Vision Flashcards
Where is the eye located?
In the bony socket so eye doesn’t pop out?
What is the inner layer of the eye called?
Lens
What is the role of the Iris?
This part lets light into the eye?
What is the coloured part of the eye called?
Iris
What is the role of the lens?
Located behind the iris, it is responsible for contracting and relaxing thus changing its focal point.
How do the lens contract and relax?
Using ciliary muscles, they pull the lens to open and close.
Where rods and cones located?
Retina and fomia
What does the retina consist of?
Rods and cones. They detect light and colour.
What does the term accommodation mean?
It means the opening and closing of the lens using ciliary muscles according to what the eye is trying to focus on.
How much refraction does the cornea do?
70%
What is the cornea?
The cornea is the transparent part of the eye covering the iris and pupil.
How many rods and cone are on each eye?
120 million rods and 6 million cones
Facts about rod cells?
- they only see black and white
- work well in the dark or low levels of illumination
- Perception of fine detail is also not possible at night (Scotopic vision)
- Mainly responsible for perception of movement
- Further away from fovea the more rod cells there are
What does visual acuity mean?
Visual acuity means the capacity of the eye to resolve dine details
Are there any rods in the fovea?
No
Facts about cone cells?
- Cones detect colour and fine detail
- They only work well in bright light
- Many cones are clustered together in fovea
For best vision during ‘__’ time is to look directly at the object through the’___’ of eye falling on the’__’
For best vision during day time is to look directly at the object through the leans of eye falling on the fovea
Do cones function efficiently during night time?
At night cones in the fovea do not function efficiently, effectively causing a night-blind spot directly in front of you.
At night what degree should you focus to view the target best.
At night focus 10-15 degrees to the side of the target for the best results.
If you stare at an object at night, the image begins to fade. Scanning will help to maintain a sharp image.
What do the lens do when focusing on near or far objects?
Lens become thicker and rounder focusing on near objects
Lens becomes flatter focusing on object in distance
Where is the fovea located?
On the retina
How much refraction do the lens do?
30% refraction
When is visual acuity best?
When the light falls directly onto the fovea. For best visual acuity we need to be staring directly at the object.
What are some visual defects?
Myopia (short sight)
Hypermetropia (long sight)
Presbyopia (age changes)
What is myopia?
Someone with myopia, a person can see near objects clearly, but not distant objects.
Lens are to weak so the light falls short of retina.
What is hypermetropia?
Someone with hypermetropia is a person can see distant objects clearly but not near objects
Lens are too powerful so light rays travel to far to focus on the retina.
What is presbyopia?
As people age the lens become less elastic and ciliary muscles get weaker
In most people over the age of 40, the ability to focus deteriorates
Due to the disparity of eyes, each eye views an object from slightly different angle. This is called?
Depth perception.
Binocular vision is reliable up to ‘__’ metres after ‘__’ metres we guess
Binocular vision is reliable up to 6 metres after 6 metres we guess
Binocular vision up to ‘__’ metres becomes like looking with one eye
Binocular vision up to 60metres becomes like looking with one eye
What are two types of binocular cues?
- Accommodative reflex
- Convergence reflex
What is accommodative reflex?
Is the contracting and relaxing of the lens using ciliary muscles to adjust to what the eye is trying to focus on whether far or near objects
What is convergence reflex?
As an object approaches, the eye must converge to maintain binocular fixation on the target. Through experience, the distance of the object gives a more accurate cue.
