Workbook questions 7 - Optic Flashcards
What do you understand by the term visual fields as they apply to the sense of vision?
The physical world from which sources of light that impinge on a defined piece of retina arise .
What do you understand by the term retinal fields as they apply to the sense of vision?
The piece of retinal tissue upon which light from external objects falls upon
Name the visual deficit that would arise from a lesion et the optic chiasm
Tunnel Vision or more technically, Bitemporal Hemianopia (goes without saying that this would be a case of Heteronymous Bitemporal Hemianopia)
What region of the brain is implicated in lesions of central visual pathways sited at the optic chiasm?
Diencephalon and in particular, hypothalamus and more accurately the pituitary gland. The optic chiasm is an anterior relation of the pituitary gland.
At the chiasm, optic nerves from the nasal half of the retina decussate. An enlarging pituitary tumour may compress and damage these decussating fibres. The nasal half of the retina corresponds to the temporal half of the visual field. Therefore it is vision from the temporal half of each visual field that is lost. This phenomenon is called bitemporal hemianopia.
Sympathetic fibres arising from T1/T2, ascend to the head along what?
Carotid arteries
Mydriasis is a _____ of the pupil due to the loss of the _______ innervation from the ____ part of the CN III nucleus. The ______ innervation is intact which explains the effect upon the pupil
DILATION
PARASYMPATHETIC (autonomic)
Edinger - Westphal
SYMPATHETIC (autonomic)
Explain the pupillary reflex
The reflex is driven by parasympathetic motor fibres from the Edinger Westphal nucleus in response to a sensory input from the retina/optic nerve. Loss of the pupillary reflex without oculomotor signs indicates a lesion in the afferent arm of the reflex.
The parasympathetic fibres run in a bundle on the surface of the oculomotor nerve and in some conditions are unaffected by an insult to the oculomotor nerve - ‘sparing the pupil’
Flattened forehead creases and a drooping eyebrow due to a weakness of the ___ muscle.
FRONTALIS
Disabled eye closure caused by the failure of ____ muscle.
ORBICULARIS OCULI
In an LMN facial palsy the patient may experience corneal drying T/F?
TRUE Lacrymation is a function of parasympathetic fibres in the facial nerve. A lesion of the facial nerve close to the brainstem may disable tear formation. More peripheral lesions do not.
Corneal drying in facial palsy is caused by disabled eye closure and loss of lachrymal secretions from interruption of parasympathetic fibres in the facial nerve. T/F?
True
If the VIIth nerve compression was below the level of the junction of the chorda tympani and facial nerves, taste will be affected only in the ipsilateral anterior two thirds of the tongue
FALSE (see above). Although the nerve does innervate the ipsilateral anterior two thirds of the tongue, chorda tympani is not affected here so taste will be preserved.
