Final answer:
Post Rotary Nystagmus happens after a person stops spinning, where their eyes move in the opposite direction of the head rotation to stabilize the visual field through the Vestibulo-Ocular Reflex. Deficiencies in this reflex can be due to vestibular damage or brain stem issues, impacting the accommodation-convergence reflex needed for focusing on near objects.
Step-by-step explanation:
Post Rotary Nystagmus (PRN) occurs following a brief, intense period of vestibular stimulation, such as spinning in a chair. After stopping the spin, the Vestibulo-Ocular Reflex (VOR) works to stabilize the visual field, as the eyes attempt to compensate for the continued sensation of spinning by moving in the opposite direction of the perceived spin. Vestibular damage, such as in Ménière's disease, or damage to the dorsal brain stem affecting the eye movement nuclei or their connections through the Medial Longitudinal Fasciculus (MLF), can lead to deficits in the VOR, resulting in impaired PRN. It is important to understand the coordination of gaze control how the medial recti muscles control convergence and accommodation.
The parasympathetic fibers of the oculomotor nerve are instrumental in altering the shape of the eye's lens to focus on stimuli that move closer to the face, a process known as accommodation-convergence reflex. With age, this process can be affected and may necessitate corrective lenses.