optical low vision aids
DESCRIPTION
How to prescribe a magnifying glassTRANSCRIPT
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.
Low vision aids
Images from Schweizer Products for Improved Vision October 2012
Low vision aids
Magnifying power (MP) of an optical system is defined as:
MP = retinal image size with aid
retinal image size without aid
Don’t forget about accommodationConsider whether your patient
needs to accommodateThis will affect working distance
◦The closer the object is, the more accommodation required
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
OPTICAL AIDS
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
FD(cm) = 100/d8.3cm = 100/12d
8cm
4cm
FD(cm) = 100/d8.3cm = 100/24d
Focused correctly Focused incorrectly
Field of view
Field of view
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