Digital analysis of flap parameter accuracy and objective assessment of opaque bubble layer in femtosecond laser-assisted LASIK: a novel technique

Abstract

Background:The purpose of this study was to determine flap parameter accuracy, extent of the opaque bubble layer, and incidence of skip lines in femtosecond laser-assisted stromal in situ keratomileusis (LASIK) using the WaveLight® FS200 laser and optoelectronic clinical measurements.Methods:Images from 101 flaps were automatically recorded during consecutive routine LASIK procedures performed using the WaveLight FS200 femtosecond laser and the EX500 excimer laser. Digital processing of these images was used to evaluate objectively the diameter of FS200-created flaps, by comparing planned versus achieved procedures and to evaluate the incidence and extent (area) of the opaque bubble layer.Results:The intended flap diameters were between 8.00 mm and 9.50 mm. The achieved flap diameters showed extremely high precision, and were on average −0.16 ± 0.04 mm smaller for a 8.00 mm intended flap diameter, −0.12 ± 0.03 mm smaller for a 8.50 mm flap, and up +0.06 ± 0.06 mm wider for a 9.50 mm flap. With an average flap area of 72.4 mm2, the mean area of the opaque bubble layer (4.1 ± 4.3 [range 0–14.34] mm2) corresponded to a 6% opaque bubble layer-to-flap area. Specifically, 80% of the femtosecond-created flaps had an essentially zero opaque bubble layer (<2.7% of the flap area).Conclusion:In our clinical experience, flaps created using FS200 and this novel highly objective assessment technique demonstrate both precision and reproducibility. The incidence of opaque bubble layer was minimal.

FS200 femtosecond laser LASIK flap digital analysis parameter evaluation: comparing two different types of patient interface applanation cones

“…Our results indicate a similar pattern with impressive accuracy, as compared with the findings in our previous study5 with the interface 1504 (metal and glass cone). Specifically, for the small flap size (diameter 8.00 mm), the mean achieved flap diameter was minimally smaller (ie, for the horizontal diameter there was a negative difference of −0.13 mm and for the vertical diameter −0.16 mm).…”

“…The reading error for each measurement was ±1 pixel, which corresponds, based on the resolution of the original images and subsequent conversion, as described in our previous publication,5 to ±0.05 mm of accuracy.…”

“…These images are created by default during the refractive procedure, stored in the system software, and are available for documentation. Digital analysis of such images provided the methodology of flap diameter, as presented in detail in our previous work 5. Flap diameter was thus measured for the horizontal plane (X) along the nasal-temporal line (N-T), as well as for the vertical line of the coronal plane (Y) along the superior-inferior line (S-I).…”

“…In an effort to validate flap precision and accuracy, our team has introduced a digital analysis flap diameter technique during the LASIK operation and prior to flap lifting,5 as well as a flap thickness study,6 examining the FS200 flap thickness characterization achieved with the interface 1504.…”

Essential opaque bubble layer elimination with novel LASIK flap settings in the FS200 Femtosecond Laser

“…Creation of a LASIK flap with a femtosecond laser is considered advantageous to microceratome7,8 for a more centered, higher controlled-geometry, both in depth9 as well as diameter 10. In an earlier effort to validate the precision and accuracy of flap creation, we had introduced a quantitative digital analysis technique for accurate measurement of flap diameter and extent of OBL for flaps created using the Alcon/WaveLight FS200 femtosecond laser during LASIK and prior to lifting of the flap 10…”