Focus Shift And Defocusing; Focus Shift Control - Zeiss VISULAS YAG III Mode D'emploi

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1

Focus shift control

2 Magnification changer
Fig. 36 Focus shift control
Operation

Focus shift and defocusing

The optimal mechanical effect of the optical breakdown occurs at a
specific distance from the focus of the therapy beam. For this reason,
the aiming beam and therapy beam of the VISULAS YAG III are not
parfocal, but are shifted (focus shift). Depending on the application,
you can select one of three settings:
Posterior:
Labelled as post, switch to the right.
The therapy beam is focused 150 µm posterior to the aiming
beam focus. This setting should only be used for applications in
which the area to be treated is posterior to the tissue to be
protected (see also Fig. 14).
Anterior:
Labelled as ant, switch to the left.
The therapy beam is focused 150 µm anterior to the aiming
beam focus.
This setting should only be used for applications in which the
area to be treated is anterior to the tissue to be protected.
Zero:
Labelled as 0, switch in mid-position.
The therapy beam and aiming beam are focused in the same
plane (parfocal). This setting should only be used for
applications in which there is no tissue which needs to be
protected either directly anterior or posterior to the treatment
region.
The laser is intended for use with the focus in these three positions
only.
Note
Always turn the focus shift control until it clicks into position
(an audible click should be heard).
The focus shift of the VISULAS YAG III is designed for pulse energies of
up to about 1.5 mJ.
If you wish to work with higher energy levels (e.g. for fibrotic
secondary cataracts), you must increase the focus shift distance by
defocusing:
- In switch position ant., you must defocus in the anterior
direction.
- In switch position post., you must defocus in the posterior
direction.
Note
The degree of defocusing required depends on factors such as
the application and the specific conditions of the eye to be
treated. It is therefore not possible to give a general
recommendation.
000000-1354-664 VISULAS YAG III 15.08.2005