Year 9 Science - The Structures and Function of Eye Name: _______________
Aqeous Humour - Choroid - Cornea – Blind Spot - Iris - Lens
Optic Nerve - Pupil - Retina – Sclera - Vitreous Humour
Structure
Function
Clear, watery fluid found in the anterior chamber of the eye – in between the cornea and lens.
The location on the retina where there is no cell sensitive to light.
The middle layer of the eye with dark pigments to prevent internal reflection.
Transparent tissue covering the front of the eye – known as the window of the eye.
Circular band of muscles that controls the size of the pupil. The pigmentation of the iris gives
"colour" to the eye.
Transparent tissue that bends light passing through the eye. This structure is biconcave in shape
and can change its shape for focusing
Hole in the center of the pupil where light passes through.
Tissue at the back of the eye that contains cells responsive to light (photoreceptors).
The tubular structure carries nerve messages (impulses) from the light sensitive cells to the
brain for interpretation.
The outermost layer of the eye – white in colour with blood vessels
Jelly-like Structure, taking up the largest portion of the eye for maintaining the shape of the eye
Cornea - the clear, dome-shaped tissue
covering the front of the eye.
Iris - the colored part of the eye - it
controls the amount of light that enters the
eye by changing the size of the pupil
Lens - a crystalline structure located just
behind the iris - it focuses light onto the
retina
Optic nerve - the nerve that transmits
electrical impulses from the retina to the
brain
Pupil - the opening in the center of the iris- it changes size as the amount
of light changes (the more light, the smaller the hole)
Retina - sensory tissue that lines the back of the eye. It contains millions
of photoreceptors (rods and cones) that convert light rays into electrical
impulses that are relayed to the brain via the optic nerve
Vitreous - a thick, transparent liquid that fills the center of the eye - it is
mostly water and gives the eye its form and shape (also called the vitreous
humor)
1.
What is the name of the tough white protective layer?

Sclerotic
2.
Why is there also a black layer?

to pre
vent reflection inside eye (which would degrade the image)
List (in order) 6 structures or substances that light passes through, on its way from the front to the
back:

conjunctiva / cornea / aqueous humour / lens / vitreous humour /retina
3.
4.
5.
Which parts "bend" the light as it passes through them?

cornea > aqueo
us humour ns
Assuming that the diagram is viewed from above, which eye is shown (left or right)?

right ______
The response of the eye to changing light intensity
Complete the diagrams below (by drawing in circles of appropriate sizes) to show the response of the iris of the
eye to different lighting conditions. This is an example of a reflex action.
Two opposed sets of muscles in the iris - the radial muscles and the circular muscles - contract to alter the size of the
pupil.
What is the difference between the iris and the pupil?
>The iris is a disc with a hole in the centre > The pupilis the hole!
Interestingly, the colour of the iris is due to the dark pigment melanin, whatever the "colour" of the eyes.
The pupil usually looks black because not much light is reflected out of the eye. Cats' eyes are exceptions, as they have
a layer to reflect light and so maximise their sensitivity to dim light.
What is so special about the yellow spot (at the back of the eye)?
> zone of maximum sensitivity
What cells is it composed of, and what is their function?
> cones > give a clear picture, and sensitive to colour
What is the rest of the retina composed of?
> rods (and a few cones)
What are the advantages and disadvantages of these cells?
> work in dim light > vision not as clear
At the blind spot, what structures are missing, and what is there instead?
> light sensitive cells > optic nerve (and blood vess