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153 Cards in this Set
- Front
- Back
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What structures must light pass through before reaching the retina? |
- Transparent cornea
- Anterior chamber - Lens - Vitreous body |
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What happens at the fovea?
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Where 99% of the vision occurs
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What are the other names for the part of the optic nerve that can be seen in the retina?
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- Optic disk
- Optic nerve head - Disk - Papilla |
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What does the term peripapillary mean?
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Near or around the nerve head
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What does papilledema mean?
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Swollen nerve head
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What are the functions of the cornea?
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- Helps to shield the rest of the eye from germs, dust, and other harmful matter
- Outermost lens - controls and focuses entry of light into eye |
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Which eye structures contribute to protection of the eye?
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- Cornea
- Eyelids - Eye socket - Tears - Sclera (white part) |
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What percentage of the eye's total focusing power is from the cornea?
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65-75%
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How does the cornea receive nourishment?
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- NOT from blood vessels
- Rather from tears and aqueous humor that fills chamber behind it |
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Why is it important that the cornea not contain blood vessels?
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It needs to be transparent to refract light properly (blood vessels would interfere with this process
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What are the layers of the cornea, outermost to innermost?
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- Epithelium
- Bowman's membrane - Stroma - Descemet's membrane - Endothelium |
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How much of the thickness does the epithelium contribute to the cornea?
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10%
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What are the functions of the corneal epithelium (outermost layer)?
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- Block passage of foreign material, such as dust, water, and bacteria, into the eye and other layers of the cornea
- Provides smooth surface that absorbs oxygen and cell nutrients from tears, then distributes them to the rest of the cornea |
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Why is the cornea so sensitive to touch?
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The epithelium is filled with thousands of tiny nerve endings that make the cornea extremely sensitive to pain when rubbed or scratched
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Which layer of the cornea has a high regenerative capacity?
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Epithelium
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What kind of cells are in the epithelium of the cornea?
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Stratified squamous cells
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What part of the cornea provides a foundation on which the epithelial cells anchor and organize themselves?
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Bowman's Membrane
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Bowman's layer of the cornea is composed of what?
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- Strong layered protein fibers - collagen
- Acellular |
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What happens if Bowman's layer of the cornea is injured?
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Can form a scar as it heals - this can impact vision if they are large and centrally located
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What is the function of Bowman's membrane of the cornea?
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Barrier to infection
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What layer of the cornea is beneath Bowman's membrane? What percentage of the eye thickness does it contribute?
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Stroma - 90% of cornea's thickness
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What are the contents of the stroma of the cornea?
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- 78% water
- 16% collagen - No blood vessels |
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What is the function of the collagen in the stroma of the cornea?
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- Gives cornea strength, elasticity, and form
- Unique shape, arrangement, and spacing are essential to produce the cornea's light-conducting transparency |
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What layer of the cornea is under the Stroma?
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Descemet's Membrane (D=deep)
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What is the structure of Descemet's membrane in the cornea?
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- Collagen fibers (different from those of stroma)
- Endothelial cells |
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What happens to the thickness of Descemet's membrane in the cornea?
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- Thin sheet originally
- Increases in thickness with age |
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What are the functions of Descemet's membrane in the cornea?
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Protective barrier against infection and injuries
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What happens to Descemet's membrane after injury?
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Regenerates
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What is the thin, innermost layer of the cornea?
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Endothelium
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What is the function of the endothelial cells of the cornea?
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- Keeps the cornea clear
- Pumps excess fluid out of the stroma |
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What would happen if the endothelial layer of the cornea didn't pump water out of the stroma?
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- Stroma would swell with water, become hazy, and ultimately opaque
- Cause loss of vision |
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What happens to endothelial cells of the cornea after injury? The eye?
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- Destroyed forever
- Can lead to corneal edema and blindness - Only therapy is for a corneal transplant |
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What is the term for nearsightedness? Where does the image focus? What kind of lens is used to treat this?
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Myopia - light from far away focuses in front of the fovea (eye is too long or cornea too strong)
- Use concave lens (diverging -) |
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What is the term for farsightedness? Where does the light focus? What kind of lens is used to treat this?
