ASTIGMATISM AND PRESBYOPIA

1. ASTIGMATISM AND PRESBYOPIA Dr. Vidya Hegde

2. OBJECTIVES At the end of the class, a student should kow • Clinical features of astigmatism and its management • Correlate types of regular astigmatism with Sturm conoid • Able to diagnose prebyopia

3. CONTENTS • Definition • Classification • Clinical features • Management

4. ASTIGMATISM Ametropic condition of the eye, where parallel rays of light from infinity do not come to a point focus on the retina Type of refractive error where in refraction varies in different meridia

5. STURM CONOID • The rays after refraction will be perfectly symmetrical but will have two foci • The whole bundle of rays –sturmsconoid • Distance between the two foci is –focal interval of sturms • Circle of least diffusion-point where horizontal rays come to a focus and vertical diverge

6. CLASSIFICATION OF ASTIGMATISM REGULAR ASTIGMATISM IRREGULAR ASTIGMATISM MIXED COMPOUND SIMPLE MYOPIC HYPERMETROPIC MYOPIC HYPERMETROPIC

8. CLASSIFICATION OF ASTIGMATISM REGULAR ASTIGMATISM OBLIQUE BI OBLIQUE Against the rule With the rule

9. CLASSIFICATION OF ASTIGMATISM OBLIQUE BIOBLIQUE

10. CLINICAL FEATURES Eye strain – • Headache • Aching of eyes • Ocular fatigue while reading • Letters running together Decreased Vision

11. MANAGEMENT If error is small (<0.5D) and no symptoms – spectacles unnecessary If asthenopic symptoms present – full optical correction with spectacles OTHER MEASURES – Rigid contact lenses, toric contact lenses, Astigmatic LASIK (1.5 – 5D), arcuate keratotomy and toricphakic IOLs

12. ACCOMODATION

13. OCULAR CHANGES IN ACCOMODATION • Slackening of zonules • Change in the curvature of the lens surface(anterior) • Increase in axial thickness of the lens • Pupillary constriction and convergence CM

14. AA FP NP RA NEAR POINT NEAREST POINT AT WHICH THE SMALL OBJECTS CAN BE SEEN CLEARLY FAR POINT FARTHEST POINT AT WHICH THE SMALL OBJECTS CAN BE SEEN CLEARLY RANGE OF ACC DISTANCE BETWEEN NEAR AND FAR POINT

15. AMPLITUDE OF ACCOMODATION Difference between the diopteric power needed to focus the distance and near 10 years-7cm 40years-25cm 45years -33cm Far point is infinity Near point varies with the age of the patient Amp of acc=100/7=14D Amp of acc=100/25=4D

16. Distance in meters Accommodation in Dioptres 1/3 m 3 1/2 m 2 1 m 1 3 m 1/3 6 m 1/6 Infinity 0 Role of accommodation

17. PRESBYOPIA • Physiological condition where there is difficulty in near vision due to recession of the near point with age

18. PRESBYOPIA Failing near vision due to decrease in the amplitude of accommodation CAUSES Decrease in elasticity of the lens Decrease in the power of ciliary muscle

19. SYMPTOMS Difficulty in near vision (start-evening, later-good light) Asthenopia

20. TREATMENT Convex lens Rough estimate - 40 years-1D 45 years -1.5D 50 years -2D 55 years-2.5D Single vision, bifocal, progressive glasses

21. PRINCIPLES Correct refractive error for distance for each eye Find presbyopic correction needed for each eye separately Weakest convex lens which can be seen clearly is selected Presbyopic add should leave 50% of the accommodation reserve Profession of the patient should be considered

22. THANK YOU