Official sources said preliminary observation indicated infection setting in after last week's operation was the reason for the patients losing sight.
The operation was conducted on August 21.
Two of the four persons were admitted to the Medical College Hospital here. One woman was discharged the same day. Those admitted complained of losing vision in their right eye, hospital sources said.
Another person has sought treatment at a hosptial in Kochi.
Meanwhile, Health Minister V S Sivakumar has ordered a probe into the incident.