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Dizziness is usually linked to either the inner ear, which is responsible for maintaining proper balance, or to the central nervous system.
The inner ear may be affected by an infection or inflammation. ENT doctors are best at evaluating and treating these conditions. Patients often resort to ophthalmologist as the symptoms are manifested in a visual manner, however, a consultation with an ENT doctor will probably provide better answers to the problem.
In your case, MS has to also be considered as a possibility. As you may already know, MS affects the central nervous system. DIzziness is a common symptom of this condition; as well as optic neuritis, which you have experienced before. In order to rule out MS as the cause, an MRI is indicated to look for new white matter lesions in the brain. You should be under the supervision of a neurologist for management of this condition.
I would probably visit an ENT doctor first. If your exam is normal, then a neurologist should be seen for a full evaluation.
I hope this is helpful and that you feel better soon...
If difficulty focusing is the primary symptom, and you feel that this is making you dizzy, then one has to consider other diagnosis.
One possibility may be accomodative spasm. This occurs when the ciliary muscle (the muscle that controls the lens of the eye) goes into spasm. This can be triggered by long periods of near work such as reading or computer work. If the muscle goes into spasm the lens cannot assume the position needed for clear vision. The usual treatment for this condition would be reading glasses during this sort of activity. I know you describe symptoms while driving, but this may be when the symptoms become manifest after a long period of near work. A full eye exam would be indicated to help resolve this problem.
MS must still be considered as the symptoms can include blurry vision and dizziness in many situations. I definitely would look into this by visiting a neurologist to rule this out.
I hope this answers your concerns a bit better...