Vertex Distance Conversion Calculators
Hirst Contact Lens Limited, Manufacturer
In this inner circle is a scale on either side for Plus and Minus lenses. The plus scale on the right starts from 24 and descends in increments of 2 down to 0. The arrow on the right reads “+ / Plus / Lenses / mm. / Scale”. The arrow on the left reads “- / Minus / Lenses / mm. / Scale”. The text for this is written upside-down and the scale starts from 0 and ascends in increments of 2 up to 24. This scale refers to the distance in millimetres the lens sits from the cornea. The outer circle has a scale starting from 5.25 divided into increments of .25 up to 25.00 – This refers to the power of the patient’s prescription (Dioptre scale).
The function of the calculator is to calculate the distance between the back of a contact lens and the patient’s cornea (back-vertex power) when a trial spectacle frame is used. It means that the eye care professional can determine the correct strength for the contact lens without the patient trialling the lens. For example, for myopia - the strength of the prescription is stronger for glasses wearers because the lens is further away from the eye than the contact lens.
On the back of the disc are the directions for use for spherical and compound lenses. “VERTEX DISTANCE CONVERSION CALCULATOR / DIRECTIONS FOR USE / SPHERICAL LENSES […] COMPOUND LENSES […]”.
+ / Plus / Lenses / mm. / Scale Printed
- / Minus / Lenses / mm. / Scale Printed
VERTEX DISTANCE CONVERSION CALCULATOR / DIRECTIONS FOR USE / SPHERICAL LENSES […] COMPOUND LENSES […] Printed
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