Gross Anatomy And Development Of He Orbit And Eye Flashcards
What are the boney margins of the orbit?
Boney margins of the orbit:
• frontal, maxilla, zygomatic
Walls:
• frontal, maxilla, zygomatic, sphenoid, ethmoid, lacrimal, palatine
What are the contents of the superior or ital fissure?
Superior orbital fissure
- CN III, IV, V1, VI, superior ophthalmic v.
What are the contents of the inferior orbital fissure?
Inferior orbital fissure
- V2, zygomatic nerve, inferior ophthalmic v., infraorbital a. and v.
What are the contents of the optic canal?
Optic canal
- CN II, ophthalmic a.
What are the contents of the nasolacrimal canal?
Nasolacrimal duct from lacrimal
fossa to nasal cavity (inferior
meatus)
Explain the development if the eye
- The eyes originally develop as a diverticulum of the forebrain neural tube
- The hollow diverticulum becomes the optic stalk and near surface ectoderm forms the optic cup
- Invagination process of optic cup extends into the ventral part of optic stalk to form a fissure called the retinal fissure
- Inside the fissure will run the hyaloid a. which will supply the internal structures of the eye
- Fissure normally closes around artery around the 6th week of development
- Hyaloid artery will eventually become the central retinal a.
explain the development if the opticc nerve
The axons from the ganglion cells of the retina grow towards the brain in the inner layer of optic stalk
-The optic nerve develops from the optic stalk
• The proximal part of hyaloid vessels get closed within optic nerve to form the central retinal a. & v.
How do Sclera and Cornea develop?
- Sclera and choroid develop from mesenchyme tissue surrounding the optic cup
- Cornea develops from:
- Corneal epithelium - from skin ectoderm
- Fibrous stroma - from the mesodermal capsule covering the optic cup
- Corneal endothelium - from the neural crest cells of optic cup
• The eyelids develop from skin folds filled with mesenchyme
How does the iris develop?
The iris develops from the rim of the optic cup
• Ciliary body develops from the optic cup (smooth muscle from mesenchyme)
- The hyaloid vessels supply the lens till 6th month of fetal life, after which the artery obliterates (lens becomes avascular). The remaining hyaloid artery becomes the central artery of the retina
- Eyelids remain adherent to each other till the 26th week
What is keyhole pupil?
Coloboma of the iris “keyhole pupil”
- Results due to incomplete closure of the retinal fissure
- Defect can extend to the ciliary body and retina
Describe the development of the retina
• The retina develops from the layers of the optic cup
- pigment layer of retina from the outer layer of
optic cup
- neural layer of the retina from the inner layer of
optic cup
• The cavity of the cup (intraretinal space) obliterates as the 2 layers fuse
Explain the detachment of the retina
The intra-retinal space provides an easy plane of cleavage for detachment of the retina
The detachment occurs between the neural and pigment layers of the retina
Detachment can occur secondarily during development or after birth as a result of a blow on the eye
Explain the development if the lens
Lens develops from the lens vesicle (surface ectoderm)
• The anterior wall of the lens vesicle becomes the sub- capsular lens epithelium
- The epithelial cells in the posterior wall lose their nuclei and elongate forming primary lens fibers (transparent) which fill the cavity of the lens vesicle
- Secondary lens fibers, cuboidal, from the equatorial region, overlap the primary fibers – increasing the lens diameter as it grows
What is cataracts?
- Opaqueness of the lens giving the eye a grayish white appearance
- May be congenital due to teratogenic agents or infections during pregnancy (especially between 4th-7th week when the lens is forming) or occur later in life due to normal aging, trauma, radiation etc.
- Can be removed surgically as outpatient procedure under local anesthesi
Whats the flow of tears?
Canaliculi drain into lacrimal sac which is continuous with nasolacrimal duct
• Nasolacrimal duct empties into inferior meatus of nasal cavity