Is there a medical reason why a person can start to loss vision and the nuro ophthalmologist cant find a answer? and do graves disease affect the eyes

Many causes: A neuroopthalmologist specializes in problems involving the brain & connections with the eye to the brain. A general DR could determine if vision loss involves a systemic problem, such as uncontrolled diabetes, medications/toxins, nutritional deficiencies or infection. Graves Disease would only cause sudden temporary blindness due to compression of the optic nerve. This would show up on imaging.