The function of the eye was formerly understood analogous to tue way of function of a camera. The reflecting light (active) falls into the eye (passive) and produces than on the retina an image which is passed on to the brain. This understanding has been disproved in the middle of tue 20th century by measurements which were made on eyemovements. The fact is, that the sharp vision is concentrated on only 0,02% of the sensory-cells covered retina. This area - which covers 2° of the total 200° horizontal field of vision - is called yellow spot, Makula (lat. Macula lutea) or fovea (lat. fovea centralis). About 50% of the optic nerv orinate of the makula joining the visual center. The remaining 50% of the visual nerv are reserved for the peripheric system, which captures up to 90 compacted images of the field of vision in a second. But only in the intersection point of the two optic axis' (straight line cutting makula and pupil) of both eyes a pin sharp image is rendered. The anyway calm and definite overall picture comes of the repeated process of a split-second fixation of a multitude of points which are enabled by the eyemuscles which spots them - by unconsciously controlled rapid eyemovements - to the fovea. This abrupt movements are so called saccades. When quietly regarding s.th. the times of fixation are longer and the number of saccades lower then in case of a fast look (short time of fixation, high number of saccades). Specifications mention a range of fixationtime between 0,2 to 0,6 seconds and saccades between 2 and 5 a second. The overall picture which is perceived is then no result of a bare reflection of light (passive/limited to optical function of the eye) but a pointwise scanning of an object of which an overall picture is generated by the brain (active/in cooperation of optical apparat of the eye and visual center of the brain).
