Sideline

Secondary directions are always based on a main direction of vision (fixation). They differ from each other by different spatial values ​​and are important for the development of the sense of space. A rearrangement of the secondary directions always causes a change in perception in the room.

What is the secondary direction?

A secondary viewing direction is defined as a subjective viewing direction that deviates from the main viewing direction. It forms a line between an object and a point on the retina. In doing so, it passes the approximate optical center of the eye, which all light rays cross.

There are many secondary directions but only one main direction. The image of a fixed object falls on the center of the retina, the fovea centralis (also called foveola). There is the point of sharpest vision, because the resolution is best here due to the high density of cones. What is depicted on the fovea centralis subjectively conveys the feeling of looking directly at it and forms the spatial value straight ahead. It is the main direction.

All other objects in the field of vision are perceived spatially relative to this main viewing direction. Extrafoveolar stimuli are set that are perceived as secondary directions. The image of an object then takes place on a different retinal site than the fovea centralis. The visual acuity is noticeably lower in all these other places. As a result, an object in the secondary viewing direction is seen blurred and its spatial value is not straight ahead.

Function & task

The function of a secondary view consists in the formation of spatial values ​​by relating the objects shown on the retina to one another. Spatial values ​​in turn determine the direction in which an object is perceived. Everything that is depicted on the Foveola is perceived as straight ahead. Retinal points to the right of the foveola have the spatial value on the left. Objects that stimulate these places are perceived as lying on the left. Retinal points on the left / above / below the foveola have the spatial value on the right / below / above. Accordingly, objects that irritate these areas are perceived as lying on the right / below / above.

The fact that the retina receives two-dimensional optical stimuli and that these stimuli can be placed in a spatial relationship to one another enables a sense of space to arise. The entirety of all objects perceived in the field of vision is assigned to what is directly looked at and thus to the main viewing direction. This is known as relative localization. It is independent of the viewing direction. Relative localization, in turn, is the prerequisite for egocentric localization.

With the help of this, it is possible to assign where in the outside space the object being viewed is located in relation to the orientation of our body. The perception of secondary directions and how they relate to the main direction is therefore important for the sense of space and for finding one's way around.

The order of the outside world or physical space is reflected in the subjective visual space through the relative localization of the secondary directions. Foveolar fixation is the basic requirement for this normal order in space. For this, anatomical and functional structures of the retina must be intact, a physiological development and maintenance of the main direction of vision with the foveola must be ensured, and the fovea centralis must be secured as the motor zero point of the eye.

You can find your medication here

Illnesses & ailments

If the foveolar fixation is not present as a basic requirement for the development of the sense of space, the orientation in space is disturbed. This is the case with pathological changes in the center of the retina. Macular diseases can cause an organic central scotoma, which means that fixation is only possible with a different retinal site than the foveola.

Likewise, in the presence of a functional central scotoma that is the basis of a strabismus (strabismus), the point of sharpest vision can no longer be fixed. In order to be able to see the object of interest at all, it must be depicted on the edge of the scotoma. If the main direction of vision is still tied to the foveola, and the spatial values ​​of the other retinal points remain oriented towards it, it is no longer possible for the person concerned to look at something directly because the line of sight from the object to the center of the retina is disturbed. Subjectively, however, only this visual axis has the spatial value straight ahead. If this spatial value turns out to be organic or functional, then this object is only perceived with a side view. But the subjective feeling of looking past is connected with it.

In order to be able to look at something at all, you have to look past it. It is then an eccentric setting. This correlates with a noticeable decrease in visual acuity, as the resolution is clearly reduced away from the center of the retina. Thus, one sees blurred and the egocentric localization is also disturbed. It therefore becomes difficult to judge where the perceived object is in relation to one's own body.

In addition to the eccentric setting, there is also the case of eccentric fixation, in which the image of a viewed object no longer falls on the foveola, but on an eccentric retinal point. This can happen in early childhood strabismus. The main direction of vision has then passed to this retinal point and the relative localization is organized around the new main direction of vision. The secondary directions are based on her and are set in relation to her again. This rearrangement is accompanied by a significant decrease in visual acuity and in most cases the entire field of vision is no longer recorded evenly.