A management review needs numbers that mean the same thing each time. A metrics register is the definition of those numbers, not a spreadsheet of every result.
What to define
Name the metric, say which management system it belongs to, and state the unit and the target in that same unit. Describe how it is calculated, where the data comes from, and how often it is reviewed, so someone else can reproduce the result.
The owner collects the result and acts when it misses the target.
How this differs from an objective
Objectives are outcomes you are trying to reach by a date. A metric is the measure you watch. How ISMSVision helps with metrics is the product.