Astigmatism

Topic:- Astigmatic error
This presentation only explained about Definition, types, classification of astigmatism, It did not explained about correction.

1. ASTIGMATISM BY :- Harsh Jain B . Optometry B . V . P . D . M . C

2. TOPICS TO BE COVERED Introduction to Astigmatism. Aetilogy of Astigmatism. Types of Astigmatism. Classification of Astigmatism.

3. Introduction Astigmatism is the condition of refraction where in a point focus of light cannot be formed upon the Retina. In these the parallel rays of light forms Two Line Foci . It is also known as Non-Spherical type of Error.

4. Aetiology Curvature Astigmatism :- It is result of Abnormalities of Curvature of Cornea. The most common error is one where in the verticle curve is greater than horizantal . It is most common cause of Astigmatism.

5. Aetiology Lenticular Astigmatism :- It occurs in great frequency. In great majority of cases such anomalies are small but on occasion, as in lenticonus they may be marked. Positional Astigmatism :- Small amount of Astigmatism due to congenital tilting (or) oblique placement of lens is not uncommon.

6. TYPES OF ASTIGMATISM It is of Two Types :- Regular Astigmatism. Irregular Astigmatism.

7. Regular Astigmatism It is of Three Types :- With The Rule :- In this type,the two principle meridian are Right Angle to one another but Vertical Meridian is More Cured than Horizontal Meridian. Against The Rule :- In this type,the two principle meridian are Right Angle to one another but Horizonta l Meridian is More Cured than Vertical Meridian. Oblique :- The axes are Right angles to each other but are doesn’t lie in neither of Horizontal meridian nor vertical meridian but are crossed obliquely.

8. Irregular Astigmatism It has only One Type :- Bi-Oblique :- - In this,the Two Principle Meridians are not right angle to each other. - I.e - One may be 40° & another may be 100°.

9. C lassification o f A stigmatism

10. Simple Astigmatism. Compound Astigmatism. Mixed Astigmatism.

11. Simple Astigmatism In this, the Ray’s are focused on the Retina in One Meridian and either Infront of Retina {Simple Myopic Astigmatism} (or) Behind the {Simple Hyperopic Astigmatism} Retina in the other meridian.

12. Compound Astigmatism In this, the Ray’s of light in both the Meridian are focused either In front {Compound Myopic Astigmatism} (or) Behind {Compound Hyperopic Astigmatism} the Retina.

13. Mixed Astigmatism In this, the ray’s of Light in One Meridian are focused Infront { Myopic } of the Retina and another Meridian is Focused Behind { Hyperopic } of the Retina.

14. REFERENCE Duke Elder’s Practise of Refraction –Pg.No-65 Theory and practice of Optics & refraction – A.k Khurana