Visual System
What is an optic disk abnormality that is the swelling of the head of the optic nerve and is a sign of increased intracranial pressure?
Papilledema
Causes commony causing Bitemporal Hemianopia
Pituitary Ademoas meningiomas Craniopharyngiomas
What is the general function of each of these pathways: Pupilary Light reflex pathway Tectospinal Pathway Retinohypothalmic pathway
Pupilary Light Reflex: reflex control of pupil and lens Tectospinal pathway: Superior Colliculi -- orienting the movement of the head and eyes Retinohypothalmic pathway: Hypothalamus-- regulation of circadian rhythms
What will happen if you cut the left optic tract
Right Homonymous Hemianopia You will lose the right visual field. (note: tract will always carry contra lateral visual field)
A Patient gets a stroke in their left Posterior Cerebral Artery
Right loss of visual field with macular Sparing Contralateral homonymous hemianopia with macular sparing.
After processing at the primary visual cortex, what two pathways does this information stream into?
The Dorsal pathway, and the Ventral pathway from area 18
Where does the optic nerve ultimately project to?
The Lateral Geniculate Nucleus of the thalamus.
What are the 2 streams of axons that arise after the Lateral Geniculate Nucleus? (there are 4 total when you consider both hemispheres of the brain)
The Left & Right Patietal Stream and the Left & Right Temporal Stream (aka the Meyer's loop) It is here where the information begins to be carried as quadrants!
The Right brain is responsible for which visual field
The Left Visual field.
What is a region surrounding the Fovea that also has high visual acuity?
The Macula
Name the Four main Visual System pathways
The Primary Visual path way The Pupilary Light reflex pathway Tectospinal Pathway Retinohypothalmic pathway
How does the Retina "see" an image? How does the brain "see" the image?
The Retina sees the image, upside down and backwards. So the superior retina processes the inferior image. The brain (visual cortex in the occipital lobe) will adjust the image to it's proper orientation.
The left brain is responsible for which visual field?
The Right visual field The Left eye gets information from the left visual field. The information will cross through the Optic Chasm to be processed in the Right brain.
From what retinal quadrant does the parietal stream get its information from?
The Superior Retinal Quadrant
What region is favored Retinotopicly
The fovea, which is magnified.
What visual field does the superior retinal quadrant capture
The inferior visual field
What information does the Parietal Stream carry
The inferior visual field.
What are layers 1 and 2 called?
The magnocellular layers
Where does the Dorsal pathway project to
The parieto-occiptal lobe
What are layers 3-6 called
The parvocellular layers
What visual field does the inferior retinal quadrant contain?
The superior visual field
How is the visual field organized?
The visual field is divided into hemifields and into quadrants. With the fovea in the middle. Each quadrant takes a different pathway to the visual cortex.
A patient comes to your office and after doing an MRI, you find that he has a massive tumor growing at his pituitary gland. Because of this you would expect him to also to complain of _____ vision
Tunnel vision.. The Tumor from the pituitary gland will press on the optic chaism, thus stopping transmission of contralateral signals from the nasal Retinas, resulting in Bitemporal hemianopia, aka Tunnel vision, aka, Loss of Peripheral vision.
When does macular sparing only occur
in strokes or occlusions, NOT in tumors
Where inferior visual field terminate?
in the cuneus
A patient presents with damage to the right Parietal stream
lose left inferior quadrant Contralateral inferior Quadrantanopia
where does the ventral pathway project to
the temporal occiptal lobe
Describe the General Primary Visual pathway
1. Light enters through the Optic nerve and sends some singals across Optic Chiasm 2. Signal travels to the optic tract 3. Synapse in Lateral Geniculate Nucleus 4. Travel through optic radiations 5. End in Primary Visual cortex 17
What layers are sensitive to color and form?
3-6
how many layers are found in the Lateral Geniculate Nucleus
6
What symptoms do patients present when they have Optic neuritis?
Blurred vision,Pain behind the eye, and Diplopia when the trochlear nerve is affected.
Area of highest visual acuity and the central fixation point for each eye. Light reaches rods and cones without having to pass through the other layers.
Fovea
A Patient Presents with Bilateral Internal Carotid Calcification near the lateral aspects of the Optic Chiasim. How will this patients vision be effected.
He will lose the central/nasal visual field, by the bilateral compression of the uncross nerved entering the optic chiasim, which will stop sensory information from the Temporal Retina which receive information from the central visual field.
Where does the temporal stream terminate?
In the lingual gyrus
What is Optic Neuritis?
Inflamation of the optic nerve usually in patients with MS
What information does the Temporal stream carry?
Information from the inferior Retinal quadrant
Define the Optic Disc
It is an area in the posterior aspect of the eye formed by retinal ganglion cell axons leaving the retina to form the optic nerve. The Central artery and vein are found here.
What is the optic nerve responsible for? and what would happen in the case of a complete lesion to it behind the left eye?
It is responsible for sight, and you would get complete monocular vision loss in the left eye
what is the Ventral pathway responsible for.
It is the what pathway WHAT do you need to VENT? Analyses Colors, letters, faces.
What is the dorsal pathway responsible for?
It is the where pathway. WHERE does that DOOR lead? Analyses spatial and motion relationships..
What layer of the cortex (include Brodmann's areas) does the visual information go to?
Layer 4 of the Primary Visual Cortex (area 17) - Layer 4 received the afferent from the thalamus. - Brodmann's area 17 is called the "Stria of Gennari" because it's layers (4b) have myelinated axons and look pale.
What layers are sensitive to movement and contrast
Layers 1 and 2
A patient gets shot in the head and survives. Luckily the only thing damaged was the Right Lateral Geniculate Nucleus. How will this patient present
Left Homonymous Hemianopia Loss of left visual field
A patient presents with a tumor to the Right cuneus
Lose left inferior quadrant Contralateral inferior Quadrantanopia
A patient presents with damage to the Right temporal stream
Lose left superior quadrant Contralateral Superior Quadrantanopia
A patient presents with damage to the Left Parietal stream
Lose right inferior quadrant Contralateral inferior Quadrantanopia
A patient presents with damage to the Left Meyers loop
Lose right superior quadrant Contralateral superior Quadrantanopia
A patient presents with damage to the left Lingual Gyrus
Lose right superior quadrant Contralateral superior Quadrantanopia
A patient presents with a giant tumor on their left occipital lobe?
Lose right visual field. Contralateral homonymous Hemianopia!
How many photoreceptors can be found at the optic disk?
None! The optic disc has no photoreceptors and so this is our "blind spot." Thankfully, the optic disc on either eye is not at the exact same location as the other eye so there is no deficit in vision. Even with one eye closed, the visual pathways compensate or "fill in" for the blind spot.
