Histology of the Eye-Heinbockel Flashcards
Overall Eye
The eye is a photosensitive organ to analyze form and color on objects based on the light they are reflected from.
It can self-adjust, self-focus, can adjust for light intensity. It then converts light to electrical impulses that are sent to the brain.
How does light travel into and through the eye?
light comes in through cornea–>pupil–>retina which comprises of several layers of cells and the light will continue until it hits the outer segment of the photoreceptors (rods and cone)
it shouldn’t really hit the choroid or sclera
What are the structures located in the anterior of the eye?
- cornea
- ciliary body: secretes aqueous humor
- iris
- lens
- limbus: where the eyelids/conjunctiva takes off
What are the structures located in the posterior of the eye?
- sclera
- choroid: layer under the sclera
- retinal pigment epithelium
- photoreceptors
- fovea (highest visual acuity)
- optic papilla (blindspot)
How do we distinguish the anterior chamber from the posterior chamber?
-iris separates the anterior and posterior chambers
anterior is in front the ciliary body (zonule)
the posterior is behind it
What comprises the external layer of the eye?
fibrous coat, supportive function, INELASTIC (very important in terms of glaucoma)
comprises of the
- sclera: opaque white
- cornea: is transparent where light can pass through
What comprises the middle layer of the eye?
vascular, highly pigments
comprises of the:
- choroid: which has lots of melanocytes giving it its brown color, richly vascularized with BVs and it brings nutritive substances to the eye
- cillary body: has ciliary muscles that is connected to lens fibers; assist in focusing the lens (making it flatter or more round)
- iris: in the middle of the eye; pigmented with lots of melanocytes giving us our eye color
What comprises the internal layer of the eye?
retinal coat (back of the eye)
comprises of
neural retina: sensory retina that houses the rods and cones (photoreceptors)
non-neural retina: which is pigmented epithelium
What does the vitreous body behind the eye contain?
- region behind the lens
- water (99%), collagen, hyaluronic acid molecules
What type of connective tissue does sclera and choroid contain?
sclera: thick layer of DICT
choroid: loose connective tissue
What is the difference in function of the sclera and choroid?
Sclera: mainly a supportive function; protects, maintain shape; reason for being inelastic
Choroid: supplies nutrition to the eye; is richly vascularized with blood vessels; has melanocytes and can absorb stray light
Describe the layers of the retina.
top single layer of retinal pigmented epithelial cells cuboidal in shape; they absorb the light and make sure there is no bouncing back of the light
photoreceptors that have cell bodies with inner and outer segment; rods and cones
photoreceptors are then connected to bipolar cells which are connected to the retinal ganglion cells
retinal ganglion cells send their long axons out of the eye to the lateral geniculate nucleus which basically forms the optic nerve
SUMMARY:
- outer layers of rods and cones
- intermediate layer of bipolar neurons
- internal layer of ganglion cells
What is the function of the retinal pigment epithelium?
- absorbs light pigment granules
- prevents back reflection of light striking retina
- forms part of the blood-retinal barrier: tight junctions
- sustains metabolism/pigment turnover of photoreceptors
- outer segment turnover: phagocytose shed discs
bruch’s membrane is btw the retinal pigment cells and the choroid
RPE has processes full of pigments and has all of the synthetic machinery it needs to make pigment
Where does light conversion into electrical signals (phototransduction) occur in the eye?
outer segment of the photoreceptors
What are the differences and similarities between the two photoreceptors: rods and cones?
they both have a cell body with a little process that synapses to the bipolar cell; they have membrane discs and cilium that connects the outer and inner segments of the photoreceptors ; have abundant mitochondria because you need a lot of ATP for the NaATPase
RODS:
- responsible for detecting low light intensity (dark)
- images in shades of gray
CONES for color:
- color, detail
- higher light intensity
- 3 types: blue, green, red
What is the importance of the retina’s thin and transparent nature?
- allows for minimal distortion so phototransduction is not interfered with
- graded potentials instead of action portantions
What is the structural junction between the retinal pigmented epithelium and photoreceptors?
there is NO structural junction between RPE and photoreceptors
pathology: can pull the pigment epithelium from the photoreceptors which will interfere with vision; can be corrected with laser surgery
What layer of the retina would the light hit first?
nerve fiber layer of the retina that will travel to the ganglion cells eventually to the photoreceptors
How many layers of cell bodies does the retina have?
3
outer nuclear layer: photoreceptors
inner nuclear layer: bipolar, horizontal, and amacrine cells
retinal ganglion cell layer (BIGGEST CELLS)
with plexiform layers in between making the synaptic connections
What is the fovea?
the spot (thin shallow depression) that allows for high acuity vision
- is abundant with pure cone photoreceptors that are tightly packed (highest packing density)
- can discern details of anything you are looking
- central is surrounded by the macula lutea (yellow xanthophyll pigments that act as sunglasses); because there is a lot of light coming into the fovea that is potentially damaging to the photoreceptors and thus you have some pigments in the ML surrounding the fovea to prevent damage of the photoreceptors
light at the posterior region of the optical axis
What allows the fovea to have the highest visual acuity?
- pure cone photoreceptors (no rods)
- highest packing density
- thinnest retinal region
Describe Age related macular degeneration.
- macula surrounds the fovea
- somehow there is some debris that accumulates btw the RPE and the choroid where the Bruch’s membrane is located
if there is material accumulating, this has an effect on the photoreceptors pushing them away from the fovea damaging them; the photoreceptors degenerate; instead of having high visual acuity you have a dark spot in the visual field
What is the optic papilla?
- the blind spot where the optic nerve leaves the eye
- retina is all around the back of the eye but the retinal ganglion cells have axons that need to leave the eye somewhere
this occurs at the optic papilla (blindspot)
so there are no photoreceptors in the blindspot meaning you cannot see in this region
SUMMARY:
- axons of ganglion cells exit the eyeball
- no photoreceptors
What is the function of the cornea?
most focusing of light occurs here
- directs rays to converge on the retina
- this is why it is TRANSPARENT and AVASCULAR
