4.5.2.3 The Eye

What is accommodation?

An adaption that allows the eye to change its shape in order to focus on near or distant objects

What is the retina?

A layer of light sensitive cells found at the back of the eye

What does the retina do?

When light hits it, the cells are stimulated and impulses are sent to the brain which interprets the information to create an image

What is the optic nerve?

A nerve that leaves the eye and leads to the brain

What does the optic nerve do?

It carries the impulses from the retina to the brain to create an image

What is the sclera?

A white outer layer which supports the structures inside the eye

What does the sclera do?

Prevents some damage to the eye as it’s strong

What is the cornea?

The see-through layer at the front of the eye

What does the cornea do?

Allows light through so the curved surface bends and focuses light onto the retina

What is the iris?

The muscles that surround the pupil

What does the iris do?

Contract or relax to alter the size of the pupil

How does the iris respond to bright light?

The circular muscles contract and radial muscles relax to make the pupil smaller, avoiding damage to the retina

How does the iris respond to dim light?

The circular muscles relax and the radial muscles contract to make the pupil larger so more light can enter to create a better image

What do ciliary muscles and suspensory ligaments do?

Holds the lens in place as they control its shape

What is the process of accommodation when focusing on a near object?

The ciliary muscles contract and the suspensory ligaments loosen so the lens is thicker and more curved, which refracts the light more

What is the process of accommodation when focusing on a distant object?

The ciliary muscles relax and the suspensory ligaments tighten so the lens becomes thinner and light is refracted less

When do eye defects occur?

When light cannot focus on the retina

What is short sightedness called?

Myopia

Why would someone have myopia?

Their lens is too curved so distant objects appear blurry

What is long sightedness called?

Hyperopia

What would someone have hyperopia?

Their lens is too flat so it cannot refract light enough

How does spectacle lenses treat eye defects?

Concave lenses spread out the light to treat myopia and convex lenses bring the rays together to treat hyperopia

How does contact lenses treat eye defects?

They work in the same way as glasses but allow activities such as sport to be carried out, hard or soft contact lenses last for different lengths of time

How does laser eye surgery treat myopia?

Lasers can be used to either reduce the thickness of the cornea so less light is refracted

How does laser eye surgery treat hyperopia?

Lasers change its curvature so light is refracted more strongly

How does replacement lens treat hyperopia?

Hyperopia can be treated by replacing the lens with an artificial one made of clear plastic or adding the plastic on top of the natural lens

What are the risks of replacement lens treatment?

Damage to retina or cataracts developing