1. Vitamins, 2. Vitamin A (Retinoids);Ullmann's Encyclopedia of Industrial Chemistry;2020-03-23
2. Vitamins, 2. Vitamin A (Retinoids);Ullmann's Encyclopedia of Industrial Chemistry;2011-10-15
3. Vitamins;Ullmann's Encyclopedia of Industrial Chemistry;2000-06-15
4. The Pathology of Vitamin a Deficiency;Vitamins & Hormones;1961
5. Xerophthalmia, Keratomalacia and Xerosis Conjunctivae;American Journal of Ophthalmology;1924-02