Zuretinol (QLT091001, 9-cis-retinol) is a retinoid. Retinoids (vitamin A and its analogs) are essential dietary substances that are needed by mammals for reproduction, normal embryogenesis, growth, vision, and maintaining normal cellular differentiation and the integrity of the immune system. Within cells, retinoids regulate gene transcription acting through ligand-dependent transcription factors, the retinoic acid receptors (RARs), and the retinoid X receptors (RXRs). All-trans-retinoic acid binds only to RARs with high affinity, whereas its 9-cis isomer binds with high affinity to both RARs and RXRs. The actions of all-trans- and 9-cis-retinoic acid in regulating cellular responses are distinct and not interchangeable. Zuretinol is a retinal derivative for treatment of visual disorders. It is a synthetic retinoid replacement for 11-cis-retinal. It is an investigational product under development for the treatment of retinal diseases caused by gene mutations that interfere with the availability of 11-cis-retinal. The therapeutic strategy with Zuretinol is to facilitate recovery or restoration of visual function by acting as a replacement for missing 11-cis-retinal and restoring a key biochemical component of the visual (retinoid) cycle. Novelion Therapeutics is currently developing QLT091001 for the treatment of Inherited Retinal Disease caused by retinal pigment epithelium protein 65 (“RPE65”) and lecithin:retinol acyltransferase (“LRAT”) gene mutations, which include Leber Congenital Amaurosis (“LCA”) and Retinitis Pigmentosa (“RP”). QLT091001 has received orphan drug designations for the treatment of LCA (due to inherited mutations in the LRAT and RPE65 genes) and RP (all mutations) by the U.S. Food and Drug Administration (the “FDA”), and for the treatment of LCA and RP (all mutations) by the European Medicines Agency (the “EMA”).