Occurrence of Invisible Eye Movement in KLEx and Its Effect on Visual Quality and Refractive Outcomes

To investigate the effect of invisible eye movements on visual quality and refractive outcomes during intraoperative laser scanning with keratorefractive lenticule extraction (KLEx).

Eye movement direction and maximum distance were measured using ImageJ software (National Institutes of Health) in 487 patients (958 eyes). Comparisons were made among left eyes with movement of 0.1 mm or less, movement of less than 0.1 mm, and movement of 0 mm regarding refraction, astigmatism vector analysis, uncorrected distance visual acuity (UDVA), Strehl ratio (SR), modulation transfer function (MTF) cut-off, and higher order aberrations (HOAs).

Among 958 eyes, 105 eyes experienced invisible movement (10.96%). Specifically, 23 right eyes (4.80%) and 82 left eyes (17.12%) showed a mean movement of 0.07 mm. There was a significant difference in incidence of invisible movement between the different eyes (P < .001), but not in movement distances (P = .63). Movements were primarily directed between 45° and 135°. At 3 months postoperatively, no significant differences were found in refraction, astigmatism vector analysis, UDVA, SR, MTF cut-off, total HOAs, coma aberration, and spherical aberration (P ⩾ .05). Trefoil aberration was higher in the 0.1 mm or greater group compared to the other groups (P = .03). However, the difference between the less than 0.1 mm group and 0 mm group was not statistically significant (P = .48).

Invisible movement is common in KLEx surgery. It is typically observed upward (45° to 135°), and with a higher incidence in the left eye than the right eye. Although invisible movement does not affect postoperative refractive outcomes, a movement distance of 0.1 mm or greater may increase corneal trefoil aberration. [J Refract Surg. 2025;41(7):e674-e681.].