The Retina and Central Visual Pathways Flashcards
1
Q
Describe the pigmented layer of the retina
A
- Pigmented layer contains retinal pigment epithelium
- Contains melanin
- Ensures no excessive refraction
- Patients with low melanin see normal light as bright
2
Q
State the action of the neural layer cells
A
- Photoreceptor cells divided into rods and cones
- Rod cells - black and white vision, low light conditions
- Cones - colour vision, high definition vision (central vision)
- Horizontal cell
- Lateral inhibition - prevent receptors next to the receptors of central vision to send misleading signals
- Bipolar cells
- First order neurones which photoreceptor cells synapse onto
- Bipolar cells synapse with axons of ganglion cells
- Ganglion cells
- Transmits signals from bipolar cells to optic nerve
3
Q
Describe how incoming light travels through the retina
A
- Incoming light goes through the neural and reaches the pigmented layer of the retina
- Activates photoreceptor cells which activate bipolar cells
- Bipolar cells synapses with axons of ganglion cells
- Ganglion cells transmit signal to optic nerve
4
Q
Describe the macula
A
- Macula has highest concentration of cones - highest visual acuity
- Contains the fovea
- Fovea has thinner retina - less distance for light to travel into and signal to transmit back outward
5
Q
Describe amaurosis fugax
A
- Painless, temporary loss of vision in one or both eyes
- Can be due to temporary occlusion of ophthalmic or retinal arteries
6
Q
State the investigations that can be conducted for retina
A
- Fundoscopy
- Optical coherence tomography (OCT)
7
Q
Describe how to analyse an optical coherence tomography
A
- See onenote
- Bright red layer is the photoreceptors
- Dark area above that is the bipolar cells, followed by green ganglion cells
8
Q
Describe how to analyse a fundoscopy
A
- Optic disk bright light where blood vessels arise from
- Optic disk always medial to macula
- Retinal veins have a larger diameter than retinal arterioles
9
Q
Describe the nerve routes of the central visual pathway
A
- Optic nerves travel towards the optic chiasm where nasal fibres decussate while temporal fibres stay ipsilateral
- Optic tract runs to the lateral geniculate nucleus (relay pathway in the thalamus)
- Fibres then split into superior and inferior radiations towards the primary visual cortex
- Superior radiations travel through the parietal lobe
- Inferior radiations travel through the temporal lobe
- Superior radiations travel through the parietal lobe
10
Q
State the nerve fibres responsible for each field of vision
A
- Temporal fibres responsible for nasal vision while nasal fibres responsible for temporal vision
- Due to retina being curved
- Superior fibres responsible for inferior fields of vision while inferior fibres responsible for superior fields of vision
- Eg. When looking into the superior left visual field, the left eye fibre is inferior nasal and the right eye fibre is inferior temporal
11
Q
Describe monocular blindness and give examples
A
- Caused by lesion of the optic nerve
- Signs are unilateral and ipsilateral - if right optic nerve lesion, then complete loss of vision in right eye
- Eg. Optic nerve glioma or retinoblastoma (children)
- Optic sheath meningioma (middle aged)
12
Q
Describe bitemporal hemianopia and give examples
A
- Lesion at the optic chiasm
- Affects both nasal fibres - therefore loss of temporal vision (signs are bilateral)
- Eg. Pituitary gland and anterior communicating artery problems
13
Q
Describe left/right homonomous hemianopia
A
- Left homonomous hemianopia
- Lesion of the right optic tract (signs are bilateral and contralateral)
- Causes loss of vision in left visual field
- Lesion of the right optic tract (signs are bilateral and contralateral)
- Right homonomous hemianopia
- Lesion of the left optic tract
- Causes loss of vision in right visual field
- Lesion of the left optic tract
- Eg. Vascular causes the most common (stroke)
- Neoplasia and trauma
14
Q
Describe quanrantanopias and its effect on visual fields
A
- Lesions of the superior or inferior radiations causes loss of vision in a quarter of field of vision
- Lesions of superior radiations cause loss of vision in inferior portion of contralateral side
- Eg. A lesion of right superior radiations causes loss of vision in left inferior portion of each eye
- Eg. A lesion of right Meyer’s loop (inferior radiation) causes loss of vision in left superior portion of each eye
15
Q
Describe the concept of macula sparing
A
- Occipital lobe has dual blood supply from posterior cerebral artery and middle cerebral artery
- In a stroke affecting the posterior cerebral artery, most of occipital lobe will be lost
- However middle cerebral supplies the occipital pole (represents the macula)
- Therefore macular function (central vision) will be spared
- Eg. A stroke affecting the right optic tract in the occipital lobe will cause left homonomous hemianopia with macular sparing
