The senses - sight - functions & structures of eye - ch 13 Flashcards
what is the primary function of the eye?
to capture light rays
What are the light rays modified into?
nerve impules
Where are the nerve impules transferred to?
the visual cortex of the brain
What is the role of the visual cortex of the brain once it receives the nerve impulses?
to translate and interpret into images to enable a person to see.
Name the functions of the eye?
- light perception
- focusing of the light onto the retina
- refraction
- light accommodation
- transmissions of messages to the brain
- production of tears
Name the first part of the eye that light first passes through?
cornea
Describe the cornea?
curved clear outer portion of the eye
What is the role of the cornea?
It focuses light through the pupil, a round hole located in the centre of the iris.
Once the cornea has focused light through the pupil through the centre of the iris, what is the iris responsible for?
the iris controls the diameter and size of the pupil and therefore regulates the amount of light that can reach the retina.
Do muscles attached to the iris expand or contract the pupil depending on how much light is present.
Yes, the larger the pupil the more light enters
Describe what happens when light passes through the lens?
Muscles in the eye cause the shape of the lens to become thicker or thinner to focus light on the fovea centralis which is in the middle of the macula on the retina at the back of the eye.
Describe the process of refraction?
As light passes through the lens, muscles in the eye cause the shape of the lens to become thicker or thinner to focus the light on the fovea centralis, which is in the middle of the macula on the retina at the back of the eye.
What does the retina convert the light into?
electric signal.
What is the process of the electric signals that has had light received by the retina?
electric signals travel via the optic nerve to the brain stem and then to the visual cortex in the occipital lobe, where it is translated into an image.
What is the orbit?
The orbit is the eye socket
Where in the body do you find the orbit?
in a space adjoined by the bone of the cheek, the forehead, the temporal bone and the side of the nose.
What is the role of fat pads found within the orbit?
to protect the eye
What is the name of the gland found in the orbit?
lacrimal gland
Where do you find the lacrimal gland?
under the outer portion of the upper eyelid
What is the role of the lacrimal gland?
to produce tears to lubricate and moisten the eye and help clear the eye of any foreign matter, such as dust.
What is the name of the duct that tears are drained away from?
nasolacrimal duct found in the inner corner of the eye
Describe an eyelid?
a thin fold of skin that covers the eye
What is the role of the eyelid?
to protect the eye from foreign bodies and bright light
How does the eyelid protect the eye?
By keeping the eye moist through the operation of blinking which spreads tears across the eye’s surface.
What is the role of eye lashes?
To help filter out dust and debris and prevent sweat from getting into the eye
Describe the Sclera of the eye?
the protective outer wall of the eye
Describe what the Sclera is made up of?
strong, fibrous tissue that expands from the cornea to the optic nerve.
Describe what the sclera gives to the eye?
its white colour and its shape.
Name the muscle that the sclera is attached to?
the extraocular muscle
What is the role of the extraocular muscle?
it moves the eye from side to side, up and down and diagonally.
Describe the conjunctiva of the eye?
a thin transparent layer of skin
Where do you find the conjunctiva of the eye?
begins at the outer edge of the cornea, covers the outer part of the sclera and coats the inside of the eyelids.
What does the conjunctiva of the eye produce?
A thick clear fluid.
what does the thick clear fluid that the conjunctiva produces do?
lubricates the eye as well as produces some tears which help keep bacteria and foreign material from getting into the eye.
What is the conjuntiva made up of?
microscopic blood vessels
What happens to the microscopic blood vessels when the eye becomes irritated, injured or infected?
the blood vessels become dilated and make the eye look red.
Describe the cornea?
clear dome-shaped layer at the front and centre of the eye in front of the iris
What is the main role of the cornea?
to help bend or refract light into the lens as it enters the eye
What percentage of the eyes ability to focus comes from the cornea?
70%
Describe the role of the cornea?
acts as a filter to screen out the most damaging ultraviolet (UV) waves present in sunlight
Where do you find the anterior chamber of the eye?
immediately behind the cornea and the iris.
Is the anterior chamber the fluid filled space?
Yes it is
What is the name of the fluid filled space found in the anterior chamber?
aqueous humour
What does the aqueous humour fluid found in the anterior chamber provide cornea and the lens of the eye?
nourishment
What does the iris control?
the amount of light that enters the eye
Describe the iris?
a circular shape with a round opening in the centre known as the pupil.
What colour can the iris be?
green, blue, brown or a mixture
What does a ring of muscles around the iris allow?
it allows the pupil to contract in bright light and expand in darkness or dim light
Name two extreme emotional circumstances that the pupil dialates to?
- fear
2. pain
Describe where you find the posterior chamber within the eye?
in front of the lens and behind the iris
Where in the eye do you find the lens?
just behind the the iris and the pupil
Name the fluid found in the posterior chamber?
aqueous humour
Describe the lens of the eye?
a clear flexible structure
Name what produces the fluid aqueous humour?
ciliary body
Describe how aqueous humour fluid within the posterior chamber works?
The aqueous humour fluid moves throught the posterior chamber and then forward through the pupil into the anterior chamber
Describe what the ciliary body is responsible for?
ciliary body contracts, the lens thickens, increasing the ability to focus up close.
What does the ciliary body do when looking at an object at a distance?
it relaxes and the lens thins out.
What happens to the ciliary body as we age?
the body muscle and lens gradually lose elasticity.
Where do you find the vitreous cavity in the eye?
behind the lens and in front of the retina
Is the vitreous cavity filled with jelly-like fluid?
Yes
What is the name of the jelly-like fluid found in the vitreous cavity?
vitreous humour
What is the role of the vitreous humour fluid?
to help maintain the shape of the eyeball
Where in the eye do you find the retina?
at the back of the eye
What does the retina contain?
a layer of cells
What is the role of the layered cells found in the retina?
to convert light into nerve signals which are then transferred via the optic nerve to the brain where the image is processed and we ‘see’ an object.
Name two types of cells or photoreceptors that make up the retina?
- rods
2. cones
What is the role of the rods?
rods are sensitive to light allowing vision in dim light.
Do rods allow colour to be detected?
no
What do cones provide?
colours sensitivity but need more light
Where in the eye do you find the macula?
in the centre of the retina
What does the macula provide?
sharp vision in an area known as the fovea centralis, where a concentration of cones is located. This area allows the eye to see detail and perform tasks such as reading.
Where in the eye do you find the choroid?
In between the retina and the sclera
Describe the choroid?
a layer of tissue mainly made up of blood vessels
What is the role of the choroid?
To help nourish the retina
What is the optic nerve responsible for?
transmitting visual information from the eye to the visual cortex of the brain for processing into an image.
There are 12 pairs of cranial nerves, what number is the optic nerve.
the optic nerve is the second nerve of 12 pairs of cranial nerves
