Body processes

Troxler Effect – Function, Task & Diseases

Troxler effect

Medicine understands the Troxler effect as the local adaptation of the human eye . Permanently constant light stimuli are perceived by the retina , but do not reach the brain . In everyday life, the micro-movements of the eye constantly shift the light on the retina to enable perception .

What is the Troxler Effect?

The Troxler effect is a visual perception phenomenon . The phenomenon was first described at the beginning of the 19th century. The Swiss doctor and philosopher Ignaz Paul Vitalis Troxler is considered to be the first to describe it, in honor of whom the phenomenon was named.

With the Troxler effect, the retina areas of the eyes adapt to constant stimuli. In this way, peripherally and centrally perceived objects disappear when they remain in a constant position. For this reason, people can no longer recognize constant images on the visual image after a certain period of time.

The Troxler effect is also known as local adaptation . In everyday life, this phenomenon rarely occurs because the microsaccades of the eyes know how to prevent it. These are the lightning-fast gaze target movements of the eyes, which take place one to three times per second. Microsaccades shift the light on the retina, making it possible to see.

The retina’s receptors react almost exclusively to changes in light conditions. Therefore, failure of the microsaccades can result in blindness . Although the receptors also pick up constant light stimuli, they do not necessarily pass them on to the brain.

function & task

Due to the natural anatomy of the eye, there should basically be vast amounts of fine veins in the visual image of every human being. Although these veins can be seen by the eye, the visual constant stimuli do not reach the brain. The veins in the field of vision are resolved by the eye itself, but are not perceived as such by the brain. This connection is based on the Troxler effect. 

Since the veins remain constant and are always in the same position in the field of vision, people do not perceive them as a result of the effect: they are filtered out, so to speak. The constant perception of the anatomical structure would overshadow and alienate the perception of the environment.

Man is one of the eye-controlled creatures. This means that, from an evolutionary point of view, it relies primarily on its visual perception in order to survive. With its eyes it checks its surroundings for dangers and sources of food. In this context, the Troxler effect is of particular importance.

In certain situations, people can notice the fine and constant veins in the visual image. For example, if you poke a tiny hole in a piece of paper with a needle and look through the hole you have made, you may notice the veins. The opening of the hole rotates in a circle and in a radius of about one centimeter around the center when looking through. As the eye rotates, the veins in the eyes cast shadows on the retina. The brain can re-perceive the veins in the form of shadows as a change in visual image.

In order to prevent the Troxler effect in everyday life, the permanent microsaccades of the eye take place, which continuously shift the light on the retina. The Troxler effect occurs primarily with peripheral stimuli, since the receptive fields in the periphery of the retina are far larger than in the center. The smaller the receptive fields, the more the relative impact of the microsaccades becomes apparent.

Diseases & Ailments

The receptors on the retina primarily show a reaction to changes in light conditions. The Troxler effect supports this phenomenon. Consistent light stimuli can thus cause a loss of vision. This loss of vision does not correspond to a total loss, but to a loss of vision due to receptor fatigue, which as a result gives an impression of intrinsic gray and thus corresponds to local adaptation. 

If a patient’s head is held rigid and their eye muscles are paralyzed, temporary blindness can occur due to the Troxler effect. The micro-movements of the eyes are no longer possible after paralysis of the eye muscles and the head position cannot ensure the changes in the light stimuli in the visual image, which allow visual perception to reach the brain. Without microsaccades and the constant shifting of light to different receptors of the retina, seeing is hardly possible. Peripheral vision in particular depends on the microsaccades. The receptive retina fields are too large in the peripheral area to be able to perceive a sufficient change in light through other micro-movements.

Paralysis of the eye muscles can be associated with various diseases. Eye muscle paralysis and thus the failure of microsaccades is often preceded by damage to one or more nerves that supply the eye muscle. A disturbance in the signal transmission between nerve and muscle can also lead to paralysis of the eye muscles and the absence of microsaccades.

Other causes of eye muscle paralysis or eye muscle weakness can be muscle diseases or other types of muscle impairment. These other types of impairment of the eye muscles can be injuries in the context of an accident, for example.

In addition, tumors can compress the nerves of the eye muscles, disrupting signal transmission. Neurological primary diseases are also among the conceivable causes of eye muscle paralysis or paresis, which can cause the microsaccades to fail.

The Troxler effect can help in the diagnosis of eye muscle paralysis. If the patient’s head is fixed and he still does not notice any visual loss, the eye muscles are probably not completely paralyzed.

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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.