Visual Tracts Flashcards
What is the function of the eyelid?
Protects the eye lmao
What are the tarsal glands?
Special sebaceous glands whose secretion stops evaporation of tears
What can happen is the tarsal glands are blocked?
Can lead to Chalazion
What results from an infection of the sebaceous gland of eyelashes?
A stye
Function of lacrimal gland?
Location?
Produces tears
Located beneath conjunctiva
What is the lacrimal glands made up of?
Tuboloacinar serous glands
Where does the lacrimal gland drain to?
Nasolacrimal duct
What are the palpebrae and bulbar conjunctiva?
Thin mucous membrane
What is the histology of the palpebrae and bulbar conjunctive?
Stratified columnar epithelium w/ globet cells
What is the anterior chamber of the eye?
Space b/w cornea and iri
What is the posterior chamber of the eye?
Space b/w posterior surface of iris and anterior surface of lens
What is the vitreous chamber?
Space b/w posterior surface of lens and the neural retina
What does the vitreous chamber contain? For what purpose?
Vitreous humor to help maintain shape
What are the three tunics of the eye?
Fibrous
Vascular
Retina
What does the fibrous tunic consist of?
Cornea and sclera
Corneoscleral coat
Histologically, what is the sclera?
Dense irregular connective tissue
What is the funciton of the sclera?
◦ Support eye shape
◦ Protects delicate internal structures
◦ Extrinsic eye muscle attachment site
What is the cornea comprised of?
Two layers of epithelium w/ organized connective tissue
What is the funciton of the cornea?
Protect anterior surface of eye
Refract incoming light
What pierces the sclera?
Blood vessels, nerves and optic nerve
What are the 5 layers of the cornea?
- Corneal epithelium
- Bowman’s membrane
- Corneal stroma
- Descemet’s membrane
- Corneal endothelium
What is the chief refractive element of the eye?
Cornea
Histologically, the corneal epithelium?
Non-keratinized stratified squamous
What does the corneal epithelium contain?
Stem cells for cornea in limbus region
What is bowmna’s membrane?
Anterior basement membrane
What is unique about hte corneal stroma?
Avascular
What is descemet’s membrane?
Posterior basement membrane
Very thick layer of corneal epithelium
Histologically, the corneal endothelium?
Simple squamous epithelium
What is the vascular tunic composed of? What is another name for it?
Iris
Ciliary body
Choroid
Uvea
What is the iris composed of?
2 layer of smooth muscle (sphincter and dilator pupillae)
CT
central pupil
What does the iris form?
A contractile diaphragm in front of lens
What are the functions of the Iris?
Controls pupil diameter and amount of light entering light
What is the ciliary body?
Ciliary smooth muscle and ciliary processes covered w/ secretory epithelium
What is the funciton fo the ciliary body?
Holds suspensory ligaments to lungs
Change lungs shape for far and near vision
Epithelium secretes aqueous humor
What does the ciliary muscle drive?
Accomodation of lens
What is the function of the ciliary processes?
Secretes aqueous humor
Forms and anchors zonular fibers
What are the zonular fibers?
Form suspensory ligament of lens
What is the chorid?
Areolar connective tissue that is highly vascularized
What are the functions of the choirs?
Supplies nourishment to retina
Pigments absorbs extraneous light
What is the choroid composed of?
Inner vascular layer
Bruch’s membrane (thick amorphous ECM layer)
What are the two layers of the retina?
Pigmented layer
Neural layer
What is the pigmented layer of the retina composed of/
Pigmented epithelial cells
What is the funciton of the pigmented layer of the retina?
Absorbs extraneous light
Provides vitamin A for photoreceptor cells
What is the neural layer of the retina composed of?
Photoreceptors
Bipolar neurons
Ganglion cells
Supporting Muller cells
What is the function of the neural layer of the retina?
Detects incoming light rays
What is the lens?
Transparent, vascular, bi-contacted structure suspended by zonular fibers
What are the 3 components of the lens?
Capsule
Subcapsular lens epithelium
Lens fibers
What is the capsule mode of?
