Session 4 The retina and central visual pathways Flashcards
(28 cards)
What are the three layers of the eye?
Outermost SCLERA which is tough and is continuous with the dural sheath of the optic nerve
UVEA which is the pigmented vascular layer
- choroid sits deep to sclera
- ciliary body and iris sit anteriorly
Retina = the neural layer
Describe the layers of the retina from superficial to deep and a bit about them
Retinal pigment epithelium = prevents light from ‘bouncing around’ the eyeball which would cause glare
Photoreceptors cells = convert light into signals
Bipolar cells = first order neurones receiving input from photoreceptors
Horizontal cells = connect the bipolar cells and assist with enhancing edges through ‘Lateral Inhibition’
Ganglion cell layer = receives input from bipolar cells
Axons of the ganglion cell’s form the NERVE fibre layer
Again the list:
Retinal pigment epithelium layer > photoreceptor cells > bipolar and horizontal cells > ganglion cell layer > nerve fibre layer (formed by axons of ganglion cells)
How can you examine the retina and what could it detect?
Fundoscopy which can detect signs of diseases such as hypertensive retinopathy, diabetic neuropathy and macular degeneration
Describe the normal appearance of the fundus
The macula = dark area with the fovea in the middle
Macula is lateral to the optic disk
(Can tell which eye it is because macula will be on the outside)
Left eye = macula on right and optic disk on left
Right eye = macula on left and optic disk on right
What is the optic disk
Point of exit of ganglion cell axons
What are visible on the macula?
Branches of the central retinal artery and vein
What is and what causes amaurosis fugax?
Occlusion of the central retinal artery (branch of the opthalmic artery= ICA) causes sudden visual loss = amaurosis fugax
What is the name of the specialist technique used to visualise the layers of the retina?
Optical coherence tomography (OCT)
What does OCT stand for and what does it visualise?
Optical coherence tomography
Used to visualise the layers of the retina
What is light from a lateral visual field detected by?
What is light from an upper visual field detected by?
Lateral visual field = detected by MEDIAL retina (referred to as nasal)
Upper visual field = detected by INFERIOR retina
What is the medial retina referred to and what does it detect?
= nasal
Detects light from a lateral visual field and light from the temporal field
What is the lateral retina referred to and what does it detect?
Referred to as ‘temporal’
Light from the temporal field is detected by the nasal retina
What is the name of the nucleus that ganglion cell axons project into?
A part of the thalamus called the lateral geniculate nucleus
Via the optic tract
What does the lateral geniculate nucleus protect to? Through what?
Projects to the visual cortex through the optic radiations
A) Ganglion cells supplying the temporal retina project to …
B) Ganglion cells from the nasal retina project to …
What does this imply?
A) The ipsilateral cerebral hemisphere
B) The contralateral hemisphere via the optic chiasm (i.e. they decussate)
This implies that the left binocular visual field projects to the right hemisphere an the right binocular visual field projects to the left hemisphere
What do the ganglion cells from the superior retina (i.e. the inferior field) project through? Which lobe?
What do the ganglion cells from the inferior retina (i.e. the superior field) project through? Which lobe?
Superior retina (inferior field) = superior optic radiation running through the parietal lobe
Inferior retina (superior field) = inferior optic radiation running through the temporal lobe
What is a scotoma and what causes it?
A localised defect in the retina causes a small patch of visual field loss = Scotoma
What can damage to the optic nerve lead to?
Monocular blindness
what can damage to the medial chiasm cause?
Bitemporal hemianopia
What can damage to the optic tract cause?
A contralateral homonymous hemianopia
What can cause a contralateral homonymous hemianopia?
- damage to optic tract
- damage to lateral geniculate
- damage to both optic radiations
- non-vascular damage to the occipital lobe = CTT without macular sparing
- occlusion of the posterior cerebral artery = CTT with macular sparing
Why does occlusion of the posterior cerebral artery cause contralateral homonymous hemianopia WITH macular sparing?
Due to the fact that the area of visual cortex that supplies the macular receives blood from the deep branch of the middle cerebral artery
What causes contralateral homonymous inferior quadrantanopia?
Damage to the superior optic radiations (in the parietal lobe)
What causes contralateral homonymous superior quadrantanopia?
Damage to the inferior optic radiations in the temporal lobe
