1 Biointerfaces and Biomaterials Laboratory, Department of Optics and Spectroscopy, School of Optometry, Faculty of Physics, St. Kliment Ohridski University of Sofia 5 James Bourchier Blvd., 1164 Sofia, Bulgaria.
2 Institute for Bioengineering and Biosciences, Instituto Superior Técnico, Universidade de Lisboa, 1649-004 Lisbon, Portugal.
3 Department of Ophthalmology, Kyoto Prefectural University of Medicine, Kyoto 602-8566, Japan.