Ocular Physiology Flashcards by Michael Clark

What purpose does the abundant sarcoplasmic reticulum (SR) in EOMs serve?

Allows greater access to Ca, promoting muscle contraction

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What is the approximate number of muscle fibers in an EOM motor unit?

10 muscle fibers per motor unit

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Why is it important that EOMs have very small motor units?

Allows for small, precise, accurate movements

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What two ocular conditions can Botox be used to treat?

Strabismus

Blepharospasm

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What is the MOA of Botox?

Inhibits release of ACh at the neuromuscular junction

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What is the purpose of aqueous?

Maintain the shape of the anterior chamber
Helps transmit light to the retina
Provides nutrients and oxygen
Moves waste products from the anterior portion of the eye

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Why is carbonic anhydrase important in aqueous production?

Aids in production if bicarbonate, which causes an ion gradient

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What is the mathematical relationship between liquid content of the vitreous and age?

Linear - as age increases, the amount of liquid in the vitreous increases linearly

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What is the relative charge inside an axon?

Negative

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Directing a pt to look left with both eyes would be what classification of eye movement?

Levoversion

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What is one unique characteristic of vortex veins?

They don’t contain valves

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Which layers of the cornea prefer lipophilic substances?

Epithelium

Endothelium

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Which layer of the cornea is hydrophilic?

Stroma

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When an ophthalmic drug contacts the tear film, the pH of the tears favors what?

Alteration of the drug to a more non-ionized state

-non-ionized = lipid soluble

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TBUT occurs as a result of what?

Migration of lipid into contact with mucous

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Parasympathetic innervation is the primary stimulus for increased production and secretion of all of the different layers of the tear film except:?

Lipid secretion - lipids are secreted via blinking

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Which nerve is responsible for reflex tearing?

VII

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What does the main lacrimal gland contribute to?

Emotional tears

Reflex tears

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What is the nutrient supply for the cornea?

Aqueous humor

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What is the main oxygen supply for the open eye?

Tear film

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What is the main oxygen supply for the closed eye?

Palpebral conj - anterior cornea

Aqueous - posterior cornea

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Tear drainage occurs by what mechanism?

Contraction of two muscles; one widens the lacrimal sac, and the other acts on the canaliculi to pump tears into the widened sac - stimulated by blinking

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What portions of the orbicularis oculi are used in forced closure of the lid?

Both orbital and palpebral portions

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Which nerve is responsible for reflex blinking?

CN V

-CN VII actually executes the blink

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What areas form the blood retinal barrier?

Tight junctions in the wall of retinal vessels Tight junctions between RPE cells -NOTHING in the choroid contributes to the blood/retinal barriers

Where is the majority of the blood found within the eye?

Long and short posterior ciliary arteries | -Choroid has the majority of the blood flow

What does the long posterior ciliary artery supply?

Anterior choroid | Contributes to the major arterial circle of the iris

What does the short posterior ciliary artery supply?

Posterior choroid | Forms circle of Zinn (provides blood for the surface of the optic disc)

The majority of in the eye is in the choroid. Where is the majority of oxygen in the eye?

Retinal arteries

Stimulation of sympathetic receptors can cause what IOP response?

Both increase or decrease, depending on which receptors are acted upon A2 - decrease (decreases blood in MACI) B1/B2 - increase (increases aqueous production)

Sympathetic stimulation of uveal vessels leads to what change?

Vasoconstriction

Which vasculature of the eye doesn't respond to sympathetic stimulation? Why?

Retina - it autoregulates

What does perfusion pressure refer to?

The pressure difference between arteries and veins of a particular tissue

Which is good for the lens: glutathion or calcium?

Glutathion | -"Ca is crappy for the lens"

Are crystallins soluble or insoluble?

Soluble lens proteins

What does alpha crystallin do for the lens?

Molecular chaperone, reducing cataract formation

What does the gradient lens allow for in regards to aberration?

Reduces spherical aberration in the periphery

Which fibers does a Pancoast tumor affect?

Preganglionic sympathetic fibers

Where does the sympathetic nervous system synapse in the way to the eye?

Superior cervical ganglion

Where does the ocular sympathetic system start, and where it its first synapse?

Hypothalamus | Center of budge

Pupillary constriction in response to the location of a near stimulus begins where?

