The Eye & Sight Problems Flashcards
Which two parts of the eye focus light?
The cornea and the lens
Where is the image formed?
The retina
How are images sent to the brain?
The nerves in the retina convert the image into electrical signals that are sent to the brain along the optic nerve.
When does the eye lens need to be more or less curved?
1) Eye lens needs to be more curved when looking at a near object
2) Eye lens needs to be less curved when looking at a distant object
What is the “far point” and how far is it?
The most distance point an eye can focus on. For a normal eye, this is infinity.
What is the “near point” and how near is it?
The near point is the closest point on which the eye can focus. For a normal adult, this is about 25cm. Young people can focus on objects closer than this.
How does a converging lens work?
It bends rays of light towards one another, bringing them to a point.
How does a diverging lens work?
It bends rays of light away from each other.
What do the terms “long sighted” and “short sighted” mean?
Long sighted people can focus on distant objects but not near ones.
Short sighted people can focus on near objects but not distant ones.
What may be some causes of short sight?
1) A person may have eyeballs that are too long
2) Or eye lenses that are too powerful even when the muscles are relaxed
What may be some causes of long sight?
1) A person may have eyeballs that are too short
2) Or have eye lenses that are not powerful enough (which happens when we get older and the lens does not bend enough)
How can wearing glasses correct ones sight?
Long sight - Wear a converging lens which brings the rays together so light it focused on the retina
Short sight - Wear a diverging lens which makes the rays come together further away so light is focused on the retina
How is laser treatment used to correct sight problems?
Patients are given a local anaesthetic. Lasers are used to make small, precise cuts in the cornea which permanently shape it. Shaping the cornea this way can make it act like a diverging or converging lens, depending on the patients condition
What are the advantages of contact lenses?
1) They are safe when playing sport because the cannot be knocked off or broken
2) People may prefer not to wear glasses
What are the disadvantages of contact lenses?
1) Contact lenses must be kept very clean otherwise they can cause infection
2) Some people may find them uncomfortable to wear
Where does light enter the eye from?
The pupil
