Fig. 1

The operation of SMILE surgery (a). Tear film mark centration method was used to determine the process of centration. At 80% size, the green light was modified to coincident with the tear film center. green light = treatment center. (b). After centration, the operation of femtosecond laser treatment and the lenticule extraction were performed (c). Decentration was measured on the tangential curvature difference map, with the corneal vertex shown by the white dot (arrow). A prepared best fitting circle and central grid was superimposed to the tangential curvature difference map to determine the location of the optical zone center (x,y) with reference to the corneal vertex (0,0) by the Adobe. N = nasal; T = temporal