Optical low vision aids
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Transcript of Optical low vision aids
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ORT5LVRLow 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.
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Low vision aids
Images from Schweizer Products for Improved Vision October 2012
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Low vision aids
Magnifying power (MP) of an optical system is defined as:
MP = retinal image size with aid
retinal image size without aid
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Don’t forget about accommodationConsider whether your patient
needs to accommodateThis will affect working distance
◦The closer the object is, the more accommodation required
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Amount of accommodation
Accommodation demand = 100/working distance (cm)
Example 1: Reading material held at 40cm◦Accommodation demand = 100/40
=2.50DExample 2: Reading material held at
10cm◦Accommodation demand = 100/10 = 10D
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OPTICAL AIDS
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Focusing power of a lensUnit 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
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FD(cm) = 100/d8.3cm = 100/12d
8cm
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4cm
FD(cm) = 100/d8.3cm = 100/24d
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Focused correctly Focused incorrectly
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Field of view
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Field of view
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Factor Effect on field of view
Diameter Wide diameter = wide FOVRelated to lens powerStrong 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