Eye

Eyes It is an organ that detects light , so it is the basis of the sense of sight. It is made up of a system sensitive to light changes, capable of transforming these into electrical impulses. The simplest eyes do nothing more than detect whether the surroundings are bright or dark. The most complex serve to provide the sense of sight.

Summary

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• 1 Features
• 2 Vision defects
  • 1 Myopia
  • 2 Hyperopia
  • 3 Presbyopia
  • 4 Astigmatism
  • 5 Falls
• 3 Function
  • 1 The eyelids
  • 2 tears
  • 3 Sclera
  • 4 The iris muscles
  • 5 The lens
  • 6 The retina
  • 7 Towards the brain
• 4 Origin of the main structures of the eye
• 5 Different structures of the eye according to their embryogenic nature
  • 1 Superficial ectoderm
  • 2 Neural ectoderm
  • 3 Mesoderm
• 6 Related Links
• 7 Sources

features

50% of the information we receive from our environment we receive through the eyes. The vast information that we receive in a simple glance at our environment is stored for a second in our memory and then we discard almost all of it. We don’t look at almost anything! The human eye is an optical system formed by a spherical diopter and a lens, which are respectively called the cornea and the lens, and which are capable of imaging objects on the inner surface of the eye, in an area called Retina , which is sensitive to light.

The parts that make up the eye are clearly seen in the figure above. It is approximately spherical in shape and is surrounded by a membrane called the sclera, which on the anterior side becomes transparent to form the cornea.

Behind the cornea is a diaphragm, the iris, which has an opening, the pupil, through which light passes into the eye. The iris is the one that defines the color of our eyes and the one that automatically controls the diameter of the pupil to regulate the light intensity that the eye receives. The lens is linked by ligaments to the ciliary muscle. In this way the eye is divided into two parts: the posterior one containing vitreous humor and the anterior one containing aqueous humor.

The refractive index of the lens is 1,437 and those of the aqueous humor and vitreous humor are similar to that of water. The lens focuses the images on the inner envelope of the eye, the retina. This envelope contains nerve fibers (extensions of the optic nerve) that end in small structures called cones and rods that are very sensitive to light. There is a point on the retina, called the fovea, around which there is an area that only has cones (to see the color). During the day the fovea is the most sensitive part of the retina and the image of the object we are looking at is formed on it.

The millions of nerves that go to the Brain combine to form an optic nerve that leaves the retina through a point that does not contain receptor cells. It is the so-called blind spot.

The cornea refracts light rays and the lens acts as an adjustment to focus on objects at different distances. This is handled by the ciliary muscles that modify the curvature of the lens and change its power. To focus on an object that is close, that is, for the image to form in the retina, the ciliary muscles contract, and the thickness of the lens increases, shortening the image focal length. On the contrary, if the object is distant, the ciliary muscles relax and the lens becomes thinner. This adjustment is called accommodation or adaptation.

The healthy and normal eye sees objects located at infinity without accommodation focused on the retina. This means that the focus is on the retina and the so-called remote point (Pr) is at infinity. Remote point is called the maximum distance at which an object can be located so that a person can clearly distinguish it and point close to the minimum distance.

A normal eye will be one that has a point close to a distance “d” of 25 cm, (for a child it can be 10 cm) and a remote point located at infinity. If it does not meet these requirements, the eye has a defect. The eye is an optical system that concentrates and manages to focus on the retina the rays that diverge from an object (otherwise the rays that leave a point could not be collected on a screen to give their image). Play with the accommodation of the eye by dragging the clown in this applet. What happens to the focus while accommodation varies?

Practice with this application. “Glisser l’object avec la souris” means that you can drag the object with the mouse . In it you can see that when the object is located anywhere between the remote point and the next point, the image is formed on the retina of the normal eye. You can also compare and see what happens when the eyes have a defect. If an object is located close to the eye, it looks the largest and at the widest angle that can be seen with the naked eye.

