Freiburg Vision Test  ‘FrACT’
by Prof. Michael Bach – FAQ


I have a question not covered here
  1. Take a look at the Manual 😇
  2. If that does not answer your question, don’t hesitate to email me:
How do I find out about FrACT₁₀’s version?

The version will only increment when I make major changes. However, the release date is updated whenever anything changes. Find the release date at the main screen, top right; or use the About button – there not only FrACT₁₀’s version date is given but also the versions of embedded frameworks. The export format has its own version scheme, the exported data set starts with this version number; this allows your analysis software to easily deal with changes here.

How do I show FrACT₁₀ on a second screen?

When the window is on the second screen, you can use the Fullscr. button to go fullscreen. Also note: repeat size calibration (“plastic card / blue ruler”) on the 2nd screen – its pixel size might be different.

How do I invert the optotype = negative contrast = reversed polarity?

Enter a negative value for the Weber contrast in Settings>Acuity>Optotype contrast, e.g. with the max– button.

Can I use FrACT₁₀ for near / reading acuity?

Yes, but you need a visual display unit (VDU) with really tiny pixels. In the Manual there is a note on display resolution… on this, with examples of suitable VDUs.

What is the lowest possible acuity with FrACT₁₀?

The technical limitation is screen size and distance. Going close and using a large screen can bring you into ultra-low vision range. Then the problem arises if the observer has sufficient vision. Here is a discussion on this.

Can I use mirrors to extend testing distance?

Yes, use Settings>Display Transformation to compensate for the image inversion. [Need to use surface mirrors to avoid double images.]

What is the spatial frequency of the optotype used in the contrast test?

This was a real question… and the answer is difficult. First: it depends on the size (Diameter), defaulf 60’. Second: an optotype (be it letter, Landolt C, tumbling E…) does not have a spatial frequency, rather it is a mixture (I’ve calculated the spectrum but never published it).

I see only a blank screen (or a thin star) when I start the test

I see two possible scenarios:

If nothing rings a bell, use Settings>Set all to defaults: Now you should something, and you can proceed to apply your preferences in Settings.