Alexander's law

Alexander's law is a phenomenon observed in patients with nystagmus, a condition characterized by involuntary, rapid, and repetitive eye movements. This law states that the intensity of the nystagmus increases when the patient looks in the direction of the fast phase of the nystagmus. Conversely, the intensity decreases when the patient looks in the direction opposite to the fast phase. Alexander's law is most commonly associated with vestibular nystagmus, which can be caused by an imbalance in the vestibular signals to the brain from the inner ears.

Overview

Nystagmus can be classified into several types, including vestibular, gaze-evoked, and congenital or infantile nystagmus. Alexander's law is particularly relevant in the context of peripheral vestibular nystagmus, where it is often used as a diagnostic clue. The law is named after Gart Alexander, who first described this observation in the early 20th century.

Mechanism

The exact mechanism underlying Alexander's law is not fully understood, but it is thought to involve the neural integrators that control eye movements. These integrators receive inputs from the vestibular system, among other sources, to generate the sustained eye positions needed for gaze stabilization. When there is a vestibular imbalance, the integrators may overcompensate when the eyes move in the direction of the fast phase, leading to an increase in nystagmus intensity.

Clinical Significance

Alexander's law has significant clinical implications in the diagnosis and management of patients with nystagmus. Observing the changes in nystagmus intensity with different gaze positions can help differentiate between central and peripheral causes of nystagmus. It is also useful in assessing the severity of vestibular dysfunction and monitoring the progress of patients undergoing rehabilitation for vestibular disorders.

Treatment

Treatment of nystagmus and associated conditions that exhibit Alexander's law involves addressing the underlying cause. In cases of vestibular nystagmus, vestibular rehabilitation therapy (VRT) may be beneficial. VRT is a specialized form of therapy that aims to restore vestibular function and improve gaze stability through a series of exercises. Medications may also be used to manage symptoms in some cases.

See Also

• Nystagmus
• Vestibular system
• Vestibular rehabilitation therapy
• Eye movement