The topographic chart
model which we define has the following
characteristics: it is divided into
360 degrees and 8 coronas.
- Division into degrees:
The division into 360 degrees has its
origin in the geometric centre of the
pupil (O1). Drawing a Cartesian axis
in the origin of the pupil, the degrees
begin at the upper part of the axis
Y1 (axis Y of the pupil). In the left
iris they proceed clockwise. In the
right pupil they proceed anti-clockwise.
For this reason, the Y1 axis will coincide
with 360º and 180º, and the
X1 axis will coincide with 90º
and 270º in both irises.
- Division into coronas:
8 concentric coronas are established
which have the following references:
C1, C2, C3, C4, C5, C6, C7 and C8. In
marking out the coronas, iris topography
and location of disorders have been
taken into consideration. Three coronas
are established to delimit the area
between the inside edge of the iris
(pupil edge) and the collar (collarette)
(C1, C2, and C3) and five coronas for
the space between the collarette and
the outside edge of the iris (base edge)
(C4, C5, C6, C7, and C8).
The collar or collarette is an area
which is marked by nature in the form
of a concentric circle (in reality irregular)
which divides the iris into two different
areas. The areas which it marks out
have different characteristics, because
of their different colour or tone or
because they project different signs.
The concentric circles which divide
the iris into coronas have the following
characteristics
- The geometric centre of each of them
is slightly displaced.
The chart is created in this way for
the following reason:
A displacement between the geometric
centres of the pupils and the outer
edge of the pupils (base edge) exists.
In most cases they do not coincide,
thus there is a greater iris surface
on one side of the pupil.
The displacement of the origin of the
base edge with respect to the origin
of the pupil edge occurs in the following
way: Taking the Cartesian axis which
we placed in the pupil origin as a reference,
the displacement of the geometric centre
of the base edge is slightly towards
the lateral angle of the eye and to
a lesser extent downwards. If we draw
an axis along 40 and 220 degrees, the
iris is divided into two areas of 180º
each. However, the area limited by the
lateral angle of the eye between 40º
and 220º has a greater surface
area. The area placed beyond 220º
and up to 40º by the medial angle
of the eye has a lesser surface area.
This pupil displacement varies from
person to person thus making it difficult
to give measurements. We merely reflect
this fact and include it in our topographic
chart. By reflecting the reality of
the iris, we locate the projection areas
more exactly.
- The thickness of some coronas is
different.
The percentage of space taken up by
the coronas is divided as follows:
- Coronas 1, 2 and 3 share the space
occupied as follows: the distance between
pupil edge and the collar is divided
equally, with a width of 33.3% each
in the coronas.
- The distance between the outside edge
of the iris and the collar is divided
in the following proportions:
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