Astigmatism is a refractive error where the eye focuses light unevenly due to an irregularly shaped cornea or lens. It causes blurred vision and difficulty seeing fine details. There are several types of astigmatism classified by its cause, axis, degree of refractive error in different meridians, and location of the focal points. Common symptoms include blurred vision, eye strain, headaches, and occasional tilting of the head in severe oblique astigmatism. Diagnosis involves an eye exam using a retinoscope or autorefractor to detect the different refractive errors in different meridians. Treatment options include eyeglasses, contact lenses, or refractive surgery to correct the astigmatism.

2. ASTIGMATISM
BY: SUMAYYA NASEEM
INTERNEE OPTOMETRIST

3. CONTENTS OF LECTURE

4. CONTENTS OF TODAY’S LECTURE
What is Astigmatism?
Incidence
Optics
Etiology
Classification
Signs & Symptoms
Diagnosis
Treatment

5. 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 may 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 detail, and in
some cases vertical lines (e.g., walls) may appear to the
patient to be leaning over.

9. WHAT IS ASTIGMATISM?
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.

12. OPTICS OF ASTIGMATISM

13. OPTICS OF ASTIGMATISM
In astigmatism, the rays of light from one sector
fall on one point & rays from another sector fall on
another point. In other words, a point focus of
light cannot be formed upon the retina.
The configuration of rays refracted through the
astigmatic surface (toric surface) is called sturms
conoid.

15. ASTIGMATISM
Vertical Focal
Line
Circle of Least C
Confusion
Horizontal
Focal Line
Power Meridian A
Axis Meridian B D
Object
Source
Interval
of
Sturm

16. OPTICS OF ASTIGMATISM
Thus, there are 2 focal points separated from
each other by a focal interval, called as interval
of sturm.
The length of this focal interval is the measure
of the degree of astigmatism & the correction of
the error can only be accomplished by reducing
these two foci in to one.

17. INCIDENCE

18. INCIDENCE
No eye is perfectly stigmatic as almost all individuals have a
minor degree of physiological astigmatism.
About 60% cases of refractive errors have astigmatism which
needs to be corrected.
Occurs with equal frequency in males and females.
Approximate distribution according to degree of astigmatism
is:
0.25-0.5 D 50%
0.75-1.0 D 25%
1.00-4.00D 24%
>4.00 1.0%

19. INCIDENCE
The most common type is compound myopic
followed by compound hyperopic, mixed, simple
myopic & simple hyperopic.
One study reports as:
 With the rule 38%
 Against the rule 30%
 Oblique 32%

20. Etiology

21. ETIOLOGY
1.Corneal astigmatism:
It occurs due to abnormalities of curvature of cornea
Most common cause of astigmatism
e.g. keratoconus, pterygium, mild corneal opacities, chalazion

22. PTERYGIUM

24. CORNEAL OPACITY

28. CHALAZION

29. ETIOLOGY
2. Lenticular astigmatism:
It is comparatively rare.
It may be:
Curvatural….lenticonus
Positional…..congenital tilting & traumatic subluxation of lens
Index……….developing cataract/nuclear sclerosis/diabetic cat.

30. ANTERIOR LENTICONUS

31. ANTERIOR LENTICONUS

32. CATARACT

33. LENTICULAR SUBLUXATION

34. Severity of Astigmatism
 The severity of astigmatism can be classified as
follows:
 Mild Astigmatism < 1.00 diopter
 Moderate Astigmatism 1.00 to 2.00 diopters
 Severe Astigmatism 2.00 to 3.00 diopters
 Extreme Astigmatism > 3.00 diopters

35. Classification

36. CLASSIFICATION
ASTIGMATISM
PHYSIOLOGICAL PATHOLOGICAL
REGULAR IRREGULAR
SIMPLE
MYOPIC
HYPEROPIC
COMPOUND
MYOPIC
HYPEROPIC
MIXED

37. CLASSIFICATION
1. Astigmatism - Based on asymmetry of structure
• Corneal astigmatism - astigmatism due to an irregularly shaped
cornea
• Lenticular astigmatism - astigmatism due to an irregularly shaped
lens

