Astigmatism

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A simple concise presentation of Astigmatism with recent advances in treatment of this optical defect,..

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Astigmatism

  1. 1. ASTIGMATISM Dr Rajvin Samuel 1 1 st yr Pg Ophthalmology
  2. 2. <ul><li>Definition : </li></ul><ul><li>  A defect of an optical system causing light rays from a point source to fail to meet in a focal point resulting in a blurred and imperfect image. </li></ul><ul><li>Rays of light converge forming Focal lines </li></ul><ul><li>The word is derived from Greek α –without and stigma – Spot </li></ul>
  3. 3. <ul><li>Astigmatism begins in the 1 st yrs of life > 1 D </li></ul><ul><li>This arises from recti muscles pulling upon delicate infant sclera in different gazes </li></ul><ul><li>This astigmatism helps to attain position of best focus </li></ul><ul><li>This incidence of astigmatism decreases with age </li></ul>
  4. 4. <ul><li>A toric lens is a lens with two different powers in two orientations perpendicular </li></ul><ul><li>to each other </li></ul><ul><li>A toric surface resembles a section of the surface of an doughnut where there are two regular radii, one smaller than the other one. </li></ul>
  5. 5. <ul><li>Conus of Sturm :- </li></ul><ul><li>Geometric configuration of light rays emanating from single point source & refracted by spherocylindrical lens </li></ul>
  6. 6. <ul><li>Focal interval of Sturm :- </li></ul><ul><li>Distance between 2 focal </li></ul><ul><li>lines </li></ul><ul><li>Circle of least diffusion </li></ul><ul><li>At the dioptric mean of focal lines the cross section of sturms conoid appears as circular patch of light rays – best overall focus </li></ul>
  7. 7. <ul><li>Based on axis of the principal meridians </li></ul><ul><li>Regular astigmatism – principal meridians are perpendicular </li></ul><ul><ul><li>With-the-rule astigmatism </li></ul></ul><ul><ul><li>Against-the-rule astigmatism 2] </li></ul></ul><ul><ul><li>Oblique astigmatism </li></ul></ul><ul><li>Irregular astigmatism - principal meridians are not perpendicular </li></ul>
  8. 8. <ul><li>Based on focus of the principal meridians </li></ul><ul><li>Simple astigmatism </li></ul><ul><ul><li>Simple hyperopic astigmatism </li></ul></ul><ul><ul><li>Simple myopic astigmatism </li></ul></ul><ul><li>Compound astigmatism </li></ul><ul><ul><li>Compound hyperopic astigmatism </li></ul></ul><ul><ul><li>Compound myopic astigmatism </li></ul></ul><ul><li>Mixed astigmatism </li></ul>
  9. 9. Regular Astigmatism : <ul><li>Correctable by Spherocylindrical lenses </li></ul><ul><li>Etiology : </li></ul><ul><li>1. Corneal - abnormalities of curvature [common] </li></ul><ul><li>2. Lenticular is rare. It may be: i. Curvatural - abnormalities of curvature of lens as seen in lenticonus. ii. Positional - tilting or oblique placement of lens , subluxation. 3. Retinal - oblique placement of macula [rare] </li></ul>
  10. 10. <ul><ul><li>Symptoms : </li></ul></ul><ul><li>Blurring of vision </li></ul><ul><li>Asthenopic symptoms </li></ul><ul><li>Tilting of head </li></ul><ul><li>Squinting [Half closure of eyelid] </li></ul>
  11. 11. Investigations: <ul><li>Retinoscopy </li></ul><ul><li>Keratometry </li></ul><ul><li>Computerized corneal Tomography </li></ul><ul><li>Astigmatic fan test </li></ul><ul><li>Jackson cross cylinder </li></ul>
  12. 12. Irregular Astigmatism <ul><li>Etiology : </li></ul><ul><li>Corneal [ Scars , Keratoconus , flap complications, </li></ul><ul><li>marginal degenration , </li></ul><ul><li>Lenticular [Cataract maturation] </li></ul><ul><li>Symptoms : </li></ul><ul><li>Defective vision </li></ul><ul><li>Distorsion of objects </li></ul><ul><li>Polyopia </li></ul><ul><li>Investigations: </li></ul><ul><li>- Placido's disc test reveals distorted circles </li></ul><ul><li> - computerized corneal topography </li></ul>
  13. 13. Treatment : <ul><li>Optical treatment : </li></ul><ul><li>RGP contact lenses </li></ul><ul><li>Hybrid contact lenses </li></ul><ul><li>Scleral lenses </li></ul><ul><li>Piggyback lens </li></ul><ul><li>Phototherapeutic keratectomy </li></ul><ul><li>Corneal Cross-Linking With Riboflavin and Ultraviolet Irradiation </li></ul>
  14. 14. <ul><li>Penetrating Keratoplasty [PKP] </li></ul><ul><li>Intacs corneal implants </li></ul><ul><li>Deep Anterior Lamellar Keratoplasty [DALK] </li></ul><ul><li>Descemet's Stripping Endothelial Keratoplasty </li></ul><ul><li>[DSEK] </li></ul>
  15. 16. Residual astigmatism : <ul><li>The amount of astigmatism that still remains after correction of a refractive error. </li></ul><ul><li>In the case of correction of corneal astigmatism using rigid contact lens ,lenticular residual astigmatism is exposed. </li></ul>
  16. 17. Treatment <ul><li>Eyeglasses </li></ul><ul><li>contact lenses </li></ul><ul><li>refractive surgery </li></ul>
  17. 18. <ul><li>Astigmatism correction requires prescription of convex cylindrical lenses at 180 +/- 20 deg or concave cylindrical lenses at 90 +/- 20 deg with the rule and vice versa. </li></ul>
  18. 19. Contact lenses <ul><li>Toric contact lenses </li></ul><ul><li>Soft lenses [SL] </li></ul><ul><li>Rigid gas permeable lenses </li></ul><ul><li>[RGP] </li></ul><ul><li>RGP do not conform to the asymmetry of corneal surface but replaces it totally and also provides clarity of vision ,more durable. </li></ul><ul><li>Soft lenses are more comfortable to wear ,easy to fit, adhere more tightly to cornea . </li></ul>
  19. 20. Refractive surgeries <ul><li>Astigmatic Keratotomy </li></ul><ul><li>Photoastigmatic refractive Keratectomy [PRK] </li></ul><ul><li>Relaxing incisions with compression sutures </li></ul><ul><li>LASIK surgery </li></ul>
  20. 21. <ul><li>THANK YOU </li></ul>

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