Optokinetic nystagmus

Optokinetic nystagmus

As optokinetic reflex (OKN) a natural movement is reflex of the eye called a nystagmus (nystagmus), which is not morbid, but a normal response of the visual system is to stabilize the image.

The reflex is made up of two phases of opposing eye movements of different speeds: The slow phase, in which the moving environment is viewed with a subsequent movement , the speed of which roughly corresponds to that of the moving stimulus, ensures a relative stabilization of the image position in the foveolar area of ​​the retina (retina). The fast phase, a saccade , then brings the lines of sight back to their original position against the retinal image shift. The direction of impact of the nystagmus is named after this rapid return movement. A right hand OKN, for example, consists of a slow movement of the eyes to the left and a quick return movement to the right. The reflex can be observed, among other things, when the passing landscape is viewed from a train window ("railway nystagmus ").

There are two processing pathways for triggering this response: cortical and subcortical. In the cortical path, the visual information is passed from the retina via the corpus geniculatum laterale into the visual cortex (MT, mediotemporal area). From there there are projections to the pretectum , from which the nuclei of the eye muscle nerves in the brain stem can be controlled. The subcortical path projects directly into the area pretectalis , where both systems are coupled.

Smaller moving image sections are sufficient for the cortical path. In order to address the subcortical path, there must be extensive movement of the environment. This can be explained using the example of “railroad nystagmus ”: If you look out of the window lost in thought, your eyes perform what is known as staring nystagmus. It is characterized by relatively short follow-up phases. But if you suddenly see something interesting, or if you try to find out where you are, the eyes perform the looking nystagmus, in which the subsequent phases are very long and the speed of the eyes corresponds very well to the speed of stimulation.

In contrast to this, vestibular compensatory movements such as the vestibulo-ocular reflex serve to compensate for short-term and rapid rotational accelerations in order to avoid "wobbly images". The vestibular triggered and the optokinetic reflexes complement each other with their services for image stabilization.

In many mammals, the OKN can only be triggered in the temporo-nasal direction (from the outside in) when viewed monocularly, but in humans it can be triggered in both the temporo-nasal and the naso-temporal direction. The naso-temporal direction must first be learned, however, it is not yet answered in infants.

Disorders of optokinetic nystagmus can be signs of neurological disorders or symptoms of a supranuclear eye movement disorder .

literature

• Herbert Kaufmann (Ed.): Strabismus. With the collaboration of Wilfried de Decker et al. Enke, Stuttgart 1986, ISBN 3-432-95391-7 .

This article is about a health issue. It is not used for self-diagnosis and does not replace a diagnosis by a doctor. Please note the information on health issues !