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Leonardo the VisionaryThe eye

Task 2Group B2

01How does the eye work?

Anatomy of the eye

1-pupil2-cornea3-iris4-ciliary body5-retina6-optic nerve7-fovea8-choroid layer9-sclera10-lens











The electrical messages from the retina travel along the optic nerve to your brain. These ganglion cell roots or "axons" are intertwined throughout the optic nerve and extend into the brain.

This is the vascular layer of the eye, containing connective tissues, and lying between the retina and the sclera.

This is the hole in the middle of the coloured iris. Its diameter changes depending on the amount of light.

The iris controls the amount of light that enters the eye. The iris is the coloured part of your eye.

This is the layer that covers the front of your eye. It's clear like glass and it has no blood vessels in it. It focuses the light that is coming in through it.

This is the tough white skin which covers the outside of the eyeball (except for the see-through cornea). We call it the 'white' of the eye.

The retina is the light sensitive membrane that covers the back of the eye. The cornea and lens focus light onto the retina. It contains two types of cells: rods and cones. Rods can 'see' black and white. Cones 'see' colours. They turn the picture into an electrical message for the brain.

The fovea centralis is a small, central pit composed of closely packed cones in the eye. It is responsible for sharp central vision.

The lens helps the cornea to focus light onto the retina. It changes shape to make sure that the 'picture' on the retina is as clear as possible. The lens' job is to focus light rays on the back of the eyeball.

The lens is suspended by a bunch of fibers. These fibers are attached to a muscle called the ciliary body. It has the job of changing the shape of the lens.

How does theeye work?




In a normal eye, the light rays come to a sharp focusing point on the retina. The retina functions much like the film in a camera. It is responsible for capturing all of the light rays, processing them into light impulses through millions of tiny nerve endings, then sending these light impulses to the brain. The image formed on the retina is the same as the original one, but it's way smaller and upside-down.

Light rays enter the eye through the cornea, the clear front “window” of the eye.After passing through the iris, the light rays pass through the eye’s natural crystalline lens. This clear, flexible structure works like the lens in a camera, shortening and lengthening its width in order to focus light rays properly.Then they pass through a dense, transparent gel-like substance, called the vitreous that fills the globe of the eyeball and helps the eye hold its spherical shape.

When light stimulates the nerve cells in the retina, messages are sent along the optic nerve to the brain. The optic nerves from the two eyes join inside the brain in a place called the optic chiasm. The brain uses information from both nerves to combine the vision from the two eyes allowing you to see one clear image.


In dimmer light the pupil dilates. This is caused by the iris relaxing, enlarging the diameter of the pupil. More light enters the eye and reaches the retina.

With light adaptation, the eye has to quickly adapt to the background illumination to be able to distinguish objects in this background. The process for light adaptation occurs over a period of five minutes. The iris constricts, causing the pupil's diameter to shorten. Less light enters the eye, protecting the retina from damage.

In visual physiology, adaptation is the ability of the retina of the eye to adjust to various levels of light. In order for humans to transition from day to night vision they must undergo a dark adaptation period of up to two hours in which each eye adjusts from a high to a low luminescence

The acommodation of the eye

For objects which are placed up to 6m from the eye, the cilliary muscles relax and the lens is at minimum strenght. That is because these light rays are almost parallel and don't need much refraction to bring them to a focus.Acommodation is no longer necessary for objects over 6m.

For objects placed very close to the eye, the ciliary muscles are contracted and the lens is rounded for more strength. Light rays from close objects diverge and require more refraction for focusing.

02Why do leaves look green and tomatoes red?

The green color of the leaves is due to the pigment, chlorophyll, which is essential in photosynthesis. The green light coming from the leaves is "seen" by the green cones.

Red colour in tomato fruits is due to the pigment, lycopene. The red light coming from tomatoes is "seen" by the red cones.

How do we see colors?

