Humans have lenses in their eyes; to focus light on the retina. The lens must be precisely built, flexible, and remain transparent throughout life. If anything fails, our ability to see is seriously affected. Lack of flexibility affects practically everyone over the age of 50. Cataract affects transparency and is the most common cause of blindness in the world. The biological lens grows throughout life, via a complex, but still regular process. Starts with some 350 mitotically-active cells and reaches some 7 million cells in a 60 year old human. How to describe and understand such a remarkable process? What is its effect on pathological developments? Even data collection looks extremely difficult, while the sheer complexity of the problem requires truly interdisciplinary approach, including the help of advanced mathematics. Thanks to the unprecedented technological development, it is now possible to label single cells within the eye lens, and to follow the path of its daughter cells. The Bassnett lab at Washington Univ School of Medicine is the leader in this labelling technique and has a very ambitious program to answer questions above. Two years ago we joined Prof. Steven Bassnett in this fascinating endeavor. We bring more than 20 years of research experience in probability theory and mathematical analysis, leadership on several NSF grants, as well as more than 10 years of leading the Division of Prob. & Stats, Dept of Mathematics, Univ of Zagreb. We propose to develop mathematical models of various stages in the growth of the lens. Initial period of our collaboration is completed and we are now at the level where daily contact is needed. Our model is Markov in nature, and would involve branching processes with immigration and emigration. At the ultimate level we need to consider also measure-valued processes, technically a highly demanding topic. We plan to return to Zagreb and fully develop student program and research group in biomedical mathematics.