Vision defects

Myopia

The myopic eye has an optical system with excess convergence. The focus is in front of the retina when the eye is relaxed, without accommodating, and upon reaching maximum accommodation is closer to the lens than in the normal eye. The myopic person does not see well from afar. As the focal point of the eye is closer to the cornea than in a normal eye, objects at infinity form the image in front of the retina and are blurred. They start to look good when they are close (at the remote point). From the remote point to the next point it accommodates like the normal eye.

In consecuense. The far point and the near point are closer than in the normal eye. To correct myopia, divergent lenses are needed: incoming rays diverge.

The outer wall of the eye at its posterior portion is configured by the sclera. This white portion of the ocular wall has a protective function and corresponds to the five sixths of the ocular surface. The anterior portion of the wall is configured by the cornea, which is the transparent layer that allows the entry of light rays into the eye. Behind it is a space filled with a clear liquid (the aqueous humor) that separates the cornea from the lens of the lens.

The middle or uveal layer has three different parts: the choroid is a vascular layer, it covers the three fifths of the posterior part of the eyeball. The ciliary body is continued forward, followed by the iris, which extends across the front of the eye. The choroid, being a vascularized layer, is responsible for providing nutrition to the retina. The ciliary body is responsible for producing the liquid that fills the anterior chamber, the aqueous humor. The iris that gives color to the eyes, is also in charge of regulating the amount of light that enters the eye and thus allows to see well in different lighting conditions. The central opening of the iris is the pupil or girl of the eye.

The retina is the innermost layer. It is complex, made up mostly of nerve cells. The light-sensitive receptor cells are located on their outer surface in front of a layer of pigmented tissue. These photoreceptors are called rods and cones and are sensitive to different types of light. The retina in the center has a small yellow spot, called the macula lutea; within which is the fovea, the eye area with the greatest visual acuity. The sensory layer of the fovea consists of only cone-shaped cells, while rod-shaped cells are also found around it. As we move away from the sensitive area, cone-shaped cells become scarcer and only rod-shaped cells exist on the outer edges of the retina.

Inside, behind the iris is the lens. It is a flattened sphere-shaped lens made up of a large number of transparent fibers arranged in layers. It is linked to the ciliary muscle, which is ring-shaped and is surrounded by ligaments . The ciliary muscle and surrounding tissues form the ciliary body and this structure flattens or rounds the lens, changing its ability to focus on objects at different distances. Divergent s used to correct myopia must be at the remote point so that the rays that come out of them are focused on the retina.

Farsightedness

It is a defect of convergence of the optical system of the eye. The focus image of the eye is behind the retina when the eye is at rest without starting accommodation. The focus is outside the eyeball. The myopic eye when at rest (without initiating accommodation), has the lens of the lens very little convergent.

To see the objects located at infinity you have to make accommodation. Go well in the distance but to do it you already spend accommodation. It has the next point farther than the normal eye (more than 25 cm) because it “spends before” the accommodation it is capable of. The remote point is virtual and behind the eye. Hyperopia is corrected with convergent lenses. In some cases it is corrected as the person grows and the eyeball enlarges.

Presbyopia

Tired sight. Over the years the adaptability of the lens decreases (it loses flexibility) and the distance at which the proximal point is located increases. This defect is called presbyopia and is corrected with convergent lenses.

Astigmatism

If the eye has a deformed cornea (as if the cornea were spherical with an overlapping cylindrical surface), the point objects give short lines as images. This defect is called astigmatism and a compensating cylindrical lens is necessary to correct it.

waterfalls

It is very common that as the lens ages, it becomes opaque and does not allow light to pass through. This is the waterfall. Remember that many historical figures who lived for many years became blind in their old age. Today they operate by removing the lens and installing an intraocular plastic lens in its place that does its job and does not need to be replaced in the rest of life.

Function

The eyes work from the moment you wake up until you close them when you go to sleep. They assimilate lots of information about the world around you – silhouettes and shapes, colors, movements and much more. They then process the information and transfer it to the brain so that it knows what is going on outside the body. The eye is approximately 2.5 centimeters in diameter and is located behind the eyelid.

