Anatomy and Embryology of the Eye Flashcards
where do the optic vesicles grow outwards from?
diencephalic part of neural tube towards surface ectoderm
what occurs once the optic vesicles reach the surface ectoderm?
cause some of the cells on this surface ectoderm to thicken forming the lens placode
what happens after the lens placode is formed?
The lens placode starts to push inwards (invaginate), which causes the optic vesicle too, to form an optic cup
how many layers of the optic cup initially form?
2 layered optic cup
what is the fissure that allows blood vessels to pass through inferior optic cup wall?
choroid fissure
what ultimately happens to the lens vesicle?
looses its connection with the surface ectoderm
what does the surface ectoderm form?
eyelids, conjunctiva, corneal epithelium
what does the mesenchyme form?
choroid, stroma of cornea, sclera and extraocular muscles
what does the outer layer of the optic cup form?
pigment layer of retina and iris
what does the inner layer of the optic cup form?
neural layer of retina, ciliary body and inner layer of iris
what forms the lens fibres?
epithelium of lens vesicle & later loose their nucleii.
how does retinal detachment usually occur?
Tends to happen when fluid gets into potential space between inner 9 layers of retina and 10th outer layer
Can occur following trauma
what occurs if the choroid fissure persists?
forms a gap in tissues which develop around it . This gap is called a Coloboma
where can coloboma occur?
iris-keyhole pupil
retina
only disc
what are strongest parts of the orbit?
orbital rims and lateral and superior walls
rest easily fractured
what can orbital floor fracture lead to?
herniation into maxillary sinus
what are common symptoms of an orbital floor fracture?
Restricted vertical movement of the eye
Subconjunctival hemorrhage
Swollen lid
Loss of sensation over upper cheek area
what eye sign can thyroid disease lead to?
Orbital fat hypertrophies leading to the staring appearance
describe the epithelium of the cornea
stratified squamous non-keratinised.
why is the cornea transparent?
Histologically – regular arrangement of collagen in stroma
No blood vessels
Endothelium cell layer has a pump that actively keeps the aqueous humor out.
give an example of an inflammatory/no inflammatory disease of the cornea
Inflammatory – corneal ulcers
Non-inflammatory – dystrophies
what do corneal pathologies frequently lead to?
opacification of the cornea. This might need to be treated by corneal transplant - Keratoplasty
why is the avascularity of the cornea such a benefit to surgeons?
a lesser chance of foreign antigens from a corneal graft being recognised by the recipient
what is the choroid made up of?
fenestrated blood vessels of varying diameter. These supply the outer layers of the retina with blood by diffusion
in the retina are the nerve fibres above or below the cones and rods?
(except for fovea)
nerve fibres above (9th layer)
layer of rods and cone below (2nd layer)
what is the layer that absorbs all the extra light, underneath the layer of rods and cones?
Pigment epithelial layer
how does the fovea centralis differ from the rest of the retina?
packed with cones, so maximum visual acuity
layers have been pushed to side bringing rods & cones up to the surface
what is the lens?
Transparent, crystalline biconvex structure which is suspended by zonules from the ciliary body. It can change shape (i.e. become less or more convex.)
how is the lens transparent?
it needs to be avascular
predisposes it to become opaque later in life
what is lens opacification called?
cataract
what is the aqueous humor and what is its role?
watery fluid anterior to the lens.It helps maintain intraocular pressure.
constantly circulating fluid that also nourishes the lens and the cornea.
what is the vitreous humor and what is its role?
transparent gel posterior to the lens.It helps cushion the retina.
where is the aqueous humor produced?
ciliary body, in the space behind the iris and in front of the lens (the posterior chamber - PC)
once inside the anterior chamber where does the aqueous humor go?
reaches the angle of the AC where it gets filtered out through a meshwork called the trabecular meshwork
at the meshwork where does the aqueous humor go through?
Schlemm’s canal
what does an obstruction along the pathway of circulation of aqueous humor lead to?
damming up of AH-increased intraocular pressure- GLAUCOMA
where do the lacrimal gland ducts open into?
conjunctival sac
During each blink, eyelids spread tears evenly on the surface of cornea
where are the tears drained into?
drains into lacrimal sac
Then drains through nasolacrimal duct into the inferior meatus of the nasal cavity.
what is the function of tears?
keeps cornea moist , prevents drying
Washes away any particulate foreign bodies
Has antibodies and lysozymes -kills microbes
providing smooth surface of cornea for refraction.
what nerve leads to secretion of tears?
Parasympathetic (VII n)
what are the three layers of the tear film?
mucinous layer
aqueous layer
oily layer-most superficial
what stimulates further blinking?
When eyelids are open, aqueous component of tears evaporates, and when oily layer touches mucin layer, tear film breaks up
