Astigmatism 2

1. AstigmatismAstigmatism
Walter Huang, ODWalter Huang, OD
Yuanpei UniversityYuanpei University
Department of OptometryDepartment of Optometry

2. DefinitionDefinition
When parallel rays of light enter the eye When parallel rays of light enter the eye
((with accommodation relaxedwith accommodation relaxed) and do ) and do notnot
come to a single point focus on or near come to a single point focus on or near
the retinathe retina

3. OpticsOptics
Power in the Power in the horizontalhorizontal plane projects a plane projects a
verticalvertical focal line image focal line image
Power in the Power in the verticalvertical plane projects a plane projects a
horizontalhorizontal focal line image focal line image

4. OpticsOptics
Refraction of light taking place at a toric Refraction of light taking place at a toric
surface: the conoid of Sturmsurface: the conoid of Sturm

5. EtiologyEtiology
CorneaCornea

The cornea has an unequal curvature on its The cornea has an unequal curvature on its
anterior surfaceanterior surface

6. EtiologyEtiology
LensLens

The crystalline lens has an unequal curvature The crystalline lens has an unequal curvature
on its surface or in its layers on its surface or in its layers

7. EtiologyEtiology
It is due to a distortion of the cornea It is due to a distortion of the cornea
and/or lensand/or lens
The refracting power is not uniform in all The refracting power is not uniform in all
meridiansmeridians
The principal meridians are the meridians The principal meridians are the meridians
of greatest and least refracting powersof greatest and least refracting powers
The The amount of astigmatism amount of astigmatism is equal to the is equal to the
difference in refracting power of the two difference in refracting power of the two
principal meridiansprincipal meridians

8. ClassificationClassification
Based on etiologyBased on etiology
Based on relation between principal Based on relation between principal
meridiansmeridians
Based on orientation of meridian or axisBased on orientation of meridian or axis
Based on focal points relative to the retinaBased on focal points relative to the retina
Based on relative locations of principal Based on relative locations of principal
meridians or axes when comparing the meridians or axes when comparing the
two eyes two eyes

9. Corneal AstigmatismCorneal Astigmatism
When the cornea has unequal curvature When the cornea has unequal curvature
on the anterior surfaceon the anterior surface

10. Lenticular AstigmatismLenticular Astigmatism
When the crystalline lens has an unequal When the crystalline lens has an unequal
on the surface or in its layerson the surface or in its layers

11. Total AstigmatismTotal Astigmatism
The The sumsum of corneal astigmatism and of corneal astigmatism and
lenticular astigmatismlenticular astigmatism

12. Regular AstigmatismRegular Astigmatism
When the two principal meridians are When the two principal meridians are
perpendicularperpendicular to each other to each other
Most cases of astigmatism are regular Most cases of astigmatism are regular
astigmatismastigmatism
The three types are with-the-rule, against-The three types are with-the-rule, against-
the-rule, and oblique astigmatismthe-rule, and oblique astigmatism

13. Irregular AstigmatismIrregular Astigmatism
When the two principal meridians are When the two principal meridians are not not
perpendicularperpendicular to each other to each other
Curvature of any one meridian is not Curvature of any one meridian is not
uniformuniform
Associated with trauma, disease, or Associated with trauma, disease, or
degenerationdegeneration
VA is often not correctable to 20/20VA is often not correctable to 20/20

14. With-The-Rule (WTR) AstigmatismWith-The-Rule (WTR) Astigmatism
When the When the greatest refractive powergreatest refractive power is is
within 030 of the vertical meridianwithin 030 of the vertical meridian (i.e., (i.e.,
between 060 and 120 meridians)between 060 and 120 meridians)
Minus cylinder axisMinus cylinder axis around horizontal around horizontal
meridianmeridian
The The most commonmost common type of astigmatism type of astigmatism
based on the orientation of meridiansbased on the orientation of meridians

15. With-The-Rule (WTR) With-The-Rule (WTR)
AstigmatismAstigmatism

16. Against-The-Rule (ATR) Against-The-Rule (ATR)
AstigmatismAstigmatism
When the When the greatest refractive powergreatest refractive power is is
within 030 of the horizontal meridianwithin 030 of the horizontal meridian (i.e., (i.e.,
between 030 and 150 meridians)between 030 and 150 meridians)
Minus cylinder axisMinus cylinder axis around vertical around vertical
meridianmeridian