The eyelids

The eye is located in a small hollow area (eye socket) of the skull, and is protected by the eyelid. The eyelid opens and closes several times a minute without your thinking, it is an involuntary act known as blinking! When you blink, the eyelid helps keep the eye clean. Also, the eyelid has many reflections that protect the eye in different situations. When it gives you a very bright light, the eyelids inadvertently close to protect the eyes. And if you try to put your finger close to a friend’s eye (but not too close!), For sure you’ll see how it blinks quickly. Her eyelids are closing in response to movement too close to the eye – it is a reflex that protects the eye from danger. And speaking of blinking, don’t forget about tabs.

Tears

The eye has its own cleaning system. Above the outside of the corner of the eye are the lacrimal glands that produce a special cleaning fluid: tears! Every time you blink, a little tear comes out of the upper eyelid. This liquid is used to kill germs, dust and other particles that do not belong to the eye. It also prevents the eye from drying out. Then the liquid is drained through the tear duct. You can see the tear opening by gently pulling on the inside of the corner of your eye. When you see a little hole. Sometimes your eye needs to produce even more tears than normal. If you’ve ever mistakenly put something in your eye or been in a place full of dust or smoke, your eyes will have worked twice as much to protect themselves producing many tears. These tears helped prevent your eyes from getting injured or dry. And what happened the last time you felt sad, scared, or upset? Well, your eyes received a message from the brain to make you cry and the tear glands produced many, many tears.

Sclerotic

It is the white part of the eyeball, which is made of a resistant material. It has to be because it covers most of the eyeball, a very important function. Look closely at the white part of the eye and you will see lines that look like very thin pink threads. These are the blood vessels that carry blood to the eye. The next layer of the eye is the cornea. The cornea is barely visible because it is made of transparent tissue. The cornea helps the eye focus. Behind the cornea are the iris and the pupil. The iris is the colored part of the eye. When we say that a person has blue eyes, it actually means that they have blue irises!

The iris muscles

The iris has muscles that adjust to control the amount of light that passes through the pupil. The pupil is the circular black hole in the center of the iris that allows light to enter the eye. The next time you go to the movies with your friends, try this experiment. When you leave the cinema, look at your eyes right away. You will see how your friends’ pupils become small! This is because when there is less light (like in a dark theater), the pupils get bigger to let in more light. But when you go out of the theater and under bright light, the pupils get smaller quickly so that not so much bright light comes in that can harm your eyes. Between the iris and the cornea is the anterior chamber. This chamber is filled with a special liquid that provides oxygen,

The lens

The next parts of the eye are the ones you can’t see. After light enters the pupil, it reaches the lens. The lens is behind the iris and is transparent and colorless. The task of the lens is to focus the light rays on the back of the eyeball (called the retina). The lens is suspended in the eye thanks to a group of fibers. These fibers are attached to a muscle called the ciliary muscle. This muscle has the incredible task of changing the shape of the lens. As you hear it – the lens changes shape inside your eye! Try to look away from the computer and focus your eyes on something else, across the room. Even though you didn’t feel anything, your lens changed shape. When you look at things closely, the lens becomes thicker to focus the correct image on the retina. When you look at things from a distance, the lens becomes thinner. The largest part of the eye is behind the lens and is called the vitreous body. It is filled with a clear, semi-gelatinous material called the vitreous humor. Have you ever touched lying eyes in a store? Sometimes they’re a little sticky or soft – that’s because they’re made to look like they’re full of vitreous humor. In a real eye, after light passes through the lens, it passes through the vitreous to the back of the eye. The largest part of the eye is behind the lens and is called the vitreous body. It is filled with a clear, semi-gelatinous material called the vitreous humor. Have you ever touched lying eyes in a store? Sometimes they’re a little sticky or soft – that’s because they’re made to look like they’re full of vitreous humor. In a real eye, after light passes through the lens, it passes through the vitreous to the back of the eye. The largest part of the eye is behind the lens and is called the vitreous body. It is filled with a clear, semi-gelatinous material called the vitreous humor. Have you ever touched lying eyes in a store? Sometimes they’re a little sticky or soft – that’s because they’re made to look like they’re full of vitreous humor. In a real eye, after light passes through the lens, it passes through the vitreous to the back of the eye.

