Ocular Physiology Flashcards
What purpose does the abundant sarcoplasmic reticulum (SR) in EOMs serve?
Allows greater access to Ca, promoting muscle contraction
What is the approximate number of muscle fibers in an EOM motor unit?
10 muscle fibers per motor unit
Why is it important that EOMs have very small motor units?
Allows for small, precise, accurate movements
What two ocular conditions can Botox be used to treat?
Strabismus
Blepharospasm
What is the MOA of Botox?
Inhibits release of ACh at the neuromuscular junction
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
Why is carbonic anhydrase important in aqueous production?
Aids in production if bicarbonate, which causes an ion gradient
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
What is the relative charge inside an axon?
Negative
Directing a pt to look left with both eyes would be what classification of eye movement?
Levoversion
What is one unique characteristic of vortex veins?
They don’t contain valves
Which layers of the cornea prefer lipophilic substances?
Epithelium
Endothelium
Which layer of the cornea is hydrophilic?
Stroma
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
TBUT occurs as a result of what?
Migration of lipid into contact with mucous
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
Which nerve is responsible for reflex tearing?
VII
What does the main lacrimal gland contribute to?
Emotional tears
Reflex tears
What is the nutrient supply for the cornea?
Aqueous humor
What is the main oxygen supply for the open eye?
Tear film
What is the main oxygen supply for the closed eye?
Palpebral conj - anterior cornea
Aqueous - posterior cornea
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
What portions of the orbicularis oculi are used in forced closure of the lid?
Both orbital and palpebral portions
Which nerve is responsible for reflex blinking?
CN V
-CN VII actually executes the blink
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
