Periodic Alternating Gaze (PAG) on Physical Exam



Periodic Alternating Gaze (PAG) is an involuntary continuous cyclic horizontal sustained conjugate deviation of the eyes, which alternates sides with a cycle of 1–2 min.

Periodic alternating nystagmus (PAN) is a spontaneous horizontal nystagmus that periodically reverses every 1–2 min, with fast phases alternating between left and right sides, separated by null phases. PAG & PAN are rarely seen together.

However, PAG and PAN share a similar time constant and a common pathological mechanism (instability of the velocity‑storage mechanism [VSM]) of the cerebellum. The VSM is like a wind up clock that stores rotational information beyond the capacity of the semicircular canals and releases it after prolonged rotation.



Dr. Boby Varkey Maramattom @bobvarkey



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