At least 12 people have lost their vision after a cataract surgery at an eye camp in Bihar's Madehepura district, sources said on Saturday.
The victims, who include many women, come from landless labourers from Madhepura and Saharsa districts.
Doctors say an infection could be the reason.
Sources said about 175 patients underwent eye operation at the free eye camp held at a missionary hospital in February.
After the shocking news was raised in the Assembly, Chief Minister Nitish Kumar took serious note of the issue and asked the health secretary to submit a report to him.