This is Video 8 on
employing the Medmont E300 Corneal Topographers, Contact
Lens Module.
Lets open up a patient file,
select a Topography.
Click on 'Home',
and then,
'Contact Lens'.
When you first start out select the manufacturers that are available from
North America, (or your Country)
you'll note
the boxes presently checked are all the manufacturers available
from North America
that have put their Contact Lenses designs into Medmont Studio.
You can click 'Ok'.
You won't have to open up this manufactures icon
unless a new manufacturer has been added
to a recent
release of the Medmont Studio software.
Otherwise you're just going to enter the patient's RX if it isn't
already entered in the patient file, so on the main window
where you enter patient information, if you
punch in your
patient Spectacle RX it automatically comes up in the contact lens design
window.
Next let's select
the
specific lens we want to fit on this eye.
Let's design for this patient a simple Multi Curve that we can get from any
lab in the world.
Say 'Okay'.
The software will then drop a theoretical contact lens on top of your
patients eye, and it
will
default the Base Curve generally very close to Flat K.
You will
manipulate the
contact lens parameters
to produce
the best possible
Fluorescein pattern.
And we start
by first determining
Visible Iris Diameter,
and we click on 'Annotate',
and then ,Ruler',
and
measure
Visible Iris Diameter.
We are getting a
close to 12 Millimeter
HVID.
We'll select to delete that annotation and you can do that by, right-clicking,
and then deleting.
Next let's pick up the contact lens,
and place it some more near the,
Geometric Center.
So ignore the Placido, and center the contact lens
in relationship
with the Sclera.
So looking at the white of the eye
around here
and placing your contact lens as it appears centered, not
to the Placido Rings that you can see
just outside of the lens, but more so
to the Iris or
Limbus.
Next
lets choose the lens diameter that we would prefer.
In this case we fit the patient with a 9.5.
'Apply'. And
click your cursor in the center
and measure the Tear Film Clearance, or 'TFC' along the right hand side
here.
It's indicated to be 24 Microns.
For Fluorescein to be seen by
the human eye
it must be
in excess of 20 Microns.
In other words, for us to see Fluorescein behind our Slit Lamp,
we must have a
thickness of Tear Layer
and density of Fluorescein Molecules
somewhere in the neighborhood of 20 or more Microns.
If you want to see a nice even central Fluorescein Pattern
on your actual fit
you must have a Tear Film
Clearance at the Apex of at least
20 Microns.
With 24 Microns
that would be comfortable, we are looking for somewhere between 20 to
25 on a normal eye.
Next
take this white axis line and find the point on the graph
where the lens seems to land
on opposing sides,
and it appears
that on our , With the Rule Corneal Astigma,
this lens lands
very close to nine o'clock,
and again on its opposing
side at three o'clock,
so we have Apical Clearance of approximately 24 Microns
down to touch
at nine o'clock, you see the dotted section of the line here corresponding
with the dotted
section on the graph,
solid section of the line here corresponding
solid section there.
So we have our
24 Microns Apical Clearance
heading down to three o'clock we have our touch
and then our edge lift,
our Apical Clearance
toward nine o'clock,
with our edge lift.
So this is
and ideal relationship to keep the lens on lateral center.
Then we take our axis line and drag it to the Vertical Meridian and we can see
that this patient has a fair amount of Tear Layer Clearance
heading toward twelve
and heading toward six o'clock,
dotted section of the line here corresponding with the dotted section of
the line here,
solid section of the line there corresponding with solid section here. If
we click our cursor at the edge of the inner pink circle which is
the, Optic Zone Junction.
we're showing 41 Microns heading North,
and
85 Microns heading South, or inferior.
This is a
significant amount of Inferior Clearance and would likely cause
the lens to tilt and rock across the Vertical Meridian because there is
excessive
lift of the lens at twelve and six o'clock.
This is a Fluorescein pattern of the actual lens on eye
designed from our Medmont,
and you can see that
this contact lens
has an acceptable level of Apical Clearance.
Fluorescein can just be seen under the center of the contact lens, so this is
good, we have landing at nine o'clock and landing at three o'clock
with a healthy edge lift on both sides.
The problem however; is the
significant Inferior Lift,
and Superior Lift, that's causing the lens to tilt and also
ride high.
This patient needs a Toric GP Lens.
So let's go back to our contact lens and try to better designed it from our Medmont
software.
Click on 'Display' to bring up the, 'Edit' box again,
and select
'Toric'.
Now we create two
Meridians of Curvature,
and 'Apply' that.
The same rules apply to the,
Toric Contact Lens.
We want to create a lens that lands at three and nine o'clock,
and lifts at twelve and six o'clock.
Presently our contact lens is
not landing across the Horizontal Meridian, the Horizontal Meridian,
you can also see is our Flat Meridian by that blue line.
So let's steepen the Base Curve along the Flat Meridian
by a half Diopter step.
On the Vertical Meridian,
we appear to be very near to bearing or definite bearing at, twelve and six.
We want our contact lens to lift so it can freely move with each blink
and create a good Tear Pump.
So let's
flatten the lens across the Steep Meridian
so that our contact lens will
be able to move with each blink. And
click 'Apply'.
Now we have a lens that lands at
three and nine o'clock
and along the Vertical Meridian it lifts
at twelve and six o'clock.
This would be ideal for a good RGP fit.
The last thing that one might do is adjust the, Optic Zone Size,
to soften its Peripheral Landing. Notice this narrow,
Point of Bearing,
and a very steep angle as the lens comes back toward the Cornea and touches.
Lets increase the Peripheral Curve Width,
reduce the, Optic Zone Size, slightly
and see what that does to those Points of Bearing. When we apply
notice how you shallow out
how that lens comes back towards the Cornea,
and creates a much wider
softer Area of Bearing.
Now here's the actual lens that was fit
by these same parameters,
and you notice
you've got virtually 360 Degrees of alignment, but
appears to be a very thin channel
at twelve and six o'clock which would allow the lands to freely
move
with each blink.
So the Tear Film definitely shows
what appears to be bearing at
three and nine o'clock and then
that bearing thins out throughout twelve and six o'clock to allow for the lens
to freely move
in the Vertical Meridian.
And we also have much better centration then we had
with the Spherical GP Lens.
This concludes
the section on Using the Contact Lens Module in your Medmont E300
Corneal Topographer