Tears

• 4 functions of the tear film...

  - supplies the nutrients for the anterior eye

  - maintains transparency for the cornea

  - remove debris around the front of the eye

  - acts as a protective barrier
• Mucin layer of tear film (3)


  - sticky inner most layer

  - mucin is secreted by goblet cells of the conjunctiva

  - converts hydrophobic epithelium to hydrophilic
• aqueous layer of the tear film (4)

  - acts as a transport mechanism by supplying oxygen to the cornea

  - contains antimicrobial lysozymes (dry eyes has more infections)

  - secreted by lacrimal glands

  - smooths the optical surface and washes away any debris
• lipid layer of the tear film (5)

  - fat/oil layer to help with the control of evaporation by increasing the surface tension to hold the tear layer up

  - lubricates the eyelids

  - secreted by Meibomian glands

  - regenerated every blink

  - thin layer and so can get reflections of anterior and posterior tear film, producing an interference fringe pattern that changes with thickness
• what is the importance of the microvilli in the epithelium of the cornea in tear film?

  allows for mucin to be locked in
• What is KCS (keratoconjunctivitis sicca)?


  condition caused by 'dry eyes' as there is a dryness in the cornea and conjunctiva
• what is SPK (superficial punctate keratitis)?

  little spots of dryness on the surface of the cornea
• What is tear break up time (TBUT)?

  tear thinning time
• measuring TBUT...

  - invasive: fluorescein?

  disadvantage and advantage?

  purposely disrupting the tear, lipid layer, by adding more 'aqueous', reducing the tear break up time.

  
  

  disadvantage = invasive

  advantage = commonly used, and easy
• measuring TBUT...

  - non-invasive: tearscope/keratometry?

  disadvantage and advantage?

  focused image on the centre of the cornea, ask patient to blink, causing the tears to thin and the mires become distort. TBUT measured by looking at the reflex of mires.

  
  

  disadvantage = keratometry only assess the central (3-4mm) of cornea but tears may have broken up in the periphery.

  advantage = non-invasive
• what does a tearscope do?

  projects a grid onto the surface of the cornea, via a cold light source, allowing to see the interference pattern of the lipid layer from a reflective image of the tear film surface.
• mamoreal pattern?

  grey marble appearance

  thin lipid layer, so tears evaporate faster leading to dry eyes
• wave pattern?

  migrating wave front and has slightly more colour

  stable tear film and normal lipid layer so no dry eyes

  good prognosis with contact lenses
• amorphous pattern?


  whitish reflection, without shape (no wave pattern)

  mixed lipid layer but still stable tear film

  may deposit on contact lenses, but not much
• colour fringes 1?

  yellow-brown-blue

  thick lipid layer, so stable tear film

  may leave greasy contact lens deposits
• colour fringes 2?

  brown-blue-green-red

  clumps of lipid surrounded by fringes so poor TBUT

  Meibomian glands dysfunction
• what do the tearscope accessories allow for?

  measure the TBUT by timing how long it takes for the grid to distort
• measuring tear volume...

  - Schirmer test?

  disadvantage?

  measure level in a set time or time taken to reach a set level

  disadvantage = can cause irritation leading to reflex tearing
• measuring tear volume...

  - disadvantage and advantage of phenol red thread?

  disadvantage = expensive

  advantage = less reflex tearing
• how does contact lenses affect tear film? (4)

  CL splits the tear film - pre and post lens tear film.

  it reduces the TBUT (patients need to blink more often)

  soft CL reduces lipid layer

  lipid layer almost absent with RGP (rigid gas permeable)
• 4 problems with contact lens wear...

  - dry eyes

  - increased awareness and occasional pain

  - reduced vision

  - redness of the eyes
• how does fluorescein assess dry corneas?

  acts as a pH indicator

  yellow colour = tears are acidic

  bowman's region = more alkaline
• fluorescein in contact lenses... (3)

  - aid fitting of RGP lenses (see how the tears are sitting around RGP - pattern)

  - rinse before inserting soft CL as it can be susceptible to pseudomonas aeruginosa, if entered in

  - inhibit the action of preservations
• Rose Bengal & Lissamine Green


  stains dead and devitalized cells
• difference between Rose Bengal & Lissamine Green?

  Rose - causes stinging and is difficult to remove from skin

  Lissamine - doesn't sting, and won't last long in the eye
• 5 ways to manage dry eyes...

  - hydration and diet

  - blinking exercises and humidity

  - general health and medication

  - artificial tears

  - treatment of the puncta