Astigmatism is a refractive error caused by unequal curvature of the cornea or lens, leading to multiple focus points rather than a single point on the retina. It can be classified into corneal, lenticular, and total astigmatism, with further subdivisions into regular and irregular types based on the orientation of principal meridians. Management options include corrective lenses, contact lenses, and refractive surgery such as LASIK and PRK.

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

2. DefinitionDefinition
When parallel rays of light enter the eyeWhen 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 nearcome to a single point focus on or near
the retinathe retina

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

4. OpticsOptics
Refraction of light taking place at a toricRefraction 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 itsThe cornea has an unequal curvature on its
anterior surfaceanterior surface

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

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

8. ClassificationClassification
Based on etiologyBased on etiology
Based on relation between principalBased 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 principalBased on relative locations of principal
meridians or axes when comparing themeridians or axes when comparing the
two eyestwo eyes

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

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

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

12. Regular AstigmatismRegular Astigmatism
When the two principal meridians areWhen the two principal meridians are
perpendicularperpendicular to each otherto each other
Most cases of astigmatism are regularMost 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 areWhen the two principal meridians are notnot
perpendicularperpendicular to each otherto each other
Curvature of any one meridian is notCurvature of any one meridian is not
uniformuniform
Associated with trauma, disease, orAssociated 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 theWhen the greatest refractive powergreatest refractive power isis
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 horizontalaround horizontal
meridianmeridian
TheThe most commonmost common type of astigmatismtype 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 theWhen the greatest refractive powergreatest refractive power isis
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 verticalaround vertical
meridianmeridian

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

18. Oblique (OBL) AstigmatismOblique (OBL) Astigmatism
When theWhen the greatest refractive powergreatest refractive power isis
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 isWhen one of the principal meridians is
focusedfocused on the retinaon the retina and the other isand the other is notnot
focusedfocused on the retinaon the retina (with(with
accommodation relaxed)accommodation relaxed)

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

22. Simple Hyperopic AstigmatismSimple Hyperopic Astigmatism
When one of the principal meridians isWhen one of the principal meridians is
focusedfocused behind the retinabehind the retina and the other isand the other is
focusedfocused 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
WhenWhen bothboth principal meridians areprincipal meridians are
focusedfocused 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
WhenWhen bothboth principal meridians areprincipal meridians are
focusedfocused in front of the retinain front of the retina (with(with
accommodation relaxed)accommodation relaxed)

26. Compound Hyperopic AstigmatismCompound Hyperopic Astigmatism
WhenWhen bothboth principal meridians areprincipal meridians are
focusedfocused 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 isWhen one of the principal meridians is
focusedfocused in front of the retinain front of the retina and the otherand the other
is focusedis focused behind the retinabehind the retina (with(with
accommodation relaxed)accommodation relaxed)

29. Symmetrical AstigmatismSymmetrical Astigmatism
The principal meridians or axes of the twoThe principal meridians or axes of the two
eyes are symmetrical (e.g.,eyes are symmetrical (e.g., both eyes areboth eyes are
WTR or ATRWTR or ATR))
TheThe sum of the two axessum of the two axes of the two eyesof the two eyes
equalsequals 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 theBoth eyes are WTR astigmatism, and the
sum of the two axes equal approximatelysum of the two axes equal approximately
180180

31. Asymmetrical AstigmatismAsymmetrical Astigmatism
The principal meridians or axes of the twoThe principal meridians or axes of the two
eyes areeyes are notnot symmetrical (e.g.,symmetrical (e.g., one eye isone eye is
WTR while the other eye is ATRWTR while the other eye is ATR))
TheThe sum of the two axessum of the two axes of the two eyesof the two eyes
doesdoes notnot equalequal 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 theOne eye is WTR astigmatism, and the
other eye is ATR astigmatism, and theother eye is ATR astigmatism, and the
sum of the two axes do not equalsum of the two axes do not equal
approximately 180approximately 180

33. PrevalencePrevalence
AgeAge

Infants are born with ATR astigmatism, whereInfants 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 noPreschool children have little or no
astigmatismastigmatism

Teenage children demonstrate a shift towardsTeenage children demonstrate a shift towards
WTR astigmatismWTR astigmatism

Older adults show a shift towards ATROlder adults show a shift towards ATR
astigmatismastigmatism

34. PrevalencePrevalence
GenderGender

In general, there are no significant differencesIn 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 ATRCaucasian infants tend to be ATR
astigmatismastigmatism

36. IncidenceIncidence
General trendGeneral trend

For older adults, the average rate of changeFor older adults, the average rate of change
towards ATR astigmatism is less than ortowards 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 anTheoretically, at NO distance does an
uncorrected astigmat have a sharp retinaluncorrected astigmat have a sharp retinal
imageimage
Clinically, if astigmatism is small (less thanClinically, 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 evenAccommodation 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 SphericalSpherical
Refractive ErrorRefractive 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 equalsWhen 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 upDue to constantly squinting to clear up
distorted visiondistorted vision
HeadachesHeadaches
SquintingSquinting

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

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

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

45. ManagementManagement
SpectaclesSpectacles

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)