Session 7 - The Eye Flashcards Preview

Semester 5 - CNS > Session 7 - The Eye > Flashcards

Flashcards in Session 7 - The Eye Deck (25)

Draw out the visual pathway from photreceptors to the primary visual cortex



Give three functional classes of neurone found in the visual system

Photoreceptors - Rods and Cones
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?



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

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)