NYSTAGMUS (Eye Disorder)

Posted: Sat Nov 22, 2008 9:29 pm

( Often found in Siamese cats and Himalayan cats )
Disturbed vestibular input to the neurons innervating extra-ocular eye muscles results in abnormal nystagmus. Nystagmus probably occurs at some time during all types of vestibular disease. Nystagmus is an involuntary rhythmic oscillation of the eyeball that nearly always affects both eyes equally. Typically, nystagmus consists of a slow phase in one direction and a fast phase in the other. It is customary to describe nystagmus in terms of the fast phase, despite the fact that in most cases the slow phase will be directed towards the affected side. Nystagmus tends to occur early in the course of peripheral vestibular disease, and to disappear later.

Physiological nystagmus may be induced in normal animals. It occurs with normal turning of the head from side to side, or up and down (vestibular in origin), or after rotation (post-rotational nystagmus). If nystagmus occurs when the head is stationary, and there is no rotation or movement of the surroundings, it is called spontaneous nystagmus. Spontaneous nystagmus is usually pathological in origin and may be horizontal, rotatory, or vertical in direction. If nystagmus occurs only when the head is placed in an unusual position (e.g., laterally or dorsally), it is known as positional nystagmus. Nystagmus that consists of eye movements of the same velocity in each direction is termed pendulous nystagmus, and is not of vestibular origin. Pendulous nystagmus is usually associated with visual deficits.

Ref: Thank you Joane for this contribution in the Library Section