38. CLASSIFICATION
2. Astigmatism - Based on axis of the principal meridians
a. Regular astigmatism
Against-the-rule astigmatism
With-the-rule astigmatism
b. Oblique astigmatism
c. Bioblique astigmatism
d. Irregular astigmatism

39. a. Regular astigmatism:
The astigmatism is said to be regular if there is different
refraction by the eye in two meridia at right angles to each
other.
Can be corrected with spectacles.
Normally, horizontal curvature of cornea is flatter than
vertical & this is attributed to the pressure of lids on the
corneal surface. This is physiological. So, vertical cornea
should be more curve than horizontal.
On this basis, it has two types:
With the rule (WTR) & against the rule (ATR)

41. With-the-rule (direct astigmatism):
Principle meridia are at right angle to each other.
Vertical curve is more than horizontal.
Concave cylinder is prescribed in horizontal axis
(180) and convex are prescribed in vertical axis
(90).
Normally the vertical meridian is rendered 0.25 D
more convex than horizontal by the pressure of
fleshy upper eyelid.

42. Against-the-rule (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.

43. b. 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 both the eyes)
Or complementary (cylinder required at 30 in one
eye & 150 in other eye)

45. c. Bioblique astigmatism:
In this type of astigmatism, the two principle
meridia are not at right angle to each other.
e.g. one may be at 30 & other at 100.

46. d. Irregular astigmatism:
o It is characterized by an irregular change of
refractive power in different meridia.
o There are multiple meridia which admit no
geometrical analysis.
o Cannot be corrected by spectacles.
o It occurs due to corneal scars, during maturation
of cataract, etc.

47. CLASSIFICATION
3. Astigmatism - Based on focus of the principal
meridians
Simple astigmatism
Simple hyperopic astigmatism
Simple myopic astigmatism
Compound astigmatism
Compound hyperopic astigmatism
Compound myopic astigmatism
Mixed astigmatism

48. SIMPLE ASTIGMATISM
 In simple astigmatism, one of the foci falls on retina &
other focus falls in front or behind retina.
 This leads to one meridian being emmetropic & other being
myopic (one focus on the retina & other focus falls in front of retina) or
hyperopic (one focus on retina & other focus behind retina), so called
as simple myopic astigmatism & simple hyperopic
astigmatism respectively.
 It can be with-the-rule or against-the-rule.
 -2 D cyl at 90 is example of simple myopic astigmatism.
 +2 D cyl at 90 is example of simple hyperopic astigmatism.

49. SIMPLE HYPEROPIC ASTIGMATISM

50. SIMPLE MYOPIC ASTIGMATISM

51. COMPOUND ASTIGMATISM
• Neither of the two foci fall on the retina.
• The condition is known as compound hyperopic
if both foci are at back of retina.
• The condition is known as compound myopic if
both foci are at front 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 +2DC at 90 is example of compound
hyperopic astigmatism.

52. COMPOUND HYPEROPIC
ASTIGMATISM

53. COMPOUND MYOPIC ASTIGMATISM

54. MIXED ASTIGMATISM
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 +8DC at 90 is an example of
mixed astigmatism.

55. MIXED ASTIGMATISM

57. NOTE:
If cyl power is less than spherical power, then it is
not mixed but compound astigmatism.
For example, -3DS with +1DC at 180 sounds as if it
is mixed astigmatism, but actually is compound
astigmatism, as cyl is less than sphere.

58. RESIDUAL ASTIGMATISM
 The largest element of the total astigmatism is due to
anterior corneal surface.
 While the other components like:
 Posterior corneal surface
 Lens
 Refractive indices
constitute the residual astigmatism.
RESIDUAL ASTIGMATISM= TOTAL – CORNEAL ASTIGMATISM

59. Signs & Symptoms

60. SIGNS & SYMPTOMS
Type of the symptoms produced, depends upon the type
of astigmatism:
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 strokes fused into a
blurred image.

