After completing his apprenticeship as an optician, Hans-Juergen Grein completed the diploma course in ophthalmic optics at the Aalen University of Applied Sciences. He then studied medicine at the University of Würzburg. He completed his ophthalmological training at the university eye clinic there. In 2001 he was offered a professorship at the Jena University of Applied Sciences, where he held a professorship for optometry until 2007.

Since September 2007 he has been a professor at the Technical University of Lübeck, where he works in the field of medical optics. He is also Head of Science at the Fielmann Akademie Schloss Plön. He teaches biomedicine of the eye, general anatomy and physiology, optometry and physiological optics. Numerous publications and international lectures point to his teaching and research activities.