Correcting lens system for perimetry.

A lens system to correct for both refractive error and perimeter test distance is frequently needed for accurate perimetry. Patients often lack appropriate near vision corrections and full aperture trial case lenses, when they are available, barely cover the central 30 degrees and hence frequently produce lens rim artefacts. A special system of correction lenses has been developed for perimetry which overcomes these problems. This system is head mounted, being based upon the Essilor presbyopia demonstration set, and is suitable for use with most perimeters.