The following demonstration presupposes some familiarity with the principles of rarebit perimetry, as outlined in the RBP overview.
The demonstration differs from the regular test in several important respects:
To minimize distractions, the demo is presented in a separate full-screen window. Click on the fixation mark to start a test. Note that the fixation mark gradually diminishes in size, signalling a pending presentation. Each presentation usually comprises a pair of rarebits, oriented vertically or horizontally. However, about 20% of the presentations are control presentations and comprise one rarebit only, or none at all. Indicate the number of rarebits seen by double-clicking for two targets and single-clicking for one, using the left mouse button. Do not click if no target is seen. Make sure the cursor is placed inside the test area outline and not in the surrounding area: clicks in the surrounding area are not recorded. Clicks on blank presentations, and double-clicks on single-dot presentations, will be recorded as errors.
The demo will run over the test quadrants three times, in random order. This takes about 20 s. The demo then stops and displays the results. To continue testing, left-click in the center of the display area. A full demo comprises five passes. Testing can be aborted at any time by tapping the keyboard function key F5. (The regular RBP test also runs in passes. Each pass probes 6 locations in each quadrant. This requires about 60 s. The subject can then rest as needed. The number of passes should be adapted to subject endurance and to the clinical need. The recommended number of passes equals five.)
Suggested test distance is 0.5 m. By altering the test distance, and possibly rotating the display screen, additional locations in the visual field can be accessed. The rarebit diameter is approximately 1.5 pixels. This is larger than the ideal but allows demonstration of the test principles also in displays with a limited contrast, for example, some laptop computers.
To use the demo as a real test, it is necessary to work in a darkness.