Eye and Vision Flashcards
What is the Aqueous Humour?
Watery fluid at the front of the eye that helps reflect light towards the lens
Cornea
Transparent and at the front of the eye. Most of the focusing is done at the Cornea!
What % of focusing is done at the cornea?
70%
Iris
Colored part of the eye that contains muscles which relax or contract to adjust the size of the pupil. It controls how much light enters the pupil.
Pupil
Hole in the middle of the Iris. Allows light to pass through as it enters the eye.
Lens
Transparent, flexible disc behind the Iris. It is attached to the cillary muscles. It refracts light to focus it onto the retina.
The amount of refractions can be adjusted by altering the thickness and curviture of the lens.
What % of focusing is done by the lens?
20-30%
Retina
What/Where & what does it contain?
It’s a light sensitive lining at the back of the eye containing two types of light receptor cells - Rods & Cones.
Vitreous Humour
A watery fluid that keeps the shape of the eyeball
Optic Nerve
The optic nerve carries impulses from the retina to the brain
Fovea
(rods or cones?)
- Most sensitive part of the retina
- At the centre of the retina
- Contains only cones and is where the central vision occurs
What is the lenses refractive power measured in?
Also, what is the Average?
Dioptres
16-30 Dioptres = Average
Tear ducts
Washes eyes with anti bacterial solutions
The eye is controlled by muscles.
How many are there and what are they called?
Extraoccular muscles
There are 6 of them
What is another word for focusing and which muscles control it in the lens?
Accomodation
It is controlled by the Cillary Muscles
What do the cillary muscles do?
They control focusing/accomodation of the lens
What affects accomodation?
Age, Fatigue
To focus on distance, the lens becomes rounder/flatter?
The lens becomes flatter (concave).
This is done when the cillary muscles relax/pull the lens
To focus on near objects, the lens becomes flatter/rounder?
The lens becomes thicker&rounder.
This is done when the cillary muscles contract and squish the lens.
What is scoptic vision?
Night vision
What is Photopic vision?
Colored vision
Rods
What are they responsible for and where are the found?
They are found on the retina and cover more surface area compared to the cones.
They are responsible for black & white vision, night vision (Scoptic vision), and Peripheral vision (vision on the sides of the eye)
What is the Peripheral vision?
It is vision on the sides of the eye.
It picks up movement, but little detail.
Cones
What&Where?
The cones are mostly found in the fovea of the retina.
They are responsible for color vision (Photopic vision) and central vision (most detail).
They are green, red and blue.
Do rods or cones show more detail?
Cones
Max amount of rods can be found ___degrees away from the fovea:
10 degrees away from the fovea
How many cones are there per mm at the Fovea?
150.000 per mm
Going from dark to light, how long does it take for the cones and rods to adjust?
Approx. 10 seconds for both
Going from light to dark, how long does it take for the cones and rods to adjust?
Cones: approx. 7 minutes
Rods: approx. 30 minutes.
Night vision is affected by which factors?
- Smoking
- Alcohol
- Hypoxia/Altitude
- Age
- Vitamin A
*
What is visual acuity?
It’s a measure of the central vision
20/20 vision means:
That you can see from 20 ft what the average person sees from 20 ft.
Alpha numeric vision is restricted to the ….
fovea
Visual acuity is affected by:
- Distance to object
- Weather
- Size of object
- Contours
- Distance from fovea
Distance from fovea vs visual acuity :
5 degrees from fovea –>
10 degrees from fovea –>
Distance from fovea vs visual acuity :
5 degrees from fovea –> 1/2
10 degrees from fovea –> 1/10
Each eye sees how many degrees?
What is the overlap?
120 degrees
They overlap by 60 degrees (binocular vision)
What is the visual field?
The sum of central and peripheral vision
Binocular vision gives us depth perception when objects are close….(how close?)
less than 1 meter
What causes the blind spot?
The place on the retina where the optic nerve leaves and goes to the visual cortex of the brain, contains no rods or cones.
This causes the blind spot.
Stereopsis or depth perception is limited to ___ft/m
200 ft / 60 m
Empty Field Myopia
What is it?
What causes it?
How to overcome it?
How to combat it?
Empty Field Myopia is when our eyes come to a natural resting point about 1-2 m in front of us.
It’s caused by a lack of a distant focal point.
Scan around view to combat empty field myopia.
To overcome it, focus on a distant object, e.g. Wintip.
Myopia
What is it?
What kind of lens is used to correct it?
Short-sightedness.
Occurs when the eyeball is longer than normal.
It is corrected by a diverging lens.
Hypermetropia
What is it?
How is it corrected?
Long-sightedness
Occurs when the eyeball is shorter than normal.
It is corrected with a converging lens.
Presbyopia
What is it?
It’s when the cillary muscles lose their elasticity, which causes the lens to be less flexible.
At what age does Presbyopia kick in?
Age 45-50
Presbyopia is a form of
a) Myopia
b) Hypermetropia
Hypermetropia.
What is Astigmatism?
It’s caused by a misshape in the cornea or misshape in lens.
Cornea = more common.
What are Cataracts?
Develops due to ____.
Can it be cured?
It is an opacity (cloud formation) of the eye lens.
Develops due to ageing.
It can be cured.
What causes glaucoma?
When the drainage canal in the eye is blocked, and fluid cannot escape (only added), it leads to a high pressure in the eyeball and can damage nerves in the eye.
It has an insidous onset with concealed progression.
It can lead to total blindness if not caught in time
What causes color blindness?
It is caused when one of the cones doesn’t work (red/green/blue).
It is genetic.
What % of men and women does color blindness affect?
7% men
0.1% women
Flash Blindness
What causes it?
How is it combated?
It is a temporary blindness caused by a very bright flash of light (e.g. lightning)
It can be combated by turning the cockpit lights on, sunglasses, curtains, etc.
What do sunglasses do?
They block UV light from the sun. This is the worst at high altitude.
Sunglasses must be:
- Must carry spare pair
- Impact resistant
- Thin metal frames
- Coated in polycarbonate for strength
- Good optical quality
- Luminous transmittence 10-15%
- Have appropriate filtration characteristics
- Transition lenses of photocromic lenses are prohibited
- Polarized lenses are discouraged (not prohibited)