Flexible, elastic ECM
What do the cells of the subcapsular lens epithelium do?
Cells of periphery proliferate and migrate to make mature lens fibers cells
What are lens fibers filled with?
Crystalline
Loses all organelles
How is accomodation accomplished?
Ciliary muscle —> tension thru zonular fibers —> lens, flatten for distant or thicken for near vision
What is presbyopia?
Loss of lens elasticity with age
Cannot do accomodation as well
What dilates the pupil?
Radial band muscle
What constricts the pupil?
Sphincter pupillae msucle (circular band)
Histologically how is the Pigemented layer of the retina composed?
Layer of simple cuboidal epithelial cells resting on Bruch’s membrane of the choroid
What are the functions of the Pigm. Layer of Retina?
◦ Serves as blood-neural retinal barrer from choroid
◦ Absorbs stray light
◦ Phagocytosis membranous discs shed from rods and cones
◦ Isomerizes all trans-retinol to 11-cis retinal, transporting it back to photoreceptors
Does the neural layer of the retina have photo sensory ability?
Yes has rods and cones
What is the optic disc?
A blind spot in retina where otic nerves from ganglion layer exit the eye
What are the Neural retina layers?
From brain to world
- Outer limiting membrane
- Outer nuclear layer
- Outer plexiform layer
- Inner nuclear layer
- Inner plexiform layer
- Ganglion layer
- Layer of optic nerve fibers
- Inner limiting membrane
What does the optic nerve fibers consist of?
Processes of ganglion cells
What is the inner limiting membrane of the neural retina?
Basement membrane of muller cells
What visual pigment do rods have?
Rhodopsin
What visual pigment do cones have?
Iodopsin
Which photoreceptor cells are more sensitive?
Rods
What is the general strucutre of rods and cones?
Outer segment
Connecting stalk
Inner segment
Where do we see no photoreceptors?
Optic disc
What is the fovea centralis?
Place of sharpest visual acuity
No vessels, cell bodies or axons of gland lion ic and inner nuclear layer (no junk)
What do we see the highest concentration of cones?
Fovea centralis
Where is the muscle lutea?
Surrounding the fovea
What are the functions of the Macula Lutea ?
Antioxidant properties
Short wave UV filter
Protects cones of fovea
Where is the optic disc?
At head of optic nerve
What axons make up the optic nerve?
Axons of retinal ganglion cells
When do axons of the retinal ganglion cells become myelinated?
As axons pass thru sclera oligodendrocytes will myelinate
What does the optic nerve penetrate? On its way to what?
Choroid and sclera
On its way to the brain
What is the blood supply to the retina?
Ophthalmic artery branch
Central retinal artery
What cells form the dilator pupillae muscle?
Myoepithelial cells
What does the iris stroma contain?
Melanocytes
What is unique about hte lens capsule
It is an acellular layer
Where is the lends suspended?
Behind the iris and its central pupil
How is the lens suspended?
Ciliary zonular of fibrillin fibers produced by epithelial cells covering the ciliary body
What do cells of the RPE absorb?
Scattered light
What are the functions cells of the RPE?
Form part of a blood-retina barrier
Regenerate 11-cis-retinal
Phagocytosis shedded discs from rods
Support rods and cones
What do rod cells detect?
Light intensity
What is the outer segment of cone cell seen as?
Conical outer segment
What are the cone cells receptors for?
Primary colors (light of different wavelengths)
How are rod cells composed?
Stacked membrane discs, densely packed with rhodopsins w/ bound retinal
What is the RCL closest to?
Retina pigmented epithelium
And ONL
What does the outer pigemented layer contain?
Photoreceptor’ s axons connected in synapses w/ dendrites of various integrating neurons whose cell bodies form the inner neural layer
Where do axons from cells int he Inner Nuerla layer form synapses?
In the Inner Pigmeneted layer with neurons of the Ganglionic layer
What does the ganglionic layers send axons thru? To reach what?
Thru the layer of optic nerve fibers (NLF)
To the optic nerve
What is the function of the visual system?
Photoreceptive retina forms a light image
What is the visual pathway?
