Stewart WC, Oehler JC, Choplin NT, Markoff JI, Moster MR, Ichhpujani P, Nelson LA.
A Comfort Survey of Timolol Hemihydrate 0.5% Solution Once or Twice Daily vs Timolol Maleate in Sorbate. 
J Curr Glaucoma Pract
2013;
7
(1):11-16.