Dynamic distribution of Kappa angle in myopic patients undergoing FS-LASIK and its correlation analysis

AIM: To explore the dynamic distribution of pupil size and center, the eccentricity distribution of corneal light reflection, and its correlation analysis about suitable for femtosecond laser combined with excimer laser in situ keratomileusis.METHODS: Randomly selected 225 patients(407 eyes)who underwent femtosecond laser combined with excimer laser in situ keratomileusis at Yanbian University Hospital in 2019 from January to May, preoperative use of Wavelight Allegro Topolyzer Corneal Topography to measure the pupil size and center position, the German Wavelight EX500 excimer Laser(500Hz)records the deviation between the pupil center and the coaxially sighted corneal light reflex when the patient is supine. RESULTS:The average displacement distribution between the center of the cornea and the center of the pupil is 0.322±0.194mm, and 64% of the eyes are ≤0.40mm. The average displacement distribution of P-Dist(the eccentricity between the pupil center and the coaxially sighted corneal light reflex point)is 0.225±0.102mm, and 80% of the eyes are ≤0.30mm. The coaxially sighted corneal light reflex point is mainly deviated to the superior temporal side of the corneal center(34%). The X-axis of the left eye in low light conditions: -0.061±0.084mm, and the X-axis of the right eye: -0.016±0.059mm(P=0.002)(the left eye shifted to the temporal side in the dark light). The corneal transverse diameter(WTW)was positively correlated with changes in pupil diameter(dark pupil diameter-bright pupil diameter)(r=0.270, PCONCLUSION: The left eye should be adjusted to a position of the machining center within 0.061mm. If the cornea is too large, try to maintain a dark light environment during the operation to improve the efficiency of pupil matching. This study further confirms the necessity of rationally positioning the cutting center under different angle kappa states.