This video describes the fitting
of the No7 Quasar Toric Lens
through the Medmont E300 Corneal Topography Fitting Software.
Start with a good quality image
then go to the 'Home' tab
and Contact Lens icon. Select from the 'Design' menu
the No7 Quasar entry in your Spectacle RX
and Vertex, then click 'OK'.
You can alter the lens diameter as required based on your Measured
Visible Iris Diameter. Then click on the edge of the contact lens and center it
to what you feel is the Geometric Axis of the Eye,
in other words center the contact lens as
you would like to see it centered through to Slit Lamp. Then click your
cursor in the center,
over the Center pink dot, which is the Geometric
Axis of the Contact Lens. Measure the 'TFC'
or Tear Film Clearance, in this case we predict to have 0 Microns
of fluid between Lens and Cornea. Clearly
a steeper Base Curve is required, let's therefore,
steepen the Base Curve a couple of clicks and 'Apply'.
That takes us to 16 Microns.
Ideally were looking for very close to 20. Let's try
another quarter step or .05 Millimeters.
This takes us to 24 Microns of fluid between Lens and Cornea.
This is quite optimal, we have good healthy landing
at 3 and 9 O'clock; however
the amount of fluid running through the Vertical Meridian
is excessive. When we click are cursor here
we're at 58 Microns, click our cursor here, we're at 75 Microns.
So before the Peripheral Curves kick in
we're well above the optimal 40 Micron threshold of fluid
between Lens and Cornea, in other words, when your Fluid Layer
at the edge of the Optic Zone Junction or just before the Peripheral
Curves kick in, is in excess 40 microns of fluid,
in this case somewhere around 60, on the opposite side somewhere around
80, this will create an
unacceptable amount of rocking of the Lens back and forth,
instability, and discomfort for the patient. Lets therefore select
the 'Toric' option and 'Apply'. This creates
now a radius across the Flat Meridian and a different radius across the Steep
Meridian,
a Bi-Toric Lens. The next step
is to measure the Apical Clearance,
make sure we're very close to our target of 20.
In this case we are. Then look for the axis of greatest bearing,
and it appears that running through the Vertical Meridian or close to the
Vertical Meridian
we have our landing at 12 O'clock and our landing at
6 O'clock. So the path of least resistance of the lens maybe Nasal and
Temporal
well its movements vertically and healthy Tear Pump
may be hindered by the bearing at 12 and 6. Lets
take our Flat Meridian, the blue line, and attempt to
steepen the Lens so it will land across that Horizontal Meridian.
Lets 'Apply' our change, see if we can move that bearing around. We will try another
two clicks now we're starting to get the Lens
coming around the corner and landing closer
to 3 and 9 o'clock. When we click are cursor in the
center we've now increase the Apical Clearance to 38 Microns.
Let's flattened both the Flat and the Steep Meridian
equally, see if we can reduce that down to close to 20.
Now we have the target amount of fluid at the Apex of the Lens,
and we have landing
very close to 3 and 9 o'clock, which is optimal.
This should keep the Lens on Lateral Center.
Then running through the Vertical Meridian we have a
fairly linear fluid layer
possibly we could reduce a little bit of this fluid
near 12 and 6 o'clock by steepening the Steep
Meridian by itself. And that's creating
a little flatter of a line or more linear relationship between Lens and
Cornea.
Let's try one more click, now we see a much more straight line
surface this gives us landing
close to 3 and 9 o'clock and a good channel running through the
Vertical Meridian.
So fine that ideal point where you have
landed the Lens as close to 3 and 9 o'clock
as possible. While
having that healthy channel running through the Vertical Meridian.
Then once you've created that optimal pattern
you can ordered those final parameters
from the lab here under the 'Lens Parameters'
window.