The value of double simultaneous stimulation in perimetry was noted by Bender1 in 1950. The technique is based on the principle of the extinction phenomenon which was already being used by neurologists to test other sensory modalities. Harrington and Flocks2 employed this principle in the perimetric screen which they developed in 1955. The purpose of double simultaneous stimulation is to increase the sensitivity of testing of opposite fields. While the individual subject with early hemianoptic depression may perceive a single stimulus on either side of the vertical meridian, when the stimulus is presented simultaneously to either side there occurs an extinction of the stimulus on the diseased side.
Description of Instrument
In order to test for this we have made an instrument which projects two lights simultaneously. It consists of two flashlights of the kind used by lecturers as a pointer to project a small, focused spot
LINCOFF HA. A New Instrument For Double Simultaneous Stimulation. Arch Ophthalmol. 1965;73(4):502-505. doi:10.1001/archopht.1965.00970030504010