes were compared between the bare descemet membrane (dm) group (group 1) and manual dissection group (group 2). results: the surgery was completed as dalk in 289 of 290 eyes and a bare dm was successfully achieved in 229 (79.2%) eyes. the study groups were comparable in terms of age (27.8±7.9 years in group 1 versus 27.5±8.5 years in group 2, p=0.79), preoperative best-spectacle corrected visual acuity (bscva) (1.28±0.49 versus 1.31±0.51 logmar, respectively, p = 0.15), and postoperative follow-up (38.4±20.4 versus 37.4±19.9 months, respectively, p=0.73). postoperative bscva was significantly better in group 1 than in group 2 throughout the follow-up period (p<0.05). at final follow-up examination, a bcva ≤0.30 logmar was achieved in 82.1% of group 1 and 54.5% of group 2 (p<0.001). groups 1 and 2 were comparable in terms of postoperative spherical equivalent refractive error (-4.24±3.35 versus -4.49±3.25 d, respectively, p=0.61) and keratometric astigmatism (3.62±1.92 versus 3.38±1.71 d, respectively, p=0.39). conclusion: retention of posterior corneal stroma resulted in a lower visual acuity as compared to the bare dm group.