KMK Ocular Physiology

What are the three types of eyelid closure?

blink

wink

spasm

Eyelid closure results from the _______ of the _____muscle?

contraction, obicularis oculi

What are the three types of blinking?

spontaneous

reflex

voluntary

What is the average blink rate?

15 per minute

Spontaneous blinking results from contraction of ________?

palpebral portion of the orbicularis oculi

The levator muscle and the palpebral portion of the o.o are (agonist/antagonist)

antagonists

What type of blinking occurs in the absence of external stimuli

spontaneous

The palpebral portion of the orbicularis is responsible for what two types of blinking?

spontaneous and reflex

What type of blink is caused by sensory stimuli

reflex

What two nerves are used in a touch reflex blink?

V senses it and VII closes

The dazzle reflex is mediated by what cranial nerve?

II

What are the five functions of tears?

Optical

Nutritional

Mechanical

Antibacterial

Corneal Transparency

Where is the largest refractive index change in the whole visual pathway?

air/tear

What layer of the tear film is the antibacterial properties located?

aqueous

What are three glands that produce the lipid layer of the tear film?

Zeis, Moll, Meibomian

What is the primary method of eliciting lipid secretion?

blinking

What are four antibacterial entities found in the tears?

lactoferrin

lysozyme

IgA

interleukins

What are the three glands that contribute to the aqueous layer?

main lacrimal gland, Krause, Wolfring

The lacrimal gland has what type of innervation?

parasympathetic

sympathetic

sensory

What type of tearing is provided by the lacrimal gland?

reflex and emotional

What gland supplies the basal tearing?

wolfring and Krause

What is the source of the outer mucin layer?

goblet cells

What is the source of the inner glycocalyx layer of mucin?

corneal epithelial cells

Where are goblet cells mostly found?

inferonasal fornix and on the bulbar conj

Goblet cells require what vitamin for development?

Vitamin A

A Vitamin A deficiency ca result in a _________; a foamy build up of _________on the conjunctiva?

Bitot spot, keratin

Contact between what two layers cause tear break up?

lipid touches the mucin

What is the normal tear volume present on the ocular surface?

7-9 ul

The average eye drop contains what volume?

50 ul

What is the osmolarity of the tear film?

315

What are the main ions that contribute to the tear film osmolarity?

Na and Cl

Potassium is found __________ in the tears than the plasma?

4x greater concentration

Dry eye syndrome (increase/decrease) tear osmolarity?

increase

What is the average tear pH?

7.45

What happens to the pH of tears during sleep?

decreases becoming more acidic

What happens to the pH of tears in dry eye?

increases becomes more basic

What separates the external ear from the middle ear?

tympanic membrane

What are the three bones of the middle ear?

malleus, incus, stapes

What separates the middle ear from the inner ear?

oval window

What is the function of the tympanic membrane?

to amplify sound

What is the function of the oval window?

to convert vibration to neural signal

What are the three components of the bony labyrinth?

Cochlea

Vestibule

Semi-Circular canal

What part of the bony labyrinth is responsible for the angular VOR?

semi-circular canal

What type of eye movement is rapid and maintains fixation?

saccade

What controls horizontal saccades?

contralateral frontal eye field

Where are the frontal eye fields located?

frontal lobe and superior colliculus

Pursuits are controlled by _______?

ipsilateral parietal lobe

What is thought to be the driving cause of vergence movements?

retinal disparity

The corneal epithelium is (lipophilic/hydrophilic)

highly lipophilic

THe corneal stroma is (lipophilic/hydrophilic)

highly hydrophilic

The corneal endothelium is (lipophilic/hydrophilic)

highly lipophilic

The corneal stroma prefers (ionized/non-ionized) substances?

ionized

The corneal epithelium and endothelium prefer (ionized/non-ionized) substances?

non-ionized

What is the wavelength of UV-C light?

200-290

What is the wavelength of UV-B light?

290-320

What is the wavelength of UV-A light?

