A 13-year-old girl could lose the sight in one of her eyes after a pencil was thrown in school.
Sneha Rokka underwent surgery on her left eye on Thursday but doctors said she and her anxious family must wait six weeks to learn the full extent of the damage.
It could mean permanent loss of sight in the eye.
Wales Online says a pencil was hurled during a lesson at Fitzalan High School and struck the teenager's eye.
The girl's mum Sanjula, 48, said: "I can't believe what has happened, it's so devastating.
"My daughter's eye is badly damaged. She has been in theatre all day and the doctors have said it will take six weeks to find out the full extent of the damage."
"She's absolutely petrified. When she was going in to theatre she was crying and panicking. We don't know what's going to happen but she's likely to lose her vision which is very serious.
"There was a school trip planned, summer holidays and now all of that may be ruined."
Sanjula, from Grangetown, Cardiff, dashed to University Hospital of Wales in the city after the incident on Wednesday.
The mum-to-four said it left Sneha in excruciating pain and very upset.
"She was crying all night, she's never been involved in anything like this. She loves school," Sanjula added.
"I just don't understand how this can happen. As a mother, seeing your daughter in that state is heartbreaking.
"My daughter is distraught but what can I do except reassure her and tell her she'll be okay.
"I'm trying not to think of the worst and just be there for my daughter. That's all I can do at this stage."
Further tests on the girl's lens will be carried out.
But the family faces a lengthy wait until they know the seriousness of the wounds.
Fitzalan High School caters for more than 1,700 pupils in the Leckwith area of Cardiff. Estyn, Wales' education inspection body, rated the school as 'Excellent' after its last inspection.
Following Wednesday's accident, headteacher, Catherine Bradshaw, said: "The safety and care of our pupils is a priority and it is upsetting for everyone involved when an accident of this nature occurs.
"I have spoken with Mum, as has the head of year and the school will continue to offer both pupil and family support in whichever way possible."
