Lecture 26 - Eye and Orbit Flashcards
What are the margins of the orbit?
Supraobital margin
- formed by the frontal bone
Infrobital margin
- zygomatic bone (laterally)
- maxilla (medially)
Why is the supraorbital notch imporatnt?
allows communication of nerves and BV going to the forehead
What bones form the orbit roof, floor, lateral and medial wall?
Roof
-Frontal bone
Floor
-maxilla
zygomatic, palatine
lateral Wall
Zygonmatic, greater wing of sphenoid
Medial wall
- maxilla, lacrimal bone, ethmoid, body of sphenoid
Which bones are likely to break in the orbit
thin and weak ones - lacrimal and part of the ethmoid
where is the optic canal located
Within the body of the sphenoid - for the optic nerve and its artery
Where is the superior orbital fissure?
in the sphenoid
Where is the inferior orbital fissure?
between sphenoid and maxilla
What are the 3 layers of the eye:
Outer coat:
cornea & sclera - strength
Middle: Uvea - nutrition
Inner: retina
describe the sclera
forms 5/6th of the eyeball
maintains the shape of the globe, offering resistance to internal and external forces
provides attachment for muscles
each collagen fibre forms in whirls - added strength than a parallel laydown like a ball of string
Describe the cornea
Anterior - 1/6th of eye
Prinicpal refrecting component of the eye
Avascular and transparent = optimum for vision
What is the structure of the cornea?
5 layers histologically
Epithelium Bowman's layer Stroma (large - collagenous) Desccment's membrane Endothelium
what percentage of light refraction occurs at the cornea?
60%
The stroma is continuous with the ..
.sclera (the collagen is continous)
the sclera and cornea(stroma) are..
pretty much the same histologically - yet one is transparent and one isn’t
What is the structure of collagen in the cornea?
uniform, evenly spaced
run in parallel - because it’s so ordered, provides transparency
Scleral opacity is affected by…
collagen fibres of different length, distribution - no order, looks white
Where is the anterior chamber
The anterior chamber (AC) is the fluid-filled space inside the eye between the iris and the cornea’s innermost surface, the endothelium.[1] Aqueous humor is the fluid that fills the anterior chamber. Hyphema and glaucoma are two main pathologies in this area. In hyphema, blood fills the anterior chamber. In glaucoma, blockage of the canal of Schlemm prevents the normal outflow of aqueous humor, resulting in accumulation of fluid, increased intraocular pressure, and eventually blindness.
What are the key strucutres in the AC angle?
cornea
trabecular meshwork
Canal of schlemn
ciliary body
What are the functions of the ciliary body?
produces the aqueous humour
Tethers lens (ciliary processes)
Accomodation (ciliary muscle)
what is the importance of the aqueous humour
maintaining health of lens
creates intraocular resssure
ciliary process is made of
two layers of ciliary epithelium
How is the aqueous humour drained?
through pupil, and then trabecular meshwork twoards venous drainage
What is involved in accomudation?
ciliary muscles
zonules (tiny ligaments)
Ciliary muscle runs a ring around your..
iris
contraction is for looking at things…
close up - the lensbecomes “buldgy”
The iris is part of the..
urea
Which muscles control the iris? What innervates each?
sphincter pupillae: constricts pupil - parasymp
Dilator pupillae: dilates pupil - symp n.
The choroid consists of …
3 layers of blood vessels
Most important is the choriocapillaris, which sits just below the retina
supplies nutrients to retina
The macular part of the retina allows you to see ____
centrally
True of False
The macular is void of blood vessels
true
What is the posterior pole?
region around the macular on the retina
The area where the retina cmeets the rest of the eyeball?
ora serrata
Right in the middle of the macular is a special area called
the fovea
The fovea is the part where we focus on…..
what is its make up in terms of rods/cones?
central vision
high density of cones / no rods
The optic nerve is formed by the axons of ______ cells as they exit the retina to pass visual information to higher cortical areas
The optic nerve is formed by the axons of ganglion cells as they exit the retina to pass visual information to higher cortical areas
True or false
the optic nerve pierces all 3 layers of the eyeball
true
1/3 of the collagen that forms the sclera continues across the optic nerve - what is this called?
lamina cribosa - forms a siv through which the processes pass
gives structure
The opthalmic artery is a branch of the
carotid a.
The central retinal artery travels where?
pierces the optic nerve enters the retina and fans out
The long and short posterior ciliary arterybranch from the…
opthalic a
long ones travel further in the eyeball
What supplies the anterior sections of the eye orbit?
anterior ciliary artery
the retina has a dual blood supply - what suppies what?
Central retinal artery supplies the inner retina
posterior ciliary artery supplies the outer retina (photoreceptors)
Anterior ciliary arteries anastomose with the long posterior ciliary arteries via the …
major perforating artery