320-400

What layers of the cornea protect the eye from light below 300 nm?

epithelium and Bowmans

What part of the cornea is most sensitive to UV radiation?

epithelium, ie snow blindness and UV keratitis

What are five things that contribute to corneal transparency?

crystallin proteins

Ascorbate and Glutathione

Collagen Fibrils

Avascularity

High water content

What are two ways that ascorbate and glutathione contribute to corneal transparency?

combat UVR and scavenge free radicals

How does the collagen fibrils of the cornea contribute to the corneal transparency?

uniform size and spacing of less than one half the wavelength of light

What provides for the precise spacing of corneal collagen fibrils?

Proteoglycans

The precise spacing of the collagen fibrils of the cornea provides (constructive/destructive) interference to minimize light scatter?

destructive

What is the water content of the corneal stroma?

78%

The sclera is considered (dehydrated/hydrated) to the cornea?

dehydrated

What is the major proteoglycan in the corneal stroma?

keratin sulfate

What are the three most important factors that maintain corneal deturgesence?

epithelial pump

endothelial pumps

aquaporins

Where does the corneal epithelium get Na+?

Na+ moves from the tears into the epithelium

The movement of K+ into the aqueous stimulates ____ to move into the tears?

Cl-

Movement of what two ions is thought to be the trigger for water to move from the corneal endothelium into the aqueous?

Cl- and bicarbonate

Cl- _______and Na+ _______ are the major factors in water movement in the cornea?

extrusion

absorption

Where does the cornea receive the majority of its oxygen/

tears

Which layers of the cornea gets its oxygen from the tears when the eye is open?

all

What is the pp of oxygen in the tears when the eye is open?

155

When the eye is closed what part of the cornea is supplied O2 by the superior palpebral conj and limbal vasculature

epithelium and anterior stroma

How much oxygen that will diffuse through a contact lens is called?

transmissibility

Transmissibility is given by the equation?

DK/t

Glucose concentration is ______in the tears but __________in the aqueous?

low, high

What is the source of glucose for all layers of the cornea?

aqueous

Which corneal cells can store large amounts of glycogen?

epithelial for basal cell mitosis and wound healing

The entire cornea replaces its self after ______-days?

7

What are the only type of corneal cells to undergo mitosis?

Basal cells

Where are corneal epithelial stem cells located?

in the limbus in the Palisades of Vogt

BAsal cells differentiate into ______ and then _____?

wing

squamous

What are the three steps to traumatic epithelial regeneration?

step 1 : basal cell mitosis is inhibited

step 2: epithelial migration occurs

step 3: basal cell mitosis resumes at a rapid rate

If basement membrane damage occurs in a corneal wound how long will it take to heal?

approximately 8 weeks

Corticosteroids and tetracyclines like doxy have been shown to decrease activity of _______ that degrade hemidesmosome, helping in corneal healing

matrix metalloproteinases (MMP)

What layers of the cornea can't regenerate?

Bowmans and the endothelium

What two layers of the cornea can regenerate?

Epithelium and descemets

As a person ages Descemet's grows how much?

it triples from 5 um to 15 um

Define the trophic function of the corneal nerves?

sensory innervation is needed for epithelial cell regeneration and maintenance

Neurotrophic keratitis, DM, herpes, stroke and other things lead to ______neuropathy and _______is useful in diagnosis?

CN V, cotton swab test

The Lens provides ______percent of the dioptric power of the eye?

1/3

What lens protein is known as a molecular chaperone because it offers resistance to degradation of others?

Alpha crystalline

Describe the refractive indexes of the lens?

1.336 in the aqueous and vitreous

1.38 on the outer cortical surface

1.41 in the nucleus

What two things cause spherical aberrations to decrease in the lens?

gradient index system

peripheral flattening

What are the two main metabolic activities of the lens?

constant production of new lens fibers

maintenance of Na/K pumps to maintain clear optically

What process supplies the majority of the energy for metabolism in the lens?

anaerobic glycolisis

What is the pathophysiology to a diabetic cataract?

lack of hexokinase in the gylcolysis pathway leads to sorbitol

What is the first step of gylcolysis and what enzyme is needed?

glucose gets converted to glucose 6 phosphate; hexokinase