ASTIGMATISMNishita afrin

ICOB.OPTOM

What is Astigmatism ?O one type of refractive error

,where in refraction varies in different meridian

CONTINUE..O For example, the image may

be focused on the retina in the horizontal (sagittal )plane,but not on the retina in the vertical plane

O Most Astigmatic cornea have two curves,one is steeper and another oner a flatter curve

OPTICS OF ASTIGMATISMO In Astigmatism , the rays of

light from one sector fall on one point and rays from aanother sector fall on another point.

O The configuration of rays refracted through the Astigmatic surface (toric surface) is called sturms conoid

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INCIDENCEO No eye is perfectly stigmatic ,

almost all individuals have a minor degree of physiological Astigmatism

O About 60 % cases of refractive error have Astigmatism which needs to be corrected

CONTINUEO Occurs with equal frequency in

males and femaleO Approximate distributation recording

to degree of Astigmatism 0.25 - 0.50 50% 0.75 - 1.0 25% 1.00 – 4.00 24 % > 4.00 1%

CONTINUEOOne study report as – WTR 38% ATR 30% Oblique 32%

SEVERITY OF ASTIGMATISMO Classified as follows – Mild Astigmatism <1 D Moderate Astigmatism

1.00 to 2.00 D Severe Astigmatism 2.00

to 3.00 D Extreme Astigmatism

>3.00 D

CLASSIFICATIONO Regular Astigmatism

O Irregular Astigmatism

REGULAR ASTIGMATISM Aeitiology -

1. Corneal Astigmatism2. Lenticular Astigmatism Curvatural, Positional,

Index3. Retinal Astigmatism

TYPES OF REGULAR ASTIGMATISM

O With the rule AstigmatismO Against the AstigmatismO Oblique AstigmatismO Bi-oblique Astigmatism

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REFRACTIVE TYPES OF ASTIGMATISM

O Simple Astigmatism – simple myopic,simple hyperopic astigmatism

O Compound Astigmatism – compound myopic,compound hyperopic astigmatism

O Mixed Astigmatism

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SYMMETRIC ASTIGMATISMO Regular AstigmatismO principal meridian of each

eye have similar but opposite axes

O which together add upto 180±15˚

SYMPTOMS OF REGULAR ASTIGMATISM

O DISTORTION OR BLURRING OF VISION

O ASTHENOPIC SYMPTOMO TILTING OF HEADOSQUINTING OF EYEO READING MATERIAL MAY BE HELD

CLOSE TO EYESOBURNING AND ITCHING SENSATION

IRREGULAR ASTIGMATISMO IRREGULAR CHANGE IN

REFRACTIVE POWER IN DIFFERENT MERIDIAN

O AEITIOLOGICAL TYPE – Corneal irregular Astigmatism Lenticular irregular

Astigmatism Retinal irregular Astigmatism

SYMPTOMS OF IRREGULAR ASTIGMATISM

O DEFECTIVE VISIONO IMAGE DISTORTIONOPOLYOPIA

RESIDUAL ASTIGMATISMO The largest element of the Astigmatism

is due to anterior corneal surfaceO While the other components like – Posterior corneal surface Lens Refractive indicesConstitute the residual AstigmatismRESIDUAL ASTIGMATISM = TOTAL –

CORNEAL ASTIGMATISM

INVESTIGATION OF ASTIGMATISM

I. VA with and without correction monocularly

II. RetinoscopyIII. keratometryIV. keratometry with placido

discV. computerized corneal

topography

CONTINUEO SUBJECTIVE REFRACTION –I. Jacson cross cylinderII. Astigmatic fan and block

techniqueIII. stenopic slitIV. trial and error technique

TREATMENT1. OPTICAL- SPECTACLES CONTACT LENS2. SURGICAL – LASER LASIK 3. KERATOPLASTY

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