The toddler had eaten the quinine tablets after finding them left out next to a packet of mints.
Her 75-year-old gran admitted leaving the drugs within the child's reach.
Lincoln Crown Court was told that she was put into an induced coma for a month and lost her sight for several weeks after taking the medication.
Paramedics told the hearing that when they arrived at the Skegness address to take the child to hospital, she was 'staring into space' with her eyes open but not responding verbally.
The police found the tablets – which are used for arthritis and leg pains – open alongside a packet of mints.
Phil Howes, prosecuting, said it was a 'very tragic case with a lesson to be learnt'.
"Clearly it is easy to see why a child could see them and take them," he told the court.
He added that the child's mum did not blame the pensioner, and believes it was a 'tragic accident'.
The elderly woman was given a 12-month conditional discharge, with Judge Sean Morris warning her to keep her medication in a secure place.
"You, like me, are old enough to have seen the old BBC public service adverts which warned people to keep tablets out of the reach of children," she was told. "This was a tragic accident but it could have resulted in most terrible consequences."
The Lincolnshire Echo reports that little girl went on to make a full recovery and eventually regained her sight.