Topic 17 Flashcards
Give the optical properties of the human eye
Over 180° optical view
Resolution determined by wavelength
Refractive index: 1.38 (Periphery), 1.42 (Centre)
Receptors: Rods and Cones
What is the blind spot?
The area where optic nerve leaves the eye
Wht is the yellow spot?
The area of best vision
How many more rods than cones are there?
20 times (Mostly in the optical axis)
Draw the path of light in the eye
Cornea and lens
What is the purpose of the crystaline lens?
To provide fine adjustment to focus on objects at different distances
What is the far point?
The most distant point the eye can focus
(Normal eye = ∞)
What is the near point?
The closes point an eye can focus
(Normal eye = 25cm)
What is the normal power?
4 diopter
Changes with age
What is the accomodation width?
A = Pn - Pf = 4 Diopters
- Young children = 14 D*
- Elderly = Near 0 D*
What is Visual Acuity? What is it dependent on?
The finest detail that can be seen with the eye.
Dependent on the distance between cones
There must be 1 unexcited cone between two excited ones
What is sensitivity?
The minimum intensity needed to see light, dependent on wavelength.
400-700 nm wavelength range in Humans
Higher in the dark
When are cones and rods active?
Rods: Always active
Cones: Only active in light vision
Describe colour perception
Registered by cones only
Red/Green/Blue Cones
Differing sensitivity peaks.
Combination of these three can recieve any colour.
Name given to normal vision
Emmetropia
