Lambda waves occur in the awake state elicited by saccadic eye movements often seen when the patient is visually scanning something, such as a complex geometric pattern, reading or watching TV. This transient activity is associated with eye movements while an individual’s eyes are open, when the alpha PDR is suppressed, therefore they stand out clearly from the background. They have no clinical significance. Lambda waves are bilateral, symmetric, sharply contoured positive occipital waves with a sail-like appearance, very similar to POSTS. The waveform consists of a bi- or triphasic configuration, are often asymmetric and tend to have greater amplitude in the right compared to the left occipital electrode. The amplitude is usually less than 20 to 30μV but could be greater than 40μV in children. Lambda waves are more common in children aged between 2 and 15 years than in adults.
It is generally true that subjects who have prominent lambda waves will also show prominent POSTs and photic responses by slow-frequency (1 to 3 Hz) photic flashes. These are all normal variants and have clinical significance.