Full Review Flashcards
During gestation, when does the eye form?
Between 1st and 4th months of gestation
What forms during gestation weeks 3-4?
Eye fields
Optic vesicle
What forms during gestation weeks 5-6?
Optic cup
Lens vesicle
Choroid fissure
Hyaloid artery
What forms during gestation weeks 7-8?
Cornea
Anterior chamber
Lens
Retina
What forms during gestation weeks 8-10?
Eyelids
What forms during gestation weeks 9-15?
Iris
Ciliary body
The eye fields form from a population of what cells?
Cells from the anterior neural plate
In humans, when do the frontal eye fields begin to form?
Around 17 days
Where do the eyefields start to form?
In the prosencephalon
As the eyefields get pushed forward, what begins to occur?
Folding, bringing the eyefields together
After folding of the eyefields, what beings to form?
Optic groove
Eye fields are invaginating and forming a sulcus
How long does it take for the neural folds to meet at the top?
25 days
What structure forms the optic vesicle?
Optic groove
When the neuroectoderm and the surface ectoderm come in close contact (around day 25), what happens?
The optic groove begins to push itself out (evaginates), creating the optic vessicles
Neuroectoderm coming in contact with surface ectoderm induces what?
Lens placode
What does the lens come from?
Surface ectoderm
True or false: formation of the optic vesicle occurs at the same time as induction of the lens placode.
True
When the lens placode is induced, does it begin on the outside, or the inside?
Outside
How does the lens get inside the eye?
Lens placode and and optic vessicle invaginate
When the lens vesicle invaginates with the optic vesicle, what forms?
A bi-fold
When the optic vesicle invaginates, what is formed?
Optic cup
When the lens placode invaginates, what is formed?
Lens vesicle
As the optic vesicle and cup form, what is occurring to the optic stalk?
Also ingavinating
Where the optic stalk invaginates, what is created?
Choroid fissure
What grows within the choroid fissure?
Hyaloid artery
What feeds the lens vesicle during formation?
Hyaloid artery
What surrounds the back of the lens?
Hyaloid artery
What is the role of the posterior lens fiber?
Obliterate the lens cavity
When does the cornea differentiate?
After the differentiation of the lens and retina - around one month
What serve as the scaffolding for creating the iris?
Iridopupilary membranes
When do we first see something that actually resembles an eye?
After one month
When do the pupilary membranes usually go away?
After birth
What happens if the pupilary membranes persist after birth?
They may fix the pupil, and make it so it can’t change size
What keeps the lens nice and smooth?
Crystallines
During development, is the cornea clear or opaque?
Opaque
What cells form the outer corneal epithelium?
Surface ectoderm
What cells form the inner portions of the cornea?
Neural Crest Cells
All of the structures of the eye, with the exception of _____, come from the ectoderms.
Hyaloid artery
Inner layer of the cornea
During weeks 7-8, what is occuring in the retina?
There is a gap between RPE and neural retina. Neural retina begins to differentiate into the 10 total cell types
When the eyelid first is formed, is there a fissure?
Nope. It is just one structure
During what trimester do the eyelids un-fuse?
3rd trimester
From what tissues does the iris form?
Optic cup tissues
The folding of the “rim” of the optic cup forms what two structures?
Iris
Ciliary processes
What are the two principle pathways from progenitor cell to retinal cell?
Ganglion cell pathway
Cone/horizontal cell pathway
What cells can arise from the ganglion cell pathway?
Ganglion cells
Amacrine cells
Rods
Bipolar cells
What cells can arise from the cone pathway?
Cones Horiztonal cells Muller glial cells Rods Bipolar cells
Both the ganglion and cone cell pathways may differentiate into what?
Bipolar cells
Rods
Which retinal cell types migrate more than the others?
Bipolar cells
Rods
Which cells are “born” at about the same time?
Amacrine
Cone
Ganglion
Horizontal
Which cell type begins to form after the amacrine, cone, ganglion, and horizontal cells are formed?
Rods
What retinal cell type is born after rods?
Bipolar cells
What is the last retinal cell type born?
