Korean J Ophthalmol.  2011 Feb;25(1):8-14. 10.3341/kjo.2011.25.1.8.

Factors Influencing Corneal Flap Thickness in Laser In Situ Keratomileusis with a Femtosecond Laser

• Kim CY
• Song JH
• Na KS
• Chung SH
• Joo CK

• KMID: 994405
• DOI: http://doi.org/10.3341/kjo.2011.25.1.8

Abstract

PURPOSE
To evaluate factors responsible for the variability between intended and achieved corneal-flap thickness during femtosecond laser-assisted laser in situ keratomileusis (LASIK).
METHODS
A prospective, nonrandomized, case study was performed on 35 eyes of 18 consecutive patients who underwent LASIK surgery using the 60 kHz femtosecond laser microkeratome. Eyes were assigned to three different thickness groups, with 110-, 120-, or 130-microm cut depths. Anterior segment optical coherence tomography was used to assess the morphology of 35 LASIK flaps at postoperative one week postoperatively. The flap thickness was assessed at seven measuring points across each flap. Patient age, preoperative spherical equivalent, manual keratometry, preoperative central pachymetry, and regional variability of the cornea were evaluated to determine where they influenced the achieved corneal flap thickness.
RESULTS
Cuttings of all flaps were easily performed without any intraoperative complications. Flap-thickness measurements had a mean of 115.21 +/- 4.98 microm (intended thickness, 110 microm), 121.90 +/- 5.79 microm (intended, 120 microm), and 134.38 +/- 5.04 microm (intended, 130 microm), respectively. There was no significant difference between the 110-microm and 120-microm groups when compared with the 130-microm group (one-way analysis of variance test, p > 0.05). Patients' age, preoperative spherical equivalent, manual keratometry, and preoperative central pachymetry did not affect the achieved flap thickness (Pearson correlations test, p > 0.05). The reproducibility of flap thickness in the central 1.5-mm radius area was more accurate than that in the peripheral 3.0 to 4.0-mm radius area (paired samples t-test, p < 0.05).
CONCLUSIONS
Femtosecond laser-assisted LASIK is likely to reproduce a reliable thickness of the corneal flap, which is independent of corneal shape factors or refractive status. Future studies should focus on variations in corneal biomechanical factors, which may also play an important role in determining flap thickness.

Keyword

Corneal flap thickness; Femtosecond laser; Laser in situ keratomileusis

MeSH Terms

Adult
Cornea/*surgery
Female
Humans
*Keratomileusis, Laser In Situ
*Lasers, Excimer
Male
Myopia/physiopathology/surgery
Postoperative Period
Prospective Studies
Refraction, Ocular
*Surgical Flaps
Visual Acuity
Young Adult

Figure

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  Fig. 1 Example of a horizontal cross-sectional optical coherence tomography image of the cornea. The calipers are located at the seven measurement points.

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  Fig. 2 Increasing the intended thickness by 10-µm increments increased the mean achieved thickness. The mean achieved flap thickness in the central 1.5-mm radius area was thicker than that in the peripheral 3.0 to 4.0-mm radius area.

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  Fig. 3 Correlation of achieved flap thickness and age, preoperative spherical equivalent, keratometry, and pachymetry.

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  Fig. 4 Preoperative and one-month postoperative mean uncorrected visual acuity (UCVA).

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  Fig. 5 Preoperative and one-month postoperative mean spherical refraction.

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  Fig. 6 Preoperative and one-month postoperative mean cylinder refraction.

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