Comparison of 2 femtosecond lasers for laser in situ keratomileusis flap creation

 

Meaning

A femtosecond laser for LASIK flap creation is a near-infrared pulsed laser that photodisrupts corneal tissue in a controlled plane to create a thin corneal flap. Femtosecond flap creation replaced mechanical microkeratomes for many surgeons because it improves flap thickness predictability, allows more precise flap geometry (diameter, hinge, side-cut), and generally reduces some blade-related complications. aaojournal.org+1

Introduction

Creating a predictable, uniform flap is critical for safe, precise LASIK. Different femtosecond platforms use different optics/pulse strategies and patient interfaces, which influence intraoperative factors (pressure on the eye, speed), flap morphology (thickness accuracy, stromal surface roughness), and short-term recovery. Two widely discussed platforms are IntraLase (various models/Hz generations; historically popular) and VisuMax (ZEISS—also used for SMILE and noted for its curved interface and low pulse-energy/high frequency optics). aaojournal.org+1

Quick comparison table (high level)

  • IntraLase (typical characteristics): flat applanation patient interface, mid/low rep rate (historically 30–150 kHz across generations), higher single-pulse energy relative to some modern systems; excellent flap predictability and stromal bed quality reported in several studies. aaojournal.org+1

  • VisuMax (typical characteristics): curved (non-applanating or minimally applanating) interface that preserves corneal curvature, high numerical aperture optics, low single-pulse energy with very high repetition rate; marketed for gentler application (lower transient IOP), high precision, and versatility (SMILE + Femto-LASIK). Zeiss+1

Advantages

IntraLase

  • Very predictable flap thickness across many generations; historically set the standard for femto-LASIK consistency. aaojournal.org

  • Good stromal bed smoothness in some studies (improves flap lift and may impact interface healing). Healio Journals

  • Wide clinical experience and a large body of outcome data. aaojournal.org

VisuMax

  • Curved patient interface → less corneal applanation and generally less transient intraocular pressure rise during docking (patient comfort and ocular perfusion considerations). ClinicalTrials.gov+1

  • Low-energy, high-repetition pulse strategy can produce very precise Z-axis spot placement (fine control of flap plane) and is associated with fast cutting and smooth side cuts. CRSToday

  • Very flexible flap parameter settings and fast treatment times on newer models; also used for SMILE (added capability). Zeiss

Disadvantages

IntraLase

  • Older applanating designs flatten the cornea during docking, which transiently raises IOP more than curved interfaces — relevant in glaucoma/fragile eyes. ClinicalTrials.gov

  • Some older IntraLase generations used higher single-pulse energy which can produce more gas bubble formation or microcavitation artifacts vs some low-energy systems (this depends on model/generation). aaojournal.org

VisuMax

  • The curved interface requires precise centration and alignment; learning curve exists for surgeons transitioning from flat applanation devices. CRSToday

  • Device cost, maintenance, and need for trained staff may be limiting for some practices (true of most premium femto platforms). (manufacturer pages and clinical adoption notes). Zeiss+1

Challenges (shared + platform-specific)

  • Flap thickness variability: Even with femtosecond lasers, small deviations occur; different lasers and parameter sets produce different variability and bias (some studies show one platform produces statistically thinner or thinner-but-more-consistent flaps than another). Surgeons must account for this when planning residual stromal bed. PubMed Central+1

  • Interface gas bubbles/opaque bubble layer (OBL): Gas bubbles can transiently obscure the pupil or interface and are influenced by energy, spot/line separation, and interface geometry. Surgeons use parameter tweaks and techniques (gas venting) to reduce OBL. us.alconscience.com

  • IOP elevation during docking: Flat applanation systems tend to increase IOP more than curved interfaces — important in eyes with optic nerve vulnerability. Monitoring and minimizing compression time are important. ClinicalTrials.gov+1

In-depth technical & clinical analysis

1) Patient interface and intraocular pressure

  • IntraLase (flat applanation): flattens the cornea against a flat plate to stabilize the eye; this reliably creates the treatment plane but generates higher transient IOP during docking. Several trials and device descriptions note the higher applanation pressure relative to curved interfaces. ClinicalTrials.gov+1

  • VisuMax (curved interface): docks to the natural corneal curvature, reducing the degree of flattening required and producing lower IOP spikes during flap creation. This is often marketed as more “patient-friendly”. Clinical measurements and device literature support reduced IOP elevation with curved interfaces. Zeiss+1

Clinical implication: For patients with borderline optic nerves or concerns about transient IOP, a curved interface may be preferable. For routine eyes both approaches are widely used.

