This document summarizes different types of refractive errors including myopia, hypermetropia, and astigmatism. It describes their causes, classifications based on severity and progression, associated signs and symptoms, and methods of correction through lenses, refractive surgery, or other treatments.

1. REFRACTIVE ERROR Gauri S. Shrestha, M.Optom, FIACLE

2. Refraction and its components during the growth of the eye Two distinct phases in the growth of the eye Infantile phase (a rapid and marked) Juvenile phase (slower and much slighter)

3. Refraction and its components during the growth of the eye At birth anteroposterior length of the eye= 16 mm At 2 years of age, anteroposterior length = 22mm Eye assumes hyperopia during 1-3 years Astigmatism= against the rule B/W 3-14 years, elongation of eye= 0.1 mm/yr

4. Emmetropia The parallel rays of light coming from infinity are focused at the retina with accommodation being at rest

5. The component that maintains the emmetropia 1/2 axial length 1/5 th , crystalline lens 1/4 th corneal curvature 1/20 th depth of AC

6. Ametropia The parallel rays of light coming from infinity (with accommodation at rest) are focussed either in front or behind the retina in one or both the meridian Myopia: image is focussed in front of retina Hypermetropia: image is focussed behind the retina Astigmatism: refraction varies in different meridian resulting in loss of point focus

7. MYOPIA

8. Classification of Myopia According to origin Axial: eye too long Refractive: system of eye too strong for axial length Index – nuclear sclerosis Curvature - radii of curvature too steep AC - decrease in AC depth

9. Classification of Myopia According to amount Very low up to –1.00D Low –1.00D to –3.00D Medium –3.00D to –6.00 D High –6.00D to –10.00D Very high above –10.00D

10. Classification of myopia Rate of progression – Donders 1864 Stationary myopia usually of low degree not progressing throughout the life Temporarily progressive myopia progressing only in the early years of life Permanently progressive myopia high myopia by 15years of age continues to progress throughout life

11. Classification of myopia Pathology – Duke Elder 1946 Simple myopia as a result of normal biological variability, appears between 5years and puberty and tends to stabilize after adolescents Degenerative myopia due to degenerative changes in the posterior segment of the globe

12. Myopia symptom Poor distant vision Asthenopic Symptoms Watching T.V. from close distance Keeping books close to face Squinting of eyes Poor academic performance

13. Myopia sign Eyes appear larger and somewhat prominent Anterior chamber is slightly deeper than normal Dilated appearance of the pupil Myopic crescent

14. Significance of myopia lattice degeneration Snail track degeneration Vitreous degeneration and PVD

15. The disc is often tilted and may be surrounded by chorioretinal atrophy

16. Peripheral chorioretinal atrophy (paving stone degeneration)

17. Optics of myopia

18. Treatment of myopia

19. Methods of correction Spectacle lens correction Refractive surgery Contact lens correction Clear lens extraction Phakic IOL implantation

20. Hypermetropia People with hyperopia can see distant objects, but have difficulty seeing objects that are of close

21. Components of hypermetropia Due to inherent tone of ciliary muscle Not corrected by ciliary tone within range of patients accommodation can’t overcome by accommodation Total Latent Manifest Facultative Absolute

22. Classification: Simple Axial –eye too short Refractive – too weak refractive system Index – due to acquired cortical sclerosis Curvature – Flatter cornea or lens AC – decreased depth of AC

23. Classification: Degree Very low +0.25D to +1.00D Low +1.25D to +3.00D Medium +3.00D to +5.00D High > +5.00D

24. Classification: pathological Deformational Short axial length eg; microphthalmus, optic edema Absence of element : aphakia Displacement of lens : posterior Paralysis of accommodation

25. Symptom Blur near vision Intermittent sudden blurring of vision Asthenopia during near work

26. Sign small to normal Eye ball size Cornea smaller than the normal Shallow AC and narrow angles Small optic disc Short AP length of the eyeball

27. Associated problems Recurrent styes, and chalazion Accommodative convergent strabismus Amblyopia Predisposed to primary narrow angle glaucoma

28. Optics of Hypermetropia

29. Treatment of Hypermetropia

30. Mode of correction Spectacle Contact lens Refractive surgery LASIK Laser thermal keratoplasty Phakic IOL implant Laser Thermal Keratoplasty

31. Astigmatism A variation of power in the different meridians of the eye Causes Corneal At birth – against the Rule, Adult – With the Rule , elder – Against the Rule Lens – tilt of lens, difference in thickness of lens Eccentric fovea Fundus irregularity

32. Classification: meridian With the rule astigmatism Greatest power lies in vertical meridian (60-120º) Against the rule astigmatism Greatest power lies in horizontal meridian (30-150º) Oblique astigmatism Greatest power lies in oblique meridian (30-60 or 120-150º)

33. Classification; component Total astigmatism = Corneal astigmatism + Internal astigmatism Corneal astigmatism = anterior cornea Internal astigmatism = Posterior corneal, Lens, Retinal = -0.50DC X 090

34. Classification: regularity Regular astigmatism Irregular astigmatism 90º ≠ 90º Either the two principle axes are/aren’t right angle to each other or The curvature of any one meridian is/ isn’t uniform

35. Causes of irregular astigmatism Cornea Injuries of cornea, congenital opacities, pterygium, wound healing, keratoconus Lens Inequality in density, deformity, incipient cataract, Coloboma, sublaxation, Tilting

36. Sturm's Conoid CIRCLE OF LEAST CONFUSION F 1 F 2 INTERVAL OF STURM Rays of light entering cannot converge to a point focus but forms a focal lines

37. Clinical classification: Sturm’s conoid Compound myopic astigmatism Simple myopic astigmatism Mixed astigmatism Simple hyperopic astigmatism Compound hyperopic astigmatism

38. Symptom and sign Asthenopia Distortion or blurring of vision Narrowed palpebral fissure and contracted eyebrows head tilt possible

39. Correction Glasses Contact lens Refractive surgery Arcuate keratotomy LASIK

40. Assessment History: Blurring of vision D or N Asthenopia : near or distance Distortion Head tilt Diplopia Family history: glasses, squint, amblyopia

41. Assessment Examination: VA, Pin hole examination refraction, keratometry, axial length, cycloplegic refraction, anterior segment examination, posterior segment examination

43. Thank you