Visual field —> retina —> lateral genicular body
What forms the otic tract?
fibers from lateral retina (ipsilateral eye) + fibers from medial retina (contralateral eye)
Why does the optic tract have fibers from both eyes?
brings together info from comparable areas of both retina
—-> GIVES DEPTH PERCEPTION
Where does te optic tract terminate?
How do they terminate?
LGN
In a precise retinotopic pattern
What is a visual field?
Area that a person can see when both eyes are fixed in one position
What is a retinal field?
location on retina that an object in the visual field is projected to
Where is the object of attention focused and centered at?
Fovea centralis
Macula lutea
What two zones are the visual fields divided into?
Binocular zone
Monocular zones
What is the binocular zone of the visual field?
Broad central region seen by both eyes
What are the monocular zones of the visual fields?
R or L Area seen only by corresponding eye
How is the retina divided?
Into hemifields
And further into quadrants
What is projected onto the LLQ of the retina?
Upper right visual field
How is the image formed on the retina?
Inverted both laterally and vertically
Why is the image formed on the retina inverted laterally and vertically?
Due to partial decussation of CN2 at optic chiasm
What is the pathway of light to vision?
Light —> retina —> optic nerve —> optic tract —> LGN in thalamus —> optic radiation fibers —> primary visual cortex
What are optic radiations?
Large bundle of myelinated fibers of 2ndary neuron from LGN
Where do optic radiations travel to ?
What is this pathway called?
Priamry visual cortex (striate cortex).
On the upper and lower banks fo the calcarine sulcus
—> Geniculostriate or Geniculocalcarine pathway
Where do the lower quadrants of the optic radiations go?
Dorsomedial LGN —> retrolenticular limb —> superior bank of calcarine sulcus on cuneus
Where do the upper quadrants of the optic radiations go?
Ventrolateral portion of LGN —> arch up and into white matter of temporal lobe (forming a broad U-turn = Meyer Loop)
How do you get the “Pie in the Sky” phenomenon?
Lesion to Meyers loop
Where is the macula represented?
In LGN and Visual cortex (in region of occipital pole)
How do the fibers from LGN representing the lower half half of the visual field course?
course above to terminate in visual cortex above Calcarine sulcus
How do the fibers from LGN representing the upper half of the visual field course?
course to temporal lobe’s Meyers loop and terminate below Calcarine sulcus
What does retinotopic organization mean?
What does this allow for?
Precise, point to point relationship b/w retina and visual cortex
Can pinpoint a lesion based on where you have visual deficits
What are homonymous visual fields?
Overlapping fields (both left halves etc)
What are heteronymous visual fields?
Non overlapping fields
What are congruous lesions?
Lesions that present as symmetrical to that of the other eye
What are incongruous lesions?
Lesions that do not produce a symmetrical visual field loss
What is more likely to result in a
Congruous visual field defect?
Incongruous visual field defect?
Congruous: if lesion is close to visual cortex
Incongruous: if lesion is in optic tract or optic radiations
What will a lesion before the chiasm affect
Ipsilateral eye
What will a lesion at the chiasm affect?
Lateral edges of vision
Heteronymous visual field deficits
What will a lesion behind the chiasm cause?
Homonymous visual field deficits
What can visual field defects be caused by?
Acutely?
Chronically?
Acute: infarcts/CVA
Chronic: mass effect from tumor
What is monocular blindness?
Cause by?
Total loss of vision in one eye
Lesion of optic nerve before chiasm
What is bitemporal hemianopia?
Due to?
Outer visual fields are missing
Lesion at optic chiasm
What is homonymous hemianopia?
Caused by?
Both right or left sides of vision are missing
Lesion at optic tract
What causes contralateral superior quadrantanopia? Or pie in the sky?
Lesion at temporal lobe to meyer’s loop
What causes incongruent contralateral homonymous hemianopia with macular sparing?
Lesion of upper banks of calcarine fissure
What is binasal hemianopia?
Caused by?
Inner aspects of visual fields are missing
Could be caused by calcified ICAs or hydrocephalus
Anything that impinges on those lateral fibers of the optic nerve or optic tract
