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.