Lecture 20-21: The Eye Flashcards
1
Q
Describe the anatomy of the 3 layers of the eye:
A
- Fibrous tunic:
- Sclera (Tunica fibrosa)
- Cornea
- Vascular tunic
- Choroid
- Ciliary body
- Iris
- Inner tunic
- Retina
- Refer to Figure 9-4
- See Slides 4-10
2
Q
Describe the sclera
A
2 Layers:
- Episcleral layer:
- Loosely arranged collagen and elastic fibers:
- Highly vascular
- Attaches the lining of the eyelid (conjunctiva) to the sclera
- Sclera proper:
- Made up of interlacing collagen fibers
- Attachment site for tendons of extrinsic eye muscles
- Collagen bundles are always parallel to outer surface of sclera
- Lamina cribrosa:
- Perforated disc of sclera
- Pass through for optic nerve fibers
- Anteriorly the sclera is continuous with the cornea.
- The junction between the two is the limbus; it is highly vascularized.
- Posteriorly the sclera is continuous with the dural covering of the optic nerve.
3
Q
Describe the cornea layers
A
- Corneal epithelium:
- Stratified, nonkeratinized squamous epithelium: 5-6 layers
- High mitotic activity in the basal layer: Turnover ≈ 1 week
- Bowman’s membrane:
- Acellular layer separates epithelium from stroma.
- Randomly arranged collagen fibers
- Corneal stroma:
- Thin layers of ordered arrays collagen fibers
- Descemet’s membrane:
- Acellular layer of collagen bundles
- Separates stroma from endothelium
- Corneal endothelium:
- Single layer of large squamous cells
4
Q
I’m not starting the chegg flashcards yet because of where I am, but you should prepare those at some point today for lectures 20-21.
A
Do it.
5
Q
Describe the choroid
A
- Extends anterior to ora serrata of the retina
- Highly vascularized with loose connective tissue:
- Forms choriocapillary network: Contains small blood vessels that supply cells of the retina
- Provides nutrients to outer layers of the retina
- Consists of medium and large arteries and veins as well as a widebore capillary network
- Contains melanocytes
- Bruch’s (glassy) membrane
- Acellular fused basal laminae of choriocapillaris and pigmented retinal epithelium
See Slide 18
6
Q
Describe the ciliary body
A
- Wedge-shaped expansion of choroid peripheral to the lens
- Covered by a double layer of cells
- Innermost layer is continuous with the pigmented layer of the retina.
- Surface layer is from the sensory layer of the retina.
- Produces aqueous humor.
- Suspensory ligaments (of Zinn) extend to just behind lens equator and anchor the lens in place.
- Ciliary muscles
- Smooth muscle mass that changes the shape of the lens
- Innervated by parasympathetic neurons
- Ciliary muscles and accommodation:
- One group of muscles is responsible for flattening the lens
- A second group of muscles is responsible for allowing the lens to become thicker.
- Nonpigmentedsurface layer of cells produces aqueous humor.
- Basal infoldings
- Secrete aqueous humor into posterior chamber
- Aqueous humor:
- Percolates through trabecular meshwork
- Flows into canal of Schlemm
- See Slides 20-26
7
Q
Describe the iris
A
- The iris is located anterior to the lens and separates the anterior and posterior chambers.
- Angle:
- Formed at lateral borders of the anterior chamber
- Loose connective tissue
- Part of passageway for aqueous humor
- Surrounds pupil
- Double layer of epithelium
- Inner layer = pigmented epithelial cells.
- Outer layer of radially oriented myofilaments:
- Dilator pupillae muscle.
- Sympathetic innervation
- Dilates pupil
- Concentric layer of myofilaments:
- Constricts the pupil.
- Parasympathetic innervation
- Melanocytes:
- The more melanocytes, the darker the iris.
8
Q
Describe the retina
A
- Two subdivisions divided by the ora serrata:
- Photosensitive region lies posterior to the ora serrata.
