As all current commercial perimeters use a fixed pattern of locations to test visual fields, computing simple averages of the measured locations to get visual field indices like Mean Defect (MD) and Mean Deviation (MD) can be used to summarise the field and changes in the field. In this short paper we show the modifications required to compute visual field indices if the test pattern changes between visual field tests. We show by taking the average with locations weighted by the area of the field they represent and computing change between two tests only on locations that are common to both tests, MD can be computed for a series of fields that vary their test patterns.

The authors have declared no competing interest.

This study did not receive any funding

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

Yes

I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.

Yes

I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).

Yes

I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable.

Yes

All data produced in the present work are contained in the manuscript