Biology - The Eye

What type of organ is the eye?

A sense organ

Give the 13 parts of the eye.

Vitreous humour

Retina

Sclera

Choroid

Optic nerve

Suspensory ligaments

Ciliary muscles

Lens

Iris

Pupil

Cornea

Aqueous humour

Conjunctiva

What is conjunctivitis

Inflammation of the conjunctiva

What does the cornea do?

Transparent outer layer that refracts light into the eye

What does the lens do?

Refracts light onto the Retina, changes shape depending on the distance

What does the pupil do?

Hole in the centre which allows light into the eye

What does the Iris do?

Contains muscles (circular and radial) which control the diameter of the pupil

What does the Retina do?

Contains receptor cells that send signals to the brain - rods are sensitive to light intensity, cones are sensitive to colour

What does the choroid do?

Contains blood vessels and prevents internal reflection of light

What does the Sclera do?

Protective outer layer, coloured white

What does the Optic nerve do?

Sensory neurone that carries signal fron light receptor cells to the brain

Why is there a blind spot in the eye?

There is no retina in front of the Optic nerve

How does the Iris respond to bright light

Circular muscles contract, radial muscles relax, causing the pupil to become smaller

How does the Iris respond to dim light

Circular muscles relax, radial muscles conteact, causing the pupil to become larger

What is accommodation?

The eye changing the shape of the elastic lens to focus light from near or distant objects onto the retina. It is a reflex

How does the eye focus on near objects

Ciliary muscles contract

Causes Suspensory ligaments to slacken

Causes the lens to become more rounded and therefore refract light more

How does the eye focus on distant objects?

Ciliary muscles relax

This causes the Suspensory ligaments to pull tight

This causes the lens to become a less rounded shape, meaning light is refracted by a smaller amount

What is short-sightedness?

When people can’t focus on distant objects

Why does long-sightedness occur?

When the eye is too short or has the wrong shaped lens, the image focused by the lens behind the retina

How can long-sightedness be corrected?

Using a convex lens, which focused light bringing the image forward into the retina

What is long-sightedness?

When people can’t focus on near objects

Why does short-sightedness occur?

When the lens is the wrong shape or the eye is too long, the image focused by the lens is infront of the retina

How can short-sightedness be corrected?

Using a concave lens, which disperses the light, moving the image back onto the retina

How does newborns see the world?

Upside down, with 2 black circles in the middle of each side

Give 2 eye defects

Colour blindness

Cataracts

What is colour blindness and how does it occur

When people can’t tell the difference between 2 colours (usually red/green)

Occurs when some cones in the retina are dysfunctional

There is no cure as we cannot replace cone cells

What are cataracts and how do they occur

Cloudy patches on the lens, which stop light entering properly, leading to blurred vision, dull colours, difficulty in bright light

They develop over time as proteins In the lens/aqueous humour denatured and become cloudy

It can be cured surgically by replacing the lens with an artificial one