One important characteristic of pattern stimulations if that the average luminance
should be constant (ISCEV standards for pattern ERG and for pattern VEP).
There should be no change in luminance, even transient when reversing the stimulus of when switching from the "on" to the "off" pattern.
If constant luminance is not achieved, the PERG stimulus generates a response not only from the ganglion cells but also from other layers of the retina. In a similar way the PVEP stimulus activates different types of cortical cells. This may results in a diagnosis error.
Standard LCD monitors produce a transient light flash at each pattern reversal or pattern on-off. This is due to a different velocity of the liquid crystals between the on-off and off-on transitions.
Metrovision's patented technology involves the use of a LED backlight monitor. A light sensor constantly measures the luminance output and adjusts the backlight in real time so as to achieve constant luminance.