The ability to see is one of our most amazing and complicated senses. Muscles play a very important role in the process of vision, as they are responsible for the movement of the eyes. These muscles, known as the extra-ocular muscles (EOM's), let you look up, down and sideways. These muscles are controlled by two systems in the brain - the visual (or oculomotor) system and the inner ear (or vestibular) system. These systems act together to aim the eyes so that they both look at the same place at the same time, thereby creating a single, clear image (fusion).
Anything that makes it difficult for the eyes to aim properly can cause symptoms including dizziness, headaches, reading difficulty and blurred vision. Some patients with vision alignment problems have only one of these symptoms, while others may have two or more symptoms. With the wide array of symptoms, it is not unusual for these people to have sought help from many different medical specialists, usually without adequate relief. Most people would not have thought that the visual system could be the cause of these symptoms and, as a result, have not sought help from a vision specialist.
Binocular Vision Dysfunction (BVD) is a condition where the line of sight from one eye tends to be out of alignment with the line of sight from the other eye, making it difficult for the eyes to work together as a coordinated team. Two common forms of BVD are Vertical Heterophoria (VH) and Superior Oblique Palsy (SOP).
Evidence indicates there is a problem with coordinating eye aiming. In VH, the inner ear (or vestibular system) seems to be at fault, and in SOP, the Superior Oblique eye muscle or its nerve appears to be faulty. In both cases, a subtle vertical misalignment
results, and if left untreated, would cause double vision, which humans do not tolerate well. To prevent this, the visual system acts to realign the eyes. Then the faulty system (inner ear or Superior Oblique) acts again causing misalignment, followed again by realignment from the visual aiming system.
These repeating cycles of misalignment/realignment cause headaches and eye pain (from eye muscle strain), and dizziness, lightheadedness, nausea, motion sickness and anxiety (from the back and forth eye movements).
Another way the body corrects the misalignment is to tilt the head toward a shoulder (this moves the image up in one eye and down in the other eye). However, this can cause chronic neck and back pain.
Many people are born with facial asymmetry (where one eye is physically higher than the other eye or with an eye muscle or nerve abnormality. They develop BVD over time as their eye muscles become overwhelmed. While this can occur at any age, many people develop symptoms around the age of 40. Others develop BVD due to a brain injury, stroke, or other neurological disorder, which can occur at any age.
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