In the animal world, there exist many at least forty types of visual bodies which one calls “eyes” . This diversity raises the question of the origin of perception visual. The simplest eyes are just able to detect the difference between light and darkness while the most complex eyes, like the human eye, make it possible to distinguish the Forme S and the Couleur S.
One of the broad objectives of the contemporary Technologie is to manage to manufacture “eyes electronic S” able to even equalize to exceed the aptitudes of the eyes which exist in the alive world for, for example, to replace the eye of a person who would have had an accident.
The human eyeThe eye adapts initially to the ambient Lumière. The man can thus perceive with an equivalent sensitivity in full sun or under the light of full moon, that is to say with an luminous intensity 10 000 times less. A first adaptation comes from the spacing of the iris which in mode of night can reach a maximum opening of 7 mm for young people (maximum who decrease to 4 mm with the age).
Anatomy and ocular physiology
the Cornea, left former the ocular sphere, it is a transparent lens whose role is to collect and to focus the light on the crystalline lens.
- the aqueous Humor, located between the posterior face of the cornea ahead and the former face of the crystalline lens behind.
- the Uvea, made up of the iris (allowing the modification of the entering luminosity), of the Choroid and the Body ciliaire;
- the Pupille is the hole located at the center of the iris;
- the Crystalline , biological lens being used for the Accommodation (" setting with the point" on the object to be visualized making it possible to obtain from a point object a focal point image on the retina) is connected to the bodies ciliaires via the zonule;
the Retina, membrane gathering of the nervous cells photoréceptrices called cones or of the Stick S, being used for the transformation of the electromagnetic Wave into electric impulses, for image processing by the nervous system;
- the choroid, feeder membrane of the retina and genuine “vascular sponge” which papers the inner face of
- the Sclère.
- the Vitreous body.
Appendices of the eyeThere are four of them:
the orbit, osseous cavity, covered with a membrane fibro-rubber band (the périorbite). Role of protection.
- the Muscle S oculomoteurs, role of displacement. 6 at the human :
- 4 right muscles: right superior, right lower, internal rights (or médial) and external right (or side);
- 2 oblique muscles: large oblique (or oblique superior) and small oblique (or oblique inferior)
- the Eyelid, membrane allowing a more or less important insulation of the electromagnetic Radiation, the spreading out of film of tears and the protection of the cornea.
- the lachrymal Gland: located in top and outwards, it secret 40% of our tears, the remainder being secreted by additional glands.
Receivers of the eyeThe receivers of the eye are used to break up luminous information into electric signals which will be sent to the Optical nerve.
- At the man, there exist 3 types of cones (Rouge, Vert, Bleu) being used to break up the light into Couleur S. They are four in certain reptiles and birds. Those can detect the ultra-violet and their cones do not detect the same colors completely.
- the Stick S limited to the light, more rapids and more significant than the cones.
Fabrics of the eyeAs at the Mammalian majority of the S, Bird X, Reptile S and Poisson S, the human eye consists of a Eye-ball, including:
- the Cornea, left former the ocular sphere, transparent lens, it is the port-hole of the eye
- the sclerotic Sclère or .
Pathologies of the eyeThe Ophtalmologie is the science which studies the eye. All the parts of the eye can be touched:
- Muscles oculomoteurs: Diplopia, paresis or paralysis of the muscles.
- Orbit: enophtalmy, Exophtalmie etc
- Eyelid: Ptôsis, Ectropion, Entropion, orgelet, Blépharite, Tumor, Lagophtalmie, Distichiasis, Chalazion, etc
- lachrymal Apparatus: Dacryoadénite, Canaliculite, Dacryocystite etc
- Conjunctive: Conjunctivitis (bacterial, fungic, parasitic or viral), Pinguécula, Ptérygion etc
- Sclère: Sclérite, Scléromalacie perforating or not, Sclère blue etc
- Cornea: Keratitis (bacterial, fungic, parasitic or viral), Kératocône, Gérontoxon etc
- Uvea: Uvéite, Colobome etc
- Pupil: fix, in Mydriase (dilated), in Myosis (contracted), irregular (of which the origin is often a last ignition of the iris or presents)
- Cristallin: cataract, Ectopia, Myopia, Aphakie, Presbyopia etc
- Glazed: hemorrhage, Separation etc
- Retina: tear, separation, arterial occlusion or venous, decays (macular Degeneration related to the age), retinite (pigmentary Retinite) etc
- Optical nerve: optical neuritis, papillary edema, Glaucome
Optical operation of the eye
The first modeling of the eye, known as " eye réduit" consist in regarding it as a spherical Dioptre, provided with a diaphragm and allowing to place itself in the Conditions of Gauss allowing the approximate Stigmatisme. This model makes it possible to include/understand the formation of the images on the retina and the effect of the curve (modified by the crystalline lens) for the Accommodation.
The practical model used in experimental activities consists in modelling the retina by a flat panel display (white sheet) and the crystalline lens by a convergent lens.
In certain didactic devices the lens is a soft lens made up of a plastic membrane which one can more or less fill with water. One can thus show the Accommodation and approach the concepts of Punctum proximum and of Punctum remotum .
