J. Eur. Opt. Society-Rapid Publ. 22, 24( 2026) 255
clinically validated, but also associated with exceptional visual and anatomical outcomes in real-world settings [ 35, 36 ]. Furthermore, personal communication with experienced users of the SCHWIND ATOS system indicates that a single-pulse energy of 75 nJ combined with a spot-track setting of 7.0 2.6 lm performs well in practice, with no perception of clinically relevant tissue bridges during dissection. Assuming a threshold energy of Eth = 40nJanda resulting bubble diameter of 4.9 lm( usingk = 1.5from the Photodisruption model [ 9 ]), these settings correspond to F1 = 0.7, F2 = 1.9, F1F2 = 1.32, andF2 / F1 = 2.69. These values align closely with the proper optimum identified in the present analysis, suggesting consistency between the theoretical framework and practical observations.
The benefits of low energy, asymmetric geometry are underscored by long-term outcome data. In a four-year retrospective study evaluating over 4000 SmartSight procedures, excellent safety and efficacy profiles were demonstrated across a wide range of myopic and astigmatic corrections. Specifically, mean uncorrected distance visual acuity( UDVA) of 20 / 20 or better was achieved in 91.7 % of eyes, with 99.7 % achieving 20 / 40 or better. Furthermore, 96.2 % of eyes were within ± 0.50D of the intended spherical equivalent refraction, and only 0.2 % lost one or more lines of corrected distance visual acuity( CDVA), confirming both predictability and safety over time [ 37 ].
Additional insight into the effects of asymmetric spacing and low-energy parameters is provided in studies examining the physical quality of the lenticule interface. Using ex vivo and imaging analyses, researchers have shown that asymmetric, low-energy cuts produce smoother stromal surfaces and more regular lenticule geometry, compared to higherenergy or symmetric settings. Specifically, no visible tissue bridges or cavitation-related roughness were observed at the interface, and lenticule edge thickness remained welldefined and reproducible across varying cut depths and diameters [ 36 ]. These findings suggest that asymmetric pulse geometry allows efficient tissue separation without overexposure, supporting gentle and controlled dissection. This renders the question how can the“ ease of dissection” be assessed as objectively and quantitatively as possible. Different previous works determined the“ ease of dissection” as a subjective cardinal score [ 38 ]. We believe that one of the simplest objective, and quantitative metrics to determine“ ease of dissection” may be the required dissection time over a series of treatments [ 39 ]. This is simple, objective, and quantitative; and allows to perform statistical comparisons for different approaches.
New scanning technologies for femtosecond laser ophthalmic surgery, such as multi-spot parallel scanning or strip scanning have been proposed [ 40 ]. The potential applicability of these findings to those the new scanning approaches can be discussed. If multi-spot parallel scanning or strip scanning set a fixed distance in one direction, then this work can provide the corridor of distances in the other direction, to balance dose and asymmetry in the best possible region. If multi-spot parallel scanning or strip scanning sets a distance range of selectable distances in one direction, then this work can provide the range of corridor of distances in the other direction, to balance dose and asymmetry in the best possible region. If multi-spot parallel scanning or strip scanning provides fully selectable distances in one direction, then this work can provide the full range of distances in the other direction, to balance dose and asymmetry in the best possible region. Based on these considerations, a practical framework compatible with emerging multi-spot or parallel scanning systems can be outlined. First, the optimum pulse energy should be identified, typically around 1.7 Eth, from which the corresponding bubble size can be inferred. The optimum total dose( F2 F2) may then be selected within identified optimum ranges of 1.3 – 1.6, and the asymmetry ratio( F2 / F1) within identified optimum ranges of 2 – 3.5. Once these parameters are defined, the spot distance can remain fixed to avoid overlap along the pathway, while the dose can be modulated solely by adjusting the track distance. This approach allows energy and spot spacing to remain near their optimal values, while treatment efficiency and tissue separation quality are fine-tuned through a single parameter, track distance, constrained within well-defined limits.
All findings presented in this work are derived from geometric analyses, with no explicit treatment of the temporal domain. Nonetheless, the geometrical principles are consistent with and reinforced by temporal considerations, which we address here.
Bubble dynamics remain a source of uncertainty, as validated estimates of cavitation bubble collapse time in the living cornea are lacking. Reported values vary from ~ 8 – 10 ls for sub-lJenergiesinwaterto ~ 1 ms for multi-lJ pulse energies in ex vivo corneas [ 17, 41 ]. Basedonavailabledata, we reasonably assume that bubble lifetime in the cornea is < 1 ms, scales with bubble size( and thus pulse energy), and is shorter than in water due to the higher substrate fraction. For low pulse energies near threshold, bubbles typically undergo a single expansion – collapse cycle. With low energies(< 100 nJ), lifetimes in the cornea are likely even shorter(< 8 ls), reinforcing the benefits of temporal separation.
For a given dose, asymmetric pulse arrangements, where pulses are closely packed along the spot pathway but tracks are more widely separated( e. g., ELITA, Z8, Johnson & Johnson Surgical Vision, Inc) result in overlapping pulses separated by sub-microsecond intervals( MHz repetition rates), while overlaps between tracks occur over milliseconds. Under these conditions, consecutive pulses interact within the lifetime of cavitation bubbles, limiting their maximum expansion and creating mutual interference. In symmetric configurations( e. g., VisuMax, Carl Zeiss Meditec AG.), both spot and track distances are equal, so pulse-to-pulse overlap remains at the microsecond scale, and track overlaps are in the order of milliseconds, again preventing full bubble development. In contrast, in asymmetric settings( e. g., SCHWIND ATOS, SCHWIND eye-tech solutions GmbH.), where spot distance greatly exceeds track distance, create non-overlapping pulses( ls separation) but overlapping tracks at millisecond intervals. This allows cavitation bubbles to reach their maximum effect without interference from subsequent pulses. The difference across settings spans more than three orders of magnitude(> 1000) in overlap timing, which makes a critical distinction in tissue response.