17. Against-The-Rule (ATR) Against-The-Rule (ATR)
AstigmatismAstigmatism

18. Oblique (OBL) AstigmatismOblique (OBL) Astigmatism
When the When the greatest refractive powergreatest refractive power is is
within 030 of the oblique meridianswithin 030 of the oblique meridians (i.e., (i.e.,
between 030 and 060 or 120 and 150)between 030 and 060 or 120 and 150)

19. Oblique (OBL) AstigmatismOblique (OBL) Astigmatism

20. Simple AstigmatismSimple Astigmatism
When one of the principal meridians is When one of the principal meridians is
focused focused on the retinaon the retina and the other is and the other is notnot
focused focused on the retinaon the retina (with (with
accommodation relaxed)accommodation relaxed)

21. Simple Myopic AstigmatismSimple Myopic Astigmatism
When one of the principal meridians is When one of the principal meridians is
focused focused in front of the retinain front of the retina and the other and the other
is focused is focused on the retinaon the retina (with (with
accommodation relaxed)accommodation relaxed)

22. Simple Hyperopic AstigmatismSimple Hyperopic Astigmatism
When one of the principal meridians is When one of the principal meridians is
focused focused behind the retinabehind the retina and the other is and the other is
focused focused on the retinaon the retina (with (with
accommodation relaxed)accommodation relaxed)

23. What Patient SeesWhat Patient Sees
One meridian is out of focusOne meridian is out of focus

24. Compound AstigmatismCompound Astigmatism
When When bothboth principal meridians are principal meridians are
focused focused either in front or behind the retinaeither in front or behind the retina
(with accommodation relaxed)(with accommodation relaxed)

25. Compound Myopic AstigmatismCompound Myopic Astigmatism
When When bothboth principal meridians are principal meridians are
focused focused in front of the retinain front of the retina (with (with
accommodation relaxed)accommodation relaxed)

26. Compound Hyperopic AstigmatismCompound Hyperopic Astigmatism
When When bothboth principal meridians are principal meridians are
focused focused behind the retinabehind the retina (with (with
accommodation relaxed)accommodation relaxed)

27. What Patient SeesWhat Patient Sees
Both meridians are out of focusBoth meridians are out of focus

28. Mixed AstigmatismMixed Astigmatism
When one of the principal meridians is When one of the principal meridians is
focused focused in front of the retinain front of the retina and the other and the other
is focused is focused behind the retinabehind the retina (with (with
accommodation relaxed)accommodation relaxed)

29. Symmetrical AstigmatismSymmetrical Astigmatism
The principal meridians or axes of the two The principal meridians or axes of the two
eyes are symmetrical (e.g., eyes are symmetrical (e.g., both eyes are both eyes are
WTR or ATRWTR or ATR))
The The sum of the two axessum of the two axes of the two eyes of the two eyes
equals equals approximately 180approximately 180

30. Symmetrical AstigmatismSymmetrical Astigmatism
ExampleExample

OD: OD: pl -1.00 x 175pl -1.00 x 175

OS:OS:pl -1.00 x 005pl -1.00 x 005
Both eyes are WTR astigmatism, and the Both eyes are WTR astigmatism, and the
sum of the two axes equal approximately sum of the two axes equal approximately
180180

31. Asymmetrical AstigmatismAsymmetrical Astigmatism
The principal meridians or axes of the two The principal meridians or axes of the two
eyes are eyes are notnot symmetrical (e.g., symmetrical (e.g., one eye is one eye is
WTR while the other eye is ATRWTR while the other eye is ATR))
The The sum of the two axessum of the two axes of the two eyes of the two eyes
does does notnot equal equal approximately 180approximately 180

32. Asymmetrical AstigmatismAsymmetrical Astigmatism
Example:Example:

OD: OD: pl -1.00 x 180pl -1.00 x 180

OS: OS: pl -1.00 x 090pl -1.00 x 090
One eye is WTR astigmatism, and the One eye is WTR astigmatism, and the
other eye is ATR astigmatism, and the other eye is ATR astigmatism, and the
sum of the two axes do not equal sum of the two axes do not equal
approximately 180approximately 180

33. PrevalencePrevalence
AgeAge

Infants are born with ATR astigmatism, where Infants are born with ATR astigmatism, where
the cornea is the source of the astigmatismthe cornea is the source of the astigmatism

Preschool children have little or no Preschool children have little or no
astigmatismastigmatism

