| |
| What
is Astigmatism? |
| Astigmatism
is a refractive
error where
in parallel
rays of light,
coming from
infinity,
after refraction
through the
eye, do not
come to a
point focus
on the retina
when the
accommodation
is a rest. |
| |
What
are the
causes
for
Astigmatism
? |
| |
| (1)
Corneal |
| |
(A)
Congenital |
| |
(B)
Acquired
|
| |
i.
Following
surgery to
the eye (cataract,
corneal) |
| |
ii.
Corneal
scar |
| |
iii.
Pterygiumiv |
| |
iv.
Large
chalazion
|
| |
| (2)
Lenticular
|
|
(A)
Congenital
à
Subluxation
of lens,
lenticonus. |
|
(B)
Acquired
à
Subluxation
of lens |
| |
| What
are the types
of astigmatism? |
- Regular
astigmatism:
- Here
the 2
meridia(
greatest
&
least
curvature)
with
the minimum
and maximum
refraction
are at
right
angles
to each
other
and they
correspond
to the
vertical
and horizontal
meridian.
- Simple
myopic
astigmatism:
Rays
from
one meridian
come
to a
point
focus
on the
retina
and from
the other
in front
of retina.
- Compound
myopic
astigmatism:
Rays
from
both
meridia
are myopic
and come
to a
focus
in front
of retina
but at
different
places.
- Simple
hypermetropic
astigmatism:
Rays
from
one meridian
focus
on the
retina
from
the other
meridian
behind
the retina.
- In
compound
hyupermetropic
astigmatism
rays
from
both
meridia
come
to focus
behind
the retina
but at
different
places/parts/points.
- Mixed
astigmatism:
- Rays
from
one meridian
are focused
in front
and rays
from
the other
meridian
are focused
behind
the retina.
|
