OnLineReadingGlasses provide an Online Eye Test to determine your reading glasses dioptre requirement

EYE TEST CHART

Before the correct glasses can be found, the dioptre value of the lenses must be determined. Associated with all reading glasses is the lens dioptre value. This value is a measure of the optical power of the lens. The optical power is the ability of the lens to converge or diverge incident light. A convergent lens of 1 metre focal length is said to have a power of +1 dioptre, a lens of 0.4 metre focal length has a power of +2.5 (1/0.4) dioptre. The usual convention is that convergent lenses are positive and divergent lenses negative. There are various methods for determining the dioptre value of reading glasses.

METHOD 1: To download a Word or PDF Test Chart, go to Downloads

METHOD 2: Dioptre value obtained from your Optical Prescription.
The two example prescriptions below indicate that, for single vision reading glasses, not bifocal or varifocal glasses, a lens dioptre value of +1.50 is required by both eyes. On some prescriptions O.D. means right eye and O.S. left eye.

Right Eye	Sph	Cyl	Axis	Prism	Base
Dist	-2.50	-0.50	160
Near	+1.50
Left Eye	Sph	Cyl	Axis	Prism	Base
Dist	-3.00	-0.75	95
Near	+1.50

RX		Sph	Cyl	Axis	Prism	Base
D.V.	O.D.	-2.50	-0.50	160
D.V.	O.S.	-3.00	-0.75	95
N.V.	O.D.	+1.50
N.V.	O.S.	+1.50

If 'Add' is written close to the Near Vision dioptre value, then the prescription is for bifocal or varifocal glasses and a conversion has to be done to provide the dioptre value for single vision reading glasses. The conversion is as follows:

Right Eye: Single vision reading dioptre = (Distance vision sphere dioptre) + ('Add' dioptre)

Left Eye: Single vision reading dioptre = (Distance vision sphere dioptre) + ('Add' dioptre)

Using the example prescription below:

Right Eye: Single vision reading dioptre = (-0.50) + (+3.00) = +2.50

Left Eye: Single vision reading dioptre = (-0.25) + (+2.75) = +2.50

Right Eye	Sph	Cyl	Axis	Prism	Base
Dist	-0.50	-1.50	56
Near	+3.00 ADD
Left Eye	Sph	Cyl	Axis	Prism	Base
Dist	-0.25	-1.25	170
Near	+2.75 ADD

It may also be necessary to incorporate cylinder correction into the reading lens.

Right Eye:	Single vision reading dioptre = (Distance vision sphere dioptre) + ('Add' dioptre)
Left Eye:	Single vision reading dioptre = (Distance vision sphere dioptre) + ('Add' dioptre)

Right Eye:	Single vision reading dioptre = (-0.50) + (+3.00) = +2.50
Left Eye:	Single vision reading dioptre = (-0.25) + (+2.75) = +2.50