The Retina And Central Visual Pathways Flashcards
Describe the anatomy of and surrounding the retina
3. Retina Neural layer (deep to superficial): Axons of ganglion cells to optic nerve form nerve fibre layer Ganglion cells Amacrine cells Bipolar cells Horizontal cells Photoreceptors cells (cone and rod) Retinal pigment epithelium (prevents glare)
- Pigmented vascular layer - uvea(absorbs light, absence albinism)
Choroid deep to sclera and ciliary body and iris - Outermost Sclera surrounds eye
Slide 4 and 46
What is the difference between rod and cone photoreceptors cells?
Rods - peripheral vision, black and white, hide details
Cones - coloured, central, high acuity, provide vision in day/ bright light
What do horizontal cells do?
Lateral inhibition of light so prevents too many signals reaching the optic nerve
Describe the retina as can be seen on a fundoscopy
Fovea centre of macula circle lateral to optic disc
Retinal arterioles/ venues -> central retinal artery/ vein over optic disc
Slide 7
What can be seen on an optical coherence tomography?
Vitreous fluid
Nerve fibre layer with central fovea (dip- axons come off splayed creates a gap to penetrate centrally= highest acuity)
Retinal pigment epithelium in orange
Choroid
Describe the central visual pathway anatomy
See slide 10
What is the nasal visual field detected by? Where are they in relation to the body?
Temporal retinal fibres
Nasal visual field is medial visual field of both eyes
Temporal retinal fibres are lateral visual fibres
Where do the retinal fibres travel through?
(As optic nerve)
All through optic disc then nasal fibres decussate as chiasm (temporal fibres remain ipsilateral)
All through the optic tracts
all move through lateral geniculate nucleus (part of thalamus)
Optic radiations: Superior fibres go via parietal lobe (continuation of superior quadrant fibres = Baum’s loop)
Inferior fibres go through temporal lobe
(Continuation of inferior quadrant fibres = Meyer’s loop)
——->
Primary visual cortex ———>
Edinburgh Westphal nuclei
(As oculomotor nerve)
Which fibres make up each of the four quadrants of the eye?
Lateral superior and inferior quadrants = temporal fibres
Medial superior and inferior quadrants = nasal fibres
What is Baum’s loop?
Continuation of superior quadrant fibres (contralateral nasal and ipsilateral temporal) from lateral geniculate nucleus via parietal lobe to primary visual cortex
What is Meyer’s loop?
Continuation of inferior quadrant fibres (contralateral nasal and ipsilateral temporal) from lateral geniculate nucleus via temporal lobe to primary visual cortex
What are visual fields?
Relates to peripheral vision - total area in which objects can be seen in the peripheral vision as you focus your eyes on a central point.
Each eye has its own set which overlap to form our binocular vision - good for depth perception
Split into lateral temporal superior and inferior and
Medial nasal superior and inferior
But light travels in straight ,Ines so nasal fibres are responsible for our temporal field and temporal fibres for our nasal field
What is monocular blindness and describe its pathophysiology?
Lose the whole of one eyes vision caused by a lesion of the optic nerve
Temporal and nasal fibres on ipsilateral side affected (lesion before decussation)
So nasal and temporal visual fields are lost on ipsilateral side
E.g. left lesion leads to left eye total vision lost
Causes of monocular blindness
Optic neuritis Retinal vein occlusion Retinal artery occlusion Pituitary apoplexy Retinal detachment Optic nerve lesion
What is bitemporal hemianopia and what is it’s pathophysiology?
Loss of peripheral vision in both eyes = tunnel vision
Caused by damage to optic chiasm
Nasal fibres on both sides affected so both temporal visual fields are lost
Causes of bitemporal hemianopia
Mid- optic chiasm tumour
Anterior communicating artery aneurysm
Pituitary adenomas
Craniopharyngiomas
What is homologous hemianopia and what is it’s pathophysiology?
