Astigmatism

ppt on astigmatism
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1. ASTIGMATISM www.knowyoureye.com

2. INDEX DEFINITION ETIOLOGY CLASSIFICATIONS STURMS CONOID/INTERVAL SIGNS AND SYMPTOMS CLINICAL TESTS MANAGEMENT

3. DEFINITION Astigmatism by definition is a condition where the parallel beam of light rays incident on the cornea after refraction are not focused to form a point image near or on the retina

4. The shape of eye ball

5. ETIOLOGY Irregular curvature or RI in the anterior surface of cornea Irregular curvature or RI and also the position of lens/IOL The refracting power is not uniform in all meridians of both lens or cornea The principal meridians are the meridians of greatest and least refracting powers

6. Classifications Based on etiology Based on relation between principal meridians Based on orientation of meridian or axis Based on focal points relative to the retina

7. Classification based on etiology

8. Based on relation between principle meridian WTR-With The Rule Astigmatism Vertical meridian of cornea is more curved Myopic power is more in vertical meridian Eg :- -3.0D cyl x 180˚ ATR- Against The Rule Astigmatism Horizontal meridian of cornea is more curved Myopic power is more in horizontal meridian Eg :- -3.0D cyl x 90˚

9. Based on orientation of meridian OBLIQUE axis is not on or near 90˚ or 180˚ Range of axis lies in between 120˚-150˚ & 60˚- 30˚ Eg :- -3.0D cyl x 45˚ BIOBLIQUE The meridians are not perpendicular Eg :- -3.0D cyl x 90˚/ -2.0 D cyl x 110˚

10. orientation of meridian

11. On focal points relative to retina Simple astigmatism One focal point on retina and the other front or behind Of 2 types simple myopic and simple hyperopic Compound astigmatism Both the 2 focal points are in front or behind the retina Of 2 types compound myopic and hyperopic Mixed astigmatism One focal point in front and other behind the retina

12. Mixed astigmatism

13. Sturm’s conoid /interval

14. Signs and symptoms Distorted vision at distance and near Letter confusion Asthenopia or ocular fatigue Headaches Squinting

15. Clinical tests Visual acuity tests – distance and near Autorefraction Keratometry Retinoscopy Monocular subjective refraction, including Jackson cross cylinder

16. Refining astigmatism Astigmatic fan Clock dial Jackson’s c0ross cylinder Stenopic slit

17. Management Spectacles Cylindrical lenses and spherocylindrical lenses in spectacles Contact lens Toric soft contact lenses rigid gas permeable contact lenses Refractive surgery Photorefractive keratectomy (PRK) Laser in-situ keratomileusis (LASIK)

18. Astigmatic prescription Astigmatism Year Plan <2.00D <2 Years Monitor 6 months >2.00D <2 Years Partial Rx >2.00D >2 Years Full Rx 1.00 to 2.00D >2 Years Rx if increasing 1.00 to 2.00D >3 Years Rx based on acuity <1.00D adult Full Rx >1.00D adult Partial Rx, then full Rx

19. Reference Walter Huang, OD ,Yuanpei University, Department of Optometry Optometry, journal of American optometric association Duke-Elder, Sir Stewart (1989). The Practice of Refraction (8th ed.). Dr.G. narayan. “Astigmatism”, eMedicine.com. August 05, 2009. Bennett AG, Rabbetts RB (1994) Clinical Visual Optics Image: Google

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