9.2 Flashcards
What is the cornea?
A clear window at the front of the eye which allows light to enter.
What is special about the shape of the cornea?
Its shape allows it to function as a fixed focusing device. Responsible for 70-80% of the total focusing ability of the eye.
What are the eye and the pupil?
The size of the iris can vary to control the amount of light that enters the eye.
The pupil is the dark area at the centre.
What is the lens and why is it important?
It adjusts the level of focus.
When is the lens thickest and thinnest.
The lens is thickest when looking at a near object.
It is flattened when looking at a far object.
What effects accommodation (the lens)
Age and fatigue.
What is the retina.
A complex layer of nerve cells at the back of the eye connected to the optical nerve.
Contains two types of light sensitive cells: cones and Rods.
What are cones and how are they different from Rods?
Cones function in good light.
Cones can detect fine detail.
Rods.
Rods cannot detect colour.
Good at detecting movement in peripheral vision.
Cones are in the centre of the retina and rods are in the peripherals.
The fovea?
A small depression at the centre of the retina that is rés poi le for central vision
What does visual acuity mean?
The ability to discriminate sharp detail at varying details.
What is hypermetropia?
Long sightedness.
Shorter than normal eyeball
Lens is shorter than normal.
Objects nearby will appear blurred
What type of lens is used to correct hypermetropia?
Convex lens.
What is myopia?
Short-sightedness.
Eyeball is longer than normal.
Image is formed in front f the retina.
Distant objects will appear blurred.
What are other forms of visual problems?
Cataracts - clouding of lens (age related)
Astigmatism - misshapen cornea
Glaucoma - a build up in pressure of the fluid
Migraine - severe headaches, distort vision.
Presbyopia - loss of lens flexibility (age related)
Fatigue
Influence of foreign substances on vision.
(Drugs)
Reduces supply of oxygen to eye which can affect the sensitivity of the rods.
How long does it take foe cones and rods to adjust to changing lighting conditions.
7 minutes for cones
30 minutes for rods
What is colour blindness called
Colour vision deficiency
What % of people are effected by colour vision deficiency
8%of men
0.5% of women
Can age affect colour vision?
Yes due to yellowing of the lens.
CAP 563 Leaflet H-60
Use of glasses or contact lenses is suitable if prescribed for an engineer
What are the three divisions of the ear
Outer
Middle
Inner