Red, green and blue are the additive primary colors of the color spectrum. Combining balanced amounts of red, green and blue lights also produces pure white. By varying the amount of red, green and blue light, all of the colors in the visible spectrum can be produced. Considered to be part of the brain itself, the retina is covered by millions of light-sensitive cells, some shaped like rods and some like cones. These receptors process the light into nerve impulses and pass them along to the cortex of the brain via the optic nerve.

Rod cells are photoreceptor cells in the retina of the eye that can function in less intense light than the other type of visual photoreceptor, cone cells. Rods are usually found concentrated at the outer edges of the retina and are used in peripheral vision. On average, there are approximately 92 million rod cells in the human retina. Rod cells are more sensitive than cone cells and are almost entirely responsible for night vision. However, rods have little role in color vision, which is the main reason why colors are much less apparent in dim light, and not at all at night.

Cone cells, or cones, are photoreceptor cells in the retinas of eyes. They respond differently to light of different wavelengths, and are thus responsible for color vision and function best in relatively bright light. Cone cells are densely packed in the fovea centralis. There are about six to seven million cones in a human eye and are most concentrated towards the macula. Cones are less sensitive to light than the rod cells in the retina, but allow the perception of color. Cones are normally one of the three types, each with different pigment: red, blue and green. Because humans usually have three kinds of cones with different photopsins, which have different response curves and thus respond to variation in color in different ways, we have trichromatic vision.

03Why do your legs look crooked underwater?

Why do objects look bent or crooked underwater?

Have you ever wondered why does your straw look bent when you drop it in your drink? Or why do your legs look crooked when you're in water? The answer is actually really simple. It is because of refraction of light. Refraction of light is the change in its direction when it passes from one medium to another obliquely.

When the rays coming from the tip of the pen, straw, or from your feet pass from water to air, they change their direction again (they get refracted).

The two mediums in this situation are air and water. When the rays of light pass from air to water, they change their direction under an angle called the angle of refraction. The refractive index (RI)is the degree to which light bends (refraction) when passing through a medium.

When the refracted rays reach our eyes, our eyes trace them back as if they were straight. Due to this, the rays appear to be coming from a point slightly above the original one, causing us to see the image crooked or bent.

04Why do we sometimes need lenses?How do they work?

What are lenses and how do they work?

A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction.

There are 2 types of lenses:convex (converging) and concave (diverging)

A double convex lens, or converging lens, focuses the diverging, or blurred, light rays from a distant object by refracting (bending) the rays twice.

It is a lens that causes a beam of parallel rays to diverge after refraction, as from a virtual image; a lens that has a negative focal length.

Lens' role in eye diseases and disorders

Near-sightedness, also known as short-sightedness and myopia, is an eye disorder where light focuses in front of, instead of on, the retina. This causes distant objects to be blurry while close objects appear normal. Corrective lenses bend the light entering the eye in a way that places a focused image accurately onto the retina. They are the concave lenses.

Hyperopia, also known as Far-sightedness, is a condition of the eye in which light is focused behind, instead of on, the retina. This results in close objects appearing blurry, while far objects may appear normal. The simplest form of treatment for far-sightedness is the use of corrective lenses, eyeglasses or contact lenses. Eyeglasses used to correct far-sightedness have convex lenses.

Other eye diseases

A cataract is a clouding of the lens in the eye which leads to a decrease in vision.Cataracts often develop slowly and can affect one or both eyes.

Astigmatismis a common vision condition that causes blurred vision. It occurs when the cornea (the clear front cover of the eye) is irregularly shaped or sometimes because of the curvature of the lens inside the eye.

05Sketch of the eye

drawings bybe_fleur.dro_alexandra.dsp_meritxell.b

Dissection of a cow eye




1-The choroid2-The lens3-The Vitreous body4-The retina


The Vitreous body is jelly, pretty much like raw egg white. It is very slippery and hard to take off the lens.

The retina goes out of the eye through a little spot, the optic disc, from where it goes up to the brain by the optic nerve.

This pretty blueish spot is found only in the eye of animals with good night vision. Humans don't have this.

The lens is a gummy on the outside, like orbeez balls, and viscous on the inside. It works as a magnifier lens, so if you put it on a piece of paper with text on it, the letters appear bigger.