Influence of flap thickness homogeneity over refractive outcomes and higher order aberrations induction after myopic femto-LASIK

Session Details

Session Title: LASIK & PRK I

Session Date/Time: Sunday 15/09/2019 | 16:30-18:00

Paper Time: 16:36

Venue: Free Paper Forum: Podium 3

First Author: : J.Gros-Otero SPAIN

Co Author(s): :    A. Parafita   M. Garcia-Gonzalez   M. Alonso   A. Rodero   A. Katsanos   M. Teus              

Abstract Details

Purpose:

Since the mechanical microkeratomes, flap morphology has been awarded some relevance regarding refractive outcomes and higher order aberrations (HOAs) induction. Modern femtosecond laser (FS) created flaps seem to be more homogeneous, therefore less HOAs should be induced. As our group has previously reported differences in flap morphology regarding the FS used, the aim is to study correlations among flap thickness homogeneity, the refractive results and HOAs induction.

Setting:

Clínica Novovisión and Clínica Rementería (Madrid, Spain)

Methods:

Observational, prospective cohort study. Flaps were created with 5 different FS (LenSx and FS200, Alcon; Victus, B&L; Intralase FS60 and iFS150, J&J Vision). Flap Thickness was measured with anterior segment OCT (Spectralis) in the center and 3 mm nasally and temporally. Flap thickness homogeneity (FTH) was defined as the difference between the thickness at 3mm nasal and temporal. Anterior corneal HOAs (using 6mm zone) were measured using the corneal tomographer (Oculyzer, Wavelight) before and 3 months after surgery. The same excimer laser was used for all the ablations (Allegretto 400).

Results:

233 eyes were analyzed. In the global group, the FTH showed statistically significant correlations with spherical equivalent(SE) (R -0,2003; p= 0,007), third order(O3) (R 0,17112; p= 0,02), fourth order(O4) (R 0,22474; p=0,002), fifth order(O5) (R 0,16449; p=0,02), total (0,18182; p=0,01) and coma-like (R 0,1737; p=0,0204) aberrations induced. Comparing the results of FS using flat (FC) versus curved cone (CC) interfaces, the FTH was (7,4+/-6,159microns vs 11,15+/-8,895microns; p=0,0003), the O4 (0,123+/-0,262 rms vs 0,258+/-0,355 rms; p=0,00) and the spherical-like (0,098+/-0,238 rms vs 0,1710,189; p=0,03) for FC and CC respectively.

Conclusions:

Even with FS created flaps, flap morphology is related with visual outcomes. Flap thickness heterogeneity correlates with more HOAs induction and worst visual outcomes after FS LASIK to correct myopia. Cone shape seems to have some influence in flap heterogeneity and in visual and refractive outcomes, being curved interfaces more prone to HOAs induction and flap heterogeneity than flat ones.

Financial Disclosure:

None