Chapter 1 (1.2 : Eye) Flashcards
What is the function of eye lens?
-Bends and focuses light to form an image on the retina
-The thickness of the lens can be altered to focus near and distant object
What is the function of iris?
Controls the size of the pupil and hence the amount of light entering the eye
What is the function of vitreous humour?
-Helps refract light and focus the image onto the retina
-Helps to maintain the shape of the eye and the pressure in the eye
What is the function of conjunctiva?
Protects the cornea
What is the function of cornea?
-Helps to focus light onto the retina by bending light rays passing through it
-Allow light to enter the eye
-Prevent internal reflection of light in the eye
What is the function of pupil?
Allow light to pass into the eye
What is the function of suspensory ligament?
Hold the lens in place and connect it to the ciliary body
What is the function of ciliary muscles?
-Contracts and relaxes to change the thickness of the lens
-Changes the focal length of the lens
What is the function of sclera?
-Protects and shapes the eye
What is the function of optic nerve?
Sends nerve impulses from the retina to the brain to be interpreted
What is the function of fovea(yellow spot)?
Detects the images of the objects formed and give the clearest vision
What is the function of retina?
-Detects light stimuli and sends information in the form of nerve impulses to the brain
-Has many receptors that are sensitive to light
(Photoreceptors : rods and cones)
-Rods: sensitive to different light intensities including dim light but not sensitive to coloured lights
-Cones: sensitive to coloured lights in bright conditions only, there are three types of cone cells which are sensitive to red, blue aand green lights
What’s the function of photoreceptors (cones and rods)?
Cones : Sensitive to coloured light in bright conditions (red, blue, green)
Rods : Sensitive to different light intensities including dim light but not sensitive to colour light
What are the characteristics of a blind spot
-This point of retina is not sensitive to light
-Images falling on this spot cannot be detected because there are no receptors cells on this spot
-Spot where optic nerve leaves the eye ball
Which part of the eye is thin, transparent and self-repairing membrane?
Conjunctiva
Which part of the eye is curved, transparent layer at the front of the eyes is a continuation of the sclera?
Cornea
Which part of the eye is the outer layer of the eyeball, white, tough and opaque?
Sclera
What’s the function of choroid
The capillaries supply nutrients and oxygen to the eye
What is the middle layer of the eyeball called?
Choroid
State the order of sight mechanism of humans
Light rays -> Cornea -> Eye lens -> Retina -> Optic nerve -> Brain
When does an optical illusion occur?
An optical illusion occurs when the brain does not interpret the nerve impulses accurately
What examples of devices are used to overcome the limitations of sight?
-Microscope
-Magnifying glasses
-Telescope
-Binoculars
-X-rays
-Ultrasound scanning device
What are the common defects of vision?
-Short-sightedness (myopia)
-Long-sightedness (hypermetropia)
-Astigmatism
-Colour blindness
-Presbyopia
What are the similarities between short-sightedness (myopia) and long-sightedness (hypermetropia)?
Caused by the condition of the lens and the shape of the eyeball
What are the characteristics of short-sightedness?
Condition of person
-Sees nearly objects clearly but can’t focus on distant objects
Focus
-Light from a distant object is focused in front of the retina
Causes
-Eye lens is too thick
-Eye ball is too long
What are the characteristics of long-sightedness?
Condition of person
-Sees nearly objects clearly but can’t focus on distant objects
Focus
-Light from a near object is focused behind of the retina
Causes
-Eye lens is too thin
-Eye ball is too short
What correction is made in order to see clearly with short-sightedness?
-Use glasses with concave lenses
Concave lenses
-Diverges the light rays before they enter the eye
-The diverging rays are focused onto the retina by the lens to form a sharp image
What correction is made in order to see clearly with long-sightedness?
-Use glasses with convex lenses
Convex lenses
-Converges the light rays
-The converging light rays are focused onto the retina by the lens to form a sharp image
What causes astigmatism?
-Astigmatism is caused by irregular surface of the cornea, or a lens that is not evenly curved
-The vertical and horizontal rays from the image cannot be focused at the same time
What does the person with astigmatism see? Explain your answer
A person with astigmatism sees some parts of an object more clearly than others because the image formed on the retina is distorted and not very clear.
What causes colour blindness?
Colour blindness is caused by a shortage of cone cells (colour receptor cells) on the retina
What causes presbyopia?
Presbyopia is caused when a person gets older, the eye lens becomes harder and less elastic.The muscles in the ciliary muscles loses their ability to contract and relax. As a result, both near and far objects cannot be focused on the retina.
