Retinal correspondence

With retinal correspondence is known in ophthalmology , a neurophysiological relationship system between both eyes , which is the basis for binocular vision ( binocular vision represents).

When seeing , a fixed object is imaged on interconnected and identically localizing retinal points of the right and left eyes, which perceive it at the same point in space and thus overlay it. This is known as a normal Sehrichtungsgemeinschaft , normal retinal correspondence (NRC) or a normal retinal correspondence .

Since this condition is normally linked to the foveae of both eyes, this is also referred to as the bifoveal vision community . The fovea as the motor zero point represents the directional value straight ahead , also called the main viewing direction . As a result, each peripheral retinal point of one eye usually has a corresponding retinal point with the same sense of direction of the other eye and correspondingly many secondary directions . Depending on the prevailing correspondence relationships, the quality of binocular vision will also appear.

The entirety of the points in the outer space that fall on corresponding retinal points when an object is fixed is called a horopter . This horopter is a line that, like a parabola , is slightly curved. Objects that are close in front of or behind this horopter are usually not seen twice, although they fall on non-corresponding retinal locations. This area is called the panum space . In this zone, the slightly offset images ( lateral disparity ) create spatial vision. So-called physiological diplopia occurs when the limits of the panum area are exceeded .

pathology

Deviations from normal retinal correspondence are caused by strabismus disorders and are the result of permanent image shifts in the panumareal during early childhood development. They can lead to an anomalous vision community called anomalous retinal correspondence (ARC). This is divided into harmonic anomalous correspondence (HARK) and disharmonious anomalous correspondence (DHARK). This is the phenomenon that when an object is fixed to the stimulant of retinal points of the eyes that are not physiologically identically located, this can nonetheless lead to an abnormal superimposition of the images. As a rule, the fovea of ​​one eye corresponds to a non-foveal, eccentric retinal point in the other eye. As a result of HARK, so-called subnormal, i.e. qualitatively differently inferior, binocular vision can arise. This is expressed, for example, in a narrow range of fusion or in only roughly pronounced spatial vision .

The basis for the development of an ARC is a relatively small squint angle that just barely allows these sensory anomalies to develop. As the squint angle increases, the likelihood of ARC decreases.

examination

The diagnostic assessment of the correspondence relationships belongs to the ophthalmological specialty of orthoptics .

Correspondence checking procedures are based on two principles, evidence of normal retinal correspondence or evidence of abnormal retinal correspondence. A statement about the existing bifoveal vision community or a foveal-peripheral localization relationship can only be made if the retinal points that are stimulated when an object is fixed are known. In both cases, the patient's cooperation and information about the location of the objects is essential. A stimulation of the fovea is achieved with color filters, afterimages or the Haidinger tuft , in the case of an eccentric fixation of the crossed eye only ophthalmoscopically with the last two methods.

To assess the correspondence, to compensate for the squint angle, prisms are held in front of the squinting eye and adjusted according to the patient's instructions until the fixed objects are superimposed. The extent of the prism strength corresponds to the so-called subjective squint angle. The unilateral masking test of the healthy eye is now used to check whether the other eye is adjusting. If this is not the case (and there is central fixation), then it is a normal correspondence (NRK), otherwise an anomalous correspondence (ARK), from which a corresponding adjustment movement emerges, which enables the so-called objective squint angle to be determined . The difference between the objective and the subjective angle is called the anomaly angle . The following rule applies:

• NRK: subjective angle = objective angle, anomaly angle = 0 °
• HARK: subjective angle = 0 °, anomaly angle = objective angle
• DHARK: subjective angle ≠ 0 °, anomaly angle ≠ objective angle.

The values ​​of the subjective angle and the anomaly angle fluctuate depending on the examination conditions.

In general, when assessing the correspondence relationships, it is assumed that the main viewing direction "straight ahead" is in principle associated with the fovea centralis. There is, however, the case that the main direction of view of the fovea has been lost and passed to a peripheral retinal point, which is now also used for eccentric fixation. In this case, the amount of eccentric fixation exactly corresponds to the squint angle and the anomaly angle. This clinical picture is called a microstrabismus with identity .

See also

• Binocular vision

literature

• Herbert Kaufmann (Ed.) : Strabismus . 4th fundamentally revised and expanded edition, with Heimo Steffen, Georg Thieme Verlag, Stuttgart, New York 2012, ISBN 3-13-129724-7 .
• Josef Lang: Microstrabismus. The importance of microtropy for amblyopia, for the pathogenesis of the large squint angle and for the heredity of strabismus (= library of the ophthalmologist. Issue 62). 2nd, revised and expanded edition. Enke, Stuttgart 1982, ISBN 3-432-83502-7 .
• Theodor Axenfeld (founder), Hans Pau (ed.): Textbook and atlas of ophthalmology. 12th, completely revised edition. With the collaboration of R. Sachsenweger and others Gustav Fischer Verlag, Stuttgart and others 1980, ISBN 3-437-00255-4 .

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