Fig. 3.

Technical difficulties that are often encountered when recording the ERG. (A) Top row. Transient responses are often associated with albino animals and light-adapted retinas, but the peak response amplitude from light-adapted retinas in normally sighted mice is less than in albino mice. Bottom Row. Inverted responses can either result from genuine genetic defects such as the mutations in nyctalopin or mGluR6 (lower left). However inverted b- and c-wave responses can also occur for reasons related to the condition of the mouse, a situation that can often be clarified by retesting the mouse. (B) Top row. Excess saline in contact with metal electrodes can cause large, unstable liquid junction potentials and poor electrical contact can cause distortion and instability of recording. Middle row. A mouse with advanced retinal degeneration will have no response whatsoever (middle left, Noerg-1, note higher amplification of trace) but the baseline of the recording will not be as quiet as when the amplifier is not connected to the mouse. A normal mouse that is not presented with a stimulus (middle right) will produce a recording with a similar baseline. Lower row. The cone or light-adapted ERG is recorded in the presence of a steady adapting light, in this case from an LED. However, some LEDs lose their ability to produce a steady light after some use and in this instance the light adaptation will be incomplete, resulting in a larger than normal cone ERG