Because the device simultaneously checks the fixation, the localization of disturbances and failures can be precisely assessed.
During this measurement the patient fixes a red cross in the device. Spontaneously, different bright light spots light up one after the other. As soon as the patient perceives a point, he/she confirms this by pressing a button. The same spot is further examined with gradually reduced light intensity in order to measure the sensitivity of the retina to light at this spot. If a point does not respond even with bright light points, the device registers a failure there.
The measurement is made monocularly and takes about 10 to 20 minutes, depending on the number of measurements to be repeated and the fixation.
Mostly this method is used to assess a macular hole (hole in the area of the visual center).