Femtosecond laser versus mechanical microkeratomes for flap creation in laser in situ keratomileusis and effect of postoperative measurement interval on estimated femtosecond flap thickness
Received 21 February 2008; received in revised form 27 November 2008; accepted 24 December 2008.
Purpose
To prospectively compare laser in situ keratomileusis (LASIK) flaps created with a femtosecond laser or a mechanical microkeratome and analyze the effect of the postoperative measurement interval on estimated femtosecond flap thickness using ultrasound (US) pachymetry.
Setting
Department of Ophthalmology, University Hospital of Coimbra, and Coimbra Surgical Centre, Coimbra, Portugal.
Methods
Flaps were created with a Hansatome Zero Compression microkeratome (Group 1), Zyoptix XP keratome (Group 2), or IntraLase 60 kHz femtosecond laser (Groups 3 and 4). Flap thickness was determined by intraoperative US pachymetry immediately after flap creation in Groups 1, 2, and 3. In Group 4, pachymetry was performed 20 minutes after the laser treatment. The main outcome measures were flap thickness and deviation from the target value.
Results
Eighty patients had LASIK for myopia or myopic astigmatism. The mean flap thickness was 149.1 μm ± 24.9 (SD) in Group 1, 124.7 ± 23.8 μm in Group 2, 143.1 ± 18.4 μm in Group 3, and 115.5 ± 12.5 μm in Group 4. The difference in flap thickness between Group 3 and Group 4 was statistically significant (P<.01). The flap thickness deviation from the target value was 22.8 μm in Group 1, 19.0 μm in Group 2, 26.1 μm in Group 3, and 10.4 μm in Group 4.
Conclusions
Results indicate that the time of measurement after femtosecond affects the estimated flap thickness. Waiting 20 minutes after laser treatment permitted easier separation and may eliminate the effect of variable corneal dehydration on flap measurement by subtraction pachymetry.
From Hospital da Universidade de Coimbra (Rosa, Neto Murta, Quadrado, Tavares, Lobo), Universidade de Coimbra, Centro Cirúrgico de Coimbra (Neto Murta, Quadrado, Van Velze), and Instituto de Oftalmologia Dr. Gama Pinto (Castanheira-Dinis), Portugal
Corresponding author: Joaquim Neto Murta, Centro de Responsabilidade de Oftalmologia do Hospital da Universidade de Coimbra, Praceta Mota Pinto, 3049 Coimbra, Portugal.
No author has a financial or proprietary interest in any material or method mentioned.
Presented in part at the XXV Congress of the European Society of Cataract & Refractive Surgeons, Stockholm, Sweden, September 2007.
ABSTRACT