Optic Nerve (Q3) Flashcards
CN are in nerve deck, Hematomas are in vasculature
What do we call the most anterior part of the optic nerve?
Optic disc
The colour (or lack thereof) of the ONH is due to the absence of …
retinal pigment epithelium
Which side of retina is the ONH located and how many degrees from fixation?
Located in the nasal retina, 15 degrees from fixation
T/F: ONH acts as a physiological blind spot in visual field tests
True
In an evaluation of the ONH, we should examine…
margins, rim tissue, disc size, C/D ratio, depth, blood vessels, and insertion of the nerve
List the sides of the rim tissue as thickest to thinnest
Inferior, Superior, Nasal, Temporal (ISNT Rule)
What is the average optic disc size (in mm)?
1.9mm vertically and 1.7mm horizontally
What measurement is considered a small disc size (in mm)?
<1.5mm
What measurement is considered a large disc size (in mm)? What might this condition be called?
> 2.2mm, Megalopapilla
What are the correction factors for measuring disc size using a +60D lens? +78D lens? and +90D lens?
1.0 (for +60D lens), 1.1 (for +78D) and 1.3 (for +90D lens)
What is optic nerve hypoplasia?
A congenital, pathologic condition in which the optic nerve head is underdeveloped
The cup-to-disc ratio indicates the diameter of the cup expressed as a fraction of the diameter of the optic disc and is given in increments of…
0.05
T/F: Cup-to-disc ratio is most accurately determined stereoscopically
True
T/F: A deep physiological cup makes it harder to judge a C/D ratio
False, a deep cup is easier to evaluate C/D ratio compared to a shallow cup which is more difficult; you may need to use the appearance of the blood vessels to judge.
Is a malinserted (insertion not perfectly perpendicular) ONH pathologic or not? And what visual condition is it usually associated with?
Not pathologic, associated with moderate to high myopia
What is a choroidal crescent?
A dark area by the ONH caused by an absence of the RPE/retina, allowing the underlying choroid to be visible
What is a scleral crescent?
A white area next to the ONH caused by the absence of the RPE/retina and choroid layers, allowing the underlying white sclera to be visible
Are choroidal/scleral crescents pathologic? And are they included in judging C/D ratio?
Not pathologic, and not included in rim tissue when judging C/D ratios
What are some other common ONH findings?
Disc hemorrhages, ONH drusen, notches in rim tissue, collaterals, laminar dots, etc.
The optic nerve is composed of bundles of axons carrying signals from the retina to the brain. Where are the cell bodies of these axons located? And what layer is also formed by these axons?
Cell bodies are in the ganglion cell layer of the retina, and the axons also form the nerve fibre layer before coming together at the optic nerve
Which side of the optic disc do the macular fibres enter and what is this bundle of nerve fibres also referred to as?
Macular fibres enter at the temporal disc and are also referred to as the papillomacular bundle
T/F: All 3 layers of the meninges fuse together and become continuous with the sclera
True
What is the longest segment of the optic nerve?
the intraorbital segment
What is the shortest segment of the optic nerve?
the intraocular segment
What is the name for the sieve-like interwoven collagen fibrils forming canals through which the optic nerve bundles pass through in the intraocular segment?
the lamina cribrosa
Which is the only segment of the optic nerve that is non-myelinated?
the intraocular segment
Which EOMs attach to the intraorbital segment of the optic nerve?
the superior rectus and medial rectus
Which structures of the brain are surrounding the intracranial portion of the optic nerve (leading up to the optic chiasm)?
Superiorly - olfactory tract, anterior cerebral artery
Medially - sphenoid sinus
Inferiorly - internal carotid artery, middle cerebral artery, pituitary gland
What is the name for a proliferation of meningeal cells of the intraorbital and intracanalicular optic nerve? What are the symptoms?
Optic nerve sheath meningioma. Affect F>M (40-50yrs of age) gradual painless vision loss usually in one eye, optic nerve head edema or atrophy, and/or optociliary shunt vessels (collaterals)
Which structures supply blood to the intraocular (pre-laminar and laminar) portions of the optic nerve?
The circle of Zinn, formed by the short posterior ciliary arteries
Which vessels supply blood to the intraorbital portion of the optic nerve?
