Petition Vision Impairment Certificate for permanent Diplopia

I would like the Government to change the criteria for the vision impairment certificate.At present it does not recognise how disabling permanent double vision is, the current Snellen eye test, concentrates on visual aquity with one eye covered, it does not give results of day to day vision using two eyes, and how disabling that is.My daughter has been under Great Ormond st and Moorfields Eye Hosp for 16 years, after 4 unsuccesful eye operations, she is left with permanent double vision.Day to day life is very difficult and dangerous with this vision. She is unable to drive as it is too dangerous, but it is not recognised, even though the department of health state there is no legal definition of sight impairment.