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- Hyperopia - light from close up focuses behind fovea (eye is too short or cornea too weak)
- Use convex lens (converging +) |
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What are the most common vision problems in the U.S.? How many?
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- Myopia (25%)
- Hyperopia - Astigmatism - Approx. 120 million people in U.S. wear glasses or contact lens to fix these conditions |
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What are wave aberrations?
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Refractive errors that cause diffraction and scattering of light
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What are the components of the uvea? Which is the largest component?
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- Choroid - largest component
- Ciliary Body - Iris |
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What are the three layers of the choroid (from out to in)?
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- Vessel layer
- Chorocapillary layer - Bruch's membrane |
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What are the contents of the vessel layer of the choroid? Is it the most outermost, middle, or innermost layer of the choroid?
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- Contains medium sized arteries and veins, loose CT and melanocytes
- Outermost layer |
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What are the contents of the choriocapillary layer of the choroid? Is it the most outermost, middle, or innermost layer of the choroid?
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- Capillaries arrange in one plane, fenestrated type
- Middle layer of choroid |
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What are the contents of the Bruch's membrane of the choroid? Is it the most outermost, middle, or innermost layer of the choroid?
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- Amorophous hyaline membrane (only 3-4 microns thick)
- Innermost layer |
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What rests upon the Bruch's membrane of the choroid?
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Retinal pigmented epithelia
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What is the ciliary body an expansion of?
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Expansion of the stroma of choroid near the lens
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What three regions does the ciliary body contact?
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- Vitreous body
- Sclera - Posterior chamber/lens |
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What are the projections from the ciliary body? Where do they project to?
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- Ciliary processes
- Project toward lens |
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What meshwork is found within the ciliary body?
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Trabecular meshwork within ciliary body near limbus
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How does aqueous humor drain from the anterior chamber?
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Via the trabecular meshwork in the ciliary body
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What structure covers the lens?
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Iris (part of uvea)
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What does the iris regulate?
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Amount of light reaching the retina
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What are the components of the iris?
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- Vascular, loose CT
- Interspersed with melanocytes |
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What determines eye color?
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- Number and type of melanocytes in the iris
- Eumelanin - brown/black melanins - brown eyes - Pheomelanin - red/yellow melanins - blue/green eyes |
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What side of the iris is lined? With what?
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Posterior surface lined with a double layer of pigmented epithelium
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What part of the iris absorbs light?
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Posterior surface which is lined w/ a double layer of pigmented epithelium
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How are the fibers of the dilator pupillae arranged? What kind of cells? What layers is it between?
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- Radially arranged myoepithelial cells
- Between vascular and pigment layers |
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What controls the dilator pupillae? What happens when it contracts?
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- Sympathetic innervation - superior cervical ganglion
- Contracts = dilates |
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How are the fibers of the sphincter pupillae arranged? Where?
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- Concentric smooth muscle bundles
- At pupil margin (inner aspect of iris) |
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What controls the sphincter pupillae? What happens when it contracts?
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- Parasympathetic innervation - CN III from Edinger-Westphal nucleus
- Contracts --> constricts |
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What does the anterior chamber contain? Function?
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- Contains aqueous humor
- Avascular (so no blood vessels) - Involved in maintaining intraocular pressure |
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Where is aqueous humor produced? Where does it move?
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- Produced in ciliary processes in the posterior chamber
- Passes from posterior chamber into anterior chamber (between iris and lens) - Drained from anterior chamber via trabecular meshwork - Humor passes into canal of Schlemm that drains into venous system |
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What is the leading cause of blindness and vision impairment? How common is it?
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Glaucoma - 2.5 million people in U.S. (3% of people older than 55 years; although 1/2 are unaware they have it)
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What are the types of glaucoma?
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- Primary Open Angle Glaucoma (POAG)
- Angle Closure Glaucoma (also normal tension glaucoma, but the first two listed are the main types) |
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What are the symptoms of glaucoma?