- Optic disc:
- Region on posterior aspect of eye where optic nerve exits
- Has no photosensitive retina and constitutes the blind spot
- Fovea centralis:
- About 2.5 mm lateral to optic disc
- Contains yellow pigment = macula lutea
- Contains only cone-type photoreceptors
- Area of most acute vision
- Two subdivisions divided by the ora serrata:
- Nonphotosensitive region lies anterior to the ora serrata.
- Consists of two cell layers covering iris, ciliary body and ciliary processes
- Photosensitive region lies posterior to the ora serrata.
- Includes rods and cones
9
Q
Describe the 3 chambers of the eye, and glaucoma
A
- Anterior chamber:
- Posterior to cornea and anterior to iris
- Posterior chamber:
- Posterior to iris and anterior to lens
- Vitreal chamber:
- Posterior to lens
- Contains vitreous body
- Gelatinous mass made up of 99% water, hyaluronic acid, and vitrein
- Hyaloid canal is the site of a fetal artery.
- Glaucoma:
- Increased intraocular pressure due to compromised drainage of aqueous humor from anterior chamber
10
Q
Describe the first 3 layers of the retina
A
- Pigmented epithelium:
- Adjacent to choroid
- Derived from outer (thinner) layer of the optic cup
- Inner and outer segments of rods and cones:
- Outer segment consists of rhodopsin-containing lamellae
- Inner segment consists of areas of rods and cones possessing mitochondria, RER, Golgi, and glycogen (metabolically active)
- External limiting membrane:
- Area at junction of inner and outer segments of rods and cones and outer nuclear layer.
- Includes adherens junctions between rods and cones and Mueller cells.
11
Q
Describe Layers 4-7 of the retina
A
- Outer nuclear layer:
- Cell bodies of rods and cones (1st order neurons)
- Outer plexiform layer:
- Area of synapses between axons of rods and cones and dendrites of bipolar neurons and horizontal cells
- Inner nuclear layer:
- Cell bodies of bipolar cells (2nd order neurons), horizontal cells, amacrine cells, and Mueller cells
- Inner plexiform layer:
- Area of synapses between axons of bipolar cells and dendrites of ganglion cells.
12
Q
Describe Layers 8-10 of the retina
A
- Ganglion cell layer:
- Cell bodies of ganglion cells (3rd order neurons)
- Optic nerve layer:
- Axons of ganglion cells
- Internal limiting membrane:
- Terminations of Mueller cell processes and their basement membrane
13
Q
Describe pigmented epithelial, bipolar, and horizontal cells
A
- Pigmented epithelial cells
- Adjacent to choroid
- Synthesize melanin
- Apical processes surround and protect outer segments of rods and cones (photosensitive areas)
- Phagocytose and degrade lamellae from rods and cones
- Connected via tight junctions to form blood-retina barrier
- Esterify vitamin A used in formation of photosensitive pigments
- Bipolar cells:
- Conducting neurons that synapse with rods and cones
- Horizontal cells:
- Interneurons that interconnect rods and cones with each other and with bipolar cells
14
Q
Describe a machine, muller, and ganglion cells
A
- Amacrine cells:
- Interneurons that connect ganglion cells and bipolar neurons
- Muller cells:
- Neuroglial cells that extend throughout retina
- Form external limiting membrane via zonulae adherens between Muller cells and rods and cones
- Internal limiting membrane is formed by the basement membrane of these cells
- Ganglion cells:
- Conducting neurons whose axons form the fibers of the optic nerve
- See Slides 12-14
15
Q
Describe the histology of the eye
A
- Macula lutea:
- Yellow region surrounding fovea
- Highest visual acuity
- Fovea centralis
- Depression of visual axis
- Highest density of cone cells
- Lacks rod cells and capillaries
- Optic disc:
- Lacks photoreceptors
- Point where ganglion cells turn into optic nerve
- = “blind spot” of retina
- See Slides 16-18
