Lacrimal apparatus

• lacrimal gland structure

  orbital portion, lacrimal fossa, palpebral portion


  orbital portion - largest and lies underneath the frontal lobe, and above the aponeurosis of levator palpebrae superioris. lacrimal fossa - in the roof of the orbit

  palpebral portion - continues with the orbital portion and lies below the aponeurosis of levator palpebrae superioris. ducts pass through this portion to superior conjunctival fornix.
• what are lacrimal glands, and what are they made up of?

  compound tubulo-alveolar exocrine gland, which produces the aqueous / watery part of the tears.

  it is made up of alveoli which have several secretory cells that produce the tears and send them into the central lumen and leave via the duct.
• secretory cells?

  they sit on the basement membrane

  have tight junctions to prevent tears going between cells.

  they secrete: lysozymes, immunoglobulins and mucous
• myoepithelial cells


  contract in response to stimulation by sympathetic nervous system and squeeze perspiration up the duct. surround the alveoli
• Glands of Krause and Wolfring


  produce the watery layer of the tear film in conjunction with the lacrimal gland

  
  

  Krause - in stroma of superior fornix

  wolf ring - in the stoma of the superior palpebral conjunctiva
• normal tear flow (3)


  sympathetic (to blood vessels supplying glands).

  influenced by bright light and air pollution

  maintains normal tear flow
• emotional tear flow (3)

  parasympathetic (to myoepithelial cells)

  stimulated by emotional state

  via emotion centres in the brain
• reflex / irritation tear flow (3)

  parasympathetic (to myoepithelial cells)

  stimulated by the irritation of the cornea or conjunctiva

  via trigeminal / sensory nerves
• crocodile tear flow (3)

  parasympathetic (to myoepithelial cells)

  stimulated by eating

  faulty connection (lacrimal gland instead of salivary gland)
• lacrimal puncta (3)

  holes on upper and lower lids where tears enter the drainage system.

  lacrimal papilla is swelling associated with the holes

  orbicularis oculi is tone that holds Punta in position (normally facing inwards)
• lacrimal canaliculi (3)


  the ducts at the inner corner of each eye that collect tears and drain them into the lacrimal sac.

  consists of vertical portion, ampulla (dilated region) and horizontal portion.

  the flap prevents tear reflux from lacrimal sac (valve of Rosen muller), and is over the top of the hole.
• lacrimal sac


  lies in between the lacrimal fossa, which is in between the anterior and posterior crests. they are holding the lacrimal sac open so it can receive the tears.
• nasolacrimal duct (3)

  tears drain into the nasal cavity from the lacrimal sac.

  it is within the nasolacrimal canal, which is formed by: lacrimal and maxilla bone; and the inferior nasal concha (bones that add humidity to the air when we breath in).

  flap at the bottom - valve of hanser - stops air and debris entering the lacrimal sac from the nose.
• tear pump (ocular surface)

  - blinking

  - tear prism

  - what 2 things happens to tears?

  blinking spreads tears medially

  tear prisms forms at the posterior margins of both lids

  some tears evaporate and others drain via the puncta.
• the cycle of eyes opening to closing to opening.

  eyes open = relaxed state: puncta is in the tear lake and the lacrimal sac is filled with tears

  
  

  eye lids closure = blinking: contraction of orbicularis closes the puncta and canaliculi, making the lacrimal sac compress. this is known as positive pressure as it pushes tears through the nasolacrimal duct.

  
  

  eyelids open: orbicularis relaxes and the puncta and sac open. this is known as negative pressure as it draws tears into the canaliculi.
• 5 features of tears?

  pH = 7.5-7.8 when open, when closed (small amounts of corneal acidosis) so pH = 7.0

  
  

  tonicity (ability to draw water) - sodium chloride about 0.9%

  
  

  thickness = 7-10um

  
  

  volume = 6-8ul

  
  

  secretion rate = 1-2ul/min
• 3 layers of tears?

  outer lipid layer: formed from Meibomian glands and glands of zies and moll. it reduced evaporation and lubricates ocular surface.

  
  

  middle aqueous (water) layer: formed from lacrimal glands and provide nutrition, oxygen and defends ocular surfaces

  
  

  inner mucin layer: formed from goblet cells, crypts of Henle, glands of manz and lacrimal glands. it wets and lubricates the ocular surfaces.
• clinical signs of lacrimal glands?

  swelling of the outer portion of upper eyelids, caused by dacryoadenitis (infection of the lacrimal gland), and a lacrimal tumour (usually benign and cause dystopia)
• watery eyes (epiphora)?

  tear prism>0.75mm. caused by malposition of puncta and obstruction/blockage of lacrimal drainage. inflammation of lacrimal sac = dacrocystitis and canaliculitis

  also caused by lacrimal pump failure when there is a weakness of orbicularis oculi
• dry eyes?


  tear break up time is longer then 10 seconds. fluorescein straining on bulbar conjunctiva.

  - hypo secretive dry eyes caused by no enough secretion of the tears, lacrimal gland affected

  - evaporative dry eyes caused by Meibomian glands dysfunction or defective blinking (contact lens discomfort)