Embryology of the Eyes Flashcards
Main points to note
The retina in the back is a cup shaped structure and extending back is the optic nerve
Focusing apparatus: is another piece of tissue
Review: Development of the Brain and Spinal Cord
Walls of cells with fluid on the inside
Neural Component (initial formation of the eyes)
- eyes develop as an outgrowth of neural tube
- forms fluid filled optic vesicles
- the tissue will bulge out on either side to form a vesicle shaped structure that’s still connected to the neural tube
- the retina is actually a projection of the neural tube, the eyes are really an extension of the brain
- these go out laterally and forward a bit
Formation of Optic Cup and Optic Stalk
- optic vessel invaginates on itself to form optic cup
- when it gets close to the surface ectoderm, invaginates on itself to form a cup (optic cup) and there’s CSF between 2 layers of the cup. Mesoderm is around the outside of the cup and fills inside of cup as it invaginates on itself
- lumen between the 2 layers of the cup is still continuous with the ventricular system
Lens (initial formation of the eyes)
- presence of optic cup influences adjacent surface ectoderm to form lens vesicle
- surface ectoderm invaginates to form a little pin. Once it invaginates completely, it pinches off from the surface and forms the lens vesicle
Lens Initial Properties
- lens vesicle is fluid-filled but cells elongate to obliterate the lumen
- There’s really no issues with this process, it happens early
BIG THING: lens has to allow light to pass thru, there are cells that are alive but it’s mostly cytoplasm and crystalline
Vascularization of the lens and retina (initial formation of the eyes)
- optic cup deficient inferiorly (choroid fissure) to allow mesenchyme and hyaloid Artery to access inner retina and lens vesicle
- hyaloid artery becomes central artery of retina, mature lens not vascularized
- inferior edges of optic cup fuse
(If deficiency doesn’t fuse, you have superior visual field defects)
Development of the Retina
Optic cup: you have 2 layers
-it’s separated by a space and it’s continuous with the ventricular system
(Pigmented retina is the outer layer and neural retina and the inner layer)
-intraretinal space in the middle
Neural Retina Divisions
It has an outer neuroblastic layer that forms your rods and cones
-inner neuroblastic layer that forms ganglion and supporting cells: send axons to LGN, transforming optic stalk to optic nerve
Ultimately they connect to each other
Detached Retina
- neural and pigmented layers of the retina are adherent but they aren’t fused
- can be separated (recreating intraretinal space)—-hence detached retina
-The 2 layers are mostly held together by intraocular pressure
- if they separate, the posterior ciliary arteries (feed rods and cones) will get sheered and blood supply will be lost in this situation
- corrective procedures: need to get the 2 layers back quickly. IF NOT, rods and cones will degenerate
Development of Choroid and Sclera
- Retina is continuous with the neural tube/brain’
- choroid continuous with pia and arachnoid mater
- sclera is continuous with the dura mater
The mesoderm outside the retina condenses and forms the choroid and the sclera (choroid and retina actually become fused with the meningeal layers on the retina)
Development of the rest of the eye: anterior and posterior chambers
Anterior chamber-forms between stromal layer and pupillary membrane
- mesenchyme between the lens vesicles and surface ectoderm break down to form anterior chamber
- mesenchyme, the pupillary membrane, remains
Posterior chamber-forms from breakdown of posterior part of pupillary membrane
-more breakdown of mesenchyme forms posterior chamber, pupillary membrane is now thin
Pupillary Membrane
Breaks down in center to form pupil
Could be a potential problem
Development of the cornea
Ectoderm+stromal layer=cornea
Stromal layer: is a mesenchyme and mesothelium
-is continuous with sclera
- you have this invagination of surface ectoderm adjacent to lens vesicle that forms a small cup-shaped structure (opposite orientation from neural cup)
- epithelium plus mesenchyme forms cornea
Development of The Conjunctiva, Lacrimal glands, eyelids
Remainder of invaginating ectoderm (i.e. Not in contact with the stromal layer) forms lining of conjunctival sac
- lacrimal glands develop as buds of ectoderm of the conjunctival sac
- eyelids are core of mesenchyme with outer ectoderm, fuse during development, open just before birth
