Download Contact Lenses

Week 3
Contact lens basics and care products
Soft Contact Lens Design
 Spin casting
 Dry casting
 Lenses are formed in a mold
 Liquid plastic is poured into a
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.
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 design
 Lathe cutting
 Lenticular
 Rigid and soft contact lenses.
 Rod of monomer (plastic) cut
 Adds bulk to a plus lens or
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.
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 Design
 Aspheric
 The back surface of the
lens is NOT spherical.
 Used on astigmatic
patients with mild to
moderate astigmatism.
Contact Lens Basics
 Base 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 Design
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Advantages
Comfort
No rigid wear schedule
Healthy
Hugs eye
Easy to fit
Soft CL’s rarely fall out
Over wear reaction is
minimal.
 No glare or photophobia
 Disadvantages
 Astigmats are harder to
fit.
 Variable VA.
 Lenses are fragile.
 High risk of infection.
Types of soft lenses
 Spherical Conventional
 Spherical Daily wear
 Spherical extended wear
 Bifocal
 Toric
 Theraputic (PlanoT)
 Aphakic
 cosmetic
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 systems
 Peroxide based cleaning
 Iospropyl Alcohol Cleaning
 No preservatives
 Lenses have to be exposed for
 Significant bacteriocidal and
systems
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.
systems
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.