The Supply of Ophthalmic Dispensing Measurements
Occasionally we get asked for a “PD” for spectacles and, whilst we are happy to provide what
measurements we can for third party spectacle supply you should understand that Ophthalmic
Dispensing is a professional discipline in it own right and therefore ask you to read the following;
The comfort, both physical & visual, of spectacles is dependent not only on the prescription but also
on the fit of the frame and the position in which it holds the lenses in relation to the eyes. The
measurements required to do this are far more complex than one might imagine and become
increasingly vital in stronger prescriptions or in cases where the left and right eyes have different
prescriptions. Measurements can be divided into three loose categories, those required for single
vision (SV) lenses, those required in addition to SV for multifocal lenses and finally those required to
make the frame fit securely and comfortably. To give a brief overview of what is required some of the
measurements required are set out below.
SINGLE VISION LENSES
Inter-Pupillary Distance is the horizontal distance between the pupil centres of your eyes
and is a facial measurement having nothing to do with the manufacture of a pair of spectacles.
Mono Centration Distance is the horizontal distance between the optical center of each eye
and the central point of the nasal bridge, taken in the plane of the properly fitting frame this is
usually, although not always the distance between the center of each pupil this is measured to
an accuracy of half a millimetre.
Mono Pupillary Distance is the distance between each eye individually and the central point
of the nasal bridge, measured to an accuracy of half a millimetre. This measurement is
essential to allow optimum performance of some modern lenses.
Vertical Fitting Position is the vertical distance from either the bottom rim, or the horizontal
centre line of the frame to the optical centre of the lens and is of vital importance in the use of
modern lens designs.
Final frame choice required.
Vertex Distance is the distance between the apex of the cornea and the back plane of the
lenses, in some prescriptions this distance will mean a registered dispensing optician or
optometrists must adjust the original lens prescription accordingly.
Final frame choice required.
Pantoscopic Angle/Side Angle is the angle at which the vertical plane of the lens lies in
relation to the vertical plane of the face; incorrect angles will induce a relative change in the
prescribed power. Adjustments to this are made if one ear is higher than the other.
Final frame choice required.
Face Form Angle determines the angle at which the horizontal plane of the lens lies in
relation to the horizontal plane of the face; incorrect angles will induce a relative change in the
prescribed power.
Final frame choice required.
ADDITIONAL MEASUREMENTS FOR PROGRESSIVE POWER AND MULTIFOCAL LENSES
These lenses require all of the above measurements in addition to the following;
Seg Inset is the amount a bifocal reading segment is decentred inwards to ensure the optical
centre of the eye and the optical centre of the lens coincide at the point of reading focus
Reading Add Location is the position of the reading add either in front or behind the distance
trial lenses and is important in more modern progressive lens designs.
Progression Height is the height at which the progression zone of a progressive (varifocal)
lens starts.
Final frame choice required.
Progression Depth denotes the minimum depth a frame must have from the distance viewing
point to enable the progression to fully fit.
FRAME FIT MEASUREMENTS
Angle of Side Let Back is the amount of adjustment made to the sides of the spectacles to
ensure that they fit at the back of the head and do not slip forwards, dependent on the frame
chosen
Final frame choice required.
Side Length to Bend is the length between the apex of the junction between the ear and the
head, and the joint where the side meets the frame front. Adjustments to this measurement
are made if one ear is further forward on the head than the other.
Final frame choice required.
Total Side Length is the length of the entire side and is required to ensure the part of the side
sloping down behind the ear is neither too long nor too short.
Final frame choice required.
Head Width is the width of the head between the apex of the junction between the each ear
and the head.
NB. We recommend that all progressive power lenses are measured only once the
frame has been fitted to the wearer’s face.
Many of these measurements can only be taken by your chosen frame being placed on your head and
used as a template for the measurements of the finished item, as such it is impossible for us to
provide all of the above. We will however provide as many measurements as possible for your
prescription. These are not the same measurements as those taken during an eye examination and
will incur a small charge for the measurements to be taken and a report written. We cannot take
responsibility for the accuracy, comfort and visual performance of spectacles not fully measured, made
up and checked under our direction.
OPHTHALMIC FACIAL MEASUREMENTS
(Practice Copy)
Patient Name:
Address
Single Vision Spectacles
Monocular Inter-Pupillary
Distance
/
Head Width
Inter-Pupillary Height
Temple Width
Vertex Distance Trial Frame
Additional Measurements for Multifocal
Lenses
Vertex Distance Fitted Frame
Monocular Reading InterPupillary Distance
Pantoscopic Angle
Seg Inset (Bifocal)
Front Bow
Reading Add Location
Side Angle
Progression Height
Side Length to Bend.
Progression Depth
Available
Total Side length
Frame Adjusted to Fit
Further comments:
Provided by:
Signature:
I have read through and understood the information above and require as many
measurements as possible for an ophthalmic dispensing off premises.
Print Name:
Signature:
/
Behind / In-front
OPHTHALMIC FACIAL MEASUREMENTS
(Patient Copy)
Patient Name:
Address
Single Vision Spectacles
Monocular Inter-Pupillary
Distance
/
Head Width
Inter-Pupillary Height
Temple Width
Vertex Distance Trial Frame
Additional Measurements for Multifocal
Lenses
Vertex Distance Fitted Frame
Monocular Reading InterPupillary Distance
Pantoscopic Angle
Seg Inset (Bifocal)
Front Bow
Reading Add Location
Side Angle
Progression Height
Side Length to Bend.
Progression Depth
Available
Total Side length
Frame Adjusted to Fit
Further comments:
Provided by:
Signature:
/
Behind / In-front