The Eye Flashcards
The eyelid
Description: fold of skin which covers the eye
Purpose: cleaning and protecting the eye
Cornea
Description: transparent covering of the eye
Purpose: protecting the eye; helping coverage (blend and join) light rays that enter the eye
Sclera
Description: white part of the eye made of tough collagen fibres
Purpose: providing protection and support
Retina
Description: layer of light sensitive cells (photoreceptors) at the back of the eye
Purpose: detecting light rays that are focused by the cornea and lens
Choroid
Description: layer of blood vessels with a black pigment
Purpose: nourishing the eye and absorbing light
Iris
Description: a ring of muscle around the pupil, provides the eye colour
Purpose: controlling the amount of light that enters the eye
Pupil
Description: hole in the middle of the eye
Purpose: allowing light to enter the eye
Lens
Description: transparent, flexible and can change shape due to the ciliary muscles
Purpose: focusing light onto the retina and focusing on objects
Ciliary body
Description: attached to the underside of the lens
Purpose: producing aqueous humour and helps with focusing by altering the shape of the lens
Vitreous humour
Description: located behind the lens
Purpose: giving the eyeball it’s shape
Aqueous humour
Description: found behind the cornea
Purpose: helping to keep its rounded shape; provides nutrients to the cornea and lens
Lateral rectus muscle
Description: found on the lateral side of the eye
Purpose: helping orientate the pupil away from the centre of the body
Medial rectus muscle
Description: found on the medial side of the eye
Purpose: helping orientate the pupil towards the centre of the body
Fovea
Description: spot located in the macula, which has a high density of cone cells
Purpose: giving Sharp central vision; light is focused onto this spot by the lens
Optic disc
Description: blind spots where there are no photoreceptors
Purpose: where the optic disc leaves the eye
Optic nerve
Description: bundle of fibres
Purpose: relaying information from the retina and fovea to the brain
The vision process
1) light rays are refracted & focused on pupil as they entre through cornea. Muscles in iris contract / relax controlling amount of light entering pupil
2) lens refracts light more so focused on retina
3) photoreceptors in retina respond to energy from light & generate action potentials = sent along optic nerve to brain for processing
Rods
. Light sensitive
. Function in dark
. Single pigment called rhodopsin
. Cannot detect colour = shades of grey
. Low level of visual sharpness
. Share connection to optic nerve
Cones
. Function at higher intensity than rods
. See in colour
. Contain photo pigments iodopsin = responds to colour
. Range of colours depends on cone type
. High level of visual sharpness
. Single connection to optic nerve
Use of light ( bleaching & depolarisation)
1) light detected by rods
2) rhodopsins is broken down into opsin and retinal via process bleaching
3) caused depolarisation = action potentials transmitted via optic nerve to brain
. Rhodopsin generated slowly so cones provide visual info when light levels are high as rhodopsin is unable to effectively generate
Nocturnal animals eye adaptions
(There are 4)
1) larger eyes with wider pupils = capture more light
2) higher concentration of rod cells
3) slit pupils = easier to contact than round
4) tapetum lucidum. Contains reflective pigment which aids sight in dark. Maximises light available by reflecting it back through photoreceptors, stimulating more receptor cells
The pupillary light reflex
Adjusts the size of pupil in response to amount of light present. Helps protect photoreceptors from damage
Predator eye adaptations
. Binocular vision (eye overlaps at front = 3D image)
. Eyes = front of face so narrower field of vision
. Focus = good depth perception
. Owls have field of vision of 110°, eyes are elongated so cannot rotate in socket. Large number of rod cells and wide range of pupil size helps them to hunt in dark
Prey eye adaptations
. Monocular vision, each eye works independently overlaps small area
. Eyes in side of head
. Wider field of vision
. Poor depth perception
. Sheep have field of vison = 270°, eyes are high up in skull giving better vison when grazing and rectangular pupils increase accuracy of depth perception when grazing
