The Eye And Vision - Chapter 6 Flashcards
Cornea is responsible for ______________% of the focussing of the eye
70% - 80%
The lens does what?
The final focussing of the eye
Iris controls the amount of…
Light entering the pupil.
This is controlled by the ANS.
If the eye observes a close object, the pupil becomes:
Smaller
If the eye observes an object at a distance, the pupil becomes:
Larger
The lens uses which muscles to make a final focus, and what is the process called?
Ciliary muscles and this is a process of accommodation.
This can be affected by age and fatigue.
If the lens focuses on an object close to it, the lens…
Thickens
If the lens focuses on a distant object, the lens…
Flattens
The image is __________ on the retina
Inverted
Light sensitive cells near the retina are called:
Cones and rods
Light sticking the rods and cones causes a _________________process which is then sent to the visual cortex via the optical nerve
Chemical, electrical process
Centre of the retina is called:
The Fovea
The fovea consists of:
Only cones
Vision through the rods is
Scotopic vision
Vision through the cones is
Photopic vision
The C’s stand for?
Cones are Colour sensitive - Central Vision
What do the rods see?
Black and white
Peripheral vision
Sensitive to low level light
Sensitive to movement
As environmental light diminishes, so does….
Colour vision
The Fovea is…
Central part of retina
Consists only of cones
Has the acuity of 20/20
Central vision is found here
Alphanumeric Information is….
Reading
Alphanumeric information reading is limited to
The Foveal area
Visual field is defined as:
Central field + peripheral field = visual field
20/20 is defined as:
You can see at 20ft what the normal person can see at 20 ft
As your sight moves away from the Fovea, the effect is….
Rapid
At 5’ from the fovea you can see only ________ what you can at 20/20
Half
At 25’ away from the fovea you can see only _________ of 20/20
A tenth
Acuity is affected by:
Angular distance from the fovea
How long does it take the rods and cones to adapt to the light (from dark)
Cones - 10 seconds
Rods - 10 seconds
How long does it take the rods and cones to adapt to the dark (from light)
Cones - 7 minutes
Rods - 30 minutes
How is night vision affected by hypoxia, what stage is it in and at what altitude does it occur?
Hypoxia can cause a deterioration in night vision, it is in the indifferent stage and occurs at 5,000 ft
Which works better for night vision, rods or cones?
Rods and they are more sensitive to low level light
Night vision is affected by:
Cabin altitude Lack of vitamin A Age Mild Hypoxia Smoking
Stereopsis
Depth Perception (up to 200ft)
Blind spots
No light sensitive cells, found at the optic nerve
Empty field myopia
If the eyes are rested, the natural focus distance is 1-1.5m
Photochromic sunglasses are _________ for flying
Prohibited
Polarised sunglasses are ____________ in flying
Discouraged
Eye movement is controlled by how many muscles?
6 extrocular muscles
Long sightedness
Hypermetropia
Short sightedness
Myopia
For both long and short sightedness, the eyeballs are:
Misshaped
To fix long sightedness (hypermetropia)
Convex lens
To fix short sightedness (Myopia)
Concave lens
In short sightedness, the light…
Doesn’t reach the back of the fovea
In long sightedness, the light…
Makes an image behind the Fovea
Presbyopia
Age affects eyesight
This is because the ciliary muscles weaken and the lens grows less flexible and so affects accommodation.
Causes a form of long sightedness.
Astigmatism
Caused by a mis-shaped cornea
Cataracts
Clouding of the lens
This can be cured by surgery
Correcting Specs
Another, spare pair is to be carried at all times whilst flying where they’re easy to access.
Glaucoma
Caused by a pressure rise of the liquid in the eye ball
If left untreated, can lead to blindness
Symptoms:
- Acute pain in the eye
- Blurred Vision
- Sensitivity to high light levels
- Visual field deterioration
- Red discolouration of the eye
Contact Lens’s
Can cause damage to the cornea with low humidity
May be dislodged by the rubbing of the eye, or an accidental knock
Bifocal contact lenses are prohibited
Must carry a pair of spare spectacles
Colour blindness
Doesn’t affect acuity
Total colour blindness is rare
Caused by defects in the cones
Passed on through genes
Monocular vision
A person with vision in only one eye cannot be accepted by EASA as fit to fly
