Dioptrimeter - Optical and optometry instrument

The dioptrimetar is optical instrument used by optometrists and opticians.
It shows what dioptry is in lens: sphere, cylinder, axis, add, and in some cases, prism.

Usually when people come to control vision acuity they don't bring any papers of earlier prescriptions or infromation about previous glasses.
Therefore, dioptrimeter is very helpful instrument so optician or optometrist can see what dioptry client use at this point.
In such a situation, the easiest thing is to put glasses on a dioptrimeter.

Also, people don't pay attention on those documents they get when they buy new glasses,that's wrong. with your new glasses, you get paper where is written many informations that may help the specialist next time, also dioptry is written and wich glasses do you wear (very important for everyone, especially for progressive wearers).
Pretty important information is from which manufacturer are lenses, types of glass, which coat was on them, how thin were they.
Many informations are important.

This dioptrimeter is older series, today there are also auto or digital dioptrimeters.
My optinion is, everyone in this profession should start from this classic type and learn how to used is because they are still much in use.
It seems a little more complicated and complex but it is not really.

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On this picture the instrument is off. It shows how a person sees when he looks inside. This is scale, those horizontal numbers are dioptries and numbers in a half circle are degrees.

A representation of the image when the instrument is turned on.

The picture shows how it looks like when you put a lens with a dioptry. It becomes blurry.

If the lens is spherical, when you spin a little wheel, the green lines (cross) will become all clear. But if the lens is toric, horizontal and vertical lines will not clear at the same dioptry.
See the example.

Horizontal lines are clear at -0,50

Vertical lines are clear at -1,25

The smaller value is a sphere and the difference is the cylinder, the degree of the cylinder is on a higher value.
THE DIOPTRY IS: -0,50 -0,75 A 90°

RULES:

• when there are - and -
  smaller value is sph, the difference is cyl and the degree is on a higher value
• when there are + and +
  bigger value is sph, the difference is cyl and the degree is on smaller value
• when there are + and -
  +is sph, the difference is cyl and the degree is on -
• when there are + and 0
  +is sph, the difference is cyl and the degree is on 0
• when there are - and 0
  0 is sph, the difference is cyl and the degree is on -