Microkeratome versus femtosecond flaps: accuracy and complications

PURPOSE OF REVIEW

To update the knowledge on differences between mechanical microkeratome and femtosecond flaps for laser in-situ keratomileusis (LASIK) in terms of accuracy and complications.

RECENT FINDINGS

Corneal flaps created with the femtosecond laser present a more planar architecture and provide greater precision in flap diameter and thickness; a more uniform flap thickness across the flap diameter and it allows the surgeon to programme the angulation of the flap periphery. Femtosecond LASIK flaps are classically related to complications derived from a more intense inflammatory response, such as diffuse lamellar keratitis and transient light-sensitivity syndrome. Newer femtosecond models allow for much lower energy delivery to cut the flap, to the point the overall inflammatory response is not significantly different from the microkeratome. The incidence of complications such as epithelial defect and flap dislocations is higher with microkeratome flaps.

SUMMARY

This review examines the accuracy and complications of flaps created with femtosecond and microkeratome. Both femtosecond and microkeratome are able to create accurate LASIK flaps. Femtosecond LASIK flaps represent significant improvement in morphology and predictability with implications for safety.

Corneal biomechanical properties after LASIK, ReLEx flex, and ReLEx smile by Scheimpflug-based dynamic tonometry

PURPOSE

To evaluate corneal biomechanical properties after LASIK, ReLEx flex, and the flap-free procedure ReLEx smile by Scheimpflug-based dynamic tonometry (Corvis ST) and non-contact differential tonometry (Ocular Response Analyzer, ORA).

METHODS

Patients treated for high myopia (-10.5 to -5.5 diopters, spherical equivalent refraction) more than one year previously at Aarhus University Hospital were included. Treatments comprised LASIK (35 eyes), ReLEx flex (31 eyes), and ReLEx smile (29 eyes). A control group included 31 healthy eyes. Cornea-compensated IOP (IOPcc), corneal hysteresis (CH), and corneal resistance factor (CRF) were measured with ORA. Corneal applanation and deformation were registered with Corvis ST during an air-pulse.

RESULTS

Multiple linear regression analysis showed that CH and CRF were significantly lower after all keratorefractive procedures compared to healthy controls (p < 0.05). No significant differences were observed in CH or CRF between the keratorefractive groups. Corvis ST showed no differences in radius at highest concavity (HC radius), time until first applanation (A1 Time), time until second applanation (A2 Time), and deflection length at highest concavity (HC deflection length) between groups. LASIK treated eyes had significantly shorter time until highest concavity than eyes treated with ReLEx smile (HC Time, p = 0.01). The A1 deflection length was significantly shorter in the keratorefractive groups compared to the healthy controls (p < 0.05).

CONCLUSIONS

Keratorefrative procedures alter the corneal biomechanical properties with regard to corneal hysteresis and corneal resistant factor. The flap-based LASIK and ReLEx flex and the flap-free ReLEx smile result in similar reduction in corneal biomechanics when evaluated by Corvis ST and ORA.