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 layer2. Aqueous layer3. Mucous layer

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 epithelium1. 5 to6 cell layers thick.( 50-60 microns thick)2. 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 membrane1. Produced by the endothelium. Corneal endothelium1. Single layer of cells.2. Endothelial cells can not regenerate.3. Acts as a pump to maintain dehydrated cornea.

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 STAININGDRY 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.

Tear flow1. Schirmer2. Hypofluorescence Tear stability1. TBUT2. Evaluation of lipid layer Condition of ocular surface1. Fluorescein staining2. 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!