The central retinal artery and pial vessels
Which arteries supply blood to the intracranial portion of the optic nerve?
The ophthalmic, anterior cerebral, anterior communicating, and internal carotid arteries
What are the possible symptoms of a pituitary adenoma?
Blurred vision, headache, diplopia, colour desaturation, visual field defect (bilateral hemianopsia), optic atrophy
Can visual field defect improve after removal of a pituitary tumour?
Depends on the amount of optic nerve damage/atrophy, it may improve if the tumour is caught early!
The Circle of Willis is an anastomosis of which arteries/circulations?
Anterior circulation: internal carotid arteries, and posterior circulation: basilar, vertebral arteries
A patient had an optic tract lesion due to a stroke which caused a left hemianopsia in his visual field testing, which side of his brain was affected?
Right side
What is the name of the nuclei where the axons of the ganglion cells synapse?
Lateral geniculate nucleus, in the thalamus
Which layers of the LGN are magnocellular and which are parvocellular? What are the layers in between these 6 layers called?
Layers 1-2 are magnocellular, layers 3-6 are parvocellular. Koniocellular layers are located in between all 6 layers
Which layers of the LGN do contralateral (crossed) fibres of the optic tract synapse in?
Layers 1,4,6
Which layers of the LGN do ipsilateral (uncrossed) fibres of the optic tract synapse in?
Layers 2,3,5
The axons that project from the LGN to the primary visual cortex (V1) are called…
optic radiations
The visual cortex is divided into an upper and lower portion by the calcarine fissure, what are these gyri called and which part of the retina do the information they process come from?
Upper - Cuneus gyrus: processes info from superior retina (inferior visual field)
Lower - Lingual gyrus: processes info from inferior retina (superior visual field)
V1 processes basic stimulus, which centers make up the extrastriate cortex that processes more complex information?
V2-V5, on lateral aspect of occipital cortex
Which layer of V1 receives visual input from the LGN?
Layer 4
Which layer of V1 provides inhibitory feedback to the LGN?
Layer 6
What structure supplies blood to the optic chiasm?
the Circle of Willis
Which arteries supply blood to the optic tract?
Anterior choroidal artery
Which arteries supply blood to the LGN?
Anterior choroidal, and posterior cerebral arteries
Which arteries supply blood to the optic radiations?
Anterior choroidal, middle cerebral, and posterior cerebral arteries?
Which arteries supply blood to the visual cortex?
Middle cerebral, and posterior cerebral arteries
Which structures of the visual pathway are supplied by the anterior choroidal artery?
Optic tract, LGN, and optic radiations
Which structures of the visual pathway are supplied by the posterior cerebral arteries?
LGN, optic radiations, visual cortex
Which structures of the visual pathway are supplied by the middle cerebral arteries?
Optic radiations, and the visual cortex
T/F: about 5,000 ganglion cells are lost per year
True
T/F: myelinated retinal nerve fibres are pathologic
False, they are not pathologic
Most retinal neurons use graded potentials or action potentials?
Graded, however ganglion cells generate action potentials
T/F: Inside of axon is more negative than outside environment
True; Na+ flows in, resulting in depolarization
An example of a disease caused by a loss of myelin, resulting in reduced conduction velocity
Multiple sclerosis
Periventricular white matter lesions/plaques in the brain almost definitively mean which disease?
Multiple sclerosis
What is Uhthoff’s phenomenon in MS patients?
A loss of conduction due to changes in body temperature, such as when exercising or having a hot shower, possibly more numbness or vision problems noticed at these times
What is Lhermitte’s sign in MS patients?
an electric shock-like sensation that occurs with flexion of the neck
What is Pulfrich’s phenomenon in MS patients?
An altered perception of motion usually because one eye is affected more than the other
What are the ocular symptoms of MS?
pain on eye movement, diplopia, flashing lights (phosphenes)
What are the ocular signs of MS?
ONH edema or pallor, optic neuritis, varying degrees of vision loss, APD, VF defects, loss of colour vision, decreased contrast sensitivity, etc.
What is an astrocytoma?
A slightly elevated, yellow-white retinal mass due to astrocyte proliferation. Rare, but when found is usually in a younger patient and can potentially be malignant
What are NG2-glia?
