It could be Horner's but with a history of trauma to the eye, we lose key components of the classical physical findings of Horner's which consists of 1)constricted pupil 2)droopy eyelid and 3)loss of sweating over forehead on affected side. Glad the MRI was ok. There are many, many causes of Horner;s syndrome such as MS, stroke, tumor, post surgical, trauma, spinal cord problem etc... but these should have showed up on an MRI. In older patients with risk factors for lung cancer, tumor in the top of the lung can cause a Horner;s. Other things this could represent if it's a new finding include a tear in one of the arteries in your neck (can be checked with MRI of the arteries), and migraine headaches (which could be the case for you and is a limited finding that will go away on its own).
It's even quite possible that it's NOT horner's at all as we are confounded by the physical findings of the previous trauma. Getting a second opinion in the states may be out of the question for you, but consider it if it's possible. Otherwise,
get help with the headaches and see if the other symptoms don't improve. A chest XR may be helpful if you're a smoker to rule out tumors. Good luck.
I developed Horners Syndrome (amoung other symptoms)after I suffered a blunt neck trauma. I also had heat related problems on one side of my body. My CT Scan and MRI's were also negative. Only after my doctor did an arteriogram did he discover a complete occlusion of my vertebral artery caused by a dissection that occurred during the trauma. My dissection was caused by a sports injury but I have read of many causes, some of which are very benign - some dissected vertebral arteries have reportedly been caused by chiropractic procedures and even having hair washed at beauty parlors. You might discuss this possibility with your doctor.
Good luck.