This is a summarized version of our 2026 paper published in the Journal of Ophthalmology and Research. (1)
Ligamentous Cervical Instability Potential Etiology of Blurry Vision
1. Ligamentous cervical instability leads to breakdown of cervical curve (dysstructure) and atlas moves forward.
2. Carotid sheath becomes compressed on one side more than the other leading to severe narrowing of the left internal jugular vein (IJV) at the atlas.
3. Intracranial cerebrospinal fluid pressure increases and as a consequence CSF accumulates around the left optic nerve.
4. Retinal image from left eye gets to the visual cortex later than the right eye because of compression of left optic nerve due to excessive cerebrospinal fluid (CSF), so blurry vision results.
At our neck center, we observed patients with chronic blurry vision frequently had cervical spine abnormalities and neurovascular changes. These observations led to findings suggesting that cervical dysfunction may contribute to unexplained blurry vision in some patients and could help guide future evaluation
Study patient’s profiles
This retrospective observational study reviewed clinical records from a single outpatient neck clinic between January and June 2022. The study included adults aged 20–50 years with unexplained blurry vision lasting longer than one year who were evaluated for a possible cervical spine contribution to their symptoms. The cohort represented patients whose symptoms had persisted despite prior conventional medical care.
All patients underwent the clinic’s standard diagnostic evaluation, including dynamic cervical structural analysis and neck vitals assessment, as part of routine clinical care. Blurry vision and the absence of significant ophthalmologic findings were based on patient self-report, as ophthalmology records were not independently reviewed. Patients with known eye diseases, refractive disorders, conditions requiring eye medications or surgery, or a history of significant head or neck trauma were excluded. The study analyzed existing clinical data to identify structural cervical findings associated with chronic unexplained blurry vision.
The most common objective eye-related finding in this study was an enlarged optic nerve sheath diameter (ONSD). The average bilateral ONSD was 15.35 mm, and only one patient did not have an elevated measurement.
Blurry vision
Blurry vision is reduced sharpness or clarity of vision that can affect one or both eyes. It is commonly caused by cataracts, macular degeneration, glaucoma, refractive errors (needing glasses or contacts), and increased eye pressure. Known contributors include digital eye strain, convergence insufficiency, accommodative dysfunction, and ocular muscle fatigue. However, these explanations do not fully account for why blurry vision is so frequent and persistent in many patients. Blurry vision can also occur in conditions where no obvious eye disease is present, such as functional visual disorders, migraine-related visual symptoms, anxiety-related visual disturbances, mild traumatic brain injury, dysautonomia, intracranial hypertension, and computer vision syndrome.
It has also been associated with musculoskeletal problems such as neck pain, cervical spondylosis, headaches, and “text neck,” and commonly reported in conditions such as whiplash-associated disorder, post-concussion syndrome, text neck, and computer vision syndrome, affecting 40–90% of people in these groups. Patients with chronic neck pain experience visual symptoms more often than the general population. This relationship has been described as cervicogenic visual disturbance.
This has led to the possibility that some unresolved cases of blurry vision may involve overlapping mechanisms related to the neck. Several mechanisms have been proposed to explain the connection, including increased sympathetic nervous system activity, neuroinflammation affecting retinal cells and the brain-eye pathways, and disrupted communication between the cervical spine and the central nervous system.
In a previous study, we reported on a group of patients with multiple symptoms, including visual complaints, and proposed a potential link between cervical spine dysfunction and eye symptoms. The present study focuses specifically on chronic blurry vision, allowing for a more detailed evaluation of the relationship between objective cervical spine findings and blurry vision. Significant cervical structural abnormalities in this group included ligamentous cervical instability, especially at the C1–C2 atlantoaxial facet joint, forward head posture as measured by an increased C6-atlas interval, and a reduced cervical curve. We examined whether these patients also had reduced internal jugular vein and vagus nerve cross-sectional areas on ultrasound, as well as eye abnormalities such as increased optic nerve sheath diameter and enlarged pupils. The goal was to identify consistent cervical spine and neurovascular patterns that may help explain otherwise unexplained chronic blurry vision.
Clinical ligamentous cervical instability (LCI)
Clinical ligamentous cervical instability (LCI) means the neck ligaments are not adequately holding the cervical vertebrae in proper alignment. This instability may occur between individual vertebrae, between adjacent spinal segments, or across the cervical spine as a whole.
LCI is especially important at the facet joints, where abnormal motion can affect bones, soft tissues, nerves, blood vessels, and overall neck function. Symptoms may occur when certain postures, positions, or movements place increased stress on the cervical spine.
In this study, LCI was evaluated using digital motion X-ray (DMX), also called videofluoroscopy. DMX allows the cervical spine, from C0 to C7, to be examined continuously while the patient moves. This makes it possible to assess instability in different planes of motion, including front-to-back, side-to-side, and rotational movements.
LCI is commonly identified when one vertebra shifts more than 2 mm beyond an adjacent vertebra during movement, although some researchers consider even 1 mm of abnormal translation to be clinically significant.
Dynamic Motion X-ray (DMX) evaluates the functional integrity of the cervical spine ligaments while the patient is upright and moving. Unlike static imaging, DMX can assess how the anterior and posterior longitudinal ligaments, supraspinous and interspinous ligaments, transverse ligament, alar ligaments, facet capsular ligaments, and ligamentum flavum perform during normal neck motion.
