3.10.1 Physics of the Eye Flashcards
What is the eye
An optical refracting system
What wavelengths is the eye sensitive to
380nm - 760nm
What does the choroid do
Contains blood vessels that supply food and oxygen
Contains a black pigment to reduce reflection
The end contains muscle fibres
What do the ciliary muscles do generally
Adjusts the shape of the lens to enable focussing on objects at different distances
What happens when ciliary muscles are relaxed
The suspensory ligaments pull the lens into a thin, flatter shape
The eye is ‘un accommodated’
Used to focus on objects at a distance >5m
What is the far point
Maximum focal length
(Infinity)
What happens when ciliary muscles contract
Tension is released and the lens takes on a fat, more spherical shape
The eye is ‘accommodated’
Used to focus on objects at a distance <5m
What is the near point
The minimum focal length
(10cm)
What is the vitreous humour
A transparent, jelly-like substance that fills the inside of the eye
What does the vitreous humour do
The pressure keeps the eye spherical
Reduces refraction at the lens due to a similar refractive index
What does the lens do
Adjusts focus only
What does the cornea do
It is the outer clear convex structure where most refraction takes place due to its (high) refractive index that directs light rays into the eye and helps them focus on the retina
What does the aperture/pupil do
Changed the intensity (size varies with length of iris)
What factors change the size of the pupil and how/why
Darker = bigger pupil
Closer object = smaller pupil - to reduce superfluous (external) rays enter in, and sharpen the image
What does the retina do
Produced electrical signals when light shines on it
The photoelectric cells / photoreceptors (rods and cells) convert light energy to electrical
What are rods
There are several
They are responsible for vision at low light levels (scotopic vision)
They are greyscale - they do not mediate colour vision and have a low spacial acuity
What are cones
They are singular
They are responsible for vision at higher light levels (photopic vision)
They are capable of colour vision
They are responsible for high spacial acuity
What are nerve fibres
They travel along the retina surface
They make up the optic nerve
What is the yellow spot (and fovea)
The yellow spot is a sensitive region of the retina
In the centre of the spot is the fovea, which is the part of the retina with the highest concentration of cones
(As we move out from this spot, the density of cones decreases and the density of rods increases)
Has good spacial resolution
What is the blind spot
Where all the nerves converge
There are no rods or cones
What happens when we look directly at an object
A clear detailed image is formed on the fovea
Everything else is not clear