The purpose of ISO/TR 28980:2007 is to explain the changes relating to power measurements in the revised editions of ISO 8980-1 and ISO 8980-2.

In order to illustrate the issues raised, an inter-laboratory power measurement study was conducted on ten different lenses measured by nine organizations worldwide. Twenty-five focimeters of different types were used. The test lenses were spherically powered allyl diglycol carbonate (ADC) hard resin lenses surfaced to -4,00 D, -2,00 D, 0,00 D, +2,00 D, and +4,00 D, each with an addition power of 2,50 D. Five were D28 bifocals and five were progressive power lenses. The measurements were front distance power, front near power, back distance power and back near power, for each lens and for each focimeter used. Each lens was measured nine times: five measurements taken without repositioning the lens and four measurements taken with the lens repositioned each time.

The assessed parameters were divided in three categories:

• discrepancies due to focimeter design and measurement methods;
• systematic errors;
• random errors.

For each parameter, experimental results are given, as well as theoretical ones when needed. Measurement data include front distance portion power, front near portion power, back distance portion power and back near portion power.

Unless stated otherwise, in order to show relevant information, the results shown are for the D28 bifocals when no different behaviour was found for the progressive power lenses.