Transcript Rigid lens verification

Week 14
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After taking all the measurements, fitting a trial
lens, and ordering the lens, we must verify the
lens once it is received.
We do this to make sure the parameters we
ordered are correct.
We do this BEFORE we dispense the lens.
The parameters we verify are:
Power
Base curve
Diameter
Center thickness
POWER VERIFICATION
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The power of the lens must
be checked for accuracy the
same way we verify a pair of
spectacles before dispensing
to the patient.
We do this by using the
lensometer.
The lens is placed convex
side up on the lens stop of
the lensometer.
You measure the lens the
same way as a pair of
glasses, the lens will be
spherical.
LENSOMETER
BASE CURVE
VERIFICATION
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Base curve is just as
important as power and
diameter and must be
verified.
To verify the base curve
is what we ordered, we
use the radiuscope.
RADIUSCOPE
USING THE RADIUSCOPE
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The lens holder is
removed and ONE drop
of water is placed in the
“depression”. The lens
floats on top of the drop
of water, convex side
up.
RADIUSCOPE
USING THE RADIUSCOPE
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The lens holder is put
on the table with the
water and lens in it.
This must be placed so
the green light from the
radiuscope is directly
on the center of the lens.
The table can be rotated
and shifted to center the
green light.
USING THE RADIUSCOPE
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Look through the eyepiece
and focus the star shaped
mire by turning the knob
on the right.
Use the knob on the left to
move the number scale to
zero.
There is a small knob
under the eyepiece to
focus the number scale.
USING THE RADIUSCOPE
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Once the star is in focus and
the number scale is at zero.
Measure the base curve by
turning the star focusing
knob away from you. The
star will disappear and then
will come back into focus,
the scale reading will also
move away from zero.
Once the star comes back
into focus, use the fine focus
knob.
USING THE RADIUSCOPE
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When the star mire
comes into focus the 2nd
time, it may not be
centered.
You can center the star
by rotating the table to
bring the star into
center again.
USING THE RADIUSCOPE
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The base curve is read by
the position of the number
scale line.
This is in radius of
curvature and is in mm’s.
There is a conversion
chart to convert to
diopters, which is how we
order BC.
This reading is about 8.41
DIAMETER
VERIFICATION
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The diameter of the lens
must be verified before
fitting it on the patient.
To do this, you can use a
pd ruler and measure the
diameter or a “V” gauge.
There is a channel in the
shape of a “V” in the
ruler.
The lens is dropped in the
channel and when it stops,
the diameter is read on the
side of the ruler in mm’s.
V GAUGE & PD RULER
CENTER THICKNESS
VERIFICATION
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Center thickness of the lens is
important, especially if you
specified a thinner or thicker lens
than the norm.
Lenses are generally fit as thin as
possible for better O2
permeability. Keep in mind a high
powered convex lens will be thick
to begin with, so you may want to
see what the lab can do to make
the lens thinner.
To verify the thickness, we use a
radiuscope,if it has a thickness
gauge on it or a thickness gauge.
RADIUSCOPE &
THICKNESS GAUGE
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After the lens is verified, we inspect for scratches,
chips and warping and then put it on the patient’s
eye for evaluation.
We evaluate by checking:
Positioning and movement
Condition
Visual acuity
Flexure
Residual astigmatism
Comfort
Fluorescein pattern
Corneal and eyelid integrety
FLEXURE
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Flexure occurs when the lens
“bends” over the cornea
(astigmatic ridge) when the
patient blinks.
We can check for this with
keratometry. With the lens on the
eye, after the patient blinks, the
mires will change. This happens
because the lens bends in a
different shape over the cornea.
We can also check for this with
retinoscopy. With the lens on the
eye, flexure is evident when the
reflex suddenly changes after
blinking.
VA AND RESIDUAL
ASTIGMATISM
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Check the VA and make sure it is
what you expected it to be, if not,
over refract and make
modifications.
If there is astigmatism not
corrected for by the “tear lens”,
this may be residual astigmatism.
This is not corneal or refractive
astigmatism but lenticular
astigmatism and is caused by the
crystalline lens.
This should have been dealt with
before fitting with a trial lens.
Residual astigmatism is usually
tolerated if it is less than the
amount of the spherical power.
POSITIONING AND
MOVEMENT
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The lens should always
move 1mm upon blinking. If
there is no movement, the
lens is too tight. If the lens is
moving all over or too much,
it is too flat.
The lens should be
positioned over the pupil,
centered. The lid attachment
fit should be under the
upper lid but centered over
the pupil and move at least 1
mm after blinking.
COMFORT
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New gas perm lens
wearers may take up to 6
weeks to build up
tolerance for the lens but if
an established wearer that
complains of discomfort
or pain, you have to find
out why.
What are some reasons a
patient will complain of
pain?
FLUORESCEIN PATTERNS
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Fluorescein can stain the tears
so you can evaluate the tear
film under the lens.
If you encounter a dumb bell
shape pattern, this signifies a
large amount of astigmatism
and you may need to modify
with a change to the BC, D or
making the lens a bi toric.
A bi toric has 2 base curves,
one horizontally and one
vertically. This is typically
used with large amounts of
astigmatism, -3.00D or more.
FLUORESCEIN PATTERNS
FLOURESCEIN PATTERNS
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It is important to remember that
even though the lens has a steep
or flat fit does not mean that it is
a bad fit.
lens is steep or flatbecause that
is the way you chose to fit the
lens. The tear lens is making up
for the cylinder that was not
ground into the lens. There is
supposed to be a fluorescein
pattern.
When evaluating the fluorescein
pattern, you should know what
to expect before looking under
the slit lamp. If you fit an apical
fit, the lens should fit tight, just
not too tight !
CORNEAL INTEGRITY
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This is regarding the patient that
has already worn CL’s.
Always inspect the cornea before
fitting with new lenses.
Check with fluorescein under the
slit lamp for any staining,
scratches, ulcers, erosion, and or
edema that may prevent the
patient form wearing lenses.
Tear film integrity should always
be tested as well.
These types of problems need be
heal before wearing lenses.
All of the above should be
evaluated in the exam, well before
the fitting starts.
CORNEAL ABRASION
That’s it !
See you next time for lens
modifications!