This is Video 7 on Disease Detection Analysis with your Medmont
E300 Corneal Topographer.
Let's open up the patient file
and select
a Corneal Topography. With
an Axial Map selected
we can see that this patient does not have
regular Corneal Astigmatism. There isn't a defined Flat Meridian nor Steep Meridian.
This is Asymmetrical eye and would be difficult to correct with
simple, Sphero-cylinder Over Refraction.
We can selective the Tangential Map and determine
that the point of great its greatest curvature change is approximately
.89 Millimeters
away from the Visual Axis.
This patient's cone is fairly centralized relative to most
Inferior Oval Cones.
However, we can see
the size of the cone by these hotter contours, and the position of the cone in
relationship
with the Visual Axis, and it's not
a very centralized
Corneal Apex.
How do we determine that this is a
diseased eye?
We look at the Simulated K readings and we see a fairly
normal, although;
slightly steeper
Flat K 44.8.
This would not be indicative of Keratoconus. Certainly the 1.5
Diopters of Corneal Astigmatism would not be indicative of
Keratoconus.
However, we could look at the scale range, the range of curvature,
with a 'Normalized' Scale selected,
shows you the flattest the Topographer can read up on this particular eye, and the
steepest the Topographer could read on this particular eye,
and that range of curvature could be indication of normal verses abnormal.
This patient has a Flattest Curvature of approximately 36 Diopters,
and a Steepest Curvature of approximately 50 Diopters, or a range of curvature of
14 Diopters.
Normal Corneas fall under
10 Diopters of scale range, so this patient would be deemed
abnormal.
Eccentricity Value is a measure of
possible disease. The higher the Eccentricity Value the more abnormal the
eye, .8 would be
the threshold for normal, verses abnormal,
and in
Ectatic Eyes, with the
steepest point in the Cornea being close to the Visual Axis,
from the steepest point to the flattest,
if that's a very broad
range of change from center to periphery,
that can be indicated in the Eccentricity value, so the greater the E value
possibly the better indication of disease.
Again, normal
would be under .8 Eccentricity.
Another method of determining if this is a diseased or Asymmetrical Eye, is to click
on the 'Attributes' and look at the 'IS', 'SAI', and 'SRI'
value.
The 'IS' value looks at the Inferior Cornea,
verses the Superior Cornea,
and says what is the average Inferior Corneal Power,
compared to the average Superior Corneal Power.
If the Inferior Cornea is greater than 1.5 Diopters
steeper than the Superior Cornea,
that could be indication of
Keratoconus or Pellucid
Marginal Degeneration.
In this case the patient has 2.67
Diopters
steeper Inferior Corneal shape, then Superior Corneal shape,
and that would be deemed abnormal.
Surface Asymmetry Index
looks and the Oblique Axes
and determines
if the curvature across
this
hemi-chord
is similar in shape
to the surface across this hemi-chord.
Are the two
very similar to each other, or symmetrical across that
axis or asymmetrical comparing one side to the other,
and the same thing goes for the
opposing meridian.
Is this
axis
similar to this
axis,
and the higher the Surface Regularity Index is the more abnormal the eye.
The threshold for normal verses abnormal is .8.
So the higher the 'IS'.
the 'SRI', and the
'SAI' values are, the more asymmetrical the eye shape.
And in review,
if you have a scale range greater than 10 Diopters that would be
considered abnormal. If you have Eccentricity value above .8, that
would be considered abnormal.
'IS' value greater than 1.5
Surface Asymmetry greater than 1,
and Surface Regularity greater than .8 would be
indicative of abnormal or possible
diseased eye.
This concludes our section on
Disease Detection Analysis with your Medmont E300 Corneal Topographer