The retina

In the most posterior part of the eye, passing the vitreous body, is the retina. The retina is tiny (about the size of a postage stamp), but it is filled with millions of light-sensitive cells. It receives blood from the retinal vessels (from the retina) so that it can function properly. The retina takes the light that already passes through the cornea, the pupil and the lens and transforms it into nerve signals that the brain can understand. It processes light with special cells called rods and cones. There are many of these, you have about 100 million rods and three million cones in each eye! The canes are the ones that check the silhouette of your friend and how he moves. Cones are somewhat different because they perceive color. Cones need more light than rods to function well. This explains why it is difficult to distinguish colors in the dark. So, when you see that your friend has dark skin, brown hair, and is wearing a red T-shirt and jeans, it means that your cones are processing light to give your eyes all the information about color. Sometimes the cornea, lens, and retina don’t work perfectly as a team, and the image ends up in the wrong place at the back of the eye. Sometimes the image appears in front of or behind the retina, instead of just above it. When this happens, it is not scary or unusual, it just means that the person needs glasses to help the image focus correctly on the retina. and jeans, it means that your cones are processing light to give your eyes all the color information. Sometimes the cornea, lens, and retina don’t work perfectly as a team, and the image ends up in the wrong place at the back of the eye. Sometimes the image appears in front of or behind the retina, instead of just above it. When this happens, it is not scary or unusual, it just means that the person needs glasses to help the image focus correctly on the retina. and jeans, it means that your cones are processing light to give your eyes all the color information. Sometimes the cornea, lens, and retina don’t work perfectly as a team, and the image ends up in the wrong place at the back of the eye. Sometimes the image appears in front of or behind the retina, instead of just above it. When this happens, it is not scary or unusual, it just means that the person needs glasses to help the image focus correctly on the retina. and the image ends in the wrong place at the back of the eye. Sometimes the image appears in front of or behind the retina, instead of just above it. When this happens, it is not scary or unusual, it just means that the person needs glasses to help the image focus correctly on the retina. and the image ends in the wrong place at the back of the eye. Sometimes the image appears in front of or behind the retina, instead of just above it. When this happens, it is not scary or unusual, it just means that the person needs glasses to help the image focus correctly on the retina.

Today, during the surgery of the eye, it is used Silicone Oil 5000 centistokes to prevent or treat the problem called detachment of the retina .

Towards the brain

After the retina converts colors and shapes into nerve signals, these signals go to the optic nerve. The optic nerve comes out of the back of the eye and is a great messenger – it carries all the messages from the retinal nerves to the brain! But there is a problem: when the light passes through the lens and the image touches the queen, the image is inverted. So the message that carries the optic nerve to the brain is also.

Origin of the main structures of the eye

The structures of the eye are 26:

• From the superficial ectoderm come 9.
• 7 are formed from the neural ectoderm.
• From the mesoderm, 10.

Different structures of the eye according to their embryogenic nature

Superficial ectoderm

2. Corneal epithelium.
3. Conjunctival epithelium.
4. Lacrimal gland.
5. Eyelid epithelium.
7. Meibomian glands.
8. Möll and Zeiss glands.
9. Lacrimal apparatus epithelium.

Neural ectoderm

1. Retina and pigment epithelium.
2. Epithelium of the ciliary processes.
3. Pigmentary epithelium of the posterior aspect of the iris.
4. Pupil sphincter and dilator muscles.
5. Nervous and neurological elements of the optic nerve.
6. Vitreous humor.
7. Suspensory ligament of the lens.

Mesoderm

1. Blood vessels.
3. Optic nerve sheath.
4. Ciliary muscle.
5. Proprietary substance and corneal endothelium.
6. Stroma of the iris.
7. Extrinsic muscles of the eye.
8. Fat and orbital ligaments.
9. Bony walls of the orbit