- Study visit 2-day 2 The IOP will be measured 3 times in one 5 minute period between 7:30 and 10 am using Goldmann applanation tonometry by an individual masked to which eye had EC, and the median IOP will be recorded (24 hour IOP). The subject will be instructed to resume his/her prostaglandin that evening and will be instructed to continue EC at home in the selected eye for the designated amount of time (1 or 5 minutes) until the third study visit.