Help with your Glasses Prescription
The sphere (Sph) specifies the strength of lens required to correct your
focus - a plus sphere to correct long-sightedness (hyperopic - difficulty
focusing on close objects) and a minus to correct short sightedness
(myopia - difficulty focusing on distant objects.)
The sphere is measured in Dioptre’s, your prescription may have the word
Plano or Pl or an infinity sign, this means that you are neither long
nor short sighted but zero power for the Sphere, however you may have
astigmatism – a CYL and AXIS on your prescription. Most values range
from 0.00 to +/- 20.00 and go up in steps of 0.25.
The CYL and AXIS compensate for an astigmatism. So what's an astigmatism?
An astigmatism is where the eye is shaped slightly like a rugby ball or
referred to as ‘toric’, not a perfect sphere like a football. This just
means the eye has difficulty focusing at certain angles.
This box maybe empty or have a plus or a minus value in it. The measurement
is the Dioptre. Most values range from +/- 0.25 to +/- 4.00 and will go up
in steps of 0.25.
The AXIS is only present if there is a value in the CYL box, the AXIS
tells us where the astigmatism is on your eye. The measurement is in
Degrees. The values range between 0 and 180 and may go up in steps of ½,
1, 5 or 10 degrees, we only show the AXIS to a whole number but if you
have a ½ degree on your prescription you can list this in the additional
information box when ordering.
The ADD (Addition)
The Add, short for Reading Addition, is the additional correction required
for reading, this can be used to make either reading glasses, bifocal
glasses or Varifocal glasses.
This figure is an indication of how much extra power is required ‘on top’
of the distance prescription for near or intermediate glasses. This extra
power will ALWAYS be the same for each eye and may only appear once on your
prescription but it is understood to be meant for both eyes. The measurement
is the Dioptre, and most values range from +0.50 to +3.50 and will go up in
steps of 0.25.
The 'addition' is only required if the glasses are going to be used for
reading or close work. If your glasses are for distance only, this will
not be an issue. Sometimes opticians use the word 'Add' or 'Near' instead
of 'addition'. They may only write it once, but it normally applies to both
eyes and is almost always the same value for both eyes (e.g. 'Add' +2.50 -
should be entered for both eyes).
A Prism is to try and correct a lazy eye and indicates a more delicate
condition, this is included with a prescription to correct some special
conditions or some eye disorders (like squints) that require the focussed
image to move position. The measurement is Prism Dioptre. The value may be
as high as 10 and may go up in steps of ½ or 1 Prism Dioptre’s.
Prism powers will always be accompanied with a direction which is usually
seen as a base diresction such as IN, OUT, UP and DOWN; for example; Prism
2.00 Base IN. Some people may have prism in two directions for one eye, for
example; Prism 2.00 Base IN & 1.00 Base UP.
We can offer up to 3.00 Dioptre's of prism online however if yours exceed
this or if you have more than one direction for each eye please contact us
to confirm suitablility and availability.
PD / Pupillary Distance
The Pupillary distance is an essential measurement. It is the distance
from the centre of one pupil to the centre of the other pupil measured in
mm (ranges from 50 to 70mm). Each spectacle lens will have an ‘optical
centre’, this is a point on the lens where it performs the best and has
the least distortion. The optical centre of each lens should be placed
directly in front of the centre of each of your pupils. That way, your
eyes are looking through the best point on each lens, some prescriptions
may have the PD/Pupillary Distance listed for each eye respectively, for
example RE: 32 LE: 32, you would enter 64mm from our list.
If the PD/Pupillary Distance for the glasses is not set correctly then
your eyes may have to strain to look through them, this can lead to
headaches, eyestrain, visual distortion and in severe cases, double vision.
The PD/Pupillary Distance is generally measured during a sight test, but is
not routinely written on a prescription, you can ask for this from your
Opticians, or ask them to add it to your prescription when you are tested.
If you experience difficulty in obtaining this measurement we can record
it, if necessary, from an existing pair of your glasses, to find out more
Distance / Intermediate / Near
Dist, refers to distance, this is the prescription required to correct
distance vision. This correction is often used for driving, television
and general wear (walking around). These glasses are often worn full time.
Inter, refers to intermediate, this is the prescription required to correct
intermediate vision, and may appear in full, or as an additional power (ADD)
to the distance. If you require spectacles for intermediate use include the
INTER ADD in the ADD box when ordering and also advise us in the additional
info box that you require these for intermediate use. This correction is
often used for computer (VDU) operation.
Near is the prescription to correct near vision and may appear in full, or
as an additional power (ADD) to the distance. This correction is often used
for reading, sewing and any detailed close work.
Your prescription gives us, your Opticians or Doctors recommendation for
clear and comfortable vision. All Opticians and Doctors worldwide work to
the same procedures when writing a prescription, which can be printed or
written in a similar fashion to this sample prescription.
You will notice there is no CYL or AXIS for the left eye, this means there
is no astigmatism present. Your optician may or may not write DS (Dioptres
Sphere) in the CYL box. DS (Dioptres Sphere) means you only have a Sphere
power. DS simply means no power is present in the CYL box so leave this as
NONE or DS.
If your prescription only shows the SPH box with a value, leave the CYL
and AXIS blank.
BVD - Back Vertex Distance
The BVD stands for Back Vertex Distance, this is a measurement that is
included on any prescription where the sphere or cylinder powers are
higher than + or - 5.00D and to a lesser extent some prescriptions where
it is less than this power.
This measurement is important as it explains at what distance your lenses
should sit from your eyes. Usually your lenses will be positioned around
10-12mm from your eyes, however this will vary from person to person. If
your prescription includes a BVD, it is important that the lenses sit at
the correct distance to ensure comfortable vision.
If in doubt...
If in doubt just enter your prescription as you see it, if you’re not sure
what type of lenses are suitable, hover your mouse over the question mark
next to the lens type to reveal more detailed information about the product.
We always recommend attaching a copy of your prescription to the order, or
fax this through or email it separately, we will double check the
prescription this end to ensure the correct lenses are produced.