Open Perimetry Interface R package OPI version 3.1.1 Implementation of the Open Perimetry Interface (OPI) for simulating and controlling visual field machines using R. The OPI is a standard for interfacing with visual field testing machines (perimeters) first started as an open source project with support of Haag-Streit in 2010. It specifies basic functions that allow many visual field tests to be constructed. As of February 2022 it is fully implemented on the Haag-Streit Octopus 900 and 'CrewT ImoVifa' ('Topcon Tempo') with partial implementations on the Centervue Compass, Kowa AP 7000 and Android phones. It also has a cousin: the R package 'visualFields', which has tools for analysing and manipulating visual field data. Software Imports: jsonlite, Rfast, abind, openssl Suggests: testthat (>= 3.0.0) Andrew Turpin <andrew.turpin@lei.org.au> Comprehensive R Archive Network (CRAN) Andrew Turpin [cre, aut, cph] (ORCID: 0000-0003-2559-8769), David Lawson [ctb, cph], Ivan Marin-Franch [ctb, cph], Matthias Muller [ctb], Jonathan Denniss [ctb, cph], Astrid Zeman [ctb], Giovanni Montesano [ctb] Apache License (>= 2) 2026-06-11 application/tgz https://CRAN.R-project.org/package=OPI doi:10.32614/CRAN.package.OPI