4.2 Vision Flashcards
What structures are located in the anterior segment of the eye? What delineates this boundary?
- Cornea
- Iris
- Ciliary body
- Lens
(Everything in front of vitreous humor)
What are the boundaries of the anterior and posterior chambers of the anterior segment of the eye?
Anterior: from posterior cornea to iris
Posterior: from iris to vitreous humour
What membrane separates the vitreous humor from the rest of the eye?
Vitreous membrane
What is contained in the posterior segment of the eye?
- Vitreous humor
- Retina
- Choroid
- Optic nerve
What is the limbus of the eye?
The boundary between the cornea and the sclera
Is the choroid thickest at the back or the front of the eye? Why does this make sense?
- Thicker at back
- More blood supply needed as there are more retinal cells in this area
What are the three anatomical “tunics” of the eye?
- Fibrous tunic (sclera and cornea)
- Vascular tunic (choroid, iris, ciliary body)
- Nervous tunic (retina)
What is the structure and function of the sclera?
Structure: white part of eye. Made of fibrous connective tissue.
Function: Protects eye and provides attachment for extraocular muscles.
What is the function of the cornea?
- Focuses light as it enters the eye
- Also protects the rest of the eye from the external environment
What is the function of the iris?
Mediates how much light enters the eye
What is the specific function of the lens of the eye?
Focuses light onto retina
What are the functions of the ciliary body of the eye?
- Accommodation (changes lens shape)
- Aqueous humor production/resorption
By what structures are the ciliary bodies connected to the lens of the eye?
Fibres called zonules (AKA suspensory ligaments)
What is the function of aqueous humor?
- Provide nutrients to eye
- Carry away waste
(Basically blood)
What enters and exits the eye at the optic disc?
- Optic nerve
- Retinal blood vessels
This region lies in the middle of the retina, and light is focused onto it by the cornea and lens…
The macula
This region is a dark spot in the centre of the macula where the retina is thinnest…
Fovea
The ____ the density of cones, the more acute the vision.
Higher density cones = more acute vision
What ARE rods and cones? (One word answer)
Photoreceptors
Differentiate between the rods and cones of the eye
Rods: low acuity, high sensitivity, dark vision
Cones: high acuity, low sensitivity, bright vision, colour vision
Are there more rods or cones in the eye?
Rods, by 20 : 1
We have three different types of cones in our eyes, each of which expresses a different colour pigment. What are the three pigments?
- Red
- Green
- Blue
(RGB colour system)
Describe the distribution of rods and cones in the retina
Everywhere except fovea: many rods, few cones.
Fovea: many cones, few rods
Describe the three layers of cells in the retina of the eye
Furthest back: photoreceptors (rods and cones)
Middle: bipolar cells
Furthest forward: ganglion cells (form optic nerve)
This kind of interneuron is able to control the messages between photoreceptors and bipolar cells…
Horizontal cells
This kind of interneuron is able to control messages between bipolar cells and ganglion cells…
Amacrine cells (a macr ine = non long fibre)
80% of the focusing of light in the eye happens at the level of the…
Cornea
Describe the physics of how accommodation enables us to see stuff close up
- Close vision = ciliary muscle contracts
- Suspensory ligaments loosen
- Lens is less stretched (therefore thicker)
- Light has to pass through more lens -> refracts more
- Sharper bending enables light to hit the retina at the right point
What to proteins are found in visual pigment in the photoreceptors of the eye?
- Retinal
- Opsin
Describe the intracellular signalling cascade that enables photoreceptors to function
- Light hits retinal -> causes shape change
- Shape change increases transducin activity
- Cascade, resulting in activation of enzyme known as phosphodiasterase
- Closes Na+ channels
- No more transmitter release -> inhibiting inhibition of bipolar cells
- AP fires from bipolar cells
SIMPLIFIED VERSION:
- Light hits retinal pigment
- Intracellular signalling cascade
- Closes Na+ channels = no more depolarisation
- No more inhibition of ganglion cells = signal transmission
What would be the consequence of a lesion in the optic chiasm?
Bitemporal hemianopia
What are the three sites of termination of the optic tract?
- Lateral geniculate nucleus of thalamus (most)
- Superior colliculus
- Pretectal nucleus (for light reflexes and accomodation reflex)
What is caused by damage to the optic tract?
Homonymous hemianopia
What are the superior colliculus visual field projections important for?
Orienting eyes in response to new stimuli
Which eye (ipsi/contra) is represented in each of the six layers of the lateral geniculate nucleus?
Ipsi: 2, 3, 5
Contra: 1, 4, 6
What does damage to one of the lateral geniculate nucleus cause?
Patchy homonymous hemianopia
Where do fibres from the inferior vs superior optic radiations terminate?
Superior: cuneus
Inferior: lingula
Is V1 located medially or laterally in the brain?
Medially
Name the two sections of the occipital lobe on either side of the calcarine fissure
Superior: cuneus
Inferior: lingula
Describe the “what” stream: which lobe and cortex is it associated with, and what is it important for?
- Temporal lobe
- Occipitotemporal association cortex
- Analyses form, faces, letters etc.
Describe the “where” stream: which lobe and cortex is it associated with, and what is it important for?
- Parietal lobe
- Parieto-occipital association cortex
- Important for analysing motion and spatial relationships
