Fixation (visual)

With fixation, the targeted viewing ( fixing) is called an object in outer space in ophthalmology, which in the normal case with the highest resolution retina, the fovea centralis, happens. Another term for this is central or foveal fixation. This conveys this point the direction sense of " straight " and thus represents the main physiological Ehrich below the eye, which is a straight line between foveola and Fixierobjekt also called in physical space line of sight. All other retinal points and objects in the visual field represent addition Ehrich lines that differ by a different localization of the objects from the main Ehrich Tung. This is also called the relative localization of the eye. It is maintained as long as there is a foveal fixation.

From their distinction is the egocentric localization, which refers to one's own body and be retained even if no foveal fixation longer exists. In addition to intact anatomical and functional structures are therefore the development and maintenance of the main Ehrich Tung the fovea and its status as motor zero point of the eye conditions for a central fixation.

Pathophysiology

Loses its status as the foveola Focus point, two different states can occur: the eccentric adjustment and eccentric fixation.

Eccentric adjustment

An eccentric adjustment is available if the use of the foveola, their main Ehrich Tung is still obtained for example by macular degeneration, no longer possible. Subjectively, the person concerned in such cases, the feeling of " look past " on an object to have, otherwise it will be covered by a central scotoma. However, the foveola is still the center of the visual field. In general, this situation is only in adulthood.

Eccentric fixation

The term eccentric fixation is then used when the main Ehrich heating is no longer associated with the foveola, but with another point on the retina that is used for the fixation. This happens usually with strabismus and leads to amblyopia. At the same time the main Ehrich Tung passes to the eccentric retinal point. Subjectively, a data subject has to look directly in this situation the impression an object. Accordingly, the relative location on the new main Ehrich Tung, which is now represented by the retinal position of the eccentric fixation oriented.

There are basically the following types eccentric fixation:

• Parafoveolare fixation ( within the Wall reflex to about 2 °)

• Parafoveal fixation (outside of Wall reflex of about 2 ° to 5 °)

• Peripheral fixation ( > 5 °)

• Fixationslosigkeit ( Afixation )

• For completeness, here is the nystagmiforme fixation called an erratic or unstable variant of said fixation forms.

It is assumed that with increasing eccentricity of the fixation is also accompanied by a higher visual acuity, however, has not been proven a reliable relationship between these parameters. A corresponding importance is also the test methods used here.

Investigation

Assessing opportunities in studies in free space are very limited. Although various features on amblyopia may indicate, however, allow little reliable information about the fixation, and certainly not by its location on the retina. Therefore offers usually a ophthalmoscope ( Visuskop ) on, with which one. A small Fixierobejekt, usually a star, projected onto the fundus and possibly by means of Upstream appropriate corrective lenses compensates an existing refractive error, until the object is sharply imaged on the fundus The control is done by the examiner who looks from the other side of the ophthalmoscope in the eye and on the back of the eye and can be seen as always, where the Fixierobjekt being imaged. Even infants can be assisted by an optomotor reflex, which provides a central setting of a peripherally presented stimulus image, examined. Nevertheless, the inspections make not easy, and the results should be evaluated with care. Older children and adults will be asked to look into the exact center of the presented Fixierobjekts. Due to demand, the examiner ascertain whether the respondent actually has even the impression straight to fix the center of the object.

If there is an eccentric setting, the fixing image itself is first mapped to a network Telle house next to the foveola, but then straight usually after repeated requests to look centrally on the same. When an eccentric fixation, the object will be located next to, above or below the foveola, where the examinee indicates also in this situation this to have a direct and straight.

Another possibility is an examination haploscope, which is equipped with a so-called Haidinger tufts. This is an entoptic phenomenon which can be observed only with the foveola. Not all patients with eccentric fixation it can detect, as well as persons with organic conditional central scotoma. In contrast with eccentric fixation the Clump Haidinger is located exactly where the direction of view of the foveola actually shows.

Treatment

In order to actively influence the pathological fixation behavior pleoptische method may optionally be applied. Otherwise, occlusion of the better eye for amblyopia treatment the rule. In special cases, the worst eye is occluded (inverse occlusion) with the aim to "solve" a very stable eccentric fixation to. It is hoped that in general the return to a foveolaren, central fixation, the restoration of the order Associated Ehrich Tung and thus an improvement in visual acuity and orientation.

Others

Scientific analysis of the fixation process, such as when looking at an image or reading is effected by eye tracking. So-called eye-tracker are used as an aid.