Teenage children demonstrate a shift towards Teenage children demonstrate a shift towards
WTR astigmatismWTR astigmatism

Older adults show a shift towards ATR Older adults show a shift towards ATR
astigmatismastigmatism

34. PrevalencePrevalence
GenderGender

In general, there are no significant differences In general, there are no significant differences
between males and femalesbetween males and females

35. PrevalencePrevalence
EthnicityEthnicity

Higher prevalence in North Americans, Higher prevalence in North Americans,
LatinosLatinos

Asian infants tend to be WTR astigmatismAsian infants tend to be WTR astigmatism

Caucasian infants tend to be ATR Caucasian infants tend to be ATR
astigmatismastigmatism

36. IncidenceIncidence
General trendGeneral trend

For older adults, the average rate of change For older adults, the average rate of change
towards ATR astigmatism is less than or towards ATR astigmatism is less than or
equal to 0.25D every 10 yearsequal to 0.25D every 10 years

37. Visual AcuityVisual Acuity
Theoretically, at NO distance does an Theoretically, at NO distance does an
uncorrected astigmat have a sharp retinal uncorrected astigmat have a sharp retinal
imageimage
Clinically, if astigmatism is small (less than Clinically, if astigmatism is small (less than
0.50DC), the patient may not notice blur0.50DC), the patient may not notice blur

38. Visual AcuityVisual Acuity
Simple or compound myopic astigmatismSimple or compound myopic astigmatism

Accommodation may make the retinal image even Accommodation may make the retinal image even
more blurrymore blurry
Simple or compound hyperopic astigmatismSimple or compound hyperopic astigmatism

Accommodation may improve VA to some extentAccommodation may improve VA to some extent
Mixed astigmatismMixed astigmatism

VA is relatively goodVA is relatively good

May not need much accommodationMay not need much accommodation

39. Spherical and Astigmatic AmetropiaSpherical and Astigmatic Ametropia
Uncorrected VAUncorrected VA Spherical Spherical
Refractive Error Refractive Error
(D)*(D)*
Astigmatism (D)Astigmatism (D)
20/3020/30 0.500.50 1.001.00
20/4020/40 0.750.75 1.501.50
20/6020/60 1.001.00 2.002.00
20/8020/80 1.501.50 3.003.00
20/12020/120 2.002.00 4.004.00
20/20020/200 2.502.50 >4.00>4.00

40. Spherical and Astigmatic AmetropiaSpherical and Astigmatic Ametropia
Spherical refractive error (D)*Spherical refractive error (D)*

Myopia or absolute hyperopiaMyopia or absolute hyperopia

When multiplied by a factor of two, it equals When multiplied by a factor of two, it equals
astigmatism (D)astigmatism (D)

41. SymptomsSymptoms
Distorted vision at distance and nearDistorted vision at distance and near
Letter confusionLetter confusion
Asthenopia or ocular fatigueAsthenopia or ocular fatigue

Due to constantly squinting to clear up Due to constantly squinting to clear up
distorted visiondistorted vision
HeadachesHeadaches
SquintingSquinting

42. SignsSigns
Decreased visual acuities at distance and Decreased visual acuities at distance and
nearnear

43. Clinical TestsClinical Tests
Visual acuity tests Visual acuity tests –– distance and near distance and near
AutorefractionAutorefraction
KeratometryKeratometry
Retinoscopy Retinoscopy

Most reliable source of information for cylinder Most reliable source of information for cylinder
power and axispower and axis
Monocular subjective refraction, including Monocular subjective refraction, including
Jackson cross cylinderJackson cross cylinder

44. ManagementManagement
Cylindrical lenses and spherocylindrical Cylindrical lenses and spherocylindrical
lenses in spectacles and contact lenses lenses in spectacles and contact lenses
for simple astigmatism and compound for simple astigmatism and compound
astigmatism, respectivelyastigmatism, respectively
Refractive surgeryRefractive surgery

45. ManagementManagement
Spectacles Spectacles

Single vision glasses with cylinderSingle vision glasses with cylinder

46. ManagementManagement
Contact lensesContact lenses

Toric soft contact lensesToric soft contact lenses

Toric rigid gas permeable contact lensesToric rigid gas permeable contact lenses

47. ManagementManagement
Refractive surgeryRefractive surgery

Photorefractive keratectomy (PRK)Photorefractive keratectomy (PRK)

Laser in-situ keratomileusis (LASIK)Laser in-situ keratomileusis (LASIK)