The Visual System Flashcards
What are the three layers of the eye?
Outermost sclera
Uvea
Retina
Describe the sclera
tough and continuous with dural sheath of the optic nerve
Describe the uvea
Pigmented vascular layer.
Choroid sitting just deep to the sclera and the ciliary body and the iris sitting anteriorly.
Describe the layers of the retina from superficial to deep.
Retinal pigment epithelium (prevent light from ‘bouncing around’ in the eyeball, causing glare)
Photoreceptor cells
Bipolar cells (first order neurones receiving input from photoreceptors) -Bipolar cells are connected by horizontal cells which assist with enhancing edges through lateral inhibition.
Ganglion cell layer (receives input form the bipolar cells. Axon of ganglion cells form the…)
Nerve fibres layer
What is the macula?
The point of highest acuity.
You can see branches of the central retinal artery and vein here.
Where does the macula sit in relation to the optic disc?
Macula is lateral to the optic disc.
What is the optic disc?
Point of exit of ganglion cell axons.
What is amaurosis fugax?
Occlusion of the central retinal artery (branch of the ophthalmic) causing sudden visual loss.
What things can be seen on fundoscopy?
Retinopathies -hypertension, diabetes
Vascular occlusions - brach of central retinal artery or vein
Macula - degeneration
Optic disc - papillodema
Describe the pathway of ganglion cell axons to the brain
Ganglion cell axons project to part of the thalamus called the lateral geniculate nucleus via the optic tract.
The lateral geniculate nucleus projects to the visual cortex via the optic radiations.
What is the difference between the routes of ganglion which supply the temporal retina and ganglia which supply the nasal retina?
Temporal retina - ipsilateral cerebral hemisphere (no decussation)
Nasal retina - contralateral cerebral hemisphere via optic chasm (decussation occurs).
Where do ganglion cells from the superior retina go?
Ganglion cells from the superior retina (inferior field) project through the superior optic radiation running through the parietal lobe.
Where do ganglion from the inferior retina go?
Ganglion cells from the inferior retina (superior field) project through the inferior optic radiation running through the parietal lobe.
What is a scotoma?
A localised defect in the retina causing a small patch of visual field loss.
What causes monocular blindness?
Damage to the optic nerve.
Monocular blindness = can’t see out of one eye
What is bitemporal hemianopia and what causes it?
Bitemporal hemianopia = tunnel vision
Caused by damage to the medial chiasm.
What is contralateral homonymous hemianopia?
When one side of both the eyes is blind. e.g. can’t see left side of both eyes.
What things could cause a contralateral homonymous hemianopia (without macula sparing)?
Damage to lateral geniculate nucleus
Damage to both optic radiations
What things could cause a contralateral homonymous hemianopia (wit macula sparing)?
Non-vascular damage to the occipital lobe
Occlusion of the posterior cerebral artery
Why do you get macula sparing?
Because the area od the visual cortex that supplies the macula receives blood from the deep branch of the middle cerebral artery as wells the posterior cerebral artery.
What visual defect occurs if there is damage to the superior optic radiations?
Damage to the superior optic radiations in the parietal lobe causes contralateral homonymous inferior quadrantanopia
What visual defect occurs if there is damage to the inferior optic radiations?
Damage the inferior optic radiation in the temoral lobe causes contralateral homonymous superior quadrantanopia.
What is the afferent arm of the pupillary light reflex and accommodation reflex?
Optic nerve
What are the processing centres of the pupillary light reflex?
The pretectal nucleus which projects bilaterally to Edinger-Westphal nuclei that contain parasympathetic preganglionics.
What is the efferent arm of the pupillary light reflex and the accommodation reflex?
Oculomotor nerve
What are the processing centres of the accommodation reflex?
Visual cortex (via lateral geniculate nucleus) allowing processing of visual image which then project to oculomotor and Edinger Wesphal nucleus.
What does the accommodation reflex do?
Focusing on a near object leads to pupillary constriction, convergence of themes (contraction of medial recti) and thickening of the lens.
What does the pupillary light reflex do?
Illumination of the eye leads to both direct and consensual pupillary constriction. The consensual reflex is mediated by the bilateral projections from the pretectal nucleus.
