2 - EYES AND IMAGES Flashcards
proximal stimulus in vision
the light images produced by the optical apparatus of the eyes
- patterns of different light intensities and wavelengths
- patterns contain information
- enable you to perceive the world
- if no patterns in light then the light stimulating the eye will cause you to see nothing at all
pupil
the small hole in which light enters the eye
called aperture in cameras
pupillary light reflex
adjusts the pupil size to ensure the correct amount of light enters the eye
- low light = hole gets larger to allow more light in
- bright light = hole gets smaller to ensure not too much light gets in
pin hole camera
when the hole is so small that it can create an image itself
a light-proof box with a very small hole
image is no longer sharp if it’s larger than a pin-hole
size of hole that makes image too blurry
6mm
why are lenses needed
when the hole is too large so the image is blurry, need lenses to sharpen the image
name of the lenses
THE LENS
- behind the pupil
CORNEA
- in front of the pupil
- transparent and can see iris and pupil behind it
- space between them is filled with aqueous humour (transparent watery substance)
vitreous humour
fills the space within the chamber of the eye behind the lens
transparent jelly
focus
sharp image = in focus
blurry image = out of focus
which lens has a greater focusing power
the cornea
- however the lens is thicker so it’s focusing power can be adjusted
accommodative reflex
automatic mechanism to adjust image focus through the alteration of lens thickness
- modern cameras do this via auto focus
- this is done by changing the relative positions of the lenses instead of the thickness
eye diagram on page 6 week 1
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retina
thin sheet of cells on the back surface of the eye where the image is projected (retinal image)
how are light patterns formed?
some surfaces/parts of surfaces reflect more light than others
these differences create a pattern in reflected light which corresponds to the arrangement of the objects viewed
this pattern of light is projected onto retina by the optical apparatus of the eye, forming a retinal image which is upside down - the photoreceptors respond to this pattern of light
retinal images
are upside down and two dimensional
- this two dimensional image must have information about 3D as the world is 3D
‘seeing (aka visual perception) is a process carried out by the brain on the pattern of signals transmitted to it from the retina along the ganglion cell axons’ from the optic disk
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orbit
socket in the skull that the eye sits in
circular tendon of zinn
- at the back of the socket
- pg 20 week 1 for diagram
- extraocular musckles are attached
optic nerve leaves through the back of the orbit and passes below the frontal lobes and connects to regions in the midbrain and forebrain
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how the eye works to see
- ‘to form an image, you first need a source of light to shine on the surfaces of things’
- ‘when light rays strike most surfaces they are reflected in virtually all directions (except mirrors)’
- ‘this means light will reach your eye regardless of where you’re looking from’
- ‘the reflected light that reaches the eye forms an image’
- ‘this is because eyes are lightproof boxes except for one small hole (pupil)
- ‘the hole needs to be small enough - as hole gets bigger, the image gets blurry’
- ‘use lenses to sharpen image’
how big is too big for the pupil?
6-7mm in diameter
