At stereoscopic vision is the ability to get a spatial impression with both eyes. Both functioning eyes are required for this. The two-eyed vision is also called Binocular vision beichnet. If one can see with only one eye, one speaks of Monocular vision (monovision).
If you imagine a ray of vision through the center of the lens of the eye, which is exactly on the fovea (place of sharpest vision) in the center of the macula, the central region of the retina, inside the eye, then the rays of vision of the two eyes are not parallel, but have a point of intersection. The following graphic can illustrate this:
Stereoscopic vision
Ideally, the eyes move synchronously: with respect to an imaginary central axis, which runs exactly from the targeted object centrally between the eyes, the angles of the two visual rays are identical. The further away the targeted object is, the smaller this angle becomes.
Spatial vision thanks to stereoscopic vision
Each eye takes in the information of the seen object separately – and each from a slightly different angle. So, for example, if we look at a ball, we see a little more of the right side of the ball with our right eye. With the left eye we see minimally more from the left side.
Each eye filters the information and sends it to the brain through the optic nerve. There the two slightly different visual impressions are combined: the result is a three-dimensional impression.
Stereoscopic vision – visual impression : left and right eye combined
3D glasses are also based on this principle, generating a separate image for each eye.
Problems with stereoscopic vision
There are various refractive errors that cause stereoscopic vision disorder.
Anisometropia
Usually a refractive error is corrected with glasses. However, if one eye is cursighted and the other is farsighted (sog. Anisometropia), the images are delivered to the brain in different sizes (farsighted glasses enlarge the image, shortsighted glasses reduce the image, in each case by the distance of the lens to the eye). This so-called aniseikonia makes it difficult for the brain to compute a unified stereoscopic image from both images. In this case contact lenses are more suitable as a visual aid.
A certain form of congenital vision or a vision caused by a spectacle lens or. Contact lens correction or surgery (z. B. The anisometropia (caused by cataract surgery) enables one eye to see near objects sharply and the other eye to see far objects sharply without glasses. This phenomenon is independent of accommodation and thus exists until old age and is also called monovision. Due to this condition, full stereoscopic vision is often not possible and thus u. U. considered undesirable.
The innate form of this anisometropia lay z. B. also occurs with Johann Wolfgang von Goethe and is therefore also called Goethe gaze.
Squint
Also in case of strabismus there is a disturbance of stereoscopic vision. In the case of acquired strabismus, it is relatively easy to correct it with suitable prism glasses (unlike in the case of congenital strabismus).
Winkelfehlsichtigkeit
The angle defect is a latent squint that neither the affected person nor his environment notices. This form of refractive error is still scientifically controversial, but can be diagnosed in many people. One corrects an angular defective vision also with prism glasses.
Prism glasses
3d not only through stereo vision
You can distinguish two basic things when it comes to spatial vision (Stereopsis):
- The true spatial vision due to stereo vision (as previously described)
- Vision based on visual experience.
On the second point, the experience of perspective plays an important role, z.B.
- distant objects are smaller in proportion
- The color intensity of distant objects fades away
- parallel lines run towards a vanishing point in the distance.
The complete absence or loss of spatial vision is also called anisometropia, especially in the English-speaking world Stereo blindness called.