2) Pulse strategy, optics and tissue effects

  • Pulse energy & repetition rate: VisuMax uses very small focal spots and high numerical aperture optics, allowing lower single-pulse energy and high repetition — this reduces collateral mechanical disruption and can improve Z-axis accuracy. IntraLase earlier models used larger single-pulse energy and lower rep rates; newer generations have improved. CRSToday+1

  • Stromal bed roughness: Studies using AFM and microscopy show differences in stromal surface microtopography between platforms; some studies found one platform produced a smoother stromal bed than another (results vary by model and study). For example, a PLoS ONE AFM study indicated differences in roughness between VisuMax and certain IntraLase configurations. PLOS

Clinical implication: Stromal roughness may theoretically affect early visual recovery and interface healing, but long-term visual acuity outcomes between modern femtosecond platforms are often similar.

3) Flap thickness accuracy & predictability

  • Multiple comparative studies report small differences: some femto models (e.g., Femto LDV, some IntraLase generations) gave highly accurate flaps, while others (e.g., FS200 vs IntraLase in some series) showed statistically different achieved thickness means. Differences are commonly on the order of a few microns but can be clinically relevant when planning very thin flaps. PubMed Central+1

Clinical implication: When planning very thin flaps (e.g., <90 µm), pick a platform and parameters with demonstrated predictability in the surgeon’s hands and institute intraoperative pachymetry or conservative planning to avoid compromising the residual stromal bed.

4) Visual recovery and complications

  • Short-term visual recovery (first days) may vary slightly between platforms depending on flap thickness, microfolds, or interface healing; many studies show differences in day-1 vision that equalize by 1–3 months. Overall safety profiles for modern femtosecond platforms are excellent and superior to blade microkeratomes for many metrics. PubMed Central+2PubMed Central+2

5) Surgeon workflow, flexibility and additional capabilities

  • VisuMax: used also for SMILE (lenticule extraction) — gives additional procedure options in a practice. Newer VisuMax models emphasize speed and digital alignment aids. Zeiss+1

  • IntraLase: long track record and many parameter presets; widespread familiarity among cataract/refractive surgeons. Device selection often depends on surgeon preference, cost, and existing practice patterns. aaojournal.org

Practical points for surgeons / patients

  • Device choice should reflect specific goals: extremely thin flaps → use a platform with demonstrated thin-flap predictability; patients with optic nerve vulnerability → consider curved interface to reduce IOP rise; practices seeking SMILE capability → VisuMax offers that option. Taylor & Francis Online+2Zeiss+2

  • Parameter optimization (energy, spot/line separation, flap diameter/hinge) and surgeon technique are as important as the device brand for final outcomes. us.alconscience.com

Conclusion

Both IntraLase and VisuMax are excellent femtosecond platforms for LASIK flap creation, but they differ in optics and patient interface philosophies. In general:

  • VisuMax (curved dock, low-energy/high rep) tends to cause less transient IOP rise, can give very precise spot placement, and offers SMILE capability — attractive for patient comfort and modern refractive suites. Zeiss+1

  • IntraLase (flat applanation, historically higher single-pulse energy, various Hz generations) has extensive outcome data and has produced very accurate, smooth flaps in many studies; different generations vary in performance and side-effect profiles. aaojournal.org+1

Ultimately, surgeon experience, chosen parameters, and case selection determine outcomes more than brand alone. When switching devices, surgeons should audit their own outcomes (flap thickness accuracy, OBL incidence, early visual recovery) to refine parameters. PubMed Central+1

Short summary 

IntraLase and VisuMax both create precise LASIK flaps but use different approaches: IntraLase typically uses flat applanation and has long outcome data for predictable flaps, while VisuMax uses a curved interface with low-energy, high-rep pulses that produce less transient IOP rise and very precise cuts. Choice depends on flap thickness goals, ocular risk factors, surgeon preference, and whether SMILE capability is desired. aaojournal.org+1

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