Anatomy

1
Anatomy

• Contact lenses Week 2

2
Anatomy

• Tear film consists of three layers with a pH
  level of 7.3 and a salt concentrations of 0.91
  to0.97. Normal evaporation is 1 to 2 microliters
  or 15 of total volume per minute.

3
Anatomy

• Three layers of the tear film
• Oily layer
• Aqueous layer
• Mucous layer

4
Anatomy

• The oily layer

• The outermost layer of the pre corneal tear film.
• Consists of a lipid layer that is a partially
  solid oil and wax that helps to stabilize the
  tear film and prevent evaporation.
• This oily layer is produced by the meibomian
  glands.
• An insufficient amount of the oily layer will
  cause dryness, pingueculae, pterygium and
  scarring.

5
Anatomy

• The aqueous layer

• The middle layer of the tear film.
• This layer is made of salt, sugars, urea and
  protien.
• Lactoferrin (an iron carrying protien) supports
  oxygen transfer and has significant bacteria
  inhibiting characteristics.
• The aqueous layer is produced by the lacrimal
  gland.

6
Anatomy

• The mucous layer

• The innermost layer of the tear film and also the
  thinnest.
• The corneal surface in hydrophobic(water fearing)
• The mucin layer reverses the hydrophobic
  characteristic of the epithelium to hydrophilic
  (water loving).
• The mucin layer also is produced by the
  conjunctival goblet cells.

7
Anatomy

• Tear film

8
Anatomy

• Cornea

• 5 layer of the cornea

• The cornea consists of 5 layers.
• The cornea is the most powerful refracting
  surface of the eye, with an average diopteric
  power of 48.8.

• Epithelium
• Bowmans layer
• Stroma
• Decemets membrane
• Endothelium

9
Anatomy

• Corneal epithelium
• 5 to6 cell layers thick.( 50-60 microns thick)
• This layer acts as a barrier the foreign bodies
  and friction during blinking.
• Disturbances to the epi can be directly linked to
  a CL that reduces the amount of O2 to the cornea.
• Decemets membrane
• Produced by the endothelium.
• Corneal endothelium
• Single layer of cells.
• Endothelial cells can not regenerate.
• Acts as a pump to maintain dehydrated cornea.

10
Anatomy

• Corneal layers

• Layers under the slit lamp

11
Anatomy

• Blinking spreads the tear film of the cornea.
  This is critical to the success of the contact
  lens wearer.
• The eyelids spread the tear layer over the cornea
  by blinking an average of 7 times per minute.
• This will increase to 18-20 times per minutes
  after the initial insertion of the CL.
• Lens material can affect the blink rate. If this
  is altered, it will cause lens dehydration and
  discomfort.

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Anatomical disorders and contraindications for CL
wear.

• Tear dificiencies
• Dry eye
• Sjogrens syndrome
• Blepharitis
• Entropian
• Ectropian
• Trichiasis
• Lagophthalmos
• Scleritis or episcleritis
• Keratoconus
• Diabetes
• Graves disease
• pregnancy

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CL contraindications

• trichiasis

• entropian

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LC contraindications

• Floppy eyelid syndrome

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CL Contraindications

• Graves disease

• ectropian

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CL Contraindications

• scleritis

• scleritis

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CL Contraindications

• Dry eye with staining

• Dry eye with punctate staining

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CL Contraindications

• keratoconus

• keratoconus

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Slit lamp examination

• This microscope with its high intensity lamp is
  critical for checking movement and the centering
  of a contact lens.
• Evaluating fluorescein patterns is much easier
  when checking the fit a CL.
• Tear film, corneal surface and tear break up time
  is evaluated with the slit lamp as well to see if
  the patient is a good candidate for CLs.

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Tear assessment testing

• Tear flow
• Schirmer
• Hypofluorescence
• Tear stability
• TBUT
• Evaluation of lipid layer
• Condition of ocular surface
• Fluorescein staining
• Rose bengal

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Tear assessment

• Tear quality / tear break up time test

• Tear quantity /schirmer testing

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The end!

• See you next week for soft CL basics and care
  products lecture.
• Test in two weeks!