Visual Systems 1 Flashcards
Layers of the Cornea
From outside to inside;
- Epithelium - highly regenerative, stratified squamous
- Bowman’s membrane - acellular layer of unorganized collagen fibers, barrier to infection, it can heal but scars form
- Stroma - organized type 1 collagen bundles, binds water, maintains corneal clarity
- Descemet’s membrane - increases in thickness with age. It is a basement membrane for the corneal endothelium
- Endothelium - simple squamous epithelia, pumps water out of the stroma
What is the major refractor of the eye?
The cornea, refracts about 50 Diopters, lens only does fine tuning
What is myopia?
Nearsightedness, the focal point occurs before the retina.
Eye is too long or the refraction is too great!
What is Hyperopia?
Farsightedness.
The focal length is longer than the eye.
Eye is too short or the refraction is not enough.
What are higher order aberrations?
Tend not to effect your vision normally, but distort vision. They are increased in disease called Keratoconus. Corneal surgery can increase these aberrations.
They usually only become apparent in dark light because of very dilated pupils.
What are the 3 parts of the Uvea?
The Choroid
Ciliary body
Iris
What is the Chroid?
Largest part of the Uvea. The choroid has 3 layers from out to in.
- Vessel layer, has arteries and veins, loose connective tissue and melanocytes
- Chorocapillary layer, capillaries arranged in one plane, fenestrated type
- Bruch’s membrane; 3 to 4 micron thick amorphous hyaline membrane that the retinal pigmented epithelia rests on
What is the ciliary body?
Expansion of the Stroma of choroid near the lense.
Contacts 3 regions, vitreous body, sclera, and posterior chamber
Has ciliary processes with zonule fibers to lens
Trabecular Meshwork
What is the Trabecular Meshwork?
It is within the ciliary body near the limbus, Aqueous humor drained from anterior chamber via trabecular meshwork
What is the Iris?
Covers the lens, regulates the amount of light reaching the retina.
Anterior aspect made up of vascular, loose connective tissue with interspersed melanocytes, number of melanocytes in this layer determines eye color.
posterior surface lined with a double layer of pigmented epithelium (absorbs light)
two muscle masses rest upon the pigmented epithelium and regulate iris opening (pupil size)
radially arranged myoepithelial cells form the dilator pupillae muscle between the vascular and pigment layer (sympathetic innervation)
concentric smooth muscle bundles at the pupil margin (inner aspect of iris) form the sphincter pupillae muscle (parasympathetic innervation)
Tell me about the anterior chamber. (Not the anterior compartment)
Anterior Chamber, contains aqueous humor, is avascular. Maintains intraocular pressure.
Aqueous humor produced by ciliary processes in the posterior chamber, passes into Ant. chamber via the pupil.
Drain aqueous humor through the trebecular meshwork. From here in passes through canal of Schlemm that drains into venous system.
There is no direct connection between the trebecular meshwork and the canal of Schlemm. the humor percolates through the tissue into the canal
What is Glaucoma? What Types of Glaucoma exist?
2 main types of Glaucoma.
Primary Open Angle Glaucoma
Angle Closure Glaucoma
Glaucoma causes increased intraocular pressure.
Open-angle or chronic glaucoma
Accounts for 80 to 85% of all cases and is due to an
obstruction in the drainage system of the eye.
When the fluid reaches the angle, it passes too
slowly through the meshwork drain. As the fluid builds up, the pressure inside the eye rises to
a level that may damage the optic nerve and may result in vision loss.
Angle-Closure Glaucoma
Much more rare but very severe and acute (can cause blindness in 24 - 48 hours if not treated.
Poor access to the drainage
system in the eye and is referred to as angle-closure because the angle between the iris and
the cornea narrows, blocking the drainage of the aqueous humor. This sudden increase in
pressure inside the eye causes intense pain and blurred vision.
Tell me about the Lens.
Avascular, and has little Extra Cellular Matrix
a. Structural components
Capsule - ECM surrounding lens
Epithelium - anterior surface of lens
Lens fibers - body of the lens (no organelles)
b. Functions/Specializations
Second to cornea in refractive power (~10 D)
-lens is supported by zonule fibers from ciliary body
-Accommodation - lens thinner when focused on distant objects, relaxed ciliary muscles;
lens thicker when focusing on near objects, ciliary muscles contract, relaxing tension on zonule fibers thus thickening lens
