Ocular Physiology: Eyelids, Tears, and Cornea

A comprehensive set of flashcards covering eyelid mechanics, tear film dynamics, and corneal physiological processes based on the provided lecture notes.

What muscle's contraction results in eyelid closure?

The orbicularis oculi muscles ($NOT$ relaxation of the levator muscle).

At what average rate does spontaneous blinking occur?

$12-15$ blinks per minute.

Which portion of the orbicularis oculi is responsible for spontaneous and reflex blinking?

The palpebral portion.

Which cranial nerve senses loud noises to elicit a reflex blink?

$CN VIII$.

Which reflex blink does NOT involve the cortex?

The dazzle reflex.

What muscles are involved in Benign Essential Blepharospasm?

Orbicularis oculi, procerus, and corrugator musculature.

What is Bell's phenomenon?

An upwards and outwards rotation of the globe that occurs after forced lid closure, present in approximately $75\%$ of the population.

Which glands are responsible for secreting the anterior lipid layer of the tears?

Meibomian glands.

Where are the Glands of Krause primarily located?

In the fornices.

According to the lacrimal pump theory, which muscle contracts to pump tears into the lacrimal sac?

The muscle of Horner.

What is the primary source of oxygen ($O_2$) for the corneal epithelium?

Diffusion of atmospheric $O_2$ through the tear film.

Which antimicrobial protein in tears chelates $Fe^{2+}$?

Lactoferrin.

Which vitamin is necessary for the development of conjunctival goblet cells?

Vitamin A (all-trans retinol).

What is the normal osmolarity of the tear film on a healthy ocular surface?

Approximately $308\,mOsm/L$.

How does the pH of tears change during sleep?

It decreases (becomes more acidic) due to the byproducts of anaerobic respiration.

Which middle ear muscle is innervated by a branch of the mandibular division ($V3$) of $CN V$?

The tensor tympani muscle.

Which inner ear structure detects angular acceleration (rotational movements)?

Semi-circular canals.

Which lobe of the brain controls horizontal saccades?

The contralateral frontal eye field (and superior colliculus).

Which corneal layer is highly hydrophilic?

The corneal stroma.

What is the major proteoglycan in the corneal stroma that helps maintain collagen spacing?

Keratan sulfate.

What is the critical partial pressure of oxygen ($PPO_2$) for the cornea?

$10-20\,mmHg$.

What is the primary contributor of glucose for all corneal layers?

The aqueous humor.

How often does the entire corneal epithelium replace itself?

Every $7-14$ days.