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