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Homonymous hemianopsia?
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MedStudentt
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#1
I'm really struggling with optic tracts etc due to the fact that it wasn't taught very well at my University.
Is it an optic tract lesion which leads to homonymous hemianopsia? All answers are appreciated!
Thank you so much!
Is it an optic tract lesion which leads to homonymous hemianopsia? All answers are appreciated!
Thank you so much!
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Baylo1
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As far as I'm aware, homonymous hemianopia could occur because of a lesion/vascular incident anywhere from the optic tracts, back.
Each optic nerve transmits impulses from both sides of the visual field of each eye independently, so any problem at this level would cause a monocular visual field problem.
Once the fibres reach the optic chiasm, the nasal fibres from each eye will decussate (swap over), and continue down the opposite optic tracts. So at this point, each optic tract contains information from only the opposite side of the visual field (i.e. left tract contains all fibres for the right visual field).
As the nerves travel further posteriorly, they align themselves more neatly, and so a defect closer to the visual cortex will appear more symmetrical between eyes. The fibres from the maculae move to the centre of the bundle, which is why sometimes a homonymous hemianopic visual field defect might show "macular sparing" - the macular fibres are protected, leaving a central point of uninterupted vision.
Each optic nerve transmits impulses from both sides of the visual field of each eye independently, so any problem at this level would cause a monocular visual field problem.
Once the fibres reach the optic chiasm, the nasal fibres from each eye will decussate (swap over), and continue down the opposite optic tracts. So at this point, each optic tract contains information from only the opposite side of the visual field (i.e. left tract contains all fibres for the right visual field).
As the nerves travel further posteriorly, they align themselves more neatly, and so a defect closer to the visual cortex will appear more symmetrical between eyes. The fibres from the maculae move to the centre of the bundle, which is why sometimes a homonymous hemianopic visual field defect might show "macular sparing" - the macular fibres are protected, leaving a central point of uninterupted vision.
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MedStudentt
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#3
(Original post by Baylo1)
As far as I'm aware, homonymous hemianopia could occur because of a lesion/vascular incident anywhere from the optic tracts, back.
Each optic nerve transmits impulses from both sides of the visual field of each eye independently, so any problem at this level would cause a monocular visual field problem.
Once the fibres reach the optic chiasm, the nasal fibres from each eye will decussate (swap over), and continue down the opposite optic tracts. So at this point, each optic tract contains information from only the opposite side of the visual field (i.e. left tract contains all fibres for the right visual field).
As the nerves travel further posteriorly, they align themselves more neatly, and so a defect closer to the visual cortex will appear more symmetrical between eyes. The fibres from the maculae move to the centre of the bundle, which is why sometimes a homonymous hemianopic visual field defect might show "macular sparing" - the macular fibres are protected, leaving a central point of uninterupted vision.
As far as I'm aware, homonymous hemianopia could occur because of a lesion/vascular incident anywhere from the optic tracts, back.
Each optic nerve transmits impulses from both sides of the visual field of each eye independently, so any problem at this level would cause a monocular visual field problem.
Once the fibres reach the optic chiasm, the nasal fibres from each eye will decussate (swap over), and continue down the opposite optic tracts. So at this point, each optic tract contains information from only the opposite side of the visual field (i.e. left tract contains all fibres for the right visual field).
As the nerves travel further posteriorly, they align themselves more neatly, and so a defect closer to the visual cortex will appear more symmetrical between eyes. The fibres from the maculae move to the centre of the bundle, which is why sometimes a homonymous hemianopic visual field defect might show "macular sparing" - the macular fibres are protected, leaving a central point of uninterupted vision.
Perhaps, a silly question, but what is the difference between an optic nerve and an optic tract?
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Helenia
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(Original post by MedStudentt)
Thank you so much for your response.
Perhaps, a silly question, but what is the difference between an optic nerve and an optic tract?
Thank you so much for your response.
Perhaps, a silly question, but what is the difference between an optic nerve and an optic tract?
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macpatgh-Sheldon
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Hi,
The optic nerve originates from the nerve fibres of the ganglion cells (on the cell bodies of which the axons of the bipolar neurones have synapsed), which in turn are submitting info from the rods and cones.
ALL the ganglion cells axons from one eye jointly form the optic nerve on each side i.e. the R optic nerve has ONLY fibres from the R eye, and vice versa.
The two optic nerves decussate (cross over partly) at the optic chiasma (looks like the letter "X" therefore the prefix chi [Greek letter X]. As explained by Baylo1, the fibres follow a certain pattern as to which fibres go into which optic tract. The R and L optic tracts are the nerve fibre bundles AFTER the chiasma, the optic nerves before the chiasma.
To understand the various visual field defects seen in various types of impingement of the visual pathway, I shall upload a pic for you later, which is from my book, Systemic Pathology.
The optic nerve originates from the nerve fibres of the ganglion cells (on the cell bodies of which the axons of the bipolar neurones have synapsed), which in turn are submitting info from the rods and cones.
ALL the ganglion cells axons from one eye jointly form the optic nerve on each side i.e. the R optic nerve has ONLY fibres from the R eye, and vice versa.
The two optic nerves decussate (cross over partly) at the optic chiasma (looks like the letter "X" therefore the prefix chi [Greek letter X]. As explained by Baylo1, the fibres follow a certain pattern as to which fibres go into which optic tract. The R and L optic tracts are the nerve fibre bundles AFTER the chiasma, the optic nerves before the chiasma.
To understand the various visual field defects seen in various types of impingement of the visual pathway, I shall upload a pic for you later, which is from my book, Systemic Pathology.
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