The facet capsular ligaments are particularly important because they stabilize the four primary movements of the cervical spine: flexion, extension, rotation, and lateral bending. In this study, ligament laxity in the upper cervical spine was identified by excessive overhang of the inferior articular pillar of the atlas (C1) over the superior articular pillar of the axis (C2). In the lower cervical spine, abnormal vertebral motion was observed during flexion and extension.
- The internal jugular vein (IJV) was smaller at the C1 level than at the C4-C5 level in 87% of patients. Most ultrasound exams measure the IJV only at the C4-C5 level. Our findings suggest that measuring the vein at C1 may better detect upper cervical compression that could otherwise be missed.
Forward head posture and neck pain
In our study, 137 out of 145 patients (94%) reported neck pain. Neck pain and muscle tightness are often linked to forward head posture, but ligament injury or instability may also play a role.
In this group, we suggest that neck pain may be related to ongoing muscle tension caused by instability in the upper and lower neck. This may happen through the ligamento-muscular reflex, a protective response in which muscles tighten to help stabilize an unstable joint and protect nearby structures such as blood vessels and nerves.
We also suggest that changes in neck structure – including lower cervical instability (LCI), increased C6AI (measurement indicating degree of forward head posture), and decreased DOC (depth of curve)- may lead to poor outcomes. These changes may cause neck pain and may also affect the visual system by stretching or compressing important structures such as the internal jugular vein (IJV) and vagus nerve, which could contribute to blurry vision or other visual symptoms.
The internal jugular vein
We used ultrasound to measure the size of the internal jugular vein (IJV), one of the main veins that drains blood from the brain. In 87% of patients, the vein was much narrower at the top of the neck near the atlas (C1) than it was lower in the neck (C4-C5).
Most ultrasound examinations measure the jugular vein only in the middle of the neck (C4-C5). Our findings suggest this approach may miss important narrowing that occurs higher in the neck near the base of the skull. Measuring the vein at the C1 level appears to be a more sensitive way to detect possible jugular vein compression.
While some degree of upper cervical jugular vein narrowing has been reported in people without symptoms, the vein measurements in our patients were substantially smaller than those typically reported in healthy individuals, even in the middle of the neck. These findings suggest that evaluating the jugular vein near the atlas may provide additional information in patients with chronic, unexplained neurological or neck-related symptoms.
Intraocular Pressure (Patient-Friendly)
Only 19% of patients in this study had elevated intraocular pressure (IOP), meaning pressure inside the eye greater than 21 mmHg. While we found a significant relationship between larger pupil size and higher eye pressure, most patients did not have ocular hypertension or signs of glaucoma.
This suggests that, in this patient population, blurry vision may be related less to elevated eye pressure itself and more to increased pressure surrounding the optic nerve. We believe this may result from impaired venous drainage through the internal jugular veins, which can contribute to elevated cerebrospinal fluid (CSF) pressure and intracranial hypertension.
The optic nerve is uniquely affected by pressure from two directions: pressure inside the eye (IOP) and pressure from the cerebrospinal fluid surrounding the nerve (intracranial pressure). If either pressure becomes abnormal, the optic nerve can be stressed. If both are elevated simultaneously, the optic nerve and retina may experience compression from both sides—a concept we describe as a “double eye squeeze.” This could contribute to blurry vision, double vision, difficulty focusing, and, over time, potentially increase the risk of glaucoma or retinal damage.
We believe many patients may experience intermittent increases in intracranial pressure that cause visual symptoms before permanent eye damage develops. If future research confirms this, identifying and treating abnormal pressure dynamics early may help relieve symptoms and reduce the risk of long-term vision problems.
Vagus nerve compression
The changes we found in vision may be related to changes in the autonomic nervous system—the body’s automatic control system that regulates functions such as pupil size, tear production, blood flow, and eye pressure.
One possible explanation is that a forward-shifted upper neck, particularly the atlas (C1), may place stress on important nerves that travel through this area. Two important clusters of the vagus nerve (the nodose and jugular ganglia) lie just in front of the atlas, while the superior cervical sympathetic ganglion, which helps regulate the “fight-or-flight” response, sits just in front of the second cervical vertebra (C2).
Research has shown that stimulation of the superior cervical sympathetic ganglion can increase eye pressure, highlighting its important role in eye function. Normally, the vagus nerve helps keep sympathetic activity in balance by acting as a natural brake. If this balance is disrupted, the result may be excessive sympathetic activity, which could contribute to enlarged pupils, elevated eye pressure, and other signs of autonomic dysfunction seen in our patients.
These nerves do not work in isolation. They communicate extensively with one another and with several cranial nerves responsible for facial sensation, eye movement, swallowing, speech, and other head and neck functions. They also connect with the upper cervical spinal nerves (C1-C3). Because of this complex network, structural problems in the upper neck may have effects that extend well beyond neck pain, potentially influencing vision, eye function, and other neurological symptoms.
Many patients in this study with chronic blurry vision had measurable abnormalities involving the neck, including changes in cervical spine alignment and blood flow. While this study does not prove that neck problems cause blurry vision, the findings suggest that the neck may play a role in some people whose vision problems cannot be explained by an eye condition alone. These results highlight the importance of looking beyond the eyes when evaluating persistent blurry vision and support a team approach involving spine specialists, eye doctors, neurologists, and other healthcare providers. More research is needed to better understand how neck problems may contribute to blurry vision and which patients are most likely to benefit from evaluation and treatment.
Our published research