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- Increase in intraocular pressure (IOP)
- Can damage CN II (Optic N.) - Visual field defect (perimeter) |
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What happens in normal tension glaucoma?
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Optic nerve damage despite normal IOP (intraocular pressure)
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What is secondary glaucoma?
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When another disease causes or contributes to increased eye pressure, resulting in optic nerve damage and vision loss (as a result of ganglion cell death)
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What is Open-Angle, or Chronic Glaucoma? Frequency?
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- Obstruction in drainage system of eye
- When fluid reaches angle, it passes too slowly through meshwork - Fluid builds up, pressure rises, and damage to optic nerve and vision loss may occur - 80-85% of all glaucoma cases |
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What is Angle-Closure Glaucoma? Frequency? Severity?
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- Poor access to drainage system in eye
- Angle between iris and cornea narrows, blocking drainage of aqueous humor - Acute, sudden increase in pressure in eye causes intense pain and blurred vision - Very rare - Very severe, can cause blindness in 24-48 hours if not treated |
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Is there anything wrong with this eye?
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No - normal
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Is there anything wrong with this eye?
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Yes - Angle-Closed Glaucoma
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What are the clinical signs of glaucoma?
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- Elevated pressure (tonometry) - normal pressure is 12-22 mm Hg
- Visual field defect will reveal a selective peripheral loss of sensitivity - Increased cupping of Optic Nerve |
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How do you assess the cupping of the optic nerve?
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Cup to disk ratio: 0-1, higher is worse
(Left is better) |
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At what percent loss of peripheral vision does a patient usually come in?
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Not until 75% loss!!
(dark = decreased sensitivity) |
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What is the lamina cribrosa?
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Network of collagen fibers through which the fibers of the optic nerve exit the eye - may be altered in glaucoma
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What percent of the refractive power of the eye is contributed by the lens?
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Only 20% (~10D vs. ~50D for cornea)
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What are the structural components of the lens?
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- Capsule - ECM surrounding lens
- Epithelium - anterior surface of lens - Lens fibers - body of lens (no organelles) |
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What are the functions of the lens?
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- Refraction
- Accommodation |
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What supports the lens?
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Fibers (suspensory ligaments or zonules) attached to ciliary body
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How does the thickness of the lens change with accommodation?
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- Thinner when focused on distant objects (relaxed ciliary muscles)
- Thicker walls when focusing on near objects (contracting ciliary muscles) |
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What is a cataract?
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Opacification of the lens
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By 80 years old, what percent of Americans have or have had cataracts?
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50%
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How are cataracts described?
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Based on location within lens
- Nuclear cataracts - center of lens - Cortical cataracts - layer surrounding lens - Posterior capsular cataracts - back outer layer of lens (more rapid progression) |
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Which type of cataracts develop more rapidly?
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Posterior Capsular Cataracts
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How are cataracts removed?
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Removal of the lens (phacoemulsification or extracapsular surgery) and implantation of an IOL (intraocular lens)
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What are the structural components of the vitreous body?
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- Nearly acellular
- Major macromolecules: Type II collagen and hyaluronic acid - 99% water |
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What is the function of the vitreous body?
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- Transparent structure
- Nutrition |
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What are the two main layers of the retina?
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1. Neural (sensory) retina
2. Retinal pigment epithelium (RPE) |
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What is the location of the fovea relative to CN II?
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Fovea is temporal to CN II
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What is the fovea?
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Latin for small pit; region used for high acuity vision
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What are the regional specializations of the neural (sensory) retina?
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- Fovea
- Anteriorly, number of neural elements in retina declines, becoming a single layer of epithelium (unpigmented) that covers the ciliary body |
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What are the layers of the neural retina (from external to internal - following path of light stimulus)?
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- Photoreceptor (rod and cone) outer and inner segments
- Outer nuclear layer (ONL) - Outer plexiform layer (OPL) - Inner nuclear layer (INL) - Inner plexiform layer (IPL) - Ganglion cell layer (GCL) - Nerve fiber layer (NFL) - Inner limiting lamina |
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What is the most posterior (external) layer of the neural retina?
