[1] Inst Municipal Assistencia Sanitaria, Studies Dept, Barcelona, Spain
[2] Inst Municipal Invest Med, Hlth Serv Res Unit, E-08003 Barcelona, Spain
[3] Hosp Esperanza, Dept Ophthalmol, Barcelona, Spain
[4] Inst Municipal Invest Med, Resp & Environm Hlth Res Unit, E-08003 Barcelona, Spain
[5] Univ Pompeu Fabra, Dept Expt & Hlth Sci, Barcelona, Spain