History of Vertical Heterophoria
Vertical Heterophoria (VH) was first mentioned by Dr. George T. Stevens in 1887. He unsuccessfully tried to treat using large amounts of prism but was successful treating the condition with surgery. No one has been able to duplicate his results.
In the 1950s and 1960s, Dr. Raymond Roy discussed his treatment of VH in a series of 11 articles. His treatment included patching each eye for 6 days to determine the misalignment, but his methods were not well received by patients or eye care professionals and failed to become the standard of care.
Dr. Debby Feinberg diagnosed and treated her first patient with VH in 1995. In the past two decades, she has treated thousands of patients with the condition as well as being a pioneer in research-based screening techniques and treatment using microprism.
VH has been identified and discussed in optometric textbooks like Borish; however, previous understandings have failed to appreciate the clinical impact of microprism heterophorias, and previous testing techniques have failed to identify small amounts of vertical misalignment.
What is VH and its connection to BVD?
Binocular Vision Dysfunction (BVD) is a condition where the eyes have difficulty working in a coordinated manner, resulting in eye misalignment and even double vision. Many of these patients have suffered from symptoms their entire lives without a diagnosis.
VH is a BVD resulting from a vertical misalignment of the eyes. While being one of the most common types of BVD (estimated at 20% of the population 5), it is rarely diagnosed by clinicians. VH may be present from birth due to facial asymmetry or eye muscle abnormality or can be acquired due to stroke, brain injury or other neurological disorders.
Vertical misalignments as small as 0.25 diopters may result in many vestibular, and ocular and systemic symptoms which originate from the body’s attempt to correct for the error by overusing and straining the eye muscles or by tilting the head to realign the images.
There are two forms of vertical heterophoria: monocular and binocular. The monocular form is a malfunction of the visual system and is commonly recognized as a superior oblique palsy. A superior oblique palsy can be genetic or acquired in a head injury or due to poor blood supply in diabetes.
The binocular form appears to be a vestibular system problem, most likely due to faulty eye alignment signals sent from the vestibular system through the vestibular ocular reflex (VOR).
The visual system responds to impending diplopia (possibly through the fusional vergence reflex) by trying to align the two images. The faulty vestibular signal asserts itself again, which sets up a misalignment/realignment cycle at a rapid frequency and is the cause of the patient’s symptoms.
The overuse of the opposing elevator and depressor muscles trying to re-align the lines of sight results in muscle strain, headache, asthenopia, and eye pain with movement. The rapid misalignment/realignment cycle is hypothesized to cause visual shimmering or a sensation of image vibration, as well as dizziness, and other vestibular-type symptoms.
Most patients experience a head tilt, as this has the propensity to help bring vertically misaligned images closer together, but can cause neck and upper back pain.
What to Look Out for as an Optometrist
VH Symptoms and Physical Findings
Patients report a wide variety of symptoms which can make diagnosis more difficult. The two most common symptoms are headache and dizziness. Patients with BVD typically experience headaches in the front of the face or the temples. The dizziness is described as feeling disoriented or lightheaded.
Reading Symptoms of VH
Difficulty with reading and comprehension, words that blur or run together, skipping lines, and trouble concentrating are reported by patients with VH. The symptoms are like those experienced by patients with learning disabilities, dyslexia and even ADHD.