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 2. Aqueous layer 3. 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 LAYER OF THE CORNEA  Epithelium  Bowman’s layer  Stroma  Decemet’s membrane  Endothelium

 Corneal epithelium 1. 5 to6 cell layers thick.( 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 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.

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 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

TRICHIASISENTROPIAN

FLOPPY EYELID SYNDROME

GRAVE’S DISEASEECTROPIAN

SCLERITIS

DRY EYE WITH STAINING DRY EYE WITH PUNCTATE STAINING

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 flow 1. Schirmer 2. Hypofluorescence  Tear stability 1. TBUT 2. Evaluation of lipid layer  Condition of ocular surface 1. Fluorescein staining 2. 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!