We have been opticians for three generations
in our family, and our activity is targeted on three areas, optometry,
contact lenses and optical instruments.
A subject monocular (blind in one eye or amblyopic of an
eye), as we have already seen , he is capable of having a perception of the
space. This perception is made by using dynamic factors and perceptive factors
Dynamic factors
The subject can sweep the surface of the object. To see
clearly each points, he is going to have to involve an accommodation depending
on the distance of the point to the eye. The analysis of the variations of the
accommodation allows him an awareness of the relief of the object.
When the subject moves the head, the visible movement of
objects, the other way around rotation of the head, is going to depend on their
distance in the eye. The most moved closer seem to move with regard to the
remote objects (phenomenon of monocular parallax).
Perceptive factors
These factors appeal to the knowledge acquired by the
visual system.
- The analysis of the covering of objects (the close
object masks the remote objects) informs about their relative position in the
space.
- The carried shadows and the appropriate shadows inform
too about the shape of objects (we use them to realize paintings deceive the eye
which give the illusion of the relief).
- The visible angle under which we see known objects
allows an appreciation of their distance.
- Other factors are also useful. For example, in the case
of the observation of a landscape, we know that the background objects are seen
in a kind of mist.
Binocular vision
The subject having a binocular vision is going to arrange,
for every eye, the same means as the monocular. He is going to have at his
disposal two new means of appreciation of the relief.
Dynamic factor
When the subject fixes a point of the object, to see him
simple and clearly, he involves the accommodation and the necessary convergence.
As the accommodation, the necessary convergence is a function of the distance of
the point. When the point of fixation sweeps the object, the variation of the
values taken by the couple A-C is going to inform the subject in a more precise
way than the only variation of A which the monocular has.
Stereoscopic vision
The retinal images right and left are not strictly
identical because both eyes are separated by a distance of the order of 60 mm
(stereoscopic parallax). The analysis of the disparity of both images by the
cortex allows an awareness of the relief. This capacity is the only one used to
create the impression of relief during the use of a stereoscope or anaglyphs and
in the three-dimensional cinema. Both eyes look at slightly different flat
images (dissociations which can be done by optical systems, red-green filters or
polarized filters).
French
Anaglyph
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