Optokinetic Nystagmus Definition, Test, Drum, Pathway

It is an eye related disease in which eyeball moves along with the moving field. In simple words, eye moves if patient focus on the whole scenery moving or rotating. It is not tracking of a single object placed far ahead but it is the tracking of whole field rotating in front. In moving field, there are different targets, so we can say that smooth pursuit is counted under optokinetic nystagmus. Patient tried to move his eyes with the moving object.

One common example of optokinetic nystagmus is: person sitting in a moving car tries to match his eye velocity (vision velocity) with the velocity of moving object. An optokinetic stimulus is used to check movement of eyes. Stimulus should present things moving in both peripheral and central visual fields. The following methods are used commonly to provide stimulus.

• Physical drum beat
• Stripe projector or LCD projector
• Large screen array
• And light bar.

LCD projector is the stimulus which closely matches with the definition of optokinetic nystagmus. All the above mentioned methods are used for eliciting optokinetic nystagmus. Optokinetic nystagmus is also used as a parameter of assessment of visual system. It is used specially in new borns.

Optokinetic Nystagmus Drum

Optokinetic nystagmus can be elicited with an optokinetic drum. The drum is rotated in front of the patient. Patient is asked to focus on the drum movement. Start rotating that drum in front of patient. In case, if optokinetic drum is not available, a simple paper with black and white strips can be used. The strips are at the distance of at least 2 inch. This paper is moved in front of patient horizontally and patient is asked to focus on it. Nystagmus can occur in both adults and infants with normal vision. Visual pathway can be checked with nystagmus.

Optokinetic Nystagmus Test

Optokinetic nystagmus is tested with the help of an optokinetic stimulus. The stimulus used can be LCD projector, stripe projector, large screen aray, light bar or physical drum. LCD projector is the stimulus which matches the definition of optokinetic nystagmus. In physical drum stimulus, an optokinetic drum is used. But in stripe projector, a simple paper sheet is used with black and white lines on it. In LCD projector, a proper video is played and fast forward and patient is asked to focus on it. A light bar is also used as a stimulus, in which a light rod is used to move fastly in front of patient and patient tries to focus on its light.

Optokinetic Nystagmus Pathway

The pathway of nystagmus consists of initial smooth pursuits which means patient start focusing on an object placed far ahead in front of patient. That object works as a stimulus for the vision of patient. When smooth pursuit phase ends, it is followed by fast phase or corrective phase known as saccade. The same pathway is followed in case of optokinetic nystagmus but the time period of each phase becomes extremely short. Normally presence of nystagmus shows normal pathway of vision.