Upon entering the study, participants receive a 90-minute infusion of daclizumab through a catheter (plastic tube) placed in an arm vein. They return to the clinic after 14 days and again after 28 days for repeat eye examinations, blood tests, and daclizumab infusions. Four weeks after the third infusion, patients are examined for response to treatment. Those who have benefited from daclizumab may continue receiving monthly infusions of the drug for up to one year. A blood test and eye examination are done at the time of each infusion. Patients whose disease has remained active 12 weeks after the first infusion are taken off the study and treated with other medications.