The Eye Flashcards
Identify the structures of the eye
https://pmt.physicsandmathstutor.com/download/Biology/GCSE/Notes/Edexcel/2-Cells-and-Control/Flashcards/Flashcards%20-%20Topic%202%20The%20eye%20-%20Edexcel%20Biology%20GCSE.pdf
A= cornea B = iris C = ciliary muscle D = lens E = suspensory ligaments F = retina G = optic nerve
Outline the structure and function of the cornea
● Transparent outer covering of the eye
● Refracts light entering the eye
Outline the structure and function of the iris
● Pigmented ring of circular muscles and
radial muscles
● Controls the size of the pupil to alter how
much light enters the eye
What is the pupil?
Ahole in the iris centre that allows light
rays to enter the eye
Outline the structure and function of the lens
● Transparent, bi-convex structure
● Suspensory ligaments attach the lens to a ring
of ciliary muscle
● Refracts light, focusing it onto the retina
What is the function of the ciliary muscles and
suspensory ligaments?
Change the shape of the lens (accomodation)
to focus light onto the retina
Outline the structure and function of the retina
● Light sensitive layer composed of rod and
cone cells
● Converts light energy into neural signals which
are sent to the brain via the optic nerve
What are rod cells?
Cells in the retina that are sensitive to
low light intensity (dim light)
What are cone cells?
Cells found in the retina that are sensitive
to high light intensity (bright light) and can
detect different colours.
What is the function of the optic nerve?
It transmits nerve impulses to the brain
from the retina.
Describe how dim light affects the size of the pupil
● Light receptors detect dim light ● Circular muscles relax ● Radial muscles contract ● Pupil dilates ● More light enters the pupil
Describe how bright light affects the size of the pupil
● Light receptors detect bright light ● Circular muscles contract ● Radial muscles relax ● Pupil contracts ● Less light enters the pupil
Why is the iris reflex important?
It prevents bright light from damaging the
retina.
What is accommodation?
● Process by which the elastic lens changes its shape
(with the aid of ciliary muscles and suspensory
ligaments) to focus on near or distant objects
● Light is focused onto the retina
Describe how the eye focuses on near objects
● Near object ● Ciliary muscles contract ● Suspensory ligaments slacken ● Lens becomes more convex (more rounded) ● Light is refracted more ● Light rays focused onto the retina
Describe how the eye focuses on distant objects
● Distant object ● Ciliary muscles relax ● Suspensory ligaments tighten ● Lens becomes less convex (less rounded) ● Light is refracted less ● Light rays focused onto the retina
What is long-sightedness?
● Can focus on distant objects clearly
● Cannot focus on near objects
What are the causes of long-sightedness?
● Eyeball is too short
● Lens is less elastic (usually age-related)
● ∴ light rays are not focussed onto the retina,
instead converging behind the retina
How is long-sightedness treated?
● Using a convex lens (causes light rays to
converge) in glasses or contact lenses
● Replacement lenses
● Laser eye surgery
What is short-sightedness?
● Can focus on near objects clearly
● Cannot focus on distant objects
What are the causes of short-sightedness?
● Eyeball is too long
● Lens is too thick and too rounded
● ∴ light rays are not focussed onto the retina,
instead converging in front of the retina
How is short-sightedness treated?
● Using a concave lens (causes light rays
to diverge) in glasses or contact lenses
● Replacement lenses
● Laser eye surgery
What are cataracts?
● Acloudy patch forms on the lens of the eye
which negatively affects vision
● Vision becomes blurry, difficult to see the
intensity of colours, problems with glare etc.
How are cataracts treated?
The clouded lens is exchanged for a
synthetic lens during surgery.
What is colour-blindness?
● Adeficiency of the eye that makes it difficult to
distinguish between colours
● e.g. individuals with red-green colour blindness have
difficulty differentiating between red and green
What is the cause of colour-blindness?
Damage to cone cells in the retina