FEF | -Goes on to Edinger Westphal, to ciliary ganglion

What is the pathway of pupil constriction due to light?

FEF | -goes to pretectal nucleus, to EW to ciliary ganglion

Argyll Robertson Pupil results from disruption in what tract?

Tectotegmental tract that connects the pretectal to the EW nucleus

Patients with Argyll Robertson Pupil will constrict to which stimulus: Near, light?

Near | -Poor constriction to light

Uveitis is a breakdown of what?

Blood aqueous barrier

Aqueous production relies almost entirely on what type of secretion?

Active secretion

Why might a neck tie increase IOP?

Increase in venous pressure, which decreases the outflow via TM

Uveitis, blood acidosis, and plasma hyperosmolality may cause what change to IOP?

Decrease

How does isosorbide decreas IOP?

Increases plasma osmolarity | -high concentration of ions draws water out

Tonometry on a thick cornea may be under or overestimated?

Overestimated

Tonometry on a thin cornea may be uner or overestimated?

Underestimated

Which layer of the cornea thickens with age?

Descemet's

Which layer of the cornea shows decreased cell count with age?

Endothelium

What is the first corneal response mounted to an abrasion?

Inhibition of basal cell mitosis | -followed by migration

The epithelium can help combat edema by pumping what ion where?

Cl- into the tears (water follows)

What helps to ensure that collagen fibrils are regularly spaced in the cornea to maintain transparency?

GAGs

Corneal deturgescence is the primary responsibility of what layer of the cornea?

Endothelium

What is corneal deturgescence?

Dehydration of the corneal stroma

The corneal stroma is what percent water?

78%

What type of potentials do amacrine and ganglion cells create?

Action potentials

What type of potentials do horizontal, bipolar, and PRs generate?

Graded potentials

Which cells of the retina use excitatory neurotransmitters?

PRs Bipolar cells Ganglion cells

Which cells of the retina use inhibitory neurotransmitters?

Amacrine cells | Horizontal cells

What are the inhibitory neurotransmitters used by amacrine and horizontal cells?

GABA | Glycine

What is the excitatory neurotransmitter used by PRs, bipolar cells, and ganglion cells?

Glutamate

Stimulation of the PRs results in what?

Hyperpolarization

Phototransduction in the outer segment leads to what occurrences?

Hyperpolarization Generation of graded potentials Decrease in glutamate release from PRs

What is one of the main differences between rod spherules and cone pedicles?

Opsin component | -Rhodpsin vs Iodopsin

Where is collagen concentration the highest in the vitreous?

Vitreous base

Where is collagen concentration the lowest in the vitreous?

Center

What causes the A wave of an ERG?

PRs

What causes the B wave of an ERG?

Bipolar and mueller cells

What causes the C wave of an ERG?

RPE

What should the normal Arden ratio in an EOG be?

Greater than 1.8 | - less tan 1.65 is very abnormal

Where do simple and complex cells first appear along the visual pathway?

Primary visual cortex (V1)

What are simple cells programmed to specialize in?

Objects with a particular orientation

What are complex cells programmed to specialize in?

Objects with a particular orientation, moving in a specific direction

Which is the first place in the visual pathway to combine monocular input for binocular processing?

V1 - primary visual cortex

Name 4 common causes of retinal artery occlusions.

Hollenhorst plaque Calcification from heart valves Giant cell arteritis Sickle cell anemia

Artery occlusions cause the retina to turn what color?

White

Emboli cause what type of vessel occlusion?

Arterial occlusions

Which is generally larger, Hollenhorst plaques, or calcific plaques?

Calcific

Hollenhorst plaques are a build-up of what?

Cholesterol

Thrombi cause what type of vessel occlusion?

Vein occlusions

What causes a vein occlusion?

Artery compresses a vein, causing the thrombus formation

What is the largest risk factor for diabetic retinopathy?

Duration of DM

What is the most common reason for legal blindness in a diabetic?

Macular edema

What are the 3 series of rules for diabetic retinopathy?

4-2-1 rule High risk characteristics Definition of CSME

What are the layers of the tear film, and what structures secrete those layers?

Mucin - goblet cells Aqueous - Main lacrimal gland/glands of Krause and Wolfring Meibum - meibomian glands/Zeis and Moll