Vision Flashcards
What is light made up of
Energy waves of different lengths of electromagnetic radiation
What is visible light
Visible light is the part of the spectrum that our eyes respond to. Visible light travels in waves and in straight lines - reflection of light accounts for most of the light reaching our eyes
The structure of the eye
1) Sclera - white part of the eye
2) Cornea - protects the front of the eye and to bend light
3) Conjunctivi - protects the cornea from friction and helps to moisturise
4) Aqueous humour - the inside of the Cornea and is a chamber of fluid
5) Lens - Bi-convex - assists with light bending - it also gets thicker and thinner depending on where an object is
6) Ciliary body - helps to change the shape of the lens and secreates aqueous humor
7) Iris - The coloured part of the eye
8)Pupil - Controlled by the iris
10) Vitreous humour - water, salt and protein - gives the eye structure and keeps it in place
11) Retina- coats the entire back of the eyeball - composed of photoreceptors that convert the light ray into neural impulses - tinted red
12) Optic nerve - retina send fibres to the back of the eye so that the fibres can go to the brain - the fibres form the optic nerve
13) Choroid - inside the retina
a network of blood vessels that nourishes the rational cells and other cells in the eye pigmented black
14) Fovea - also inside the retina allows you to see in detail
Describe the basic visual pathway
- Light passes into eye via the cornea
- Light then passes through the fluid-filled
space between the cornea and the lens
(the fluid is called aqueous humour) - Light then passes through the circular
aperture of the pupil which is surrounded
by the iris diaphragm muscles - Light then moved through the vitreous
humour and hits the retina - At the retina the light then hits the
photoreceptors which convert the light to
electrical signal which are then sent to the
brain for processing (primary visual cortex
of occipital lobe)
Describe the function of the retina
The retina is made up of two layers: the outer layer helps to absorb light and the inner neural layer contains neurons and photoreceptors (rods and cones) to provide the pathway of light to the brain. Ganglion cells send messages to the brain via optic nerve via action potentials
Describe the function of rods and cones
Rods:
More of these than cones
Sensitive to low levels of light
Not good at fine detail
Many rods will synapse with one ganglion
Cones:
sensitive to daytime light (colour perception).
Detect fine detail
Three types of cone cell- red, green and blue
(each stimulated by a different wavelength of light
L- M- S- Cones)
One cone synapses with one ganglion
What are rods and cones
they are photoreceptors in the layers of the retina
What is accommodation
adjustment of the eye for various distances is called accommodation
Allows us to focus on distant and near objects Near objects: 1. the ciliary muscle contracts causing increased rounding of the lens 2. the pupil contracts 3. optic axes converge “accommodation”
Describe some of the age related changes to vision
Macular Degeneration: This is a medical condition which develops as one ages and
there is progressive loss of vision in one eye or both and is caused due to natural
degeneration of the macula.
Cataracts: Clouding of the lens of the eye
Diabetic retinopathy: blood vessels in the retina bleed and distort vision
Glaucoma: gradually eyesight deteriorates
Describe some of the symptoms of Usher Syndrome
Usher syndrome is a genetic condition that affects hearing, vision and balance, it varies person to person and it changes over time
The main symptoms of Usher syndrome are hearing loss and an eye disorder called RP - this causes nightblindness and loss of peripheral vision through the progressive degeneration of the retina
