Eye II Flashcards
What are the different subdivisions of the retina?
Inner vs. Outer:
Retinal pigment epithelium
Neural Retina
Anterior vs. Posterior:
Photosensitive Retina
Nonphotosensitive retina
What are the characteristics of the retinal pigment epithelium?
Outermost layer of the retina
Develops from outer layer of optic cup
Simple cuboidal epithelium
Attached through Bruch’s membrane to the choriocapillary layer of the choroid but is only loosely attached to the rest of the retina
What are the characteristics of the neural retina?
Consists of the remaining 9 layers of the retina
Contains photosensitive cells and a variety of other neurons
Develops from inner layer of optic cup
What are the characteristics of the photosensitive retina?
Area posterior to ora serrata
Ora serrata is a zig zag line that marks anterior limit of the choroid and visual retina
Contains all layer of neural retina including rods and cones (photosensitive cells)
What are the characteristics of the nonphotosensitive retina?
Area anterior to the ora serrata
Made up of two layers of cuboidal cells, does not includes rods and cones
Continuous with ciliary epithelium and pigment epithelium of iris
What is the structure of the retina?
10 layers
Photosensitive cells in outer layer
Optic nerve fibers in inner layer
Light must pass through all layers of the retina to reach rods and cones
Nerve impulses are passed back through layers to optic nerve fibers in inner layer
What are the major features of the retina?
Fovea centralis
Macula lutea
Optic disc
What are the characteristics and function of the fovea centralis?
Point of greatest visual acuity - allows maximal light penetration
Contains highest density of cone cells in the retina and has no rod cells
Conducting and association neurons are deflected at fovea to allow light to reach the cones unimpeded
What are the characteristics and function of the macula lutea?
Yellow region surrounding fovea
Ganglion cell layer thickest in this region
What are the characteristics and function of the optic disc?
Blind spot - no photoreceptors or photoreceptive cells
Where optic nerve pierces the retina
What does the central artery and vein of the retina do and where does it enter and travel?
Enters at optic disc
Travels with optic nerve fiber layer
Supplies inner layer of retina
Where are the photosensitive cells located in the retina? What does that mean for the cells and nerve fibers?
Located outside the neural retina, close to the choroid
Therefore light must travel all layers of the retina before it reaches the photosensitive cells and nerve impulse must be transmitted back through all the layers to the optic nerve fibers on the inner surface of the retina
How is the blind spot made at the optic disc?
Because the optic nerve fibers begin on the inner surface of the retina, they must pierce the retina to reach the brain, deflecting photosensitive cells and creating a blind spot
What are the 4 types of cells of the neural retina? What do each of them do?
Association neurons - horizontal and amacrine, regulate neural impulses
Conducting neurons - bipolar and ganglion, transmit visual information towards visual centers of the brain
Supporting cells - Muller’s cells, provide structural support to the retina
Photosensitive cells - rods and cones, react with light
What are the 10 layers of the retina from outside to inside?
- Retinal Pigement Epithelium
- Rods and Cones
- Outer limiting membrane
- Outer nuclear layer
- Outer plexiform layer
- Inner nuclear layer
- Inner plexiform layer
- Ganglion cell layer
- Optic nerve fibers
- Inner limiting membrane
What are the characteristics and function of the retinal pigment epithelium?
Simple cuboidal epithelium
Microvilli surround rods and cones and contain melanin granules
Strongly attached to Bruch’s membrane of choroid
Functions:
Melanin absorbs light and prevents reflection
Maintains blood-retina barrier
Phagocytosis and disposal of shed discs from rods and cones
Stores and supplies photosensitive cells with vitamin A
What are the characteristics and function of layer of rods and cones?
Outer segment of photosensitive cells - Contains specialized dendrites, site of photosensitivity, contains mostly rods and some cones
Inner segment - organelles, mitochondria, RER, golgi
Rods and Cones function on diff flashcard
What are the characteristics of the rods?
Most numerous
Most sensitive to light - activated in low light and inactive in full light
Discs separated from plasma membrane
Visual pigment rhodopsin reacts with light and depends on vitamin A
Insufficient uptake of vitamin A results in night blindness
What are the characteristics and functions of the cones?
