Hi YL
I agree with many of the points Dr Chan has mentioned.
Very simply, the doctor is more important than the machine in many ways. A good, experienced doctor will automatically use a good machine, and also be good at all the other non machine aspects of the procedure such as planning the treatment, the manual parts of the surgery as well as taking care of potential complications. It's also important that the doctor knows all the ins and outs of the machine (which ever he or she uses) so that he/she can troubleshoot any problems quickly as t and make the most of the particular machine's capabilities.
Having said all that, there are differences between machines.
However, the biggest differences are between generations of machines, rather than within generations of machines. If you are into photography you could draw an analogy where there are more differences between a Nikon D4 and D5 than between say the D5 and a Canon 1Dx Mk II.
And I would consider all the machines you have mentioned to be of the same, current generation. Yes, each has their strengths and weaknesses, but in the right hands, the visual outcome for a particular patient is likely to be very similar regardless of the machine used.
Personally, I am most familiar with the iFS and the Schwind Amaris 750s, so perhaps I will just say a few things about these machines.
The iFS is a femtosecond laser (like the Ziemer) and is used to create LASIK flaps. Its strengths are flaps that are relatively easy to lift, and that tend to be larger rather than smaller. Owing to relatively stronger suction pressures, it is less likely that the dreaded 'suction loss' occurs, which may necessitate repeating the flap creation or converting to a surface ablation procedure. The iFS allows real time monitoring of flap creation, so that the procedure can be stopped at any time a problem is noticed. On the other hand, the strong suction pressures make it somewhat more likely that some patients may get 'subconjuntival haemorrhages' or little red spots on the eye after the procedure.
The Schwind Amaris' strengths are fast speed, topography or wavefront guided capabilities, as well as both static and dynamic cyclotorsion control. The latter allows more accurate astigmatic and wavefront corrections, and is a capability I particularly value.
As you can see, it all gets rather technical and complicated. It is likely that many people will still be rather confused with all the facts laid out in an answer here.
At the end of the day, find a doctor that you trust and that you are comfortable with. The doctor should be able to offer you a range of different surgical options, like LASIK vs epiLASIK/PRK vs ICL surgery, so that he/she can offer you something that suits you best. You can check what machines he or she uses, but I think as long as it is a current generation machine (like the ones you mentioned above), don't get too caught up in the marketing spiels.
