Terminology

 

P.D, pupillary distance

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. If the p.d 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 p.d has to be 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 take it, if necessary, from an existing pair of your glasses.

We will not use average figures for this, because of its importance, so we cannot proceed with a reglaze without it.

 

Sph/ Sphere.

This value gives the overall power of the eye and determines if you are long or short sighted. The measurement is called the Dioptre. If the Value is a minus then you are short sighted if a plus then you are long sighted. It may also have zero or the word ‘plano’ in this box, this means that you are neither long nor short sighted but you may have astigmatism.
Most values range from 0.00 to +/- 20.00 and go up in steps of 0.25

 

Cyl/Cylinder

This value indicates the amount of astigmatism you may have. Astigmatism is often described as having an eye ‘rugby ball shaped’ or referred to as ‘toric’, this is where the eye is slightly distorted in shape and is very common. 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 +/- 6.00 and will go up in steps of 0.25.

 

Axis

This box will only have a value in it if there is a value in the Cyl box, as this is an indication of 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.

 

Prism

There may be a value in this box, this is a lens that is used rarely and only to correct some special conditions or some eye disorders (like squints) that require the focused image to move position. The measurement is Prism Dioptre.
The value may be as high as 15 and may go up in steps of ½ or 1

 

Base

This gives an indication as to the position for the movement of the image. There will only be an entry in this box if there is one in the Prism box.
The value may say base in, out, up or down.

 

ADD

This figure is an indication how much extra power is added ‘on top’ of the distance prescription for near or intermediate glasses. This extra power will be the same for each eye so may only appear once. There may also be different values for intermediate and near. The measurement is the Dioptre.
Most values range from +0.50 to +4.00 and will go up in steps of 0.25

 

Dist/Inter/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. 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. This correction is often used for computer 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.