Previous studies demonstrated that the 11-cis isomer of vitamin A prevented retinal rod degeneration in rats. Uncontrolled human studies suggested that 11-cis vitamin A given intramuscularly benefited patients with retinitis pigmentosa. A long-term rigidly controlled study was performed to determine whether or not 11-cis vitamin A may be of value in the treatment of retinitis pigmentosa. Final results were negative.
Chatzinoff A, Nelson E, Stahl N, Clahane A. Eleven-CIS Vitamin A in the Treatment of Retinitis PigmentosaA Negative Study. Arch Ophthalmol. 1968;80(4):417-419. doi:10.1001/archopht.1968.00980050419001