Tear Drainage (M1)

Question 1

what is distribution of the tear film a result of

Answer 1

spontaneous blinking.
occurs every 3 - 8 seconds.

Question 2

what occurs during eyelid closure

Answer 2

Tear film components are secreted:
- mechanical pressure on meibomian glands leads to secretion of meibum
- stimulation of CN V leads to
Secretion of mucin and aqueous
drainage of the tear film:
- UL and LL meet at temporal canthus and zip toward the medial canthus –> pushes tears into puncta by capillary action and action of Horner’s muscle
- allows removal of cellular debris, toxins, inflammatory cells, and other waste products

Question 3

what occurs during eyelid opening

Answer 3

Lid wiper region of the UL spreads tear film across ocular surface:
- aqueous mixes with mucin and lipid layer spreads across mucoaqueous layer

Question 4

what occurs between blinks

Answer 4

tears evaporate.
this is the stimulus for secretion/distribution/drainage cycle to be repeated

Question 5

what drains the tears

Answer 5

Nasolacrimal apparatus
- puncta
- canaliculi
- lacrimal sac
- nasolacrimal duct

Question 6

what and where is the punctum

Answer 6

hole located in the lacrimal portion of the eyelid margin (superior and inferior)
- in the middle of the lacrimal papilla
each punctum opens into the lacrimal canaliculus

Question 7

what is the lacrimal canaliculus

Answer 7

tubes that join the puncta to the lacrimal sac.
lined by epithelial cells

Question 8

what are the 3 portions of the lacrimal canaliculus

Answer 8

Vertical (superior and inferior):
- extends from punctum about 2 mm
- slight dilation at the base (ampulla)
Horizontal (superior and inferior):
- runs along the lid margin about 8 mm
Common canaliculus:
- superior and inferior canaliculi join to form a single common canaliculus
- enters the lacrimal sac - the angle that it enters the lacrimal sac produces valve of Rosenmuller

Question 9

Valve of Rosenmuller

Answer 9

physiologic valve that prevents reflux of fluid

Question 10

what is the lacrimal canaliculus surrounded by

Answer 10

elastic tissue: permits dilation of the normal diameter
horner’s muscle: contraction aids in pumping of the tears towards the lacrimal sac

Question 11

what is the lacrimal sac

Answer 11

sac that collects tears.
lined by epithelial cells.

Question 12

location of the lacrimal sac

Answer 12

Sits in the lacrimal fossa - formed by the lacrimal bone and frontal process of maxillary bone.
In front of the orbital septum - isolates the lacrimal sac from the orbit to prevent infection
Medial palpebral ligament holds the sac against the anterior and posterior lacrimal crests - ridge in maxillary bone forms anterior lacrimal crest and ridge in lacrimal bone forms posterior lacrimal crest

Question 13

what is the lacrimal sac surrounded by

Answer 13

elastic tissue: permits dilation of the normal diameter
horner’s muscle: contraction aids in pumping of the tears towards the nasolacrimal duct

Question 14

tears drain from the lacrimal sac into ____

Answer 14

lacrimal duct

Question 15

what are the 2 portions of the lacrimal duct

Answer 15

Intraosseous: situated in nasolacrimal canal within the maxillary bone, about 12 mm long.
Membranous/Meatal: situated within the nasal mucosa, about 5 mm long
- opens into the inferior meatus of the nasal cavity, covered by a mucosal fold called the valve of Hasner that prevents reflux of fluid
- can be obstructed by the contents of the maxillary sinus (sinusitis)

Question 16

what are tears absorbed into

Answer 16

epithelial cells that line the nasolacrimal duct.
minor portion is absorbed into ocular surface epithelial cells.
minor portion enters inferior meatus of the nasal cavity.

Question 17

normal amount of time tears stay on the time before evaporating

Answer 17

greater than 10 seconds

Question 18

how does a poor lipid layer affect tears

Answer 18

leads to faster evaporation and poor tear film stability

Question 19

what happens to lipids as evaporation occurs

Answer 19

diffuse towards the mucoaqueous layer (down).
Mucin at the ocular surface, now contaminated by lipids, loses hydrophilicity.
Tear film begins to rupture, leading to isolated islands of tear break-up.