astigmatism
TRANSCRIPT
ASTIGMATISMNishita afrin
ICOB.OPTOM
What is Astigmatism ?
O one type of refractive error ,where in refraction varies in different meridian
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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 ASTIGMATISM
O 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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INCIDENCE
O 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%
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OOne study report as – WTR 38% ATR 30% Oblique 32%
SEVERITY OF ASTIGMATISM
O 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
CLASSIFICATION
O 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 ASTIGMATISM
O 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 ASTIGMATISM
O 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 ASTIGMATISM
O The largest element of the Astigmatism is due to anterior corneal surface
O 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
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O SUBJECTIVE REFRACTION –I. Jacson cross cylinderII. Astigmatic fan and block
techniqueIII. stenopic slitIV. trial and error technique
TREATMENT
1. OPTICAL- SPECTACLES CONTACT LENS2. SURGICAL – LASER LASIK 3. KERATOPLASTY
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