astigmatism 2
TRANSCRIPT
AstigmatismAstigmatism
Walter Huang, ODWalter Huang, OD
Yuanpei UniversityYuanpei University
Department of OptometryDepartment of Optometry
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 the come to a single point focus on or near the retinaretina
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
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
EtiologyEtiology
CorneaCornea The cornea has an unequal curvature on its The cornea has an unequal curvature on its
anterior surfaceanterior surface
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
EtiologyEtiology
It is due to a distortion of the cornea It is due to a distortion of the cornea and/or lensand/or lensThe refracting power is not uniform in all The refracting power is not uniform in all meridiansmeridiansThe principal meridians are the meridians The principal meridians are the meridians of greatest and least refracting powersof greatest and least refracting powersThe 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
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
Corneal AstigmatismCorneal Astigmatism
When the cornea has unequal curvature When the cornea has unequal curvature on the anterior surfaceon the anterior surface
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
Total AstigmatismTotal Astigmatism
The The sumsum of corneal astigmatism and of corneal astigmatism and lenticular astigmatismlenticular astigmatism
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
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
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
With-The-Rule (WTR) With-The-Rule (WTR) AstigmatismAstigmatism
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
Against-The-Rule (ATR) Against-The-Rule (ATR) AstigmatismAstigmatism
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)
Oblique (OBL) AstigmatismOblique (OBL) Astigmatism
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)
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)
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)
What Patient SeesWhat Patient Sees
One meridian is out of focusOne meridian is out of focus
Compound AstigmatismCompound Astigmatism
When When bothboth principal meridians are focused principal meridians are focused either in front or behind the retinaeither in front or behind the retina (with (with accommodation relaxed)accommodation relaxed)
Compound Myopic AstigmatismCompound Myopic Astigmatism
When When bothboth principal meridians are focused principal meridians are focused in front of the retinain front of the retina (with accommodation (with accommodation relaxed)relaxed)
Compound Hyperopic AstigmatismCompound Hyperopic Astigmatism
When When bothboth principal meridians are focused principal meridians are focused behind the retinabehind the retina (with accommodation (with accommodation relaxed)relaxed)
What Patient SeesWhat Patient Sees
Both meridians are out of focusBoth meridians are out of focus
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)
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
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
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
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
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
PrevalencePrevalence
GenderGender In general, there are no significant differences In general, there are no significant differences
between males and femalesbetween males and females
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
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
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
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
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
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)
SymptomsSymptoms
Distorted vision at distance and nearDistorted vision at distance and nearLetter confusionLetter confusionAsthenopia or ocular fatigueAsthenopia or ocular fatigue Due to constantly squinting to clear up Due to constantly squinting to clear up
distorted visiondistorted vision
HeadachesHeadachesSquintingSquinting
SignsSigns
Decreased visual acuities at distance and Decreased visual acuities at distance and nearnear
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
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
ManagementManagement
Spectacles Spectacles Single vision glasses with cylinderSingle vision glasses with cylinder
ManagementManagement
Contact lensesContact lenses Toric soft contact lensesToric soft contact lenses Toric rigid gas permeable contact lensesToric rigid gas permeable contact lenses
ManagementManagement
Refractive surgeryRefractive surgery Photorefractive keratectomy (PRK)Photorefractive keratectomy (PRK) Laser in-situ keratomileusis (LASIK)Laser in-situ keratomileusis (LASIK)