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In the Annual Review by Irwin M. Siegel, PhD, "Optics and Visual Physiology," which appeared in the July 1971 issue of the Archives (86:100-112), the demonstration sentence on page 103 should have been printed upside down rather than right side up.
ERRATUM. Arch Ophthalmol. 1971;86(5):609. doi:10.1001/archopht.1971.01000010611023