The use of a lens out of glass, makes it possible to model the normal eye (emmétrope, clear vision ad infinitum without accommodation) then, by modifying the distance screen-lens, to model the Myopie (too distant screen) and the Hypermétropie (screen too near), with the possibility then of adding a correct lens to model the Lunettes of sight.
Let us approach some optical data (average) of the eye:
The eye can be reduced to a centered system whose characteristics follow:
- focal distance image: +22 mm
- focal distance object: -17 mm
- distance (hearth object → former face of the cornea): +15mm
- thus distance (former face of the cornea → plane principal): +2 mm
- thus distance (former face of the cornea → retina): +24 mm
- radius of curvature: +6 mm
- power: D = +60 δ
- index of refraction: N = 1,337
- accommodation: AC = 6,667
- minimum separable: αmin = 1 '
Diversity of the eyes
The Vertebrate eye of the S, whose human being, consists of a Eye-ball papered inside by the Rétine which collects the luminous rays which enter by an opening located in front of the eye-ball. The Cristallin that cross the luminous rays while entering the ocular sphere is a transparent lens which allows to adapt in order to obtain a clear image on the retina. Contrary to the Vertebrate S, the Insect S and more generally many Arthropode S have pairs of made up Yeux made up each one of a compact unit of sensory receivers called Ommatidie S which break up the image into a mosaic kind of of which each piece is analyzed by single a photoreceiver.
To the Prédateur S like the Chat S or the Rapace S, the eyes are placed one beside the other what allows, in Binocular vision, of better to perceive the distances from the Proie S located opposite them; contrary, the eyes of other animals like the Lapin S or the Souris are generally placed on both sides head what makes it possible to cover larger Field of vision and to better detect the presence of a danger in the environment.
The eyes made up of the Arthropode S (in particular in the insects and shellfish) consist of a receiving whole of S (until 30 000 at some Coléoptère S) sensitive to the Lumière which are called Ommatidie S. One more vulgarly calls the made up eye: eye with facets . For the Copépode S there is, in the majority of the cases, an eye odd, median, which corresponds to the eye of the Nauplius larva. It is then usually called eye nauplien .
At the majority of the Vertebrate S and some Mollusc S (the Octopus S inter alia), the eye consists of the projection of the image on a photosensitive fabric: the Retina. This one detects the light and information is transmitted to the Cerveau by the Optical nerve. The eye of form about spherical, and is generally filled with a transparent Gel called glazed Humeur. The eye often has of a convergent lens and an obturating muscle, the iris, which controls the level of light which penetrates in the eye. Although the eyes of vertebrate and the Céphalopode S seem identical in function and form once the Morphogénèse completed, the embryologic study watch that if the visual body of vertebrate comes from the differentiation of cells of the brain, that of molluscs comes from the differentiation of cells of the Peau. One quotes this case like example of convergent evolution.
Certain mammals like the Cat or some night Rapace S are nyctalopes. The spectral band visible varies according to the species. Thus some Bird X (hummingbirds, Swallow S, Pigeon S…), Arthropod S (Lobster S, Bee S…), Reptile S (gecko, tortoise…) and Poisson S (Trout…) seem to see the ultraviolet rays .
Some Snake S " voient" in the Infra-red but thanks to their Small cavity S. The vision of the colors also differs according to the species or the individuals.
The Shrimp-mante is famous to have the most complex eye of the animal kingdom.
Evolution of the eyeDuring a long time, one has to think that the various shapes of eyes had developed in a way independent starting from species of various origins (one speaks about development Paraphylétique). However the discovery of the existence of a gene common to the animal kingdom controlling the development of the eyes, rather makes think of a common origin (one speaks about development Monophylétique). It thus seems that the diversity of form and structure is the fruit of series of evolutions due to the Natural selection. This mechanism of evolution thus caused controversy between the evolutionists and the creationnists.
The diversity of the organizations and the types of vision is, as underlined it already Charles Darwin in the Origin of the species , a intellectual challenge for the partisans of the evolution. The photoreceivers of the eye, the retinal structure, and the other elements of the visual system are adapted to a lifestyle in a precise environment. However, there exist common points in the operation of the eyes of the various species.
For example, there exist similarities in the way in which the visual stimuli are transmitted receivers to the central nervous system. These similarities are very numerous at the Amniote S. the ancestral eye of these animals would derive from species about the Captorhinida disappeared there are 300 My.
The electronic eye
In the devices electronic S aiming at restoring a defective vision, 8 systems are being studied. They depend on the eye-level which one wants to substitute:
- is the " rétine". They are plates containing of the thousands, even million Semi-conducteur S, which will make it possible to transform the light into electrical signal.
- is the " highly-strung person optique".
- is the " optimum cortex cérébral". The image is recorded by a DIVx camera, transformed into electrical signals by DSP, transmitted to pure copper electrodes which simulate the visual cortex occipital.
- Precaution in the event of wound with the ocular eye
- visual Prospect
- Vision for the birds
- (very complete site of the National union of the Ophthalmologists of France)
- visual Bodies of the marine planktonique Copepoda
- * ''' defects of the vision ''' and ''' Some experiments to highlight the properties of the eye ''' of the site CultureSciences-Physics of the ENS Lyon
- descriptive Diagram of the human eye (animation flash).
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