Astigmatism By Sumayya Naseem

ASTIGMATISM

BY: SUMAYYA NASEEMINTERNEE OPTOMETRIST

CONTENTS OF LECTURECONTENTS OF LECTURE

CONTENTS OF TODAY’S CONTENTS OF TODAY’S LECTURELECTURE

What is Astigmatism?

Incidence

Optics

Etiology

Classification

Signs & Symptoms

Diagnosis

Treatment

ASTIGMATISMASTIGMATISM

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.

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.

WHAT IS ASTIGMATISM?

OPTICS OF ASTIGMATISM

OPTICS OF OPTICS OF ASTIGMATISMASTIGMATISM

In astigmatism, the rays of light from one sector In astigmatism, the rays of light from one sector fall on one point & rays from another sector fall on fall on one point & rays from another sector fall on another point. In other words, a point focus of another point. In other words, a point focus of light cannot be formed upon the retina.light cannot be formed upon the retina.

The configuration of rays refracted through the The configuration of rays refracted through the astigmatic surface (toric surface) is called astigmatic surface (toric surface) is called sturms sturms conoidconoid..

ASTIGMATISMASTIGMATISM

Axis Meridian

Horizontal Focal

Line

Vertical Focal Line

Circle of Least Confusion

Power Meridian

Object Source

AB D

C

Interval of

Sturm

OPTICS OF OPTICS OF ASTIGMATISMASTIGMATISM

Thus, there are 2 focal points separated Thus, there are 2 focal points separated from each other by a focal interval, called from each other by a focal interval, called as as interval of sturminterval of sturm..

The length of this focal interval is the The length of this focal interval is the

measure of the degree of astigmatism & measure of the degree of astigmatism & the correction of the error can only be the correction of the error can only be accomplished by reducing these two foci accomplished by reducing these two foci in to one.in to one.

INCIDENCEINCIDENCE

INCIDENCEINCIDENCE No eye is perfectly No eye is perfectly stigmatic stigmatic as almost all as almost all

individuals have a minor degree of physiological individuals have a minor degree of physiological astigmatism.astigmatism.

About 60% cases of refractive errors have About 60% cases of refractive errors have astigmatism which needs to be corrected.astigmatism which needs to be corrected.

Occurs with equal frequency in males and females.Occurs with equal frequency in males and females.

Approximate distribution according to degree of Approximate distribution according to degree of astigmatism is:astigmatism is:

0.25-0.5 D 50%0.25-0.5 D 50% 0.75-1.0 D 25%0.75-1.0 D 25% 1.00-4.00D 24%1.00-4.00D 24% >4.00 1.0%>4.00 1.0%

INCIDENCEINCIDENCE

The most common type is compound The most common type is compound myopic followed by compound hyperopic, myopic followed by compound hyperopic, mixed, simple myopic & simple mixed, simple myopic & simple hyperopic.hyperopic.

One study reports as:One study reports as: With the rule 38%With the rule 38% Against the rule 30%Against the rule 30% Oblique 32%Oblique 32%

EtiologyEtiology

ETIOLOGYETIOLOGY

1.Corneal astigmatism:

It occurs due to abnormalities of curvature of cornea Most common cause of astigmatisme.g. keratoconus, pterygium, mild corneal opacities, chalazion

PTERYGIUMPTERYGIUM

CORNEAL OPACITYCORNEAL OPACITY

CHALAZIONCHALAZION

ETIOLOGYETIOLOGY

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.

ANTERIOR LENTICONUS

ANTERIOR LENTICONUSANTERIOR LENTICONUS

CATARACTCATARACT

LENTICULAR LENTICULAR SUBLUXATIONSUBLUXATION

Severity of AstigmatismSeverity of Astigmatism The severity of astigmatism can be The severity of astigmatism can be

classified as follows:classified as follows:

Mild Astigmatism Mild Astigmatism < 1.00 diopter< 1.00 diopter

Moderate Astigmatism Moderate Astigmatism 1.00 to 2.00 diopters1.00 to 2.00 diopters

Severe Astigmatism Severe Astigmatism 2.00 to 3.00 diopters2.00 to 3.00 diopters

Extreme Astigmatism Extreme Astigmatism > 3.00 diopters> 3.00 diopters

ClassificationClassification

CLASSIFICATIONCLASSIFICATIONASTIGMATISM

PHYSIOLOGICAL PATHOLOGICAL

REGULAR IRREGULAR

SIMPLE

COMPOUND

MIXED

MYOPIC

HYPEROPIC

MYOPIC

HYPEROPIC

CLASSIFICATIONCLASSIFICATION

1. Astigmatism - Based on asymmetry of structure1. Astigmatism - Based on asymmetry of structure

• Corneal astigmatism - astigmatism due to an irregularly Corneal astigmatism - astigmatism due to an irregularly shaped cornea shaped cornea

