how much prednisolone acetate 0.12% ophth. susp. was prescribed for the first time in their first hospital visit to patient 20066?
select prescriptions.dose_val_rx from prescriptions where prescriptions.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 20066 and admissions.dischtime is not null order by admissions.admittime asc limit 1 ) and prescriptions.drug = 'prednisolone acetate 0.12% ophth. susp.' order by prescriptions.startdate asc limit 1