Horizontal gaze or nystagmus testing (follow the finger) is not designed to diagnose for treatment. It is just an indicator of neurological impairment. That is why it is used for drunk driver testing. A Neuro Ophthalmologist may be helpful or a Behavioral Optometrist. If you search this forum for behavioral optometrist, you will find some previous threads from a few years ago. There is an association that can be used to find a local specialist.

There are some sophisticated nystagmus testing protocols. There is also a system that watches the eyes electronically as you are put through various body positions similar to the Gyro Stim device.