• Lenticular astigmatism - astigmatism due to an irregularly Lenticular astigmatism - astigmatism due to an irregularly shaped lens shaped lens


2. Astigmatism - Based on axis of the principal 2. Astigmatism - Based on axis of the principal meridiansmeridians

a. Regular astigmatism a. Regular astigmatism Against-the-rule astigmatism Against-the-rule astigmatism With-the-rule astigmatism With-the-rule astigmatism

b. Oblique astigmatismb. Oblique astigmatismc. Bioblique astigmatism c. Bioblique astigmatism d. Irregular astigmatism d. Irregular astigmatism

a. Regular astigmatism:a. Regular astigmatism:

The astigmatism is said to be regular if there is different The astigmatism is said to be regular if there is different refraction by the eye in two meridia at right angles to refraction by the eye in two meridia at right angles to each other.each other.

Can be corrected with spectacles.Can be corrected with spectacles.

Normally, horizontal curvature of cornea is flatter than Normally, horizontal curvature of cornea is flatter than vertical & this is attributed to the pressure of lids on the vertical & this is attributed to the pressure of lids on the corneal surface. This is physiological. So, vertical cornea corneal surface. This is physiological. So, vertical cornea should be more curve than horizontal. should be more curve than horizontal.

On this basis, it has two types:On this basis, it has two types: With the rule (WTR) & against the rule (ATR)With the rule (WTR) & against the rule (ATR)

With-the-rule With-the-rule (direct astigmatism): (direct astigmatism):

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

Against-the-rule Against-the-rule (indirect (indirect astigmatism):astigmatism):

Principle meridia are at right angle to Principle meridia are at right angle to each other.each other. Horizontal curve is more than Vertical.Horizontal curve is more than Vertical.Convex cylinder is prescribed in Convex cylinder is prescribed in horizontal axis (180) and concave are horizontal axis (180) and concave are prescribed in vertical axis (90).prescribed in vertical axis (90).Usually associated with old age.Usually associated with old age.

b. Oblique astigmatism:b. Oblique astigmatism:

A type of astigmatism in which principle A type of astigmatism in which principle meridia are not horizontal or vertical but are meridia are not horizontal or vertical but are at right angle to each other (45 & 135).at right angle to each other (45 & 135).Usually symmetrical in both the eyes (cylinder Usually symmetrical in both the eyes (cylinder required at 30 in both the eyes) required at 30 in both the eyes)Or complementary (cylinder required at 30 in Or complementary (cylinder required at 30 in one eye & 150 in other eye)one eye & 150 in other eye)

c. c. Bioblique astigmatism:Bioblique astigmatism:

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

d. Irregular astigmatism:d. Irregular astigmatism:

o It is characterized by an irregular change It is characterized by an irregular change of refractive power in different meridia.of refractive power in different meridia.

o There are multiple meridia which admit There are multiple meridia which admit no geometrical analysis.no geometrical analysis.

o Cannot be corrected by spectacles.Cannot be corrected by spectacles.o It occurs due to corneal scars, during It occurs due to corneal scars, during

maturation of cataract, etc.maturation of cataract, etc.

3. Astigmatism - Based on focus of the 3. Astigmatism - Based on focus of the principal meridiansprincipal meridiansSimple astigmatism Simple astigmatism

Simple hyperopic astigmatismSimple hyperopic astigmatismSimple myopic astigmatism Simple myopic astigmatism

Compound astigmatism Compound astigmatism Compound hyperopic astigmatism Compound hyperopic astigmatism Compound myopic astigmatism Compound myopic astigmatism

Mixed astigmatism Mixed astigmatism


SIMPLE ASTIGMATISMSIMPLE ASTIGMATISM In simple astigmatism, one of the foci falls on retina In simple astigmatism, one of the foci falls on retina

& other focus falls in front or behind retina.& other focus falls in front or behind retina.

This leads to one meridian being emmetropic & This leads to one meridian being emmetropic & other being myopic (other being myopic (one focus on the retina & other focus falls one focus on the retina & other focus falls in front of retinain front of retina) or hyperopic () or hyperopic (one focus on retina & other one focus on retina & other focus behind retinafocus behind retina), so called as ), so called as simple myopic simple myopic astigmatismastigmatism & & simple hyperopic astigmatismsimple hyperopic astigmatism respectively.respectively.

