Visual Tracts Flashcards
What are the 3 layers/tunics of the eye from superficial to deep?
Fibrous layer
Vascular layer
Retina
What is included in the Fibrous layer of the eye?
Sclera and cornea
What is included in the Vascular layer of the eye?
Choroid, ciliary body, iris
What is included in the Retinal layer of the eye?
Retina
Function of the sclera?
External layer of dense regular CT that protects internal structures and is an attachment site for the extraocular muscles
How many layers does the cornea have?
5
What are the layers of the cornea from superficial to deep?
Corneal epithelium Bowmen's (anterior limiting) membrane Stroma Descemet's (posterior limiting) membrane Inner endothelium
What type of tissue is the most superficial layer of the cornea?
The corneal epithelium is made of nonkeratinized stratified squamous
What cell type is in the 3rd layer of the cornea?
The stroma consists of keratocytes
What is the thickest layer in the cornea?
The stroma (3rd layer)
Where is the limbus?
It encircles the entire cornea and is the site where the cornea and sclera merge together
What is the purpose of the limbus?
It creates the conjunctiva that lines the anterior sclera and contains epithelial stem cells that will give rise to progenitor cells that move into the cornea
Qualities of the choroid in the vascular layer of the eye?
Contains many melanocytes and absorbs scattered light, prevents light from entering other places besides the pupil
2 main layers of the retina?
Pigmented Epithelium and the inner neural layer
What type of cells are the outer Pigmented Epithelium of the retina?
Simple cuboidal
What does the inner neural layer of the retina become once it moves anteriorly?
Ora serrata
What are the layers of the inner neural layer of the retina from first to receive light to last?
Inner limiting membrane (ILM) Nerve fiber layer (NFL) Ganglionic layer (GL) Inner plexiform layer (IPL) Inner nuclear layer (INL) Outer plexiform layer (OPL) Outer nuclear layer (ONL) Outer limiting membrane (OLM) Rods and cone layer Pigmented layer (PL)
Once light travels to the rod and cone layer of the retina (9), then what happens?
The signal propagates back the way it came to find the nerve fiber layer (2) that contains the ganglionic cell axons that will form CN2 - optic nerve
Area in the retina with the highest concentration of cones and the highest visual acuity?
Fovea
Area surrounding the fovea that protects the cones?
Macula lutea
Where do ganglion axons converge and what is missing there?
Optic disc, no photoreceptors = blind spot
What forms the optic nerve?
Axons of retinal ganglion cells that become myelinated as they pass through the sclera going towards the brain
What is a visual field?
Area that a person is able to see
Central region of the visual field that is seen by both eyes
Binocular zone
One region for the right eye and one for the left = 2
Visual field seen only by the corresponding eye
Monocular zones
What is a retinal field?
Location on the retina that an object in visual field is projected to
How are visual fields divided into retinal hemifields?
Nasal and temporal hemifields and then upper and lower quadrants
How are lesions in the visual pathway describe?
Their visual field deficits
How is the image formed on the retina different than the image we see?
The image is inverted and flipped laterally
The left visual field projects to?
Right side of retina and right side of brain
What does the optic tract contain?
Ipsilateral temporal field and contralateral nasal field
Where do the optic tracts terminate?
Lateral geniculate nucleus of the thalamus
Outgoing fibers from the LGN are called?
Optic radiations
The top part of the visual field projects?
To the bottom part of the retina
The bottom part of the visual field projects?
To the top part of the retina
The bottom part of the retina containing the upper hemifield projects to the LGN and then to where?
Lingual gyrus - inferior to the calcarine sulcus
The upper hemifield fibers have to travel around the lateral ventricle, through the temporal lobe. What is created?
Meyer’s loop
Damage to meyer’s loop?
Upper visual field deficits
The top part of the retina containing the lower hemifield projects to the LGN and then to where?
Cuneus - superior to the calcarine sulcus
Where do fibers from the macula and fovea target in the visual cortex?
Most posteriorly - occipital pole
What consumes disproportionately large volumes of the LGN and visual cortex compared to its size?
Fovea and macula
Important in directing eye movements
Superior colliculus
Important in pupillary light reflex
Pretectal area
Besides the visual cortex, the LGN sends targets where?
Parieto-occpital-temportal area = visual association area for interpretation
Blindness in 1 half of visual field
Hemianopia
Blindness in quadrant of visual field
Quadrantanopia
Visual field losses are similar in both eyes
Homonymous visual field
2 eyes have non-overlapping field losses
Heteronymous visual field
Visual field loss that preserves vision in center of visual field
Macular sparing
When deficit of visual field from 1 eye can be superimposed on to the other eye (symmetrical)
Congruous
Where are deficits most likely to be congruous?
Closer to the visual cortex
Damage anterior to chiasm
Affects ipsilateral eye
Damage at chiasm
Heteronymous deficits
Damage behind chiasm
Homonymous deficits
Associate visual agnosia
Pt cannot name or describe object but can recognize and demonstrate its use
Disconnects the language area from visual association area
What may cause associate visual agnosia?
Infarction of LEFT occipital lobe and posterior corpus callosum
