A femtosecond laser produces extremely short pulses of laser light which are used to divide layers of corneal tissue.

The accuracy of all femtosecond lasers is adequate to cut a flap of corneal tissue which is then lifted out of the way, allowing the tissue under the flap to be reshaped with the excimer laser, thus correcting the refractive error. This procedure is known as LASIK. However most femtosecond lasers are not accurate enough to correct visual errors by themselves.

Only the VisuMax® laser, used by the Wellington Eye Centre, has sufficient accuracy that it can be used to reshape the cornea for correction of visual errors as well as cut a corneal flap. The VisuMax® laser can therefore be used to perform LASIK like other femtosecond lasers, but it is also able to perform complete laser eye surgery procedures, as in SMILE® surgery.

Carl Zeiss VisuMax®

Competing femosecond laser

Pulse rate

500hz *

60 to 150hz

Pulse energy

100 nanojoules **

Up to 800 nanojoules

Accuracy of cutting 100 micron flap

108 – 112 microns ***

106 – 160 microns

Eye pressure during procedure

Average 84.9mmHg ****

Maximum 104.9mmHg

Average 180 – 285mmHg

Maximum 192 – 328mmHg

Able to correct refractive errors

Yes *****


All data in table is based on published studies.

* Higher pulse rate allows lower pulse energy and shorter procedure time.

** Lower pulse energy results in less tissue damage outside treatment zone.

*** Higher accuracy reduces the risk of flap being too thick and safely allows thinner corneal flaps – this is turn should allow greater corneal stability after laser eye surgery.

**** With a lower eye pressure, the eye remains more comfortable and is able to see during the procedure. A high eye pressure may be associated with damage to the retina.

**** The VisuMax® is the only femtosecond laser which is able to correct refractive errors as well as being able to cut a corneal flap. This has opened the way for truly “flapless” laser eye surgery.