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 (Figure 1). 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 a number of different types of doctors, 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.
Figure 1: Extra-ocular muscles
Figure 2: Facial asymmetry
Binocular Vision Dysfunction, Vertical Heterophoria and Superior Oblique Palsy
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).
An important cause of VH and SOP appears to be a problem with the coordination of the two main eye aiming systems – the inner ear (or vestibular) system and the visual (or oculomotor) system. The inner ear system appears to be faulty and is causing a slight misalignment, and if left alone, would cause double vision, which humans do not tolerate. To correct the misalignment and prevent double vision, the other aiming system (visual) moves the eyes in the other direction (i.e.- back toward their “correct” position). Then the faulty inner ear system 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 fatigue), 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 pain.
Many people are born with facial asymmetry (where one eye is physically higher than the other eye (see Figure 2) 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, and that can occur at any age.
Some patients have few symptoms of BVD and are minimally affected, while others have many symptoms and are completely disabled. This condition tends to run in families.
Treatment of BVD
Patients must undergo a NeuroVisual Evaluation, which is detailed and thorough examination of vision, including assessment for small amounts of vision misalignment that are causing the symptoms of BVD (and that are not routinely identified on standard eye examinations). Problems with near vision, far vision and alignment will be corrected using glasses with aligning lenses, resulting in a reduction (or sometimes elimination) of symptoms.
Headache or head pain/pressure
Face ache / “sinus” pain
Eye pain or pain with eye movements
Head Tilt Symptoms:
Neck ache, upper back and shoulder pain due to a head tilt
Dizziness (vestibular or inner ear) Symptoms:
Off-balanced/unsteadiness with walking/slower gait
Motion sickness (is frequently the first symptom – can occur very early in childhood)
Lack of coordination
Drifting to one side while walking – bumping into the person next to them; walks into door frames and furniture, often with the same side of the body
Difficulty walking down grocery aisle
Feeling overwhelmed or anxious in crowds
Feeling overwhelmed or anxious in large contained spaces with tall ceilings like malls or big box stores
Anxiety from driving, especially on the freeway
Suicidal ideation from anxiety
Fitful and restless sleep
Difficulty sleeping unless room completely dark
Difficulty with concentration, re-reading for comprehension
Fatigue with reading
Difficulty with reading
Skipping lines while reading
Using a line guide (finger, ruler, envelope) to maintain one’s place while reading
Words running together while reading
Losing one’s place while reading
Routine Visual Symptoms:
Blurred vision at near or far distances
Difficulty with close up vision (i.e. – reading or computer use)
Difficulty with night vision
Binocular Visual Symptoms:
Double or overlapping vision
Difficulty with glare or reflection
Closing / covering one eye eases visual tasks
Poor depth perception / difficulty with eye-hand coordination (e.g.- difficulty catching or hitting balls)
Trouble stopping in time due to difficulty estimating distances
Driving causing anxiety, especially on the freeway
Difficulty maintaining eye contact when in conversations
Not uncommonly, people have been diagnosed with other conditions (like migraines, reading and learning disabilities, ADD/ADHD, anxiety/panic disorders, sinus problems, TMJ disorders, agoraphobia, Meniere’s Disease, MS, stroke, cervical misalignment) when the cause was BVD.