TEAR FILM

Question 1

TEAR FILM LAYERS

Answer 1

• lipid
• aqueous
• mucus
  (microvilli, corneal epithelium)

Question 2

THICKNESS OF TEAR FILM

Answer 2

7 μm

Question 3

LIPID LAYER

Answer 3

superficial layer, very thin (0.1 μm)

• meibomian glands
• glands of zeis
• glands of moll
  (in the lids)
• made of polar + non-polar lipids
• retards evaporation of aq
• prevents skin lipid contamination
• prevents over-spilling onto eyelids

Question 4

AQUEOUS LAYER

Answer 4

• lacrimal gland
• gland of krause
• gland of wolfring

made of electrolytes, H+
proteins/ enzymes (lysozyme)
metabolites - glucose

Question 5

MUCUS LAYER

Answer 5

• goblet cells (glands of manz + crypts of henle)
• non-goblet epithelial cells
• lacrimal gland

made of high molecular weight mucins (proteins with many carb chains attached)

allows aqueous to spread over the non-wetable corneal epithelium

essential in making tear film spread over cornea + in maintaining tear stability

Question 6

DRAINAGE SYSTEM

Answer 6

• puncta
• canaliculi
• lacrimal sac
• nasolacrimal sac
• valve of hasner

Question 7

TEAR FILM FUNCTIONS

Answer 7

• fills in corneal epithelial irregularities
• provides a smooth optical surface
• lubrication
• flushes debris
• removes water from cornea
• provides oxygen + nutrients
• antibacterial agents

Question 8

TEAR PRODUCTION VOLUME

Answer 8

total volume -> 4-10 μl

max capacity -> 25 μl

Question 9

TEAR TURNOVER RATE (%/MIN)

Answer 9

18%/min

Question 10

TEAR FLOW RATE (μl/MIN)

Answer 10

1.2 μl/min

Question 11

REFLEX TEARING DUE TO PERIPHERAL SENSORY

Answer 11

stimulation of cornea or cilia

Question 12

REFLEX TEARING AS A RESULT OF CENTRAL SENSORY

Answer 12

stimulation of retina (light) or psychogenic factors

Question 13

HOW MANY TEARS ARE LOST BY EVAPORATION?

Answer 13

10-40%