A new class of glial cells, thought to be oligodendrocyte progenitor cells that can differentiate into other cell types depending on the environment
What are the four main signs of optic nerve damage?
VA loss, VF loss, pallor/atrophy, and excavation (loss of rim tissue)
What are the risk factors of optic nerve injury due to ischemia?
age, hypertension, diabetes mellitus, migraine headaches, sleep apnea, and tobacco use
What are the signs and symptoms of optic nerve injury due to ischemia?
sudden, unilateral, painless vision loss
clinical signs: ONH edema/atrophy, and hemorrhages
What conditions may cause an optic neuropathy by compression?
tumours (ex. pituitary adenoma), aneurysms, enlarged EOMs
What is the definition of papilledema?
Optic disc edema caused by elevated intracranial pressure
What are the common symptoms of papilledema?
can be asymptomatic, or vision loss, changes in colour vision, headache, nausea, vomiting, diplopia, etc.
How should you document a case of swollen optic nerves before an elevated intracranial pressure is proven to be true?
“bilateral disc edema”, NOT papilledema unless ICP is proven to be elevated
What is the most common cause of optic neuropathy?
Glaucoma, the loss of ganglion cell axons
How can we measure a glaucoma progression objectively?
Using OCT scans of the RNFL thickness over time
In glaucoma progression, which clinical sign usually is seen earlier compared to the others?
Earliest is usually changes in RNFL thickness, then disc changes (C/D ratios), and then visual field changes in later stages
What are the signs and symptoms of optic atrophy
reduced VA, dyschromatopsia, visual field defects, afferent pupillary defect, etc.
Optic atrophy due to damage anterior to the chiasm is usually seen unilaterally or bilaterally?
Unilateral
Optic atrophy due to damage posterior to the chiasm is usually seen unilaterally or bilaterally?
Bilateral
What is a neurotrophin?
a regulatory factor that induces survival, development, and function of neurons; implicated in neurodegenerative diseases such as Alzheimer’s and possibly glaucoma
Which neurotrophin has the greatest influence on the optic nerve?
BDNF - brain-derived neurotrophic factor
Which cells’ survival does BDNF enhance?
Retinal ganglion cell survival after optic nerve injury, preserving structural integrity and visual responsiveness (therapeutic possibilities!)
Which of the non-glaucomatous causes of optic atrophy involves edema, primary or secondary?
Secondary (nerve becomes swollen and then recedes and then atrophy occurs)
What are the common causes of primary optic atrophy?
bilaterally - hereditary reasons, or nutritional/toxic cases
unilaterally - trauma
What are the common causes of secondary optic atrophy?
bilaterally - papilledema, compression
unilateraly - ischemia, occlusion, compression
At what amount of time is an average of 50% of the RNFL lost after an injury?
56 days after injury
Perfusion pressure definition
how easily blood can pass through a given tissue, it is the difference between the pressure of the blood flow entering and leaving the eye
Perfusion pressure of the eye, equation
mean arterial pressure of the arteries entering the eye is around 65 mmHg and the pressure in the episcleral veins leaving the eye is around 15 mmHg, so the perfusion pressure of the eye is approximately 50 mmHg.
Ocular perfusion pressure =
OPP = diastolic BP - IOP
What does OPP tell us for glaucoma patients?
pts with a low OPP are 1.5x more likely to develop progresisve optic neuropathy secondary to ischemia
What is the relationship between IOP and OPP?
if IOP decreases, OPP increases
if IOP increases, OPP decreases
What is the relationship between OPP and diastolic BP?
if diastolic BP decreases, OPP decreases
autoregulation
the process by which blood vessels alter their diameter (in the absence of neural control) in order to increase or decrease resistance to blood flow (pericytes are most likely responsible for this in the retina and optic nerve)
transmural pressure
describes the pressure across the blood vessel wall and is determined by subtracting the pressure outside the vessel from the pressure inside the vessel
critical closing pressure
the pressure at which the blood vessel collapses and blood flow stops
What is the immediate threat to vision in an acute angle closure?
CRAO! the pressure in the eye causes the retinal vessels to autoregulate until they reach their critical closing pressure at which point a CRAO would occur to the CRA
