Tear Drainage

Question 1

Spontaneous blinking occurs every

Answer 1

3-8 seconds

Question 2

How does eyelid closure lead to tear film secretion?

Answer 2

Mechanical pressure on the meibomian glands leads to the secretion of meibum (the lipid portion)

Blinking stimulates CN VII, which leads to the secretion of the aqueous and mucin portion.

Question 3

Spreading of the tear film across the ocular surface occurs when

Answer 3

Opening eyes. The lid wiper region of the UL spreads the tear film.

Question 4

How does drainage of the tear film occur?

Answer 4

The UL and LL meet at the temporal cants and zip towards the medial canthus. This pushes tears into the puncta by capillary action and the action of hornets muscle.

Question 5

Four parts of the nasolacrimal apparatus (nasolacrimal drainage system)

Answer 5

Puncta, canaliculi, lacrimal sac and nasolacrimal duct

Question 6

The puncta is located where

Answer 6

In the middle of the lacrimal papilla (elevation of tissue) on the superior and inferior eyelid margins. Each punctum opens into the lacrimal canaliculus.

Question 7

Describe the shape of the lacrimal canaliculus

Answer 7

Vertical extensions (superior and inferior) for 2mm

Ampulla- sight dilation before turning horizontal

Horizontal extensions (superior and inferior) for 8mm

Common canaliculus- superior and inferior canaliculi join to form a single canal.

The angle at which the canaliculus enters the lacrimal sac produces a valve that prevents reflux of fluid called the Rosenmuller valve

Question 8

Rosenmuller valve

Answer 8

The angle at which the common canaliculuous enters the lacrimal sac. Prevents the back flow or reflux of fluids.

Question 9

The lacrimal canaliculus is which tissue type

Answer 9

Elastic. Permits dilation of the normal diameter if lacrimal system becomes clogged or isn’t draining tears properly.

Question 10

Which muscle surrounds the canaliculi?

Answer 10

Horners muscle. When this muscle contracts, it aids in pumping of tears towards the lacrimal sac.

Question 11

Lacrimal sac is lined by which type of cells

Answer 11

Epithelial cells

Question 12

The lacrimal fossa is formed by which two bones

Answer 12

Anterior ridge- maxillary bone.

Posterior ridge- lacrimal bone.

Question 13

the ___ holds the lacrimal sac against the anterior and posterior lacrimal crests

Answer 13

Medial palpebral ligament

Question 14

The lacrimal sac is surrounded by which tissue type and which muscle

Answer 14

Elastic tissue

Horners muscle

Question 15

2 portions of the nasolacrimal duct

Answer 15

1. Intraosseous- Situated in the nasolacrimal canal within the maxillary bone. About 12mm long.
2. Membranous/meatal- Situated within the basal mucosa. About 5 mm long. Opens into the inferior meatus of the nasal cavity.

Question 16

Valve of Hasner

Answer 16

Valve at the end of the meatal portion of the nasolacrimal duct. Prevents reflux of fluid from the nose to the eye. Can be obstructed by sinusitis.

This valve doesn’t develop in babies until 6 months. Can have a lot of water and mucus in eyes due to this.

Question 17

Nasolacrimal duct is lined by which type of cells

Answer 17

Epithelial. Tears are absorbed into these cells, which is why you don’t constantly have to blow your nose.

Question 18

Where do tears go after being drained down nasolacrimal duct?

Answer 18

Most are absorbed into epithelial cells that line the duct.
A minor portion is absorbed into the ocular surface epithelial cells.
A minor portion of tears enter the inferior meatus of the nasal cavity.

Question 19

If eyes have a poor lipid layer, this may result in

Answer 19

Faster evaporation of the aqueous component.

Question 20

Why does a poor lipid layer result in quicker evaporation of the aqueous component?

Answer 20

As evaporation occurs, lipid diffuse towards the mucoaqueous layer. The mucin at the ocular surface, now contaminated by lipids, loses its hydrophilicity (attraction to water).

This causes the tear film to rupture, leading to isolated islands of tear break-up.

Question 21

Normal amount of time for tears to stay on the eyes before evaporating

Answer 21

Greater than 10 seconds.