Download Contact Lenses Week 5

Toric lenses and soft CL problems
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Toric Lens
Lenses used to correct
astigmatic/sphericocylin
drical patients.
Toric lenses have a
ballast or “weight” on the
bottom of the lens to
help keep the axis where
it should be.
The lens may rotate after
blinking but will return to
the desired axis because
of the ballast.
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Each toric lens has
markings on the lens
itself to help the
examiner determine if
the lens is fitting
properly.
Most toric lenses have
markings or “scribe
marks” inferiorly at 6:00
and 2 more scribe marks
at 5 and 7.
The people who will be
most successful in torics
will have a cylindrical
axis close to 90 and 180
degrees.
Types of ballast in toric lenses
Types of scribe marks on toric
lenses.
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People who will not do
well in toric lenses:
Patients with tight lids.
Narrow palpebral fissure.
Poor tear quality or
quantity.
Refractive astigmastism
grater than +2.75D.
Toric lenses are available
from +4.00 to -8.00 in
spherical power and 0.75 to-2.50 in
cylindrical power.
Base curves =8.3 to 8.9
Diameters=13.8 to 14.5
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Base curve and diameter is
fit the same as spherical CL.
Refract patient to get power
needed.
Transpose power to minus
cylinder.
Put trial lens in that power
on eye. Allow the lens 2030 minutes to settle.
Take VA, if VA is NOT what
expected, over refract
spherical/cylinder power
only. Put axis to trial lens
axis.
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Evaluate BC, D and scribe
marks with slit lamp exam.
If the slit lamp exam reveals
the scribe marks are in
good position, and BC and
D are fine you are done!
If BC and D are not correct,
note in chart and make
modifications.
If hash marks are not in
correct position, use the
Lars principle.
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Transposition
Refraction=
-5.50+150X90
Transpose to –cyl=
-4.00-150X180
Refreaction=
+3.25+0.75X90
Transpose to – cyl=
+4.00-0.75X180
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Remember…….
If the spherical
power is+/- 4.00D,
You will need to
convert the power
to compensate for
vertex distance to
get the effective
power.
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Over-refraction
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If VA is not what was
anticipated, you need to
modify the
spherical/cylindrical power of
the trial lens to improve VA.
AXIS MUST BE SAME AS TRIAL
LENS.
With the trial lens on the eye,
refract the patient with
spherical/cylindrical power
only, to see if the VA will
improve with more or less
spherical/cylindrical power.
If you get improvement,
modify trial lens power.
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Trial lens power=
-4.00-1.25X90
Over refraction=
+0.50+0.25X90
Add over refraction to existing power
after transposing
+0.75-0.25X180
-3.25-1.50X90 new trial lens
Trial lens power=
+8.75-2.25X180
Over refraction=
-0.75+0.50X180
Add over refraction to existing power
after transposing.
-0.25-0.50X90
+8.50-2.75X180 new trial lens
Do not try to refine the axis. The axis
stays the same as the trial lens!!!
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LARS Principle
Lars rule(principle) or
clockwise/counterclockwi
se rule can be used to
compensate for the
misalignment of the lens
axis so it will match the
patient’s refractive axis.
Sometimes, even though
there is a ballast, the CL
doesn’t stay where it is
supposed to and then
the axis will be “off”
causing blurry VA.
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Lars is an acronym for
Left, add, right, subtract.
When looking through
the slit lamp, if the hash
marks are rotating to the
fitter’s left, the number
of degrees off rotation
should be added to the
trial lens axis.
If the hash marks are
rotated to the fitter’s
right, the number of
degrees off should be
subtracted from the trial
lens axis.
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LARS
Picture the CL as a clock, there
are 60 minutes on the clock (360
degrees).
Every “minute” equals 6 degrees.
Every “minute” the hash marks
are “off” equals 6 degrees of
misalignment.
A hash mark that orients at 7
o’clock instead of 6 o’clock is 5
“minutes” off.
6 degrees X 5 minutes= 30
degrees.
The axis is 30 degrees off of
where it should be, causing a
blurring effect and decreased
VA.
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Trial lens=
-4.00-2.25X90
Figure 3.7= 3 minutes
off=18 degrees.
The hash marks are to the
fitter’s left, so we ADD 18
degrees to the trial lens
axis.
New trial lens axis=
-4.00-2.00X108.
Figure 3.8, also 18 degrees
off but we SUBTRACT from
the axis because it is to
OUR right.
New trial lens axis=
-4.00-2.25X 72
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Bounce back test
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CL will center and hash
marks will be on 5,6,&7
before blink.
After blink, the hash
marks will rotate.
2-3 seconds after blink,
the hash marks should
return to 5,6 & 7 and be
centered on eye.
If there is NO movement,
the lens is too tight. You
want the lens to rotate
and move, just make
sure it rotates and moves
back where it belongs!
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Perform ocular exam.
Determine power, BC,
and D.
Put trial lens on eye for
VA and fit evaluation.
Test VA, do over
refraction if needed.
Transpose and
recalculate new trial lens
power.
Do slit lamp exam for
trial lens fit ( to flat or
steep) and look where
hash marks are aligned.
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If misaligned, apply LARS
method and note new
axis.
Take all changes noted
and apply to a new trial
lens.
Reapply new trial lens to
eye and start all over!
Hopefully all of the
modifications are correct
and the fit and VA is
perfect.
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Problems and
complications can
happen because of
hypersensitivity, not
enough oxygen delivery,
bacterial, viral or fungal
colonization,
inflammatory response
or improper fitting. We
need to fit the lenses
properly and educate the
patient so these
problems can be avoided
or recognized and fixed.
Micro mechanical
trauma, corneal abrasion
Staining on corneal surface due
to dry eye or insuffient cleaning
Corneal edema due to
hypoxia
CL comlications
Mechanical, torn soft CL
Fungal cells on corneal
conjunctivitis
Subepithelial infiltrates due to
chronic hypoxia, white blood cells
collect in epithelial pockets.
Ulcerative bacterial
keratitis
pseudomonas
pseudomonas
acanthomoeba
Giant papillary
conjunctivits
More GPC
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Your instruction and fitting are very
important for the health of the patient’s eye.
Make sure the lens is fit properly. Always
evaluate your fit under the slit lamp to ensure
a good fitting lens.
Make sure the patient know the correct way
to handle and clean the lenses.
You are the person responsible for teaching
the patient care and handling. Never let a
patient leave without understanding the rules!
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See you next week for insertion and removal.
Have a great week.