How come I failed the vision test at the doctor's but passed the online one?

You probably have a severe form of color blindness that the online test cannot identify. While the online test is a valid test accessible to the general public and can correctly identify the presence of a color deficiency, research has shown that it does not indicate the type or severity of color deficiency. You will still require a doctor to determine the type and extent of the deficiency. Acquired color blindness is related to an eye condition such as an optic nerve disorder and may require more sophisticated testing by an ophthalmologist.