Anomalies of refraction


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  • This represents a decrease in ocular refraction of approximately 3 D for the whole period between 3 and 14 years, when growth appears to be complete.
  • Anomalies of refraction

    1. 1. REFRACTIVE ERROR Gauri S. Shrestha, M.Optom, FIACLE
    2. 2. Refraction and its components during the growth of the eye <ul><li>Two distinct phases in the growth of the eye </li></ul><ul><ul><li>Infantile phase (a rapid and marked) </li></ul></ul><ul><ul><li>Juvenile phase (slower and much slighter) </li></ul></ul>
    3. 3. Refraction and its components during the growth of the eye <ul><li>At birth anteroposterior length of the eye= 16 mm </li></ul><ul><li>At 2 years of age, anteroposterior length = 22mm </li></ul><ul><li>Eye assumes hyperopia during 1-3 years </li></ul><ul><li>Astigmatism= against the rule </li></ul><ul><li>B/W 3-14 years, elongation of eye= 0.1 mm/yr </li></ul>
    4. 4. Emmetropia <ul><li>The parallel rays of light coming from infinity are focused at the retina with accommodation being at rest </li></ul>
    5. 5. The component that maintains the emmetropia <ul><li>1/2 axial length </li></ul><ul><li>1/5 th , crystalline lens </li></ul><ul><li>1/4 th corneal curvature </li></ul><ul><li>1/20 th depth of AC </li></ul>
    6. 6. Ametropia <ul><li>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 </li></ul><ul><li>Myopia: image is focussed in front of retina </li></ul><ul><li>Hypermetropia: image is focussed behind the retina </li></ul><ul><li>Astigmatism: refraction varies in different meridian resulting in loss of point focus </li></ul>
    7. 7. MYOPIA
    8. 8. Classification of Myopia According to origin <ul><li>Axial: eye too long </li></ul><ul><li>Refractive: system of eye too strong for axial length </li></ul><ul><li>Index – nuclear sclerosis </li></ul><ul><li>Curvature - radii of curvature too steep </li></ul><ul><li>AC - decrease in AC depth </li></ul>
    9. 9. Classification of Myopia According to amount <ul><ul><ul><li>Very low up to –1.00D </li></ul></ul></ul><ul><ul><ul><li>Low –1.00D to –3.00D </li></ul></ul></ul><ul><ul><ul><li>Medium –3.00D to –6.00 D </li></ul></ul></ul><ul><ul><ul><li>High –6.00D to –10.00D </li></ul></ul></ul><ul><ul><ul><li>Very high above –10.00D </li></ul></ul></ul>
    10. 10. Classification of myopia Rate of progression – Donders 1864 <ul><li>Stationary myopia </li></ul><ul><ul><li>usually of low degree not progressing throughout the life </li></ul></ul><ul><li>Temporarily progressive myopia </li></ul><ul><ul><li>progressing only in the early years of life </li></ul></ul><ul><li>Permanently progressive myopia </li></ul><ul><ul><li>high myopia by 15years of age </li></ul></ul><ul><ul><li>continues to progress throughout life </li></ul></ul>
    11. 11. Classification of myopia Pathology – Duke Elder 1946 <ul><li>Simple myopia </li></ul><ul><ul><li>as a result of normal biological variability, </li></ul></ul><ul><ul><li>appears between 5years and puberty and </li></ul></ul><ul><ul><li>tends to stabilize after adolescents </li></ul></ul><ul><li>Degenerative myopia </li></ul><ul><ul><li>due to degenerative changes in the posterior segment of the globe </li></ul></ul>
    12. 12. Myopia symptom <ul><li>Poor distant vision </li></ul><ul><li>Asthenopic Symptoms </li></ul><ul><li>Watching T.V. from close distance </li></ul><ul><li>Keeping books close to face </li></ul><ul><li>Squinting of eyes </li></ul><ul><li>Poor academic performance </li></ul>
    13. 13. Myopia sign <ul><li>Eyes appear larger and somewhat prominent </li></ul><ul><li>Anterior chamber is slightly deeper than normal </li></ul><ul><li>Dilated appearance of the pupil </li></ul><ul><li>Myopic crescent </li></ul>
    14. 14. Significance of myopia <ul><li>lattice degeneration </li></ul><ul><li>Snail track degeneration </li></ul><ul><li>Vitreous degeneration and PVD </li></ul>
    15. 15. The disc is often tilted and may be surrounded by chorioretinal atrophy
    16. 16. <ul><li>Peripheral chorioretinal atrophy (paving stone degeneration) </li></ul>
    17. 17. Optics of myopia
    18. 18. Treatment of myopia
    19. 19. Methods of correction <ul><li>Spectacle lens correction </li></ul><ul><li>Refractive surgery </li></ul><ul><li>Contact lens correction </li></ul><ul><li>Clear lens extraction </li></ul><ul><li>Phakic IOL implantation </li></ul>
    20. 20. Hypermetropia <ul><li>People with hyperopia can see distant objects, but have difficulty seeing objects that are of close </li></ul>
