Orbit 2 Flashcards
What is the primary role of the cornea?
primary refraction/focusing of light entering the eye
What is the primary role of the lens?
secondary focusing of objects onto the retina
What is the primary role of the iris?
controls the amount of light falling on the retina
What are the unique elements which aid in the transduction of light into action potentials by the retina?
cornea, lens, iris, aqueous and vitreous humors, corneo scleral layer, uveal (vascular) layer, and the neural layer/retina
Describe the chambers of the eye
Anterior: between cornea and iris (filled with aqueous humor)
Posterior: between iris and lens (filled with aqueous humor)
Postremal (vitrous): behind the lens (filled with gelatinous vitreous humor)
What are the three chambers of the eye?
sclera, choroid, retina
Role: corneo-scleral layer
tough, fibro–elastic capsule which supports the eye
What is the external surface of the corneoscleral layer?
episclera
What it tenon’s capsule?
dense layer of connective tissues connected to the episclera through loose collagen fibers and connected to the conjunctiva at the junction of the cornea and sclera
Spatial: sclera
posterior 5/6s of the eye. Thickest posteriorly, thinnest at the coronal equator
Role: sclera
provides insertion for the extra-ocular muscles
Spatial: cornea
anterior 1/6 of the eye, smaller radius of curvature than the sclera
What is the cornea-sclera junction?
the limbus, which is marked internally and externally by a shallow depression
How is the cornea sustained?
Itvascular, and sustained by diffusion of metabolites from the aqueous humor and the blood vessels of the limbus. Some oxegyn is derived directly from the external environment
What is the most vascularized layer of the eye?
Uveal
What three components make up the uveal layer?
choroid, ciliary body, iris
Spatial: ciliary body
continuous with the choroid and located circumferentially between the ora serrata and the limbus. Lined by a doube layer of cuboidal epithelium. Highly pigmented deep layer is a forward contuation of pigmental epithelial layers of retina. Non-pigmented surface layer is a non photopsensite forward extension of the receptor layer of the retina
Role: suspensory ligament/zonule
attaches the ciliary body to the coronal equator of the lens
How does the smooth muscle of the ciliary body work?
contraction: used for near vision. tension on suspensory ligament is reduced, lens can thicken and overall diameter is reduced. This allows for fine focusing of images onto the retina
rest: used in far vision, relaxed muscle pulls on suspensory ligaments, flattening the lens
What innervates the ciliary muscle?
parasympathetic nerve fibers (CN III via ciliary ganglion)
Role: ciliary processes
continuously produce aqueous humor
Aqueous humor
circulates the anterior chamber via the pupil. is clear, water and similar in composition to CSF and hypotonic with respect to plasma. Maintains intra-oculuar pressure, allows for continuous exchange of metabolites to cells of avascular cornea and lens
How is aqueous humor absorbed?
throught he canal of schlemm at the angle of the anterior chamber
What is the optimal intra-ocular pressure?
15 mm of mercury
What is the most common cause of blindness?
Glaucoma, manifested by increased intraocular pressure
What are the effects of increased intraocular pressure?
compresses retina, optic nerve, and blood vessels. Damage to retina (esp. optic disc) can cause severe pain. Blurred vision, halos around bright objects. May result in eventual blindness.
What causes increased intraocular pressure?
decreased outflow through the canal of schlemm, increase in aqueous humor production.
Spatial: Iris
most anterior part of the uveal layer of the eye. Arises from the ciliary body and forms an adjustable diaphragm in front of the lens, dividing the anterior compartment of the eye into posterior and anterior chambers which communicate via the pupil. Pupillary edge of iris rests of anterior edge of the lens.
What innervates constrictor pupillae?
parasympathetic nervous system
What innervates radially oriented dilator pupillae?
sympathetic nervous system
visual: Lens
elasic, bioconvex, transparent, amorphous but composed of living cells
