To comparatively evaluate changes in chord µ and chord α after photorefractive keratectomy (PRK) and femtosecond laser-assisted in situ keratomileusis (FS-LASIK) in eyes with low-to-moderate myopia using linear change (Δ) and displacement vector (DV) analysis. This retrospective comparative case series was conducted at Istanbul University, Istanbul Faculty of Medicine. A total of 102 eyes from 56 patients who underwent PRK or FS-LASIK for myopia ± astigmatism were examined. Topographic measurements were performed using the Pentacam AXL preoperatively and at postoperative months 1 and 6. Changes in chord µ and chord α values were evaluated using Δ and DV analyses. At 6 months, chord µ increased from 0.15 ± 0.10 mm to 0.23 ± 0.12 mm, and chord α from 0.35 ± 0.14 mm to 0.41 ± 0.14 mm, with Δ values of 0.08 ± 0.07 mm and 0.06 ± 0.13 mm, respectively (p = 0.013 and p = 0.020). The increases were greater in the PRK group (p = 0.044 and p = 0.018), whereas DV magnitudes did not differ between groups (p > 0.05). Δ chord α correlated positively with pupil diameter, whereas Δ chord µ correlated negatively with trefoil (0°) and vertical coma, and chord µ DV correlated negatively with horizontal coma. Significant increases in chord µ and chord α were observed after both PRK and FS-LASIK, with a greater increase in the PRK group. These findings may aid the interpretation of chord parameters in eyes that may later undergo multifocal intraocular lens implantation.
Çakmak et al. (Sun,) studied this question.