The opticians prescription contain numbers go up in steps of 0.25. They are in units
of dioptres - which means power or strength.
Low numbers indicate low strength and less error present.
( There are two formats of recording prescriptions - in a plus cyl or minus cyl form
. The same prescription can look very different in either form but mathematically
means the same )
SPH - which is short for spherical. A plus number will mean a positive sphere that
corrects long sight. A minus number indicates short sight correction by concave
CYL - which is short for cylinder - which corrects the astigmatism or rugby ball
shape. The power can be plus or minus
AXIS - This is the direction of how the CYL is positioned. A rugby ball, when rotated
can be set at different angles. Similarly the eye astigmatism can be set at different
angles or axis and so the CYL needs to match this axis.
PRISM - This is to correct any misalignment between the two eyes. There may be a
small triangle figure to the top of the number to indicate it's a prism unit. After
the number, the direction is recorded - as either IN or OUT and UP or DOWN. This
is called the BASE.
They do not look different at the front from any other lenses but a high value may
cause some thickening of the lens edges as prisms can have a wedge shape.
PLANO or Pl - This means zero value for the SPH portion of the prescription. The
optician may also put a line through the CYL, AXIS or PRISM to indicate no value
This page is for information for anyone needing help in entering details for online
optical glasses prescription or to find out what the values actually mean on the
opticians form. In UK, NHS eye test results are recorded on GOS 2 prescription form.
RE - This is for the right eye. May also be termed as OD
LE - This is for the left eye. May also be termed as OS
Balance or BAL - this may be written on SPH or across the RE or LE and shows there
is no specific optical power. The vision in that eye may be too poor or prescription
is too different to the other eye. The person making the glasses will use their judgement
to balance out the lens - cosmetically and weight wise.
DS -This may be entered after the SPH value to show that no CYL and no AXIS are
ADD or NEAR - Reading Add or Near Add. This is the near prescription.
Either the full near prescription is written or the optician may write down the ADD
value. Both mean the same amount. See examples.
The ADD amount is then added onto the distance part of the SPH when ordering spectacles
( the CYL and AXIS part remains the same )
If there is no ADD or NEAR - you either do not need glasses for near or the distance
prescription may be intended for both distance and near. Your optician will advise
if you are not sure.
You may only need glasses for close or you may need two prescriptions - for distance
and near. This can be combined into one spectacle lens such as a bifocal or varifocal.
INT ADD or Intermediate - This is used to optimise vision for when using a computer
or a specific hobby such as reading music or playing piano. This is because the
NEAR ADD is tested at normal reading distance - but a computer screen is often further
away and the value of the ADD does not need to be as strong then.