This article is more than 5 years old. Information may no longer be current.
Femtosecond LASIK flaps produce more predictable changes in corneal biomechanics
J Cataract Refract Surg. 2008;34(12):2049-2056.
Click Here to Manage Email Alerts
LASIK with femtosecond laser flap creation produced more predictable changes in corneal biomechanics than LASIK with microkeratome flap creation or surface ablation. Changes correlated closely with ablation depth.
Enhanced understanding of preoperative corneal biomechanics may help surgeons customize refractive surgery and reduce postoperative complications such as keratectasia.
A retrospective case series included eyes that underwent myopic laser refractive surgery and were classified by type of flap creation: mechanical microkeratome (32 eyes), femtosecond laser (32 eyes) and no flap creation in PRK (33 eyes).
Mean changes in corneal hysteresis were 2.2 mm Hg in the microkeratome group, 1.9 mm Hg in the femtosecond laser group and 2.3 mm Hg in the PRK group. The results showed no significant differences in ablation depth, corneal hysteresis or corneal resistance factor between the groups. However, ablation depth and corneal hysteresis correlated significantly in all three groups.
The predictability of changes related to femtosecond laser flap creation may be attributed to precise flap diameter and minimal disruption of anterior and peripheral stromal tissue.
The biomechanical property of the cornea is a science that has been somewhat elusive over the past several years. This paper is an attempt to answer some of these questions. With refractive surgery, one of the goals is to obtain a desired outcome in the absence of complications. Patients that we felt were good candidates for refractive surgery in the late 1990s, were found out to have unstable biomechanical forces that altered the course of surgery with time.
New technology is always open to criticism. The measurement of corneal hysteresis and corneal resistance factor with the Ocular Response Analyzer (ORA, Reichert Instruments) is one such device. Although the device is giving the surgeon another data point, in some instances how we use that information in the “real world” has proven challenging. The paper by Hamilton et al is an attempt to clear the “muddy” water of refractive surgery and corneal biomechanical effects.
The authors note that the retrospective nature of the study is also in question. However, the study appears well thought out and the statistical analysis is thorough. Where the confusion arises is the differentiation of LASIK done with the femtosecond laser vs. that done with a mechanical flap or PRK. Could the PRK patients be those patients with thinner pachymetry and questionable computed topography? The demographics do support that those patients with PRK tended to have thinner corneas.
I think the paper by Hamilton et al is a beginning to help us answer which patients we should not operate on but not the end. With additional research hopefully we can make ectasia a discussion relegated to the history of refractive surgery.
– Karl G. Stonecipher, MD
The Laser Center, Greensboro, N.C.