6.1

Light entering eye

1. Refracted by cornea. 2. Refracted rays enter pupil. 3. Light rays pass lens and converge onto retina. 4. Image formed is upside down and cells in retina change the image into electrical signals. 5. Electrical signals sent to brain along optic nerve and brain changes image upright

3 things blind people can detect

1. Tiny part of the middle of the sceen 2. Edges of their vision 3.Detect light and darkness

Aqueous Humor

A water fluid that is between the lens and the cornea that helps bring nutrients to the eye and helps give it a shape.

Pupil

Adjustable opening in the center of the eye through which light enters and is not reflected.

Blind spot

Area where optic nerves enter the retina where there are no light sensing cells.

Blindness in developing countries

Blindness can be a result of disease or malnutrition an in developing countries they do not have the money to treat disease or even afford eye glasses

Cone cells

Cone cells allow us to detect colours. We have three types of cone cells each processes a different kind of pigment. The human brain combines and releases he different colours it recieves

Correcting Far sighted vision

Far sighted vision can be corrected by a convex lens, so the light rays can converge directly at the retina.

Forming images

Light rays enter the eye from the base of the object comes together at the top and the same way around causing the image to be inverted,but brains interpret it as upright.

Rod cells

Longer cylindrical cells that can absorb any colour of light, but our brains do not use this to determine colour instead it used it to detect light and dark called black white vision. In low light it helps detect shapes and movement

Cornea

Made of a clear material that lets light pass through but is tough enough to hold the eye together.

Correcting Near sighted vision

Near sightedness can be corrected by a concave lens so the light rays will diverge slightly so the image forms further back.

Snow blindness

Partial of complete blindness caused by overexposure to sunlight such as on snow fields. Treatments include wear snow glasses that include little slits and staying in a dark room for days to relieve inflammation.

Far sightedness

People who can bring images that are distant into focus, but can not bring close images into focus. Light rays that are refracted past the retina. Eye has shorter shape.

Near sightedness

People who can't bring distant images into focus because the light rays converge at a point before the retina and by the time it actually strike the retina the rays diverge and produces a fuzzy image. Eye has longer shape.

Optic Nerve

Some cells in the retina convert the light rays into electrical signals that are sent to the brain through the thick optic nerve

Iris

The iris is the coloured muscle that surrounds the pupil and controls how much light goes through the pupil. In dim light it expands and in bright light it contracts.

Lens

The lens is a piece of transparent material that refracts light passing through it. The lens has the ability to fine focus by automatically changing its shape. When the muscles contract the lens relaxes and gets thicker while when you look at distant objects then the muscles relax and there is more tension on the lens causing it to become thinner.

Focussing system

The light first passes through the cornea where immediately the light is refracted towards the retina. Most of the focussing happens in the cornea. The lens does the remaining focussing.

Retina

The light rays pass the lens and focuses on a screen called the retina. This is where the image is formed by special light sensitive cells and other cells.

Sclera

The sclera is made of an opaque tissue that is white and surrounds the iris.

Astigmatism

The shape of the cornea is irregular and light rays can focus on it one or more place on the retina making images look fuzzy

Correcting Astigmatism

Using eye glasses and contact lenses or laser surgery to correct the shape of cornea.

Blindness

Visual impairment that keeps people from doing things. Most legally blind people can see some light and in rare conditions they can not see at all.

Colour blindness

When a person is only able to see in shades of grey. Cone cells are usually involved.

Normal vision

When light rays that enter is refracted by the lens converges at the retina and produces a sharp image.Light rays from a nearby object diverges and when they enter the eye the muscles change its shape making lens thicker and gives the lens a greater ability to produce a clear image.

Night blindness

When someone can not see in dim light.