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To the Editor.
—For some time I have been aware of a peculiar phenomenon that may be observed when examining a patient at the slit lamp with early cataract spokes or other rhythmically distributed small opacities in or near the periphery of the crystalline lens. The pupils should be well dilated. A narrow to medium opening of the slit beam is focused on the opacities. When moving the slit lamp-microscope assembly from the observer's left to the right, an apparent rotation of the crystalline lens occurs as if the crystalline lens would be a wagon wheel. The apparent rotation is clockwise when moving the slit lamp from the observer's left to the right. When moving the slit lamp from the observers right to the left, the apparent rotation is counterclockwise. The slit lamp beam may be kept on either side of the microscope. A 45° illumination angle was used for
Halberg GP. THE WAGON WHEEL PHENOMENON: A DYNAMIC ILLUSION OBSERVED BY SLIT BEAM ILLUMINATION. Arch Ophthalmol. 1970;83(3):381. doi:10.1001/archopht.1970.00990030381018