Orbit II Flashcards
The only extraocular muscle which originates from the anterior aspect of the orbit is the:
Inferior Oblique
A diabetic patient complains of severe photophobia in her right eye. When light is shown directly into her right eye, her pupil does not constrict. Third cranial nerve neuropathy that involves only the periphery of this nerve, if eye movements are all still normal is a clue that which fibers running in the oculomotor nerve have been affected?
Parasympathetic, preganglionic fibers – peripheral portion of oculomotor nerve, one of the first things damaged
What are the three layers of the eye?
- Sclera
- Choroid
- Retina
What are the major components of the Sclera?Which layer is it?
- it is the Corneo-scleral layer
- dense connective tissue
- posterior 5/6th of eye is opaque
- extraocular muscles attach to sclera ***
What are the main components of the Choroid? Which layer is it?
- it is the UVEAL layer
- contain NERVE SUPPLY TO THE EYE (middle vascular layer)
- forms the iris
- heavily pigmented w/ MELANOCYTES (absorb stray photons)
What are the 9 components of the Ciliary Body, formed at the Limbus?
- Ciliary Muscles
- Ciliary process
- Canal of Schlemm
- Iris
- Sphincter Puppilae
- Dilator Pupillae
- Aqueous Humor
- Lens
- Postremal chamber
Describe the sclera
SCLERA-
- loose system of collagen fibers to a dense layer of connective tissue called Tenon’s capsule,
- The outer sclera consists of dense, fibro-elastic connective tissue,
- the fibers of which are arranged in bundles parallel to the surface.
- is the posterior 5/6ths of the eye, and is OPAQUE
- ** provides insertion for the extra-ocular muscles***
The sclera varies in thickness, being thickest posteriorly and thinnest at the coronal equator of the globe
Describe the Cornea. What is a main difference from the Sclera?
- transparent
- has a smaller radius of curvature than the sclera.
- principal refracting medium of the eye and roughly focuses an image on to the retina
- avascular structure
- HAS FIVE LAYERS*
Ep: stratified squamous epithelium
BM: Bowman’s (basement) membrane - supports the epithelium
SP: substantia propria - BULK of the cornea
DM: Decemet’s membrane - very thick elastic basement
En: endothelial layer
What is the cornea-scleral junction?
LIMBUS
- is marked internally and externally by a shallow depression.
What are the three components of the Uveal Layer?
Uveal layer:
The middle layer = the uvea or uveal tract, is a highly vascular layer which is made up of three components:
- choroid
- ciliary body
- iris.
How does the lens change from a flattened shape to a thicker shape?
Rest = flat
- PARASYMPATHETICS –> innervated to constrict circumferential (smooth muscle) fibers = lens can THICKEN
- connected to lens capsule by Zonular (suspensory) Fibers
What produces the aqueous humor? What important component does the aqueous humor provide the CORNEA and Lens?
- Ciliary process –> produces aqueous humor
- clear water similar to CSF
- balanced rate of production and reabsorption = pressure of 15 mm Hg
- METABOLITES for the cornea and lens
What component of the ciliary body reabsorbs the aqueous humor? What pumps the aqueous humor into this area?
- Canal of Schlemm!
- anterior to iris at corneo-screral junction
- continuous with venous system (lined with endothelium) - Trabeculae – pumps aqueous humor from anterior chamber to Schlemm’s
BUT –> no direct communication between the trabecular spaces and the canal of Schlemm = reabsorption of aqueous humor involves passage across two layers of endothelium and the intervening connective tissue.
What happens if there is a defect in pumping resulting from increased intraocular pressures? How does this defect usually occur
- GLAUCOMA **
- Glaucoma is the most common cause of blindness
- increased intraocular pressure compresses :
retina, optic nerve & blood vessels.
if severe = blindness
if mild = blurry vision/halos around bright objects
- production of aqueous humor > the ability of the eye to drain this fluid
OR
decreased outflow through the canal of Schlemm
OR an increase in aqueous humor production.
What are the two types of glaucoma? ***
- Open angle Glaucoma = aqueous cannot drain through meshwork
- Angle Closure Glaucoma = iris pushed over meshwork
What structure of the ciliary body forms an adjustable diaphragm and divides the eye into the anterior and posterior compartment?
IRIS
- pigmented (color) + vascularized + smooth muscle fibers
- Blue eyes contain little stromal pigment whereas Brown eyes have considerable stromal pigment
- IRIS = moveable diaphragm, purely reflexive
The brighter the light = the greater parasympathetic stimulation = CONSTRICTION OF THE PUPIL*** (sphincter pupillae)
What two muscles control the pupil? What Autonomic system is each muscle controlled by?
- Sphincter Pupillae = constricts pupil
- circumferentially oriented smooth muscle fibres in the pupillary aspect of the stroma
a. innervated by the PARASYMPATHETIC nervous system
- Dilator Pupillae = dilation of the pupil
- RADIALLY oriented fibers
- innervated by POST GANGLIONIC SYMPATHETIC FIBERS
What path does the aqueous humor follow?
- ciliary process
- to posterior chamber
- around lens
- through pupil into the anterior chamber
- reabsorbed in the Canal of Schlemm
What is the LENS of the eye? What three clinical considerations should one keep in mind for the lens?
- elastic, biconvex body of elongated epithelial cells
- few nuclei in MATURE cells
- FROM ECTODERMAL CELLS (embryology)
- crystalline*
- Presbyopia = loses its elasticity as we get older (can’t accommodate lens –> blurry vision)
- Cataracts = clouding of lens
- Astigmatism - not symmetric about the optical axis = difficulties in seeing fine detail
- can be often corrected by glasses with a lens that has different radii of curvature ground in different planes (a cylindrical lens), contact lenses, or refractive surgery.
What is the space behind the lens called?
Postremal Chamber
- filled with gel like vitreous humor (cushions retina)
Which part of the eye transduces the energy of light (photons) into action potentials for the CNS to interpret (vision)?
RETINA
What embryologically developed structure disappears as the embryo grows?
HYALOID CANAL
- exit of the optic nerve to the posterior surface of the lens - course of the degenerated HYALOID ARTERY which supplied the vitreous body during embryological development*
What are the ten divisions of the Retina?
From Outside to Inside:
- Inner limiting membrane - forms BLOOD - RETINAL BARRIER
- Optic Nerve layer
- Ganglion Cell Layer
- Inner Plexiform
- Inner nuclear layer
- Outer plexiform
- Outer nuclear layer
- Outer limiting membrane
- Rods & Cones
- Pigmented epithelium
What are the 3 functional layers of the inner limiting membrane of the retina?
- the outer layer (lying adjacent to the pigmented epithelium) = consists of rod and cone receptor cells***
- forms blood retinal barrier - the intermediate layer= interneurons and bipolar cells
- integrate sensory inputs from the receptor cells before transmission to the CNS - the innermost layer = the ganglion cells
- the cell bodies of afferent axons passing to the CNS in the optic nerve.
