2. Digital Images and the Eye Flashcards
What is the Cornea
Transparent covering protecting the front of the eye
What is the iris
It controls the pupil size and brightness accommodation
What is the Lens
Focusses image on retina by ciliary muscles
What is the retina
Light sensitive tissue on the inner layer of the eye
What is the fovea
Central pit in macula with high density of cones for central vision
What is the blind spot
A lack of rods and cones on the optic disc
Are rods scioptic or photoptic?
Scioptic (they see dim light)
Are cones scioptic or photoptic?
Photoptic (bright light)
How many rods are in the fovea?
0/ Very few
How many cones are in the fovea
About 200,000 per mm^-2
Why do cones have higher visual acuity?
They each have their own nerve end, so can distinguish finer detail
What kinds of vision are rods responsible for?
Night, sensitive motion detection, peripheral
Why does the eye move continuously?
To keep the light from the object of interest falling on the fovea
How many types of rods are there?
1
What are the 3 types of cone?
Red, Green, and Blue.
What is the focal length?
The distance from the centre of the lens to the retina
How is refractive power calculated?
1 / focal length
When is refractive power lowest?
When focusing on objects further than 3m away
When is the focal length longest?
17mm
Why is the focal length longest at 17mm?
The relaxed muscle flattens the length
For distant objects, do we want a small or a long focal length?
Small, as we do not want to ben the light much
Does a small refractive power have long or short focal length?
Long
How is a long distance image formed? (4 steps)
- Ciliary muscles relax
- Stretches and makes lense thinner
- Focal length is made longer
- Refractive power is less
How is a short distance image formed? (4 steps)
- Ciliary muscles contract
- Lens becomes thicker in the middle
- Focal length becomes shorter
- Refractive power is greater
