M9.2 (eyes) Flashcards
Parts of the eye
Cornea
Iris & pupil
Lens
Retina
Fovea
Cornea?
Clear window at front of eye, allows light to enter
Shape allows it to act as a fixed focusing device by bending incoming light rays
How much of the eyes total focusing responsibility is the cornea responsible for?
70 - 80%
Iris?
Varies the size of the pupil to control how much light enters the eye
The pupils size can change…
Rapidly
What ratio can light be adjusted by?
5:1
What part of the eye is the iris?
Coloured
What part of the eye is the pupil?
Dark centre section
What does the lens use to change its shape?
Ciliary muscles
What does the lens do?
And what is this called?
Adjusters the level of focus
Called accommodation
When is the lens thickened?
Focus on close object
Accommodation is compromised by what and what can it lead to?
Compromised by fatigue or aging
Lead to less sharp vision
Where is the retina located?
Back of the eyeball
The retina has what which are connected to what?
Nerve cells connected to the optic nerve
What are the 2 types of nerve cells in the retina?
Cones and rods
Cones?
Work in good light
Colour sensitive
Detect fine detail
Allows eye to see 1000 different colours
Rods?
Don’t detect colours
Poor at distinguishing fine details
Good at detecting movement in peripheral vision
When do rods take over from cones?
When the light decreases
Rods and cones are stimulated by what?
Light
Rods and cones transfer what?
Electrical impulses to the visual cortex in the brain via optic nerve
Rods and cones transfer what?
Electrical impulses to the visual cortex in the brain via optic nerve
What is there where the optic nerve joins the back of the eye?
A blind spot
What is there where the optic nerve joins the back of the eye?
A blind spot
Fovea?
A small depression in the centre of the retina
Responsible for central vision
Contains many cones
Where visual acuity at its highest
Visual acuity?
The eyes ability to perceive sharp detail at varying distances
How can visual acuity be assessed?
With a Snellen chart
20/20 vision (see 20 feet away clearly)
Hypermetropia?
(Long sightedness)
When you have a shorter then normal eye ball, means the image is formed behind the retina
Myopia?
(Short sightedness)
Eyeball longer then normal, image formed in front of retina
Cataracts?
Clouding of lens
(Associated with age)
Astigmatism?
A miss shaped cornea, distorts visual perception
Migraine?
Severe headaches lead to visual disturbances
Fatigue?
Temporary affect accommodation
How does smoking affect vision?
Causes a build up of carbon monoxide in bloodstream which reduces oxygen supply to the eye.
Known as hypoxia which reduces sensitivity in rods
How long does it take for rods and cones to adapt to a dark environment?
Cones - 7mins
Rods - 30 mins
Contacts can be worn for how long?
8 - 12 hrs
What can impart your vision when wearing glasses?
Dust
Rain
Mist
Colour vision deficiency?
Colour blindness
What causes colour blindness?
Defect in the structure of colour sensitive cones
What % of men and women does colour blindness affect?
Men - 8%
Women - 0.5%
What are the most common colour distinguishing for colour blindness
Red and green
Sometimes blue and yellow
