Eye Flashcards
What are the 3 layers of the eye
- Sclera
- Choroid
- Retina
Describe the structures and functions of the sclera
- Tough, white outer covering of eyeball
- Protects eyeball from mechanical damage
Describe the structures and functions of the retina
- Innermost layer of eyeball
- Contains cones and rods
- Light-sensitive layer where images are formed
Describe the structures and functions of the choroid
- Middle layer of eyeball between sclera and retina
- Contains black pigments to prevent total internal reflection of light
- Contains blood vessels that bring nutrients to eyeball and remove metabolic waste
Describe the structures and functions of the ciliary body
- Consists of ciliary muscles
- Controls thickness or curvature of lens
Describe the structures and functions of the cornea
- Transparent layer in front of eye
- Refracts light onto lens
Describe the structures and functions of the aqueous humour
- Transparent, watery fluid
- Refracts light onto lens
- Keeps eyeball firm
- Serves as a medium for diffusion of oxygen and nutrients
Describe the structures and functions of the iris
- Consists of circular and radial muscles
- Surrounds pupil, in front of lens
- Adjusts amount of light entering eye by changing pupil size
Describe the structures and functions of the pupil
- Hole in centre of iris
- Allows light to enter the eye
Describe the structures and functions of the lens
- Transparent, biconcave, elastic crystalline body
- Changes curvature or thickness to refract light onto retina
Describe the structures and functions of the suspensory ligaments
- Connective tissue attached to the lens
- Transfers effect of ciliary muscles to the lens
Describe the structures and functions of the blind spot
- Found over the optic nerves
- No photoreceptors
- Area where neurones leave the eye
Describe the structures and functions of the vitreous humour
- Transparent, jelly-like fluid
- Refracts light onto retina
- Keeps eyeball firm
Describe the structures and functions of the fovea
- Greatest concentration of cones but no rods
- Part of retina that images are focused on
- Gives detailed colour vision in bright light
Describe the structures and functions of the optic nerve
- Composed of sensory neurones
- Transmits nerve impulses from photoreceptors to brain
What are photoreceptors
Cones and rods
What are cones
- Enable us to see colour in bright light
- Red, blue, green cones
- Each cone contains different pigments that absorbs light of different wavelengths
- Most concentrated at the fovea/yellow spot
- Do not work well in dim light
What are rods
- Allow us to see black and white in dim light
- More sensitive to light than cones
- Contain visual purple, a light sensitive pigment
- Requires Vitamin A for formation of visual purple
- Lie outside the fovea
- Visual purple is bleached when eye is exposed to bright light, hence takes awhile to adjust when light settings change
Define accommodation
Accommodation is the adjustment of the lens to change curvature or thickness so that clear images at different distances can be formed on the retina
How is accommodation achieved
- Ciliary muscle movement
- Suspensory ligaments to transfer effect of ciliary muscles onto lens
- Lens to be elastic
Describe how the eye focuses on a near object
- Ciliary muscles contract
- Suspensory ligaments slack
- Lens becomes thicker and more convex, decreasing its focal length
- Light rays from near object are brought to focus onto retina
- Photoreceptors stimulated, so nerve impulses are produced and transmitted to brain via optic nerve
Describe how the eye focuses on a distant object
- Ciliary muscles relax
- Suspensory ligaments become taut
- Lens becomes thinner and longer, increasing its focal length
- Light rays from distant object are brought to focus onto retina
- Photoreceptors stimulated, so nerve impulses are produced and transmitted to brain via optic nerve
Describe pupil reflex in bright light
- Photoreceptors in retina detect an increase in light intensity
- Nerve impulses are sent along sensory neurone via optic nerve to brain
- Brain returns impulses along motor neurone to circular and radial muscles of iris
- Circular iris muscles contract
- Radial iris muscles relax
- Diameter of pupil decreases, allowing less light to enter
What reflexes does the eye have
Pupil reflex
- Strong light causes pupil to become smaller to protect retina
Blink reflex
- Object coming towards eye causes eyelids to close
Tearing reflex
- Dust causes increased tear flow
Describe pupil reflex in dim light
- Photoreceptors detect a decrease in light intensity
- Nerve impulses are sent along sensory neurone via the optic nerve to the brain
- Brain returns impulses along motor neurone to circular and radial muscles in iris
- Circular muscles relax
- Radial muscles contract
- Diameter of pupil increases, allowing more light to enter
