Lab 7: Vision, Eyeball Movement And Balance Systems I Flashcards
3 Concentric Coats of the Eyeball
External or fibrous coat: sclera posteriorly and cornea anteriorly
Middle or vascular coat: choroid, ciliary body, and iris
Internal or retinal coat: outer layer of pigmented cells and inner layers of neural elements posterior to the ora serrata
4 Refractive Media of the Eye
- Cornea
- Aqueous Humor
- Lens
- Vitreous Body
Conjunctiva
Covers the anterior surface of the eyeball (corneal epithelium) and is attached near the edge or limbus of the cornea
Edge is also called corneoscleral junction.
Lines the inner surface of the eyelids (palpebral conjunctiva) and reflects onto the eyeball (bulbar conjunctiva)
Epithelium: 2 layers of stratified columnar cells which become more squamous closer to the limbus
Cornea
Transparent disk-like anterior portion of the eyeball and has 5 layers
Suspension Ligament
Composed of zonular fibers
Holds lens in position
Lens
Has an outer capsule of hyaline material
Lens epithelium (outside the capsule): which is a layer of cuboidal epithelial cells;
Center region: composed of tightly packed cells, which have lost their nuclei and are, chock full of special transparent proteins (crystalline)
New cells from the lens epithelium are added to the margin of the lens throughout life. Cells are the center do not undergo replacement and are the oldest cells in the body
Avascular and nourished by diffusion
Ciliary Body
Extends from base of the iris to the ora serrata (saw-toothed, black margin) at which point it’s continuous with the choroid (pigmented, vascular middle layer)
Contains ciliary muscle (smooth muscle) which you will see in microscopic views. Contraction of this muscle decreases the tension on the suspensory ligament of the lens and allows the lens to round up and become more spherical
Iris
Sheet-like diaphragm anterior to the lens and separates the anterior and posterior chambers of the eyes
Pupil
Circular aperture, which can be constricted or dilated by the actions of the circular fibers of the constrictor pupillae (parasympathetic innervation) and radial fibers of the dilator pupillae (sympathetic innervation) muscles respectively
Aqueous Humor
Resembles CSF in composition and is secreted by epithelial cells of the ciliary processes in posterior chamber
It flows from there to the anterior chamber through the pupil and provides nutrients to neighboring structures.
After filtering through a network of spaces (space of Fontana) lined by endothelium, the trabecular mesh work, which runs around the circumference of the root of the iris at the peripheral of the anterior chamber, the aqueous humor enters the CANAL OF SCHLEMM.
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Canal of Schelmm
Runs around the whole circumference of the limbus within the sclera and drains into veins
There’s normally resistance to the flow of aqueous Humor through the trabecular mesh work
Consequently, continued secretion and resorption of the aqueous humor is responsible for the normal intraocular pressure of 10-22 mg Hg
Glaucoma
Results from abnormal drainage of the aqueous humor and is characterized by a rise in intraocular pressure. If not treated, blindness can result from damage to the nerve cells of the retina
Vitreous Body
Fills the space between the lens and the retina
Has a volume of about 4 mL and is considered a specialized support tissue. It’s composed of a few scattered spindle-shaped cells, fine highly dispersed collagen fibers and an extracellularly matrix rich in hylauronic acid
Retina
Attached at the back of the eye at the optic disc
The innermost layer of the eye and is composed of a non-neural layer pigment epithelial cells which absorb light and prevent distracting back scatter into the retina and a neural layer of photoreceptors cells, retinal support cells and nerve cells
Optic Disc (also called the blind spot)
Axons of the retinal ganglion cells all collect here where they penetrate the sclera (lamina cribosa) to form the optic nerve
Choroid
Middle layer of the posterior 2/3 of the eyeball
Extends from the ora serrata, the anterior margin of the neural retina, to the optic nerve and contains blood vessels and lymphatics supporting the retina.
Appears as a dark brown sheet which blends with the sclera in it’s outer portion, while in the inner portion it’s attached to the pigmented epithelium of the retina at Bruch’s Membrane.
Separation of the Retina
Occurs between the rods and cones and pigment epithelium
Tapetum Lucidum
Special reflective surface portion of the choroid layer, which reflects light within the eye and is found in the eyes of animals that liver under conditions of low-intensity light
Ophthalmic Artery
Blood supply to the neural retina
Gives 2 branches: central artery of the retina and ciliary arteries.
Central artery of the retina
Branches out from the region of the optic disc to serve inner portions of the retina
4 branches go to the 4 quadrants of the regina
These branches are end arteries and if occluded, will result in death of the ganglion cells and therefore total blindness from that quadrant of the eye
Posterior Ciliary Arteries
penetrate the sclera around the optic disc and form the choroidocapillary plexus in the choroid
Materials from this plexus provide nutrients to the outer portions of the neural retina, the rods and cones
Anterior Chamber Location
Between the iris and cornea
Posterior Chamber
Posterior to the iris
Iris
Contains the constrictor and dilator pupillae muscles
Optic Disc and the Optic Nerve
Consists of axons of ganglion cells
Note the general location of the meninges surrounding the optic nerve
Ciliary Muscles
Regulate shape of lens
Ciliary Processes
Connected to suspensory ligaments
Suspensory Ligament
Connected to lens by zonule fibers
5 layers of the cornea (we look at 3)
Corneal epithelium
Corneal stroma
Corneal endothelium
Corneal Epithelium
Lines the outer surface
Stratified squamous non-keratinized epithelium
Corneal Stroma
The main layer of the cornea and consists of some 70 broad sheets of tightly bound, parallel collagen fibers embedded in an extraocular matrix
- the direction of the collagen fibers differs in each layer for maximal mechanical strength
- the absence of blood vessels in the cornea and the regular arrangement of the collagen fibers make the cornea translucent, allowing it to transmit light
Corneal Endothelium
- single layer; lines the inner surface
- adapted for ion-pumping
- pumps fluid from the corneal stroma, prevents corneal opacification from excessive hydration
Lateral Geniculate Body
At end of the optic tract
- termination (synapse) of axons of the ganglion cells of the eyeball
- thalamic nucleus for vision
Brachium of superior colliculus
Passes dorsal to the medial geniculate body
-contains optic tract fibers en route to pretectal area and superior colliculus
Superior Colliculus
Receives fibers for visual reflexes
Calcarine fissure
Medial occipital lobe
Cuneus
Superior to calcarine fissure
Lingual Gyrus
Inferior to calcarine fissure
Calcarine Cortex
Primary visual cortex (area 17), along the banks of the calcarine fissure
Secondary and Tertiary Visual Cortex
Surrounds primary visual cortex
Optic Radiation (geniculocalcarine tract)
- pass posterior to the lentiform nucleus as retrolenticular fibers from the lateral geniculate nucleus
- pass posteriorly, lateral to the inferior horn and atrium of the lateral ventricle
Path of Optic radiation
Passes deep or subcortical to the temporal cortex and receives arterial supply mainly from cortical branches of the middle cerebral artery
Optic Chiasm
Contains crossing of ganglion cell axons from the nasal half of each retina
Loop of Meyer
Inferior fibers of the optic radiations that loop around the inferior horn of the lateral ventricle
Visual Acuity
Test for near versus distant vision; deficits often the result of inappropriate shape of refractive media of eyeball
Scotoma
Loss of part of a visual field of an eyeball
Hemianopsia
Half loss (loss of half a visual field)
Quadrantic Anopsia
Quarter loss of a visual field
Homonymous
Loss in same part of visual field for both eyeballs
Heteronymous
Loss in different part of visual field for 2 eyeballs
