Multiple sclerosis or MS is an autoimmune disorder that causes a variety of neurological complications leading to, among others, eye muscle fatigue that explains how your eyes are tired all the time as well as numbness in your extremities. You may also experience blurred vision, and diplopia or double vision. A retinal eye exam is needed to check for optic nerve inflammation or neuritis. Another effect you may be experiencing is a worsening of symptoms when you are exposed to a higher temperature. The extreme dryness is also found in Multiple sclerosis and with a symptom like that your doctor would like to rule out a CNS form of Sjogren s Syndrome. You most certainly have to use a preservative free brand of lubricating eye drops like Refresh liquigel 5 times a day and lubricating eye ointment 2 times a day including at night. This will have to be for a long time and most patients use them life long. If this does not have adequate effect, a minor procedure called a punctal plug is used where the opening of the duct connecting your eye and nose is blocked so the tears do not drain too fast and the eye stays hydrated. This is reversible and can be removed when and if needed. Your doctor will ask for tests like a blood work up, EEG ,MRI to diagnose MS or CNS Sjogren s. Many of your symptoms fall in the category of autoimmune disease but the final diagnosis needs neurological investigative procedures to confirm.