Week 3Contact lens basics and care products

Soft Contact Lens DesignSpin casting

Lenses are formed in a mold that spins liquid plastic.

Curvature is predetermined by the shape of the mold, amount of plastic, and spin rate.

Least expensive to make but have steeper fitting characteristics.

Dry casting

Liquid plastic is poured into a concave (female) mold of a specific curve. The back surface mold (male) is compresses into the female mold creating the base curve.

The mold is then placed into an oven and removed from the molds.

Cost effective for making custom made lenses.

Soft Contact lens designLathe cutting

Rigid and soft contact lenses.

Rod of monomer (plastic) cut into buttons and put onto a lathe and then cut front and back surface by a diamond blade for precision.

Hydrated when finished.Allows for a variety of

shapes and center thicknesses.

Lenticular

Adds bulk to a plus lens or reduces mass on a minus lens.

Only used for more than +/- 4.00D, usually in rigid lenses.

A rounded or bevel edge can be added for comfort.

Soft Contact Lens DesignAspheric

The back surface of the lens is NOT spherical.

Used on astigmatic patients with mild to moderate astigmatism.

Contact Lens BasicsBase Curve (BC)The base curve is the

primary curve of the CL that is designed to match the contour of the central cornea.

Sagittal depth is the vertical depth of the CL. This is also referred to a “vault”. Some labs use roman numerals to label for vault (BC).

The steeper the lens, the greater the sagittal depth will be. The flatter the lens, the flatter the sagitall depth will be and the chord will be greater.

Base curve

Steep median flat

______________________________________________8.0 8.5

9.0

Diameter (D)The overall diameter is a

linear measurement of the lens from edge to edge.

Soft CL’s should have a diameter 1 to 1.5 mm larger than the iris diameter.

Fitting the CL can be manipulated by changing the diameter. A loose lens can be tightened by increasing the diameter and a tight lens can be loosened by decreasing the diameter.

Center Thickness (CT)The center thickness is the

thickness of the geometric center of the lens. The CT determines both O2 permeability and stability of the lens.

The lens should be as thin as possible in order to get the greatest amount of O2 to the cornea.

Thicker CT lenses can be used for dry eyes or mild astigmats.

CT and water content are the major factors in determining if the CL is approved for daily wear or extended wear.

Extended wear (up to 6 nights) must have a 38% water content and have a CT of 0.03 to 0.07 mm.

Extended wear lenses also are available in 55% water content but have a 0.08 to 0.10mm CT.

The more water content, the thicker the lens will be, allowing less O2 to the cornea.

Soft Contact Lens DesignAdvantagesComfortNo rigid wear scheduleHealthyHugs eyeEasy to fitSoft CL’s rarely fall outOver wear reaction is

minimal.No glare or

photophobia

DisadvantagesAstigmats are

harder to fit.Variable VA.Lenses are fragile.High risk of

infection.

Types of soft lensesSpherical

ConventionalSpherical Daily wearSpherical extended

wearBifocalToric Theraputic (PlanoT)Aphakiccosmetic

Cleaning systems Daily Cleaners

The efffectivness of the systems depends on adequate daily cleaning.

The CL is cupped in hand and rubbed with the cleaner with your finger. Some systems are now “no rub”.

After cleaning you must disinfect the lens to protect against microbe, viruses and fungi.

Some of these cleaners have preservatives in them that can have an adverse reaction for the CL wearer.

Enzymatic cleaners can clean up proteins from the tear film that may build up on the lenses. This is recommended for conventional Soft CL’s as they can be worn for up to 2 years.

Reactions to daily cleaners: Corneal staining Ocular irritation Lens dryness Ocular trauma, if used improperly Acute red eye

Preservatives can cause: Chronic red eye (bloodshot) lens discoloration

Cleaning systemsPeroxide based cleaning

systems

No preservativesLenses have to be

exposed for 10 minutes and neutralized for at least 20 minutes to 4 hours in sterile saline.

Peroxide kills all microbes, fungi, viruses including HIV and Acanthomoeba.

If not neutralized properly, the CL can burn the corneal epithelium.

Iospropyl Alcohol Cleaning systems

Significant bacteriocidal and solvent cleaning ability.

To harsh to use for rigid lenses, causing brittleness and cracking.

What the patient need to know! Always wash your hands

before handling lenses. NEVER skip your daily

cleaning program. Do not skip a step in the daily

cleaning routine. Keep the lens case clean. If a lens drops on the floor,

countertop, ect… you MUST clean and disinfect the lens before putting in into your eye.

Do not touch the tip of the cleaning system bottle to anything or it will no longer be sterile.

Do not mix and match products. They are designed to work together.

If your eye(s) get red or sting after you put the lens(es) in, take them out immediately. Re-rinse and put back in only if the redness and stinging subside. If the problem persists, remove the lens and call the doctor.

NEVER put a CL in your mouth. Mouths have lots of bacteria that can cause infection. Your urine is actually more sterile!!

You, as a tech, are the person who needs to tell the patient all the rules for CL’s so the patient is successful.