eyes - anatomy and embryology Flashcards
what embryological structure does the eye develop from?
optic vesicles of the neural tube
what is the lens placode?
structure formed from thickening of the surface endoderm when the optic vesicles reach said endoderm
what happens when the lens placode starts to invaginate?
the optic vesicle and lens placode forms an optic cup
how many layers does the optic cup have?
2
what is the choroid fissure?
fissure in the inferior wall of the optic cup which allows blood vessels to pass through said cup
what is formed when the choroid fissure doesnt disappear as it normally does?
a gap in tissues develops around it which is called a coloboma
what is formed from the surface ectoderm?
eyelids
conjunctiva
corneal epithelium
what is formed from the mesenchyme?
choroid
stroma of cornea
sclera and extraocular muscles
what forms the lens fibres?
epithelium of lens vesicle
what can happen if the walls of the bony orbit fracture?
contents can herniate into surrounding sinuses
why is orbital fat important?
it cushions the globe and is key in supporting the contents
what forms the fibrous coat of the eye?
cornea
sclera
aqueous humor
what forms the vascular coat of the eye?
iris
ciliary body
choroid
what forms the sensory coat of the eye?
retina
what is the cornea?
the anterior sixth of the eye which is transparent and is a window to allow light rays to enter the eyeball
what is the sclera?
the opaque posterior 5/6 of the eye which gives attachment to the muscles moving the eyeball
what type of epithelium is present in the cornea?
stratified squamous non keratinised?
what is bowmans membrane?
basement membrane of corneal epithelium
what is the stroma of the cornea?
regularly arranged collagen - no blood vessels
what lies between the stroma of the cornea and the endothelium of the cornea?
descemets layer
how is opacification of the cornea treated?
corneal transplant - keratoplasty
what are the 2 broad types of cornea pathology?
inflammatory - eg corneal ulcer
non inflammatory - dystrophies
how is the avascularity of the cornea a benefit during surgery?
less chance of grafts being recognised by the recipient so less chance of a rejection
what is the purpose of the ciliary body?
suspends the lens and produces aqueous humor
what is the purpose of the choroid?
supplies blood to the outer layers of the retina
what is the function of the iris?
controls the diameter of the pupil and thereby controls the amount of light rays entering the eyeball
what are the 10 layers of the retina?
pigment epithelial layer layer of rods and cones outer limiting membrane outer nuclear layer outer plexiform layer inner nuclear layer inner plexiform later ganglion cell layer nerve fibre layer inner limiting membrane
what is the clinical term for lens opacification?
cataract
where is the anterior segment of the eye?
in front of the lens
where is the posterior segment of the eye?
behind the lens
where is the anterior chamber of the eye?
in front of the iris
where is the posterior chamber of the eye?
behind the iris
what is the aqueous humor?
watery fluid anterior to the lens - it helps maintain intraocular pressure
what is the vitreous humor?
transparent gel posterior to the lens - it helps cushion the retina
what is aqueous humor produced by?
ciliary body
what filters aqueous humor out of the anterior chamber?
trabecular meshwork
what happens if the pathway of the circulation of the aqueous humor is obstructed?
increase in intraocular pressure which leads to glaucoma
what are the conjunctiva?
thin vascular membrane that covers the inner surface of the eyelids and loops back over the sclera
does the conjunctiva cover the cornea?
no
where is the lacrimal gland situated?
in the orbit laterally
what innervates the lacrimal gland?
facial nerve
where do the lacrimal ducts open into?
conjunctival sac
what happens in regards to lacrimal secretions when we blink?
eyelids spread tears evenly on the thin surface of the cornea
where do tears drain?
through punctae on the medial side of each eyelid and then to the lacrimal sac
where is the lacrimal sac situated?
over the lacrimal bone
where does the lacrimal sac drain to?
to the inferior meatus of the nasal cavity through the nasolacriminal duct
what are the functions of the tear film?
- keeps cornea moist
- washes away any particulate foreign bodies
- has antibodies and lysozymes to kill microbes
- smoothes outer surface of the cornea providing smooth surface for refraction
what are the 3 layers of the tear film?
mucinous layer
aqueous layer
oily layer
