Differences in the corneal biomechanical effects of surface ablation compared with laser in situ keratomileusis using a microkeratome or femtosecond laser
Accepted 6 August 2008.
Purpose
To compare the effects of different flap creation techniques on the biomechanical properties of the cornea in patients having myopic laser refractive surgery.
Setting
UCLA Laser Refractive Center of the Jules Stein Eye Institute, Los Angeles, California, USA.
Methods
In this retrospective case series, eyes that had myopic laser refractive surgery were categorized according to the type of flap creation: mechanical microkeratome (MK) LASIK (n = 32), femtosecond laser (FSL) LASIK (n = 32), or no flap creation (PRK) (n = 33). The preoperative central corneal thickness, intraoperative flap thickness, and planned ablation depth (AD),and the preoperative and postoperative manifest refraction spherical equivalent, corneal hysteresis (CH), and corneal resistance factor (CRF) were recorded.
Results
The mean change in CH (ΔCH) was 2.2 mm Hg, 1.9 mm Hg, and 2.3 mm Hg in the MK, FSL, and PRK groups, respectively. There were no significant differences in AD, ΔCH, or ΔCRF between the 3 groups. The correlation between AD and ΔCH was significant in all 3 groups. The correlation was strongest in the FSL group (r = 0.82, P<.0001) and weaker in the PRK group (r = 0.47, P = .006) and MK group (r = 0.46, P = .008).
Conclusions
The biomechanical measures of CH and CRF decreased similarly after PRK and LASIK using laser or mechanical flap creation. However, LASIK using femtosecond laser flap creation caused a significantly more predictable change in corneal biomechanics, which correlated strongly with AD, than the change with PRK and LASIK with microkeratome flap creation.
From the Jules Stein Eye Institute (Hamilton, Johnson), David Geffen School of Medicine at UCLA, Los Angeles, California, and Temple University School of Medicine (Lee), Philadelphia, Pennsylvania, USA; Department of Ophthalmology (Bourla), Goldschleger Eye Institute, Sheba Medical Center, Tel Hashomer, Israel
Corresponding author: D. Rex Hamilton, MD, MS, Cornea and External Disease Division, Jules Stein Eye Institute, UCLA, 100 Stein Plaza, Los Angeles, California 90095, USA.
No author has a financial or proprietary interest in any material or method mentioned.
Presented at the ASCRS Symposium on Cataract, IOL and Refractive Surgery, San Diego, California, USA, April 2007.
Fei Yu, PhD, statistician at the Clinical Research Center, Jules Stein Eye Institute, performed all the statistical analyses.
ABSTRACT