1. University of St Andrews; School of Medicine, Medical and Biological Sciences Building; Fife UK KY16 9TF
2. Health Services Research Unit, University of Aberdeen; 3rd Floor, Health Sciences Building Foresterhill Aberdeen UK AB25 2ZD
3. University of Aberdeen; Health Services Research Unit, Health Sciences Building; Foresterhill Aberdeen UK AB25 2ZD
4. Tampere University Hospital; Eye Centre; PO BOX 2000 Tampere Finland FIN-33521