Download Anatomy

Contact lenses
Week 2

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.

Three layers of the tear film
1.
Oily layer
Aqueous layer
Mucous layer
2.
3.
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.

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.

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.

TEAR FILM
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.
5 LAYER OF THE CORNEA





Epithelium
Bowman’s layer
Stroma
Decemet’s membrane
Endothelium
Corneal epithelium
5 to6 cell layers thick.( 50-60 microns thick)
This layer acts as a barrier the foreign bodies and
friction during blinking.
3. Disturbances to the epi can be directly linked to a CL
that reduces the amount of O2 to the cornea.
 Decemet’s membrane
1. Produced by the endothelium.
 Corneal endothelium
1. Single layer of cells.
2. Endothelial cells can not regenerate.
3. Acts as a pump to maintain dehydrated cornea.

1.
2.
CORNEAL LAYERS
LAYERS UNDER THE SLIT LAMP




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.













Tear dificiencies
Dry eye
Sjogren’s syndrome
Blepharitis
Entropian
Ectropian
Trichiasis
Lagophthalmos
Scleritis or episcleritis
Keratoconus
Diabetes
Grave’s disease
pregnancy
TRICHIASIS
ENTROPIAN
FLOPPY EYELID SYNDROME
GRAVE’S DISEASE
ECTROPIAN
SCLERITIS
SCLERITIS
DRY EYE WITH STAINING
DRY EYE WITH PUNCTATE
STAINING
KERATOCONUS
KERATOCONUS
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 CL’s.


1.
2.

1.
2.

1.
2.
Tear flow
Schirmer
Hypofluorescence
Tear stability
TBUT
Evaluation of lipid layer
Condition of ocular surface
Fluorescein staining
Rose bengal
TEAR QUALITY / TEAR BREAK
UP TIME TEST
TEAR QUANTITY /SCHIRMER
TESTING


See you next week for soft CL basics and care
products lecture.
Test in two weeks!