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Chapter 5 Astigmatic Image Formation

Page 5.31. Chapter 5 Astigmatic Image Formation. Fig 5.24 Page 5.45. Page 5.47. Take the eyes that we used to define the five clinical types of astigmatism . Fig 5.24 Page 5.45. L less (+). L (). With the posterior FL on the retina, the SMA obtains some clear vision at distance

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Chapter 5 Astigmatic Image Formation

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  1. Page 5.31 Chapter 5 Astigmatic Image Formation

  2. Fig 5.24 Page 5.45 Page 5.47 Take the eyes that we used to define the five clinical types of astigmatism

  3. Fig 5.24 Page 5.45 L less (+) L () • With the posterior FL on the retina, the SMA obtains some clear vision at distance • Accommodation in distance vision is no help because it moves the entire IOS in front of the retina • Poor uncorrected distance vision rather than accommodative fatigue is the main symptom for the uncorrected myopic astigmat • Near vision is better than distance because it moves the IOS (or at least more of it) behind the retina

  4. Fig 5.24 Page 5.45 Page 5.47 Take the eyes that we used to define the five clinical types of astigmatism

  5. Fig 5.24 Page 5.45 L much less (+) L (=) • Of all uncorrected astigmats, the CMA will have the worst distance vision, but no problem with accommodative fatigue for distance • In near vision, objects would have to be moved closer (c.f. SMA) to shift the entire IOS behind the retina (then allowing accommodation to place any part of the IOS on the retina)

  6. Vision in Astigmatism (w COLC on retina) vs. Spherical Ametropia Fig. 5.25 Page 5.48 Uncorrected spherical myope Vision in the uncorrected 2D myope is “identical” to that of the 4 D astigmat with COLC on the retina COLC size is the basis for predicting magnitude of astigmatism Move the COLC to the retina with sphere. Worse vision correlates with higher astigmatism Uncorrected astigmat with COLC on retina

  7. Clinical Aspects of Astigmatism Page 5.49 Importance of Axis Direction • For general distance vision in city/indoor environments the wtr and atr astigmat should be better off than the oblique astigmat because much of the environment is made up of horizontals and verticals • Reading performance in the uncorrected astigmat will be better if the patient can move vertical focal lines to the retina

  8. Fig. 5.26, page 5.50 (a) Emmetropia (b) Uncorrected astigmatism; horizontal FLs on retina (b) Uncorrected astigmatism; vertical FLs on retina

  9. L = 2 to 4 D L = 2 to 4 D Who will have an easier time reading (near vision): a 2 D wtr CMA or 2 D atr CHA, if for distance vision both have the COLC 3 D from the retina? 2 D wtr CMA 2 D atr CHA

  10. Who will have an easier time reading distant street signs: a young 2 D wtr CHA or 2 D atr CHA, if for distance vision both have the COLC 3 D behind the retina? 2 D wtr CHA 2 D atr CHA

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