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Photoreceptor (rod and cone) outer and inner segments
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What is in the ONL?
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Outer nuclear layer - contains nuclei of rods and cones
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What is in the OPL?
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Outer plexiform layer - synapses of rod and cone axons w/ bipolar neurons
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What is in the INL?
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Inner Nuclear Layer - nuclei of bipolar neurons (also nuclei of horizontal and amacrine neurons and Muller glia)
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What is in the IPL?
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Inner Plexiform Layer - synapses of bipolar axons w/ ganglion cells
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What is in the GCL?
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Ganglion Cell layer - nuclei of ganglion cells
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What is in the NFL?
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Nerve Fiber Layer - axons of ganglion cells that converge to form optic nerve
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What is in the inner limiting lamina?
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Basement membrane of Muller glial cells
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What are the structural features of photoreceptors?
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- Inner segments
- Outer segments - Connecting cilium |
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What is in the outer segments of photoreceptors?
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- Flattened membrane discs
- Photosensitive visual pigments (opsin) |
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What structures are in the inner segment of a photoreceptor?
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Organelles for protein synthesis and energy production
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What happens in the connecting cilium of a photoreceptor?
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- Transport of proteins to outer segment from inner segment
- 10 billion opsin molecules / sec. |
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What are the two types of photoreceptors?
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- Rods
- Cones |
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What are the features of a rod photoreceptor?
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- Long, slender outer segments
- Numerous except at fovea - Very light-sensitive |
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What are the features of a cone photoreceptor?
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- Conical outer segments w/ membrane discs
- Less sensitive than rods - Responsible for high acuity and color vision |
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Which photoreceptor is more sensitive?
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Rods
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Which photoreceptor has higher acuity?
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Cones
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How do the structures of the outer segments of photoreceptors differ?
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- Rods - long and slender; free floating discs
- Cones - conical w/ membrane discs; discs persist as folds |
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When are rods active?
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Active at night; inactive in light
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How are the outer segments of photoreceptors formed?
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In folding of the plasma membrane:
- In rods the folds pinch off so the discs become free-floating - In cones the discs persist as folds and are in contact w/ extracellular space |
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Where is the densest distribution of cones?
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At 0 degrees (at fovea); basically none anywhere else
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Where is the distribution of rods on the retina?
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- Peaks about 20 degrees from fovea (around optic disk)
- None at fovea - Declines at increasing angles from 20 degrees |
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The location of cone centers at the fovea forms what arrangment?
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Triangular array
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What happens during development of the fovea?
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- Cone packing increases (increases visual acuity)
- Foveal pit develops after thickening of the retina - Site of incipient fovea is avascular all along |
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What kind of cells are int he retinal pigment epithelium (RPE)?
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Simple, cuboidal melanin-containing epithelial cells
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What is the location of the retinal pigment epithelium (RPE)?
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Between neural retina and Bruch's membrane (BM)
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What are the function of the retinal pigment epithelium (RPE)?
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- Provides outer blood-retinal barrier
- Absorbs scattered light (melanin) - Transports nutrients and ions between photoreceptors and choriocapillaries - Spatial buffering of ions in subretinal space - Reisomerization of all trans retinal - Outer segment renewal - Secretion of growth factors for maintenance and structural integrity of retina |
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What does the retinal pigment epithelium (RPE) do for scattered light?
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Absorbs it with melanin
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The retinal pigment epithelium (RPE) transports nutrients and ions between what?
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Photoreceptors and choriocapillaries
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What does the retinal pigment epithelium (RPE) buffer?
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Spatial buffering of ions in the subretinal space
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What does the retinal pigment epithelium (RPE) do to retinal molecules?
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Reisomerizes all trans retinal
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What does the retinal pigment epithelium (RPE) do to the outer segments of photoreceptors?
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- RPE engulfs, digests, and recycles approx. 10% of mass of each photoreceptor outer segment per day
- Occurs on a diurnal schedule w/ peak of rod outer segment disc shedding occurring at dawn and peak of cone outer segment disc shedding occurring at dusk |
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What does the retinal pigment epithelium (RPE) secrete?