It can be with-the-rule or against-the-rule.It can be with-the-rule or against-the-rule. -2 D cyl at 90 is example of simple myopic -2 D cyl at 90 is example of simple myopic

astigmatism.astigmatism. +2 D cyl at 90 is example of simple hyperopic +2 D cyl at 90 is example of simple hyperopic

astigmatism.astigmatism.

SIMPLE HYPEROPIC SIMPLE HYPEROPIC ASTIGMATISMASTIGMATISM

SIMPLE MYOPIC SIMPLE MYOPIC ASTIGMATISMASTIGMATISM

COMPOUND COMPOUND ASTIGMATISMASTIGMATISM

• Neither of the two foci fall on the retina.Neither of the two foci fall on the retina.• The condition is known as The condition is known as compound compound

hyperopichyperopic if both foci are at back of retina. if both foci are at back of retina.• The condition is known as The condition is known as compound compound

myopicmyopic if both foci are at front of retina. if both foci are at front of retina.• It can be with-the-rule or against-the-rule.It can be with-the-rule or against-the-rule.• -3 DS with -2DC at 90 is example of -3 DS with -2DC at 90 is example of

compound myopic astigmatism.compound myopic astigmatism.• +3 DS with +2DC at 90 is example of +3 DS with +2DC at 90 is example of

compound hyperopic astigmatism.compound hyperopic astigmatism.

COMPOUND HYPEROPIC COMPOUND HYPEROPIC ASTIGMATISMASTIGMATISM

COMPOUND MYOPIC COMPOUND MYOPIC ASTIGMATISMASTIGMATISM

In mixed astigmatism, one of the two In mixed astigmatism, one of the two foci lies at back while other at front of foci lies at back while other at front of the retina.the retina.

It can be with-the-rule or against-the-It can be with-the-rule or against-the-rule.rule.

-3 DS with +8DC at 90 is an example of -3 DS with +8DC at 90 is an example of mixed astigmatism.mixed astigmatism.

MIXED ASTIGMATISMMIXED ASTIGMATISM

MIXED ASTIGMATISMMIXED ASTIGMATISM

NOTE:NOTE:

If cyl power is less than spherical power, If cyl power is less than spherical power, then it is not mixed but compound then it is not mixed but compound astigmatism.astigmatism.

For example, -3DS with +1DC at 180 sounds For example, -3DS with +1DC at 180 sounds as if it is mixed astigmatism, but actually is as if it is mixed astigmatism, but actually is compound astigmatism, as cyl is less than compound astigmatism, as cyl is less than sphere.sphere.

RESIDUAL ASTIGMATISMRESIDUAL ASTIGMATISM

The largest element of the total astigmatism is The largest element of the total astigmatism is due to anterior corneal surface. due to anterior corneal surface.

While the other components like:While the other components like: Posterior corneal surfacePosterior corneal surface LensLens Refractive indicesRefractive indices

constitute the residual astigmatism.constitute the residual astigmatism.

RESIDUAL ASTIGMATISMRESIDUAL ASTIGMATISM= TOTAL = TOTAL –– CORNEAL CORNEAL ASTIGMATISMASTIGMATISM

Signs & SymptomsSigns & Symptoms

SIGNS & SYMPTOMSSIGNS & SYMPTOMS Type of the symptoms produced, depends upon Type of the symptoms produced, depends upon

the type of astigmatism:the type of astigmatism:1. Blurring of vision:1. Blurring of vision:

Transient blurring of vision in low Transient blurring of vision in low astigmatism.astigmatism.

Relieved by closing/rubbing the eyes.Relieved by closing/rubbing the eyes. Circles elongate into ovals.Circles elongate into ovals. A point of light appears tailed off.A point of light appears tailed off. A line appears as a succession of strokes A line appears as a succession of strokes

fused into a blurred image.fused into a blurred image.

2. Asthenopic symptoms:2. Asthenopic symptoms:

More marked in patients with low More marked in patients with low astigmatismastigmatism

(more accommodative effort)(more accommodative effort)Severe in hyperopic astigmatismSevere in hyperopic astigmatism

(more accommodative effort)(more accommodative effort)

Tiredness of eyesTiredness of eyesHeadaches Headaches (from mild frontal ache to (from mild frontal ache to explosions of pain)explosions of pain)Nervous disturbances:Nervous disturbances:

DizzinessDizziness FatigueFatigue IrritabilityIrritability

SIGNS & SYMPTOMSSIGNS & 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.)

