The Accuracy of Flap Thickness and Diameter in LASIK Using a Femtosecond Laser

Abstract

Purpose

To evaluate the resultant thickness of the WaveLight FS200 (Alcon Vision, LLC) created LASIK flap compared to intended thickness at the surgical visit, using the WaveLight EX500 (Alcon Vision, LLC) pachymeter and the resultant flap diameter compared to intended diameter.

Methods

This single arm, prospective, single surgeon study assessed the accuracy of the intended flap thickness and diameter, after successful bilateral LASIK surgery. The WaveLight FS200 femtosecond laser was used to create all flaps with an intended thickness of 120 μm. Flap thickness was calculated by subtracting the stromal bed thickness after flap lift from the preoperative corneal thickness using the WaveLight EX500 on-board optical pachymeter. Flap diameter was determined using digital analysis.

Results

A total of 58 subjects (116 eyes) completed the study. The calculated mean flap thickness was 120.6 ± 9.0 μm (range 102 to 143 μm) using the EX500 pre- and post-flap pachymetry measurements. There was no statistically significant difference between the planned and achieved flap thickness (p > 0.05). The mean difference in flap diameter between planned and actual was 0.02 ± 0.05 mm. Corneal thickness measured by Pentacam at up to 2 months preoperatively versus EX500 just prior to surgery was similar, with EX500 measuring 2 μm less on average than the Pentacam.

Conclusion

The results suggest that the WaveLight FS200 laser is reliable for LASIK flap thickness and diameter and accurately created flaps at the intended thickness and the intended diameter.

Plain Language Summary

Laser vision correction (LVC) is a popular procedure to treat refractive error and reduce or eliminate the need for spectacles. Laser in situ keratomileusis (LASIK) is one of the most common LVC procedures. With LASIK, a flap is created (using a manual blade or a femtosecond laser) in the cornea (the transparent front of the eye) and lifted to expose stromal tissue. Some of the stromal tissue is then removed by a laser to reshape the cornea and correct refractive error. Creating a flap at the desired thickness and diameter is crucial for good outcomes after LASIK. The purpose of this study was to evaluate the thickness and diameter of LASIK flaps that were created with a femtosecond laser. The results of this study suggest that the femtosecond laser accurately creates a flap at the intended thickness and at the intended diameter.

Keywords:

• LASIK
• WaveLight FS200
• WaveLight EX500
• femtosecond laser
• flap creation

Acknowledgement

This paper was presented at the 2023 American Society of Cataract and Refractive Surgery (ASCRS) Annual Meeting as a conference talk with interim findings.

Disclosure

Stephen Wexler reports consulting fees from Alcon. Brad Hall reports that he has received consulting fees from Ace Vision Group outside of the submitted work.

Additional information

Funding

This study was supported with an investigator-initiated study grant (73058121) from Alcon Vision LLC, Fort Worth, TX, USA.