This document provides an overview of astigmatism including its definition, causes, types, signs and symptoms, diagnosis, and treatment. Astigmatism is a refractive error where the eye focuses light on multiple points rather than a single point due to an irregularly shaped cornea. It is usually caused by corneal abnormalities and can be classified based on the axis of refractive error, degree of refractive error, and type of focal points. Common signs include blurred vision, eye strain, and tilting of the head. Diagnosis involves visual acuity tests, keratometry, and refraction tests. Treatment options include spectacle lenses, contact lenses, refractive surgery, and keratoplasty.

3. Contents of lecture :
A. What is astigmatism.
B. Incidence.
C. Optics.
D. Etiology.
E. Classification.
F. Signs & Symptoms.
G. Diagnosis .
H. Treatment .

4.  What is Astigmatism :
 Astigmatism is a refractive error of the eye in
which there is a difference in degree of
refraction in different meridians .
 (i-e The eye has different focal points in
different planes ) .
 For example: The image be clearly focused
on the retina in the horizontal (sagittal)plane,
but not on the retina in the vertical
(tangential ) plane .
 Astigmatism causes difficulties in seeing fine
details and in some cases vertical lines (e.g
walls) may appear to be leaning over .

7.  Most astigmatic corneas have two
curves, a steeper curve and a
flatter curve . This causes light to
focus on more than one point in the
eye resulting in blurred vision .
The cornea is normally spherical
although In people with astigmatism
it may be shaped like a rugby ball
or oval instead of tennis ball .
In astigmatism the front surface of
the eye has an irregular shape like

8. An egg verses a non-astigmatic eye,
which is shaped like an orange .
NON
Astigmatic
Astigmatic

10. Optics of Astigmatism :
 An astigmatism, the rays of light
from one sector fall on one point &
rays of another sector falls on anther
point . In other words a point focus
of light cannot be formed upon the
retina .
The configuration of the rays
refracted through the astigmatic
surface (toric surface ) is called
strums conoid.

12. Thus there are two focal points
separated from each other by a
focal interval of strum .
The length of this focal interval is the
measure of the degree of
astigmatism and the correction of
the error can only be accomplished
by reducing these two foci in to
one.

13. Incidence:
No eye is perfectly stigmatic as
almost all the individual have a
minor degree of physiological
astigmatism .
About 60% cases of refractive error
have astigmatism which needs to
be corrected .
Occurs in equal frequency in males
& females .

14. Approximate distribution according
to a degree of astigmatism is .
The most common type is
compound myopic followed by
compound hyperopic, mixed,
simple myopic & simple hyperopic .
0.25 to 0.5 50%
0.75 to 1.0 60%
1.0 to 4.0 24%
>4.0 1.0%

15.  On study as
 With the rule 38%
 Against the rule 30%
 Oblique 32%
 Etiology :
 Corneal Astigmatism .
It occurs due to abnormalities of
curvature of cornea .
Most common cause of Astigmatism
 Foe example : ( keratoconus
pterygium, mild corneal opacities ,
chalizon .

16. Lenticular Astigmatism:
It is comparatively rare it may be .
 Curvatural ……. Lenticonus .
 Positional ……. Congenital tilting
 Traumatic subluxation of lens .
 Index ……. Developing
cataract nuclear sclerosis .

17. The severity of astigmatism can be
classified as follows :
Mild Astigmatism < 1.00 D
Moderate 1.00 to 3.00 D
Severe Astigmatism 2.00 to 3.00 D
Extreme Astigmatism >3.00 D .

18.  Astigmatism
( Regular ) (Irregular)
Mixed ( Myopic &
Hyperopic)
Compound (Myopic & Hyperopic)
Simple

19.  Astigmatism –Based on asymmetry of
structure .
 Corneal Astigmatism – astigmatism
due to an irregularly shaped cornea.
 Lenticular Astigmatism – astigmatism
due to an irregularly shaped lens .
 Astigmatism – Based on axis of the
principle meridian .
 Regular Astigmatism .
Against the rule.
with the rule .

20. Oblique astigmatism.
Bi oblique astigmatism.
Irregular astigmatism.
 Regular astigmatism :
The astigmatism is said to be regular
if there is different refraction by the
eyes in to meridia at right angle to
each other .
Can be corrected with spectacles
Normally, horizontal curvature of
cornea is flatter than vertical &

21. This is attributed press of lid on the
corneal surface . This is physiological
so , vertical cornea should be more
curve than horizontal in normal eyes
.
On the basis it has two types .
With the rule
Against the rule
With the rule (Direct Astigmatism )
• Principle meridia are at right angle
to each other .

22. • Vertical curve is more than
horizontal .
• Concave cylinder is prescribed in
horizontal axis ( 180* ) and convex
are prescribed at vertical axis (90*)
• Normally the vertical meridian is
rendered 0.25 D more convex than
horizontal by the pressure of fleshy
upper eyelid .