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Growth factors for maintenance and structural integrity of retina
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How many photoreceptors are there per RPE cell?
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~40 photoreceptors / RPE cell
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When does outer segment phagocytosis happen for rods and cones?
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- Rods - at dawn
- Cones - at dusk |
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Approximately every how many days is there a completely new outer segment on a photoreceptor?
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Approximately every 10 days - because 10% is recycled per day
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What is the leading cause of blindness in elderly in developed countries?
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Age-related Macular Degeneration (AMD)
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What happens in age-related macular degeneration (AMD)?
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- Drusen develop within Bruch's membrane
- Vision loss is slow and deteriorates central vision first |
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Which disease affects central vision first? Peripheral vision first?
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Central vision - Age-Related Macular Degeneration (AMD)
Peripheral vision - Glaucoma |
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What are the risk factors for AMD?
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Family hx of AMD, smoking, blue eyes, CFH mutation
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How do you treat macular degeneration?
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Try to halt progression to "wet" with Anti-VEGF
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What is in the center of the macula?
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Fovea
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What is this a picture of?
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Are-related Macular Degeneration (AMD)
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What arteries supply blood to the retina? Percent contribution?
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ICA --> Ophthalmic Artery -->
- Retinal artery system (Central Retinal A.) ~30% - Ciliary artery system (Anterior and Posterior Ciliary aa.) ~70% |
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What artery supplies the inner retina?
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Central Retinal Artery
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What artery supplies the cornea?
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Anterior Ciliary Artery
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Which arteries supplies the ciliary body?
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- Anterior Ciliary A.
- Long Posterior Ciliary A. |
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Which arteries supplies the iris?
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- Anterior Ciliary A.
- Long Posterior Ciliary A. |
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What artery supplies the choroid (outer retina)?
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Short Posterior Ciliary A.
Choriocapillaries |
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Which part of the eye receives the greatest blood flow? Why is this important?
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Choroid (65-85%) - vital for maintenance of outer retina (photoreceptors in particular)
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Where does the remaining blood that doesn't go to the choroid go?
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Retina through the central retinal artery from the optic nerve head
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The central retina artery is a branch from what? Begins where relative to the optic nerve head?
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- Branch of ophthalmic artery
- Begins about 4 mm posterior to optic nerve head |
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Does the central retinal artery branch?
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- Divides into 2 main branches in the optic nerve
- Further divides to supply each quadrant of eye w/ an artery and vein |
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The macular vessels arise from branches of what?
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Superior Temporal and Inferotemporal arteries
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What specializations happen at the fovea?
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- Avascular zone
- Excavation of inner retinal neurons, foveal pit - High cone density - Absence of rods |
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If there is impaired foveal specialization, what happens?
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- Aniridia - absence of an iris
- Albinism - absence of pigment (melanin) |
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What is albinism?
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Inherited disorder of melanin biosynthesis - associated w/ absent or reduced melanin pigment in the eye, and often the skin and hair
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How common is albinism?
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1:17,000
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What are the two principle types of albinism? Genetic linkage? Symptoms?
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- Oculocutaneous albinism (OCA) - autosomal recessive; OCA1A-no pigment anywhere; OCA1B-some pigment due to leaky mutation allowing residual enzyme (tyrosinase)
- Ocular albinism (OA) - X-linked, typically normal skin and hair |
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What are the universal albinism visual symptoms?
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- Nystagmus - involuntary eye movement
- Refractive errors - Photophobia - Reduced acuity - Macular translucency - Iris transillumination - Altered retinostriate projections - Foveal hypoplasia (arrested foveal development) |
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What is this? What is it a sign of?
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Iris transillumination - clinical sign of albinism
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What is this? What is it a sign of?
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Macular Translucency - clinical sign of albinism
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What is this? What is it a sign of?
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Foveal Hypoplasia (top) - clinical sign of albinism
(bottom two are normal) |
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What is this? What is it a sign of?
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Altered Ipsi/Contra impairs stereo vision - clinical sign of albinism
(left is normal, right is albino) |
