OCULUS Easygraph 70620 Instruction Manual page 57

Note ⇒ The refractive index always has to be
entered manually (i.e. in the case of toric lenses). It is
not stored along with the other contact lens
parameters in the contact lens database.
To the right of the "n" field is a selection field for
specifying the name of the material; n is then
adjusted accordingly.
MAT.TXT" contains a list of material names and their
corresponding refractive indices. The user can
extend this file with a text editor, e.g. WordPad.)
Any of three different types of toric lenses can be
selected in the "Test lens toric" field:
•
Toric
The posterior surface of this contact lens is toric
(better fit), whereas the anterior surface is
spherical.
Due to the difference in refractive power between
the contact lens material and tear fluid, the toric
posterior surface causes an artificial, or induced,
astigmatism.
power values, this effect can be advantageous in
certain cases.
Due to its spherical anterior surface this type of
lens does not allow for additional cylindrical
correction.
•
Bitoric compensated
This lens type has a toric posterior surface as
well as a
The induced astigmatism which would normally
be caused by the posterior surface is here
Instruction Manual Easygraph
(The file "C:\TOPO\N-
Depending on the patient's
toric anterior surface.
compensated by a cylindrical component in the
anterior surface. With the induced astigmatism
neutralized by the shape of its anterior surface,
this type of contact lens corrects corneal
astigmatism as a spherical contact lens does,
while at the same time offering the advantage of
a better fit by virtue of its toric posterior surface.
Due to the neutralization of any induced
astigmatism the corrective effect of this contact
lens does not depend on its rotation (inclination).
However, as in the case of toric lenses, this lens
type does not allow for additional cylindrical
correction.
As the refractive index is irrelevant in the case of
bitoric compensated lenses, the "n" field and the
material selection field are both deactivated.
•
Bitoric
Bitoric lenses are toric on their anterior as
well as their posterior surface. The axis
position of the two surfaces are independent
of one another, making it possible to first
determine the torus of the posterior surface
solely for the purpose of a proper fit and then
derive the required torus and axis position of
the front surface from the overrefraction.
Bitoric contact lenses have to be calculated
by the manufacturer, and the "Sph (D):" field
is therefore deactivated.
After selecting the desired contact lens type it is
advisable to first click the [Suggestion] button in
order to obtain an optimal test lens for the selected
lens type.
Note ⇒ Clicking the [Suggestion] button does not
permit you to change the type of contact lens. This
function makes no suggestions as to the type of
contact lens, but rather determines the optimal test
lens for a manually preselected lens type.
Page 57