23. Against the rule Astigmatism :
( indirect Astigmatism )
• Principle meridia are at right angle
to each other .
• Horizontal curve is more than
vertical .
• Convex cylinder is prescribed in
horizontal axis (180*)and concave
are prescribed in vertical axis 90*
• Usually associated with old age .

24. Oblique Astigmatism :
• A type of astigmatism in which
principle meridia are not horizontal
or vertical but are at right angle to
each other (45 & 135 )
• Usually symmetrical in both the eyes
(cylinder required at 30* in one
meridia and 150* at other merida)

25. Oblique Astigmatism
Symmetrical
Complementary

26. Bi Oblique Astigmatism :
• In this type of astigmatism the two
principle meridia are not at right to
each other .
• One meridia a 30% & other at 100%
o Irregular Astigmatism:
o It is characterized by an irregular
change of refractive of the
refractive power in different meridia
.

27. o There are multiple meridia which admit no
geometrical analysis .
o Cannot be corrected with spectacles
o It occurs due to corneal scars during of
cataract etc .
 Astigmatism – based on focus of the principle
meridians:
 Simple Astigmatism .
simple hyperopic astigmatism .
Simple myopic astigmatism .
 Compound Astigmatism .
Compound hyperopic astigmatism .
Compound myopic astigmatism .
 Mixed Astigmatism .

28.  Simple Astigmatism :
 In simple astigmatism one of the foci
falls on retina & other focus in front or
behind the retina .
 This leads to one meridian being
emmetropic & other being myopic
(one of the foci falls on retina & other
focus in frontof retina & hyperopic one
focus on retina and other behind the
retina ) so called as simple myopic
astigmatism & simple hyperopic
astigmatism respectively

29. It can be with the rule or against the
rule .
-2.0 D cylinder at 90* is example of
simple myopic astigmatism .
+2 D cylinder at 90* is example of
simple hyperopic astigmatism .

30.  Compound Astigmatism :
 Neither of the two foci falls on the
retina .
 The condition is know as compound
hyperopic if both foci are at back of
retina.
 It can be with the rule or against the
rule
 -3 Ds with -2Dc at 90 * is example of
compound myopic astigmatism
 + 3 Ds with +2 Dc at 90* is example of
compound myopic astigmatism .

31. In mixed astigmatism one of the two
foci lies at back while other at front
of the retina .
It can be with the rule or against the
rule .
-3 Ds with +8 Dc at 90* is an
example of mixed astigmatism .

32. If cylindrical power is less than
spherical power than it is not mixed
but compound astigmatism .
For example -3 Ds with 1 Dc at 180*
sounds as it is mixed astigmatism but
actually it is compound astigmatism
as cyl is less than sphere .
Residual Astigmatism :
The largest element of the total
astigmatism is due to anterior
corneal surface .

33. While the other component like :
Posterior corneal surface .
Lens
Refractive indies .
Constitute the residual astigmatism
Residual Astigmatism –total corneal
astigmatism ,
Sign & Symptoms :
Type of the symptoms produced
are:

34. 1. blurring of vision :
 Transient blurring of vision in low
astigmatism .
 Relieved by closing / rubbing the eyes .
 Circles elongate into ovals
 A point of light appears tailed off .
 A line appears as a succession of strikes
fused into a blurred image .
2.Asthenopia symptoms .
 More marked in patient with low
astigmatism .

35.  Severe in hyperopic astigmatism .
 Tiredness of eyes .
 Headaches ( from mild frontal ache to
explosions of pain )
 Nervous Distribution .
 Dizziness
 Fatigue
 Irritability .
3.Tilting of the head :
 Some patient with high oblique
astigmatism may hold the head tilted

36. to one side to reduced image
distortion .
Some children may even develop
scoliosis . ( The condition of slide to
slide spinal curve is called scoliosis .
On an x rays the spine of an
individual with scoliosis looks more
like an S or a C than a straight line.
4.Half closure of the lids.
Seen in patient with high
astigmatism .

37.  This is to make a sort of stenopaeic slit
& cutting out the rays from one
meridian.
 This is also cause Asthenopia symptoms
.
5.Reading material is held too close :
 Reading material is held too close to
the eyes by the patient to achieve but
large image just like myopic .
6. Blurring and itching :
 May be seen in patients with low
astigmatism B/c of rubbing eyes .
 Falling of eyelashes .
 Hyperemia , styes and chalizon .

38. Diagnosis :
VA with and without correction
monocularly .
Pin hole VA .
Retinoscopy .
 Keratometry .
Keratoscopy with placido disc,
Computerized corneal topography
/videography.

39.  Jackson cross cylinder .
 Astigmatic fan & block .
 Trail and error technique ( axis then
power )
 Maddox v
 Stenopaeic slit .
 Treatment:
 Spectacles ‘
 Contact lenses
 Refractive surgery
 Keratoplasty .