1. Laboratory of Physics and Helsinki Institute of Physics, Helsinki University of Technology, Helsinki, Finland
2. Department of Ophthalmology and Helsinki Biophysics and Biomembrane Group, Institute of Biomedicine, University of Helsinki, Helsinki, Finland
3. Department of Applied Mathematics, University of Western Ontario, London (ON), Canada
4. Institute of Physics, Tampere University of Technology, Tampere, Finland; Laboratory of Physics and Helsinki Institute of Physics, Helsinki University of Technology, Helsinki, Finland; and Memphys-Center for Biomembrane Physics, Physics Department, University of Southern Denmark, Odense, Denmark