What is the reason for Fatigue Nystagmus beginning?

Fatigue Nystagmus occurs when the eyes are held at maximum deviation for an extended period, specifically when they are held in that position for more than 30 seconds. This prolonged position causes the eye muscles to become fatigued, leading to the involuntary jerking motion known as nystagmus. Holding the eyes at maximum deviation allows for the detection of this phenomenon, as the sustained position tests the limits of the ocular muscles and results in changes in the way the eyes react.

The other options do not correctly identify the necessary duration for fatigue nystagmus to manifest. While maximum deviation is required, the specific time is crucial, as anything less than 30 seconds is insufficient to induce the fatigue response in the eye muscles. Additionally, while rapid eye movement and drowsiness can be related to various eye or neurological functions, they do not specifically explain the onset of fatigue nystagmus itself.