Session 7 - The Eye Flashcards
Draw out the visual pathway from photreceptors to the primary visual cortex
Excellent
Give three functional classes of neurone found in the visual system
Photoreceptors - Rods and Cones
Interneurones
Ganglion cells - Bipolar, horziontal and amacrine Magnocellular and Parvocellular
What happens at the optic chiasm?
o When action potential reaches the Optic Chiasm, which is situated superior to the Pituitary fossa on the Sphenoid Bone the Nasal Fibres Cross
What is contained in the right and left optic tract, respectively?
R. Optic Tract – Fibres from R. half of each retina, carrying information from L. hemifield
L. Optic Tract – Fibres from L. half of each retina, carrying information from R. hemifield
What do the optic tracts continue to?
the Lateral Geniculate Nucleus of the Thalamus
What part of the retina has the largest representation at the lateral geniculate nucleus of the thalamus?
Fovea
What lobes do the optic radiations pass through?
Parietal and temporal lobes
What fibres loop round the temporal horn of the lateral ventricle, and what is this loop called?
Fibres corresponding to the inferior half of the retina (Superior visual field) loop around the temporal horn of the lateral ventricle to form Meyer’s Loop
Outline the afferent and efferent pathway of the light reflex
Afferent Pathway:
1. Light activates Optic Nerve (CN II) axons
2. Axons (some decussating) pass through the Lateral Geniculate Body
3. Synapse at pretectal nucleus
Efferent Pathway
4. Action potentials pass to Edinger-Westphal nucleus of the Oculomotor Nerve (CN III)
5. Parasympathetic neurones in Oculomotor Nerve (CN III)
6. Innervation of Constrictor Pupillae causes Pupil Constriction
What is constriction of the pupil in which the light is shone called, and what is it called when it happens in the other eye as well
The constriction of the pupil that the light is shone into is the Direct Light Reflex. The constriction of the other pupil is the Consensual Light Reflex.
What is the corneal reflex?
Also known as the blink reflex, the corneal reflex causes the closure of the eye in response to stimulation of the cornea
Give the afferent and efferent pathway of the corneal reflex
Afferent Pathway:
o Action potential is generated when something touches the cornea
o Nasociliary branch of the Ophthalmic Branch of the Trigeminal Nerve (CN V)
Efferent Pathway:
o Temporal and Zygomatic branches of the Facial Nerve (CN VII)
o Causes constriction of orbicularis oculi
Give the innervation of the extra-ocular muscles of the orbit
LR6SO4R3 o Lateral Rectus Cranial Nerve 6 Abducens o Superior Oblique Cranial Nerve 4 Trochlear o All the Rest Cranial Nerve 3 Oculomotor
What is the vetibulo-ocular reflex?
The vestibulo-ocular reflex is a reflex eye movement that stabilises images on the retina during head movement by producing an eye movement in the direction opposite to head movement.
Give the afferent and efferent pathway for the vestibulo-ocular reflex
Afferent Pathway:
o Head movement is detected by the vestibular apparatus of the inner ear, causing firing of action potentials conveyed by the Vestibulocochlear Nerve (CN VIII)
Efferent Pathway:
o Action potentials travel down the nerves innervating Extraocular muscles, causing eye movement in the opposite direction of head movement
What would cause an ipsilateral scotoma
Partial Optic Nerve lesion
Partial loss of visual acuity, surrounded by good acuity
What would cause complete blindness in one eye (2 main overarching causes)
Ipsilateral Optic Nerve lesion
Common causes
i. Optic neuritis as a result of MS can cause an ipsilateral optic nerve lesion, as a result of inflammation and destruction of the myelin sheath of the optic nerve.
Other causes include ethambutol and herpes zoster and syphilis
ii. Can also result from Anterior Ischaemic Optic Neuropathy (including diabetes and temporal arteritis)
What is a bitemporal hemianopia caused by?
Optic Chiasm lesion
Pituitary Adenoma, most often due to lactotrophic adenoma. Often show signs in pregnancy, as progesterone encourages growth of lactotrophs. Treated with bromocriptine.
Other causes include craniopharyngioma, which is a neoplastic transformation of rathke’s pouch
What is a homonoymous hemianopia caused by?
Optic tract lesion
What is homonoymous upper quadrantopia caused by?
Meyer’s loop lesion
What is homonymous hemianopia caused by?
Optic radiation lesion
Macular sparing
Macular sparing occurs due to collateral circulation provided by middle cerebral artery if posterior cerebral is occluded
What is horner’s syndrome caused by?
Interruption of a cervical sympathetic trunk results in Horner’s Syndrome. It is manifested by the Absence of Sympathetically Stimulated functions on the Ipsilateral side of the head.
What is retinal detachment caused by?
The Intraretinal Space separates the layers of the retina in the developing embryo. During the early foetal period, the layers fuse, obliterating this space. However, although the Pigment Cell Layer becomes firmly fixed to the choroid, its attachment to the Neural Layer is not firm.
Consequently, a blow to the eye may cause detachment of the retina, perhaps days or even weeks after trauma to the eye.
Persons with retinal detachment may complain of flashes of light or specks floating in front of the eye.
What is exopthalmos?
Protrusion of the eye, causing the eyelids to part more than normal so that the whites of the sclera are visible all around the cornea and iris. o Bilateral Grave’s Disease (Hyperthyroidism) o Unilateral Aneurysm Haematoma
What eye symptoms can raised ICP cause?
o Optic nerve is surrounded by meninges with CSF in the subarcachnoid space
o Increase in CSF pressure may compress the optic nerve compress blood vessels supplying retina blindness
o Vein is occluded before the artery, leading to oedema of the retina (Papillodema)