64. SIGNS & SYMPTOMS
2. Asthenopic symptoms:
More marked in patients with low astigmatism
(more accommodative effort)
Severe in hyperopic astigmatism
(more accommodative effort)
Tiredness of eyes
Headaches (from mild frontal ache to explosions of
pain)
Nervous disturbances:
Dizziness
Fatigue
Irritability

65. SIGNS & SYMPTOMS
3. Tilting of the head:
Some patients with high oblique astigmatism, may
hold the head tilted to one side to reduce image
distortion.
Some children may even develop scoliosis.
(The condition of side-to-side spinal curves is called scoliosis. On an X-
ray, the spine of an individual with scoliosis looks more like an "S" or a
"C" than a straight line.)

66. SIGNS & SYMPTOMS
4. Half closure of the lids:
Seen in patients with high astigmatism.
This is to make a sort of stenopaeic slit & cutting
out the rays from one meridian..
This also causes Asthenopic symptoms.

67. SIGNS & SYMPTOMS
5. Reading material is held too close:
Reading material is held too close to the eyes by
the patient to achieve blur but large image just
like a myope.

68. SIGNS & SYMPTOMS
6. Burning & itching:
May be seen in patients with low astigmatism
B/c of rubbing the eyes
Falling of eye lashes
Hyperemia
Styes& chalazia

69. Diagnosis

70. DIAGNOSIS
VA with and without correction monocularly
Pinhole VA
Retinoscopy
Keratometry
Keratoscopy with placido’s disc
Computerised corneal topography/videograph
Subjective verification:
Jackson cross cylinder
Astigmatic fan & block
Trial & error technique (axis then power)
Maddox V
Stenopaeic slit

71. VISUAL ACUITY & PINHOLE VA

72. JACKSON CROSS CYLINDER

73. Refractor head-mounted JCC

74. RETINOSCOPY

76. ASTIGMATISM CHART

77. ASTIGMATIC FAN

78. ASTIGMATISM TEST
Close one eye and then the other one , if you do not see all
the lined squares, in the same black color , if you do see
.
one or more squares grey, you then have an astigmatism.

79. Stenopaeic Slit

80. JAVAL SCHIOTZ KERATOMETER

81. BAUSCH & LOMB KERATOMETER

82. PLACIDO’S DISC

83. TOPOGRAPHY

84. The typical spiral pattern of keratoconus progression. In
color-coded topographic images, red represents steeper
corneal curvature, and the spectrum of yellow, green,
and blue represents progressively flatter curvatures.

85. Correction/Treatment

86. TREATMENT
Modes:
1. Spectacles
2. Contact lens
3. Laser
4. Refractive surgery
5. Keratoplasty

87. SPECTACLES
Astigmatism is corrected optically with a cylindrical
lens.
A combination of a spherical lens and a cylindrical
lens (spherocylindrical lens) is used to correct a
spherical error with an astigmatic error.
Cyl has power (curvature) in one meridian and no
power in the other meridian.
The axis of the cylinder is lined up with the axis of
astigmatism to correct the astigmatic power
difference.

90. Spherical Lens
Spherical surfaces
Optical Axis
Principal Meridian

91. Cylindrical Lens
Optical Axis
Principal
Meridian

92. TORIC LENSE IMAGING
Interval of Sturm

93. CONTACT LENSES
Various types of contact lenses are used:
Soft
Hard
Rigid gas permeable
Hybrid (hard center & soft periphery, used in
keratoconus)
Depending upon the degree of astigmatism:
Spherical
Toric
Bitoric

95. Eugene Kalt, MD, first to propose the use of a contact
lens for keratoconus.

97. LASER & REFRACTIVE
SURGERIES
Photorefractive keratectomy PRK
Relaxing incisions (transverse & arcuate keratotomy)
Wedge resection
Compression sutures
Continuous sutures ( astigmatism low)
Interrupted sutures (astigmatism high)
Orthokeratology (hard lens)
Keratoplasty (keratoconus)

98. References

99. REFERENCES
Theory and practice of optics and refraction by
A K Khurana
Duke Elder's Practice of refraction (Tenth
edition)
Clinical Optics by Elkington, Frank and
Greaney (Third edition)
Text book of ophthalmology (Volume : 1) by
Jaypee publishers
and many websites.