Less numerous except in fovea
Sensitive to color
Only active in well lit conditions and inactive in low light
Three types of cone cells - Long (red), Medium (green), and short (blue)
Discs connected to plasma membrane
Outer segment is conical and contains photopsin that reacts with light
What is the outer limiting membrane?
Not true membrane
Apical border of Muller’s cells
What is the outer nuclear layer?
Nuclei of the photosensitive cells
What is the outer plexiform layer?
Cell processes of photosensitive, bipolar, and horizontal cells
What are the characteristics of the inner nuclear layer?
Nuclei of bipolar, horizontal, amacrine, and Muller’s cells
Bipolar cells - conducting neurons
Horizontal cells - association neurons, facilitate/inhibit transmission of impulses
Amacrine cells - regulate which impulses are transmitted to brain via the optic nerve
Muller’s cells - supporting cells, cytoplasm spans thickness of neural retina
What is the inner plexiform layer?
Processes of bipolar, ganglion, and amacrine cells
What is the ganglion cell layer?
Ganglion cell nuclei - conducting neurons and form optic nerve
Layer varies in thickness - thickest in macula lutea and absent in fovea centralis
Hyperpolarization of rods and cones causes depolarization of ganglion cells sending action potentials through axons into the brain
What is the layer of optic nerve fibers?
Axons of ganglion cells form the optic nerve
Converge and pierce the retina at the optic disc
Central retinal artery travels within this layer from ophthalamic artery and supplies inner layers of retina
What is the inner limiting membrane?
Basal lamina of the Muller’s cells
Separates retina from vitreous body
What is the path of visual processing in the retina? 7 steps
- Rods and cones react to light
- Pass info to bipolar cells
- Horizontal cells inhibit transmission of bad data
- Bipolar cells pass info to ganglion cells
- Amacrine cells inhibit transmission of bad data
- Central processes of ganglion cells form optic nerve to transmit visual info to the brain for further processing
- Muller’s cells provide structural and metabolic support for other retinal cells, form inner and outer limiting membranes
What is a summary of what is in each of the 10 layers of the neural retina?
- Retinal Pigment Epithelium - NOT neural retina
- Rods and cones - outer segments of photosensitive cells
- Outer limiting membrane - apical border of Muller’s cells
- Outer nuclear layer - nuclei of photosensitive cells
- Outer plexiform layer - processes of photoreceptive, bipolar, and horizontal cells
- Inner nuclear layer - nuclei of bipolar, horizontal, amacrine, and Muller’s cells
- Inner plexiform layer - processes of ganglion, bipolar, and amacrine cells
- Ganglion cell layer - nuclei of ganglion cells
- Optic nerve fibers - processes of ganglion cells
- Inner limiting membrane - basal lamina of Muller’s cells
What is age related macular degeneration?
Loss of photoreception localized to macula lutea leading to loss of the center of the visual field
Dry AMD - most common and caused by build up of drusen between RPE and Bruch’s membrane and within Bruch’s membrane. Separation of RPE and Bruch’s leads to degeneration of RPE and loss of vision
Wet AMD - progression of dry AMD, development of new blood vessels in choriocapllary layer of choroid, and new vessels leak fluid and blood between RPE and Bruch’s membrane
What is retinal detachment?
Separation of neural retina from RPE, specifically between RPE and layers of rods and cones
RPE more strongly attached to Bruch’s membrane than to layer of rods and cones due to development. RPE derived fro outer layer of optic cup and neural retina derived from inner layer of optic cup. Come together when development but don’t form a firm connection
Can be due to trauma such as a strong blow to head or disease
How does colorblindness occur?
Defects in genes encoding cones cause colorblindness
Red-green is most common
2 types of Red-Green - both sex linked and involve genes on the X chromosome
Deuteranopia - most common red-green colorblindness, loss of M cones (green deficient)
Protanopia - loss of L cones (red deficient)
Tritanopia - uncommon, loss of S cones (blue deficient), autosomal on chromosome 7, males and females affected
