Astigmatism

Astigmatism
BY
RAIN HEALTH CARE

WHAT IS ASTIGMATISM

TYPES OF ASTIGMATISM

SYMPTOMS OF ASTIGMATISM

TREATMENT OF ASTIGMATISM

1. ASTIGMATISM Astigmatism is a type of refractive error where the refraction varies in which the incident parallel rays don't come to a point focus upon the retina, due to refraction varies in different meridians of the eye . Etiology : 1. Corneal astigmatism 2. Lenticular astigmatism is rare 3 . Retinal astigmatism

2. Types Regular astigmatism   1. Horizonto -vertical astigmatism:  In this type the two principal meridians are placed at right angles to one. With the rule astigmatism:  With the rule astigmatism When the vertical meridian is more curved than the horizontal meridian, this is known as with the rule astigmatism. This can be corrected either by a – (minus) cylinder x 180 or + (plus) cylinder x 90.  Against the rule astigmatism:  The horizontal meridian is more curved than the vertical meridian. This is known as inverse astigmatism or against the rule astigmatism. This can be corrected either by – (minus) cylinder x 90 or + (plus) cylinder x 180 .

3. 2. Oblique astigmatism: Here the two principal meridia are not horizontal or vertical but still they are placed at right angle to each other, e.g. the two meridia can be 45° and 135° or 10° and 100°. C.   3. Bioblique astigmatism: Here the two principal meridia are oblique and at the same time, they do not intersect at right angle to each other, e.g. one meridian may be at 10° and other at 30°. This type of astigmatism cannot be corrected by spectacles.

4. IRREGULAR ASTIGMATISM THE SURFACE IS SO DISTORTED THAT IT ADMITS NO GEOMETRICAL ANALYSIS AND IT CAN’T BE CORRECTED ADEQUATELY WITH GLASSES. SCARRING OF THE CORNEA KERATOCONUS INCIPIENT CATARACT LENTICONUS AFTER PENETRATING KERATOPLASTY

5. Refractive types of regular astigmatism Simple myopic astigmatism Simple hypermetropic astigmatism Compound myopic astigmatism Compound hypermetropic astigmatism Mixed astigmatism

6. Depending upon etiology Corneal astigmatism Lenticular astigmatism Retinal astigmatism

7. Clinical Features eyeache , headache , tiredness of eyes asthenopic symptoms.  Blurring of vision 

8. Tools used in evaluation of astigmatism Keratoscopic examination by placidos disc. Retinoscopy by concave mirror/streak Use of astigmatic fan or Maddox rod Stenopaeic slit or pinhole Keratometry   Jackson cross cylinder.

9. Treatment Regular astigmatism- -  Optical correction   - Spectacle (concave – convex cylinder lens)  - Contact lens ( toric lens - prism balastic lens)  Surgical  - Keratomiluesis   - Excimer laser  Irregular astigmatism  Hard/semi-soft contact lens  - Keratoplasty in central area of conical cornea  - Excision of scar + replacement by graft 

10. Summary Astigmatism is a type of refractive error where no point focus is formed on the retina.  Two main types of astigmatism are regular and irregular astigmatism‘With the rule’{ – (minus) cylinder x 180 or + (plus) cylinder x90} and ‘against the rule’ {– (minus) cylinder x 90 or + (plus) cylinder x 180} astigmatism are the types which are of more interest as we can understand patient symptoms.  Refractive types includes simple, compound and mixed astigmatism.  Optics of astigmatism can be explained by sturm’s conoid .  To find the axis of astigmatism we can use stenopic slit, placido’s disc, astigmatic fan and some techniques of retinoscopy .  We can use JCC to refine power and axis of astigmatism.  Cylindrical and spherocylindrical lenses can be used to correct astigmatism.  Contact lens and surgery are the other options. 

11. Key points to remember  Minimum cylinder, maximum comfort.  Give minus cylinder for more comfort.  For high cylinder, it is better to do keratometry   Refine axis and power before finalizing prescription  Check binocular comfort subjectively

12. SURGERY AK- ASTIGMATIC KERATOMY LRI- LIMBAL RELAXING INCISION CRI- CORNEAL RELAXING INCISION PARK- PHOTO ASTIGMATIC REFRACTIVE KERATOTOMY  LASIK- LASER INSITU KERATOMILESIS SMILE- SMALL INCISION LENTICULAR EXTRACTION.

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