A Dalit youth lost vision in one eye after being brutally assaulted by an attacker who allegedly pierced his eye with a motorcycle key following an argument over defecating near a canal, police said on Monday.

The victim, identified as Rahul and in his early 20s, was referred in critical condition from the district hospital to Varanasi on Sunday for specialised treatment.

According to police, the incident occurred on Friday afternoon in the Aurai area when Rahul had gone to a canal to defecate. An argument broke out after the accused, Shankar Bind, objected to him defecating near the canal.

Police said the accused allegedly hurled caste-based slurs at Rahul and assaulted him. When the youth attempted to flee, the attacker allegedly pierced a motorcycle key into Rahul’s left eye and threatened to kill him, Superintendent of Police Abhimanyu Manglik said, adding that the victim collapsed in severe pain.

The accused fled the scene after local residents gathered there.

The SP said police reached the spot after receiving information and rushed the injured youth to a community health centre, from where he was later admitted to the district hospital.

"As the injury to his left eye was severe, and he complained of loss of vision, doctors on Sunday referred him to the BHU Trauma Centre in Varanasi," Manglik said.

He said a case has been registered on the complaint of the victim’s father, Ram Dhani, against the accused Shankar Bind under relevant sections of the Bharatiya Nyaya Sanhita and the Scheduled Castes and Scheduled Tribes (Prevention of Atrocities) Act.

Necessary legal action against the accused is being taken and further investigation is underway, the SP added.