    21. 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. 22. Classification: Simple <ul><li>Axial –eye too short </li></ul><ul><li>Refractive – too weak refractive system </li></ul><ul><li>Index – due to acquired cortical sclerosis </li></ul><ul><li>Curvature – Flatter cornea or lens </li></ul><ul><li>AC – decreased depth of AC </li></ul>
    23. 23. Classification: Degree <ul><li>Very low +0.25D to +1.00D </li></ul><ul><li>Low +1.25D to +3.00D </li></ul><ul><li>Medium +3.00D to +5.00D </li></ul><ul><li>High > +5.00D </li></ul>
    24. 24. Classification: pathological <ul><li>Deformational </li></ul><ul><ul><li>Short axial length eg; microphthalmus, optic edema </li></ul></ul><ul><li>Absence of element : aphakia </li></ul><ul><li>Displacement of lens : posterior </li></ul><ul><li>Paralysis of accommodation </li></ul>
    25. 25. Symptom <ul><li>Blur near vision </li></ul><ul><li>Intermittent sudden blurring of vision </li></ul><ul><li>Asthenopia during near work </li></ul>
    26. 26. Sign <ul><li>small to normal Eye ball size </li></ul><ul><li>Cornea smaller than the normal </li></ul><ul><li>Shallow AC and narrow angles </li></ul><ul><li>Small optic disc </li></ul><ul><li>Short AP length of the eyeball </li></ul>
    27. 27. Associated problems <ul><li>Recurrent styes, and chalazion </li></ul><ul><li>Accommodative convergent strabismus </li></ul><ul><li>Amblyopia </li></ul><ul><li>Predisposed to primary narrow angle glaucoma </li></ul>
    28. 28. Optics of Hypermetropia
    29. 29. Treatment of Hypermetropia
    30. 30. Mode of correction <ul><li>Spectacle </li></ul><ul><li>Contact lens </li></ul><ul><li>Refractive surgery </li></ul><ul><ul><li>LASIK </li></ul></ul><ul><ul><li>Laser thermal keratoplasty </li></ul></ul><ul><li>Phakic IOL implant </li></ul>Laser Thermal Keratoplasty
    31. 31. Astigmatism <ul><li>A variation of power in the different meridians of the eye </li></ul><ul><li>Causes </li></ul><ul><ul><li>Corneal </li></ul></ul><ul><ul><ul><li>At birth – against the Rule, Adult – With the Rule , elder – Against the Rule </li></ul></ul></ul><ul><ul><li>Lens – tilt of lens, difference in thickness of lens </li></ul></ul><ul><ul><li>Eccentric fovea </li></ul></ul><ul><ul><li>Fundus irregularity </li></ul></ul>
    32. 32. Classification: meridian <ul><li>With the rule astigmatism </li></ul><ul><ul><li>Greatest power lies in vertical meridian (60-120º) </li></ul></ul><ul><li>Against the rule astigmatism </li></ul><ul><ul><li>Greatest power lies in horizontal meridian (30-150º) </li></ul></ul><ul><li>Oblique astigmatism </li></ul><ul><ul><li>Greatest power lies in oblique meridian (30-60 or 120-150º) </li></ul></ul>
    33. 33. Classification; component Total astigmatism = Corneal astigmatism + Internal astigmatism Corneal astigmatism = anterior cornea Internal astigmatism = Posterior corneal, Lens, Retinal = -0.50DC X 090
    34. 34. Classification: regularity <ul><li>Regular astigmatism </li></ul><ul><li>Irregular astigmatism </li></ul>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. 35. Causes of irregular astigmatism <ul><li>Cornea </li></ul><ul><ul><li>Injuries of cornea, congenital opacities, pterygium, wound healing, keratoconus </li></ul></ul><ul><li>Lens </li></ul><ul><ul><li>Inequality in density, deformity, incipient cataract, Coloboma, sublaxation, Tilting </li></ul></ul>
    36. 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. 37. Clinical classification: Sturm’s conoid <ul><li>Compound myopic astigmatism </li></ul><ul><li>Simple myopic astigmatism </li></ul><ul><li>Mixed astigmatism </li></ul><ul><li>Simple hyperopic astigmatism </li></ul><ul><li>Compound hyperopic astigmatism </li></ul>
    38. 38. Symptom and sign <ul><li>Asthenopia </li></ul><ul><li>Distortion or blurring of vision </li></ul><ul><li>Narrowed palpebral fissure and contracted eyebrows </li></ul><ul><li>head tilt possible </li></ul>
    39. 39. Correction <ul><li>Glasses </li></ul><ul><li>Contact lens </li></ul><ul><li>Refractive surgery </li></ul><ul><ul><li>Arcuate keratotomy </li></ul></ul><ul><ul><li>LASIK </li></ul></ul>
    40. 40. Assessment <ul><li>History: </li></ul><ul><ul><li>Blurring of vision D or N </li></ul></ul><ul><ul><li>Asthenopia : near or distance </li></ul></ul><ul><ul><li>Distortion </li></ul></ul><ul><ul><li>Head tilt </li></ul></ul><ul><ul><li>Diplopia </li></ul></ul><ul><ul><li>Family history: glasses, squint, amblyopia </li></ul></ul>
    41. 41. Assessment <ul><li>Examination: </li></ul><ul><ul><li>VA, Pin hole examination </li></ul></ul><ul><ul><li>refraction, </li></ul></ul><ul><ul><li>keratometry, </li></ul></ul><ul><ul><li>axial length, </li></ul></ul><ul><ul><li>cycloplegic refraction, </li></ul></ul><ul><ul><li>anterior segment examination, </li></ul></ul><ul><ul><li>posterior segment examination </li></ul></ul>
    42. 43. Thank you