Muller glial cells
What is the order of retinal cell birth?
- Amacrine, cone, ganglion, horizontal
- Rods
- Bipolar cells
- Muller glial cells
Which cells continue to be born after birth?
Amacrine, rods, bipolar, Muller cells
Which cells are largely born before birth?
Cones
Ganglion cells
Horizontal cells
What does the retina start as?
A mass fo progenitor cells
Where to the progenitor cells reside?
In the ciliary regions
What creates the optic nerve?
Axons of the ganglion cells
Where do the ganglion cells migrate to?
Thalamus
What cells are responsible for forming the barrier of the outer nuclear layer/outer plexiform layer?
Horizontal cells
Which retinal cell layer is one of the first specified?
Ganglion cell layer
Which cells “give a ride” to many of the migrating retinal cells?
Radial glial cells
Which cells start having the first neurotransmitter vesicles forming?
Horizontal and amacrine cells
Cones make contact with which cells first?
Horizontal cells
What forms the second synapses?
Off BP cells to cones
After off BP cells synapse to cones, what other synapses begin?
Ribbon synapses (on BP to cones)
Where do glutamate receptors appear first?
Off BP cells
Which cells have the strongest on response?
Amacrine cells
As the vision system develops, there are many connections being made all over the place. What must occur before it functions properly?
Pruning
What are the first responses that occur in the developing eye?
Excitatory - occurs in the dark
Center-surround organization of receptive fields is apparent as soon as ___ are detected.
Light responses
Turtles are initially ___. (anisotropic; isotropic)
Anisotropic
Dark-rearing mice until about 3 weeks after birth leads to an increase in the fraction of what?
Bistratified, On-Off ganglion cells in the retina
If you suture a kitten’s left eye, what happens in the cortex?
The ocular dominance columns will shift, so that there aren’t any cells for the left eye, and they all go to the right.
What happens if you suture a cat’s left eye closed 12 weeks after birth?
The response of cells is even in each ocular dominance column, but the number of cells is reduced.
If you suture both eyes closed at birth, what happens to the cells in the cortex?
There is a normal distribution of cells; ocular dominance columns are in tact, but they don’t work correctly. Many don’t work at all.
If you suture an eye during the critical period, but open it before the critical period ends, what will happen?
They affected eye will not recover
After suturing an eye during the critical period, what is the only way to recover brain function?
Reverse suturing before the critical period ends
What happens if you raise monkeys in darkness (binocular occlusion) from 2 weeks old up to 3-6 months?
Deterioration of the visual cortex - they behave as if they are blind, and never fully recover
After 1 year, what effect will reverse suturing have on a monkey?
No effect
When do babies begin to see clearly?
4-6 months
When do babies begin the “hand to mouth” movement?
8-12 months
How much accommodation do babies have at birth?
None - poor ciliary muscle control
What is a baby’s VA at birth?
20/600
At what age are babies capable of focusing an image on the retina, but it is still blurry?
2-3 months
At 2-3 months, why is the image still blurry for a baby?
The photoreceptors are still getting organized. Some cells are still being “born”
What VA is “expected” around 3 months?
20/200
Once photoreceptors are born, they still need to mature. What needs to occur?
Their outer segments still need to elongate
Why is a “newborn” photoreceptor less effective than a mature one?
The outer segments are short, so there is less surface area to catch photons
According to Ricco’s law, is the threshold area larger or smaller as an adult than as a child?
Larger as an adult
Compared to adult levels, in the 1st month, a baby is __ times less sensitive to light.
50
Compared to adult levels, in the 3rd month, a baby is __ times less sensitive to light.
10
Why are babies more attracted to bright colors?
They are less sensitive to light, so the brighter the color, the easier they can see it
During the first week of life, what wavelengths are babies missing?
Shorter wavelengths (they already have long wavelength cones)
Which of the cones is last to develop?
Blue cones
What contrast difference is a 1 month old able to discriminate?
5%
What contrast difference is a 2 month old able to discriminate?
0.5-0.75%
When do babies eyes begin to fixate, coordinate movement, and have some smooth tracking?
3 months