title: Posterior corneal curvature changes following Refractive Small Incision Lenticule Extraction.
abstract: OBJECTIVE
  To compare the posterior corneal curvature changes, in terms of corneal power and asphercity, following Refractive Small Incision Lenticule Extraction (ReLEx SMILE) procedure for low, moderate, and high myopia.
  
  
  METHODS
  This retrospective, non randomized, comparative, interventional trial; included 52 eyes of 26 patients, divided in three groups: low myopia (myopia ≤3 D [diopters] spherical equivalent [SE]), moderate myopia (myopia >3 D and <6 D SE), and high myopia (myopia ≥6 D SE). All patients were treated for myopia and myopic astigmatism using ReLEx SMILE. The eyes were examined pre-operatively and 3 months post-operatively using SCHWIND SIRIUS, a three-dimensional rotating Scheimpflug camera with a Placido disc topographer to assess corneal changes with regard to keratometric power and asphericity of the cornea.
  
  
  RESULTS
  A statistically significant increase in mean keratometric power in the 3, 5, and 7 mm zones of the posterior corneal surface compared with its pre-ReLEx SMILE value was detected after 3 months in the moderate myopia group (pre-operative [pre-op] -6.14±0.23, post-operative [post-op] -6.29±0.22, P<0.001) and high myopia group (pre-op -6.19±0.16, post-op -6.4±0.18, P<0.001), but there was no significant change in keratometric power of the posterior surface in the low myopia group (pre-op -5.87±0.17, post-op -6.06±0.29, P=0.143). Asphericity (Q-value) of the posterior surface changed significantly (P<0.001) after ReLEx SMILE in the moderate myopia group in the 3, 5, and 7 mm zones, and in the high myopia group in the 3 and 7 mm zones; but there was no significant change in the Q-value in the low myopia group in all three zones (pre-op 0.23±0.43, post-op -0.40±0.71, P=0.170), and in the high myopia group in the 5 mm zone (P=0.228).
  
  
  CONCLUSIONS
  ReLEx SMILE causes significant changes in posterior corneal keratometric power and asphericity in moderate and high myopia, but the effect is subtle and insignificant in low myopia.
authors.affiliation: Phaco and Refractive Surgery Department, Nethradhama Superspeciality Eye Hospital, Bengaluru, Karnataka, India.
authors.forename: Sri
authors.initials: S
authors.lastname: Ganesh
authors.affiliation: Phaco and Refractive Surgery Department, Nethradhama Superspeciality Eye Hospital, Bengaluru, Karnataka, India.
authors.forename: Utsav
authors.initials: U
authors.lastname: Patel
authors.affiliation: Phaco and Refractive Surgery Department, Nethradhama Superspeciality Eye Hospital, Bengaluru, Karnataka, India.
authors.forename: Sheetal
authors.initials: S
authors.lastname: Brar
keywords: ReLEx SMILE; Refractive Small Incision Lenticule Extraction; corneal asphericity; corneal keratometric power; posterior curvature