Intraoperative centration during small incision lenticule extraction (SMILE)

Abstract

To evaluate intraoperative decentration from pupil center and kappa intercept during small incision lenticule extraction (SMILE) and its impact on visual outcomes.This was a retrospective noncomparative case series. A total of 164 eyes that underwent SMILE at the Singapore National Eye Center were included. Screen captures of intraoperative videos were analyzed. Preoperative and 3 month postoperative vision and refractive data were analyzed against decentration.The mean preoperative spherical equivalent (SE) was -5.84 ± 1.77. The mean decentration from the pupil center and from kappa intercept were 0.13 ± 0.06 mm and 0.47mm ± 0.25 mm, respectively. For efficacy and predictability, 69.6% and 95.0% of eyes achieved a visual acuity (VA) of 20/20 and 20/30, respectively, while 83.8% and 97.2% of eyes were within ±0.5D and ±1.0D of the targeted SE. When analyzed across 3 groups of decentration from the pupil center (<0.1 mm, 0.1-0.2 mm, and >0.2 mm), there was no statistically significant association between decentration, safety, efficacy, and predictability. When analyzed across 4 groups of decentration from kappa intercept (<0.2 mm, 0.2-<0.4 mm, 0.4-<0.6 mm, and ≥0.6 mm), there was a trend toward higher efficacy for eyes with decentration of kappa intercept between 0.4 and <0.6 mm (P = .097). A total of 85.4% of eyes in the 0.4 to <0.6 mm group had unaided distance VA of 20/20 or better, as compared to only 57.8% of eyes in ≥0.6 mm group.Decentration of 0.13 mm from the pupil center does not result in compromised visual outcomes. Decentration of greater than 0.6 mm from the kappa intercept may result in compromised visual outcomes. There was a trend toward better efficacy in eyes which had decentered treatment from 0.4 to <0.6 mm from the kappa intercept. Patients with a large kappa intercept (>0.6 mm) should have their lenticule created 0.4 to 0.6 mm from the kappa intercept and not close to the pupil.

Figure 1

Intraoperative screen captures. (A) Pupil outlined with ellipse tool and center of pupil identified. (B) Decentration from pupil center measurement. Small blue dot = pupil center. Green dot = fixation light. (C) Horizontal pupil diameter measurement. (D) Vertical pupil diameter measurement. (E) Red dot = kappa intercept derived from Orbscan. Distance between fixation light and kappa intercept is calculated by trigonometry.

Figure 2

Distribution of decentration from the pupillary center.

Figure 3

(A) Distribution of kappa intercept. (B) Distribution of decentraton from kappa intercept.

Figure 4

(A) Plot of decentration from pupil center against angle kappa. (B) Plot of decentration from kappa intercept against angle kappa. (C) Plot of maximum pupil size against decentration from kappa intercept. (D) Plot of maximum pupil size against decentration from pupil center. (E) Plot of decentration from pupil center against decentration from kappa intercept. r = Pearson correlation coefficient.