Among other tests for simulated blindness, JACKSON suggest the employment of a prism of six or eight degrees placed with its base towards the temple. If there is vision, that eye will instinctively turn in, order to avoid double images.
Reference:Arch Ophthalmol. 1898;27:139.
A look at the past. . .. Arch Ophthalmol. 1999;117(5):702. doi:10.1001/archopht.117.5.702