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Optical low vision aids

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How to prescribe a magnifying glass

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Optical low vision aids

  1. 1. ORT5LVR Low vision rehabilitation Optical low vision aids – part 1 Prepared and narrated by Dr Meri Vukicevic All images used in this presentation are the author’s own unless otherwise referenced.
  2. 2. Low vision aids Images from Schweizer Products for Improved Vision October 2012
  3. 3. Low vision aids Magnifying power (MP) of an optical system is defined as: MP = retinal image size with aid retinal image size without aid
  4. 4. Don’t forget about accommodation Consider whether your patient needs to accommodate This will affect working distance ◦ The closer the object is, the more accommodation required
  5. 5. Amount of accommodation Accommodation demand = 100/working distance (cm) Example 1: Reading material held at 40cm ◦ Accommodation demand = 100/40 =2.50D Example 2: Reading material held at 10cm ◦ Accommodation demand = 100/10 = 10D
  7. 7. Focusing power of a lens Unit of measurement = dioptre (D) Increased power = decreased focal distance Focal distance of a magnifier is determined by dividing 100 by the dioptric power FD (cm) = 100/D
  8. 8. FD(cm) = 100/d 8.3cm = 100/12d 8cm
  9. 9. 4cm FD(cm) = 100/d 8.3cm = 100/24d
  10. 10. Focused correctly Focused incorrectly
  11. 11. Field of view
  12. 12. Field of view
  13. 13. Factor Effect on field of view Diameter Wide diameter = wide FOV Related to lens power Strong lens = smaller diameter Power Greater the power = smaller field of view Distance between eye & lens Field of view is larger when it’s closer to the eye