Body processes

Microsaccades – Function, Task & Diseases

Microsaccades

The microsaccades are minimal movements of the eyes that play a crucial role in visual perception. Without one microsaccade per second, the brain does not achieve visual perception, since only microsaccades cause the light to shift on the retina . This shift is important for the retina’s receptors to relay visual information to the brain.

What are microsaccades?

There are different types of eye movement . One of them is fixation , which corresponds to the eye resting on a specific fixation point. However, even when the eye is in apparent unmoving fixation, micro-movements are still taking place every second. Such micro movements are called micro saccades.

The eye performs between one and three microsaccades per second. With these jerky flash movements with amplitudes between three and 50 angular minutes, the incident light is shifted on the retina. Ultimately, visual perceptions are only possible through these microsaccades. The receptors on the retina of the eyes react primarily to changes in light. The shifting of light from one receptive area of ​​the retina to the next allows the receptors to respond and ultimately enables vision .

The term ‘ local adaptation ‘ describes a visual phenomenon that allows people to perceive fixed stimuli in the visual image, but does not perceive them as fixed. This effect occurs under certain environmental conditions. The fact that humans have no visual perception problems in everyday life due to the local adaptation of the eyes is in turn related to the microsaccades.

function & task

The amplitude of microsaccades is between five and 50 arc minutes. In microsaccades, the maximum speed of the movement depends linearly on the distance. It is therefore around eight degrees/s for amplitudes of five arcminutes or more. Analogously, it is about 80 degrees/s with amplitudes of around 50 minutes of arc. Microsaccades either correspond to low-velocity drifts or are part of the so-called micromovements under the eye movements. As part of the micro-movements, the saccades are also called the micro-tremor part of the movement. 

Each microsaccade reorients the lines of sight to the fixed point. Physiologically, the eyes constantly deviate from fixed points through drift movements in order to avoid the phenomenon of local adaptation. The microsaccades are therefore one of the most important components of visual perception. They ensure that the eye also transmits constant visual stimuli from the environment to the brain and does not filter them out as part of local adaptation.

Local adaptation is necessary because without it, people would constantly perceive the fine veins of their own eyes above the stimuli from the environment. Humans are among the eye-controlled creatures that find their way around in their environment primarily by means of visual perception. The fact that they can do this is sometimes due to phenomena such as local adaptation and microsaccades.

Typically, microsaccades occur one to three times every second. The respective rate depends on the person and is also related to influencing factors such as tiredness .

Science now assumes that similar neuronal processes play a role in the generation of microsaccades as in the generation of saccades. The movements appear to be based on common neuronal structures. The drifting movements of the eye from a fixation point are just as automatic and involuntary as the corrective microsaccades that realign the eye to the fixation point. These processes are rarely consciously perceived and take place in periods of less than a second.

Diseases & Ailments

Microsaccades are clinically relevant , especially in connection with paralysis of the eye muscles . In most cases, paralysis of this type is associated with neurological diseases and thus corresponds to neuronal lesions in the supply area of ​​the affected muscles. 

When the eye muscles are paralyzed, microsaccades can sometimes no longer take place. This can have fatal consequences for visual perception. Since the receptors on the retina (retina) react almost exclusively to changing light conditions, microsaccades cause the light on the retina to shift. If microsaccades can no longer take place, only constant light stimuli reach the eyes with a fixed head position. This phenomenon is accompanied by an absolute loss of all vision. There is also talk of vision loss due to receptor fatigue. In this way, a patient with paralyzed eye muscles would become temporarily blind if his head were fixed from the outside. Head movement can shift light stimuli on the retina in a manner similar to microsaccades.

A doctor can understand the paralysis of the eye muscles by fixing the head, since the microsaccades prevented by the paralysis in this position would lead to temporary blindness. The light constantly falling on the retina is not shifted to different receptors without microsaccades, which primarily affects peripheral vision in the corner of the eye. The receptive retinal fields on the retina cells in the periphery are too large for a change in the incident light stimuli to be possible within the framework of other micro-movements.

In the central field of vision, the shifting of the light stimuli can possibly take place through other micro-movements, since central cells of the retina are smaller in size than peripheral retinal cells. This makes the receptive fields in the center smaller, so that light stimuli can be shifted more easily.

Lisa Newlon
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Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.