4. Half closure of the lids:4. Half closure of the lids:

Seen in patients with high astigmatism.Seen in patients with high astigmatism.This is to make a sort of stenopaeic slit & This is to make a sort of stenopaeic slit & cutting out the rays from one meridian..cutting out the rays from one meridian..This also causes Asthenopic symptoms.This also causes Asthenopic symptoms.


5. Reading material is held too close:5. Reading material is held too close:

Reading material is held too close to the Reading material is held too close to the eyes by the patient to achieve blur but eyes by the patient to achieve blur but large image just like a myope.large image just like a myope.


6. Burning & itching:6. Burning & itching:

May be seen in patients with low May be seen in patients with low astigmatismastigmatismB/c of rubbing the eyesB/c of rubbing the eyes

Falling of eye lashesFalling of eye lashes HyperemiaHyperemia Styes& chalaziaStyes& chalazia


DiagnosisDiagnosis

DIAGNOSISDIAGNOSISVA with and without correction monocularlyVA with and without correction monocularlyPinhole VAPinhole VARetinoscopyRetinoscopyKeratometryKeratometryKeratoscopy with placido’s discKeratoscopy with placido’s discComputerised corneal topography/videographComputerised corneal topography/videograph

Subjective verification:Subjective verification:Jackson cross cylinderJackson cross cylinderAstigmatic fan & blockAstigmatic fan & blockTrial & error technique Trial & error technique (axis then power)(axis then power)Maddox VMaddox VStenopaeic slitStenopaeic slit

VISUAL ACUITY & PINHOLE VISUAL ACUITY & PINHOLE VAVA

JACKSON CROSS JACKSON CROSS CYLINDERCYLINDER

Refractor head-mounted JCC

RETINOSCOPYRETINOSCOPY

ASTIGMATISM CHARTASTIGMATISM CHART

ASTIGMATIC FANASTIGMATIC FAN

ASTIGMATISM TESTASTIGMATISM TEST

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

Stenopaeic SlitStenopaeic Slit

JAVAL SCHIOTZ JAVAL SCHIOTZ KERATOMETERKERATOMETER

BAUSCH & LOMB BAUSCH & LOMB KERATOMETERKERATOMETER

PLACIDO’S DISCPLACIDO’S DISC

TOPOGRAPHYTOPOGRAPHY

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

Correction/TreatmentCorrection/Treatment

TREATMENTTREATMENT Modes:Modes: 1. Spectacles1. Spectacles 2. Contact lens2. Contact lens 3. Laser3. Laser 4. Refractive surgery4. Refractive surgery 5. Keratoplasty5. Keratoplasty

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

Spherical LensSpherical Lens

Optical Axis

Principal Meridian

Spherical surfaces

Cylindrical LensCylindrical Lens

Optical AxisPrincipal Meridian

TORIC LENSE IMAGINGTORIC LENSE IMAGING

Interval of Sturm

CONTACT LENSESCONTACT LENSES

Various types of contact lenses are used:Various types of contact lenses are used:

SoftSoftHardHardRigid gas permeableRigid gas permeableHybrid Hybrid (hard center & soft periphery, used in (hard center & soft periphery, used in keratoconus)keratoconus)

Depending upon the degree of astigmatism:Depending upon the degree of astigmatism:SphericalSphericalToricToricBitoricBitoric

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

LASER & REFRACTIVE LASER & REFRACTIVE SURGERIESSURGERIES

Photorefractive keratectomy PRKPhotorefractive keratectomy PRKRelaxing incisions Relaxing incisions (transverse & arcuate (transverse & arcuate keratotomy)keratotomy)Wedge resectionWedge resectionCompression suturesCompression suturesContinuous sutures Continuous sutures ( astigmatism low)( astigmatism low)Interrupted sutures Interrupted sutures (astigmatism high)(astigmatism high)Orthokeratology Orthokeratology (hard lens)(hard lens)Keratoplasty Keratoplasty (keratoconus)(keratoconus)

ReferencesReferences

REFERENCESREFERENCES

Theory and practice of optics and Theory and practice of optics and refractionrefraction by by A K KhuranaA K KhuranaDuke Elder's Practice of refractionDuke Elder's Practice of refraction (Tenth (Tenth edition)edition)Clinical Optics by Elkington, Frank andClinical Optics by Elkington, Frank and Greaney Greaney (Third edition)(Third edition)Text book of ophthalmology (VText book of ophthalmology (Volume : 1) byolume : 1) by

Jaypee publishersJaypee publishers

and many websites.and many websites.

Astigmatism By Sumayya Naseem

Health & Medicine