Astigmatism 2
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This document defines and describes astigmatism. It begins by defining astigmatism as a condition where parallel rays of light entering the eye do not focus to a single point on the retina. It then discusses the optics, etiology, classification, types (including corneal, lenticular, total, regular, irregular, with-the-rule, against-the-rule, oblique), and what patients see with different types of astigmatism (simple, compound, mixed). It concludes by covering prevalence based on age, gender, ethnicity and incidence, as well as effects on visual acuity.
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 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
- 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
- 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)