Loss of temporal visual field in one eye and nasal visual field in the other eye
Damage to the optic tract
Ipsilateral temporal fibres and contralateral nasal fibres affected
so ipsilateral nasal visual field and contralateral temporal visual field lost
(Nasal fibres decussate)
E.g. right optic tract lesion = left homonomous hemianopia (left halves of visual field lost = left eyes temporal VF and right eyes nasal VF)
Causes of homonomous hemianopia
Stroke Trauma Optic tract tumour Following surgery Infection
What is it a right homonomous hemianopia and where would the damage be?
A right homonomous hemianopia involves loss of right vision in both eyes so nasal VF in left eye and temporal VF in right eye
Causes by damage to left optic tract
What would a superior nasal visual field be detected by? What about an inferior temporal visual field?
An inferior temporal retinal fibre radiation (projects into temporal lobe)
A superior nasal retinal fibre radiation (projects into parietal lobe)
What are quadrantanopias?
An anopia affecting a quarter of the visual field
Lesions of optic rations e.g. homonomous inferior quadrantanopia or homonomous superior quadrantanopia
What is a homonomous inferior quadrantanopia and what is it’s pathophysiology?
Loss of nasal inferior on left eye and temporal inferior on right eye visual field OR
Loss of inferior temporal VF of left eye and inferior nasal VF of left eye
Caused by lesion of superior optic radiation (in parietal lobe) so
Superior temporal gibe on ipsilateral side affected -> loss of inferior nasal visual field and
Superior nasal fibre on contralateral side affected -> loss of inferior temporal visual field
E.g. right parietal lobe lesion -> right superior fibres affected -> loss of left eye inferior temporal VF and right eye inferior nasal VF
What is a homonomous superior quadrantanopia and what is it’s pathophysiology?
Either left eye lost superior temporal VF and right eye lost superior nasal Vf OR
Left eye lost superior nasal Vf and right eye lost superior temporal VF
Caused by lesion of right inferior optic radiation (in temporal lobe)
Inferior temporal fibre on ipsilateral side is affected -> loss of superior nasal visual field and
Inferior nasal fibre on contralateral side is affected -> loss of superior temporal visual field
What would occur if both superior and inferior radiations are affected? Give an example of when this might occur
Superior and inferior temporal fibres on ipsilateral side affected and superior and infield nasal fibres on contralateral side affected -> loss of left eye temporal VF and right eye nasal VF
= homonomous hemianopia
Right problem = left HH (affects left visual fields of both eyes)
E.g. stroke
Slide 39
What is meant by macular sparing? What does it suggest is the cause?
Macular sparing means central vision is the only thing left suggests vascular cause because primary visual cortex in occipital lobe has dual blood supply (middle cerebral artery and posterior cerebral artery)
E.g. In a stroke affecting the posterior cerebral artery most of occipital lobe will be lost however middle cerebral supplies the occipital pole (represents macula) so macular function will be spared Or
If stroke affects middle cerebral artery ear both optic radiations will be affected but macular spared by PCA
Slide 41/42
What is the accommodation reflex, what does it involve, describe the reflex pathway?
Required for near vision
Involves:
Convergence (medial rectus)
Pupillary constriction (constrictor papillae)
Convexity of the lens to increase refractive power (ciliary muscle)
Cerebral cortex must be involves bc relates to image analysis
Reflex follows visual pathway via lateral geniculate nucleus to visual cortex then sends fibres to midbrain via CN3 nucleus (contraction medial recti) and edinger-Westphal (parasympathetic fibres -> contraction ciliary muscle and constrictor pupillae)
What diseases can be picked up by fundoscopy?
Examination of the retina can detect signs of many diseases
E.g. hypertensive retinopathy, diabetic retinopathy, macular degeneration
What is amaurosis fugax and what causes it?
Sudden visual loss caused by occlusion of the central retinal artery (branch of ophthalmic)
Why is the eye described as a pinhole camera?
Light from the lateral visual field is detected by the medial retina and light from an upper visual field is detected by the inferior retina
What is a Scotoma?
A small patch of visual loss caused by a localised defect in the retina
What would non-vascular damage to the occipital lobe cause?